Node.js v0.7.8 Manual & Documentation

Table of Contents

About this Documentation#

The goal of this documentation is to comprehensively explain the Node.js API, both from a reference as well as a conceptual point of view. Each section describes a built-in module or high-level concept.

Where appropriate, property types, method arguments, and the arguments provided to event handlers are detailed in a list underneath the topic heading.

Every .html document has a corresponding .json document presenting the same information in a structured manner. This feature is experimental, and added for the benefit of IDEs and other utilities that wish to do programmatic things with the documentation.

Every .html and .json file is generated based on the corresponding .markdown file in the doc/api/ folder in node's source tree. The documentation is generated using the tools/doc/generate.js program. The HTML template is located at doc/template.html.

Stability Index#

Throughout the documentation, you will see indications of a section's stability. The Node.js API is still somewhat changing, and as it matures, certain parts are more reliable than others. Some are so proven, and so relied upon, that they are unlikely to ever change at all. Others are brand new and experimental, or known to be hazardous and in the process of being redesigned.

The notices look like this: 

Stability: 1 Experimental

The stability indices are as follows:

  • 0 - Deprecated This feature is known to be problematic, and changes are planned. Do not rely on it. Use of the feature may cause warnings. Backwards compatibility should not be expected.
  • 1 - Experimental This feature was introduced recently, and may change or be removed in future versions. Please try it out and provide feedback. If it addresses a use-case that is important to you, tell the node core team.
  • 2 - Unstable The API is in the process of settling, but has not yet had sufficient real-world testing to be considered stable. Backwards-compatibility will be maintained if reasonable.
  • 3 - Stable The API has proven satisfactory, but cleanup in the underlying code may cause minor changes. Backwards-compatibility is guaranteed.
  • 4 - API Frozen This API has been tested extensively in production and is unlikely to ever have to change.
  • 5 - Locked Unless serious bugs are found, this code will not ever change. Please do not suggest changes in this area; they will be refused.

JSON Output#

Stability: 1 - Experimental

Every HTML file in the markdown has a corresponding JSON file with the same data.

This feature is new as of node v0.6.12. It is experimental.

Synopsis#

An example of a web server written with Node which responds with 'Hello World': 

var http = require('http');

http.createServer(function (request, response) {
  response.writeHead(200, {'Content-Type': 'text/plain'});
  response.end('Hello World\n');
}).listen(8124);

console.log('Server running at http://127.0.0.1:8124/');

To run the server, put the code into a file called example.js and execute it with the node program 

> node example.js
Server running at http://127.0.0.1:8124/

All of the examples in the documentation can be run similarly.

Global Objects#

These objects are available in all modules. Some of these objects aren't actually in the global scope but in the module scope - this will be noted.

global#

  • {Object} The global namespace object.

In browsers, the top-level scope is the global scope. That means that in browsers if you're in the global scope var something will define a global variable. In Node this is different. The top-level scope is not the global scope; var something inside a Node module will be local to that module.

process#

  • {Object}

The process object. See the process object section.

console#

  • {Object}

Used to print to stdout and stderr. See the stdio section.

Class: Buffer#

  • {Function}

Used to handle binary data. See the buffer section.

require()#

  • {Function}

To require modules. See the Modules section. require isn't actually a global but rather local to each module.

require.resolve()#

Use the internal require() machinery to look up the location of a module, but rather than loading the module, just return the resolved filename.

require.cache#

  • Object

Modules are cached in this object when they are required. By deleting a key value from this object, the next require will reload the module.

require.extensions#

  • Array

Instruct require on how to handle certain file extensions.

Process files with the extension .sjs as .js: 

require.extensions['.sjs'] = require.extensions['.js'];

Write your own extension handler: 

require.extensions['.sjs'] = function(module, filename) {
  var content = fs.readFileSync(filename, 'utf8');
  // Parse the file content and give to module.exports
  module.exports = content;
};

__filename#

  • {String}

The filename of the code being executed. This is the resolved absolute path of this code file. For a main program this is not necessarily the same filename used in the command line. The value inside a module is the path to that module file.

Example: running node example.js from /Users/mjr 

console.log(__filename);
// /Users/mjr/example.js

__filename isn't actually a global but rather local to each module.

__dirname#

  • {String}

The name of the directory that the currently executing script resides in.

Example: running node example.js from /Users/mjr 

console.log(__dirname);
// /Users/mjr

__dirname isn't actually a global but rather local to each module.

module#

  • {Object}

A reference to the current module. In particular module.exports is the same as the exports object. module isn't actually a global but rather local to each module.

See the module system documentation for more information.

exports#

An object which is shared between all instances of the current module and made accessible through require(). exports is the same as the module.exports object. exports isn't actually a global but rather local to each module.

See the module system documentation for more information.

See the module section for more information.

setTimeout(cb, ms)#

clearTimeout(t)#

setInterval(cb, ms)#

clearInterval(t)#

The timer functions are global variables. See the timers section.

console#

Stability: 4 - API Frozen
  • {Object}

For printing to stdout and stderr. Similar to the console object functions provided by most web browsers, here the output is sent to stdout or stderr.

console.log()#

Prints to stdout with newline. This function can take multiple arguments in a printf()-like way. Example: 

console.log('count: %d', count);

If formatting elements are not found in the first string then util.inspect is used on each argument. See util.format() for more information.

console.info()#

Same as console.log.

console.warn()#

console.error()#

Same as console.log but prints to stderr.

console.dir(obj)#

Uses util.inspect on obj and prints resulting string to stdout.

console.time(label)#

Mark a time.

console.timeEnd(label)#

Finish timer, record output. Example 

console.time('100-elements');
for (var i = 0; i < 100; i++) {
  ;
}
console.timeEnd('100-elements');

console.trace()#

Print a stack trace to stderr of the current position.

console.assert()#

Same as assert.ok().

Timers#

Stability: 5 - Locked

All of the timer functions are globals. You do not need to require() this module in order to use them.

setTimeout(callback, delay, [arg], [...])#

To schedule execution of a one-time callback after delay milliseconds. Returns a timeoutId for possible use with clearTimeout(). Optionally you can also pass arguments to the callback.

It is important to note that your callback will probably not be called in exactly delay milliseconds - Node.js makes no guarantees about the exact timing of when the callback will fire, nor of the ordering things will fire in. The callback will be called as close as possible to the time specified.

clearTimeout(timeoutId)#

Prevents a timeout from triggering.

setInterval(callback, delay, [arg], [...])#

To schedule the repeated execution of callback every delay milliseconds. Returns a intervalId for possible use with clearInterval(). Optionally you can also pass arguments to the callback.

clearInterval(intervalId)#

Stops a interval from triggering.

Modules#

Stability: 5 - Locked

Node has a simple module loading system. In Node, files and modules are in one-to-one correspondence. As an example, foo.js loads the module circle.js in the same directory.

The contents of foo.js: 

var circle = require('./circle.js');
console.log( 'The area of a circle of radius 4 is '
           + circle.area(4));

The contents of circle.js: 

var PI = Math.PI;

exports.area = function (r) {
  return PI * r * r;
};

exports.circumference = function (r) {
  return 2 * PI * r;
};

The module circle.js has exported the functions area() and circumference(). To export an object, add to the special exports object.

Variables local to the module will be private. In this example the variable PI is private to circle.js.

The module system is implemented in the require("module") module.

Cycles#

When there are circular require() calls, a module might not be done being executed when it is returned.

Consider this situation:

a.js: 

console.log('a starting');
exports.done = false;
var b = require('./b.js');
console.log('in a, b.done = %j', b.done);
exports.done = true;
console.log('a done');

b.js: 

console.log('b starting');
exports.done = false;
var a = require('./a.js');
console.log('in b, a.done = %j', a.done);
exports.done = true;
console.log('b done');

main.js: 

console.log('main starting');
var a = require('./a.js');
var b = require('./b.js');
console.log('in main, a.done=%j, b.done=%j', a.done, b.done);

When main.js loads a.js, then a.js in turn loads b.js. At that point, b.js tries to load a.js. In order to prevent an infinite loop an unfinished copy of the a.js exports object is returned to the b.js module. b.js then finishes loading, and its exports object is provided to the a.js module.

By the time main.js has loaded both modules, they're both finished. The output of this program would thus be: 

$ node main.js
main starting
a starting
b starting
in b, a.done = false
b done
in a, b.done = true
a done
in main, a.done=true, b.done=true

If you have cyclic module dependencies in your program, make sure to plan accordingly.

Core Modules#

Node has several modules compiled into the binary. These modules are described in greater detail elsewhere in this documentation.

The core modules are defined in node's source in the lib/ folder.

Core modules are always preferentially loaded if their identifier is passed to require(). For instance, require('http') will always return the built in HTTP module, even if there is a file by that name.

File Modules#

If the exact filename is not found, then node will attempt to load the required filename with the added extension of .js, .json, and then .node.

.js files are interpreted as JavaScript text files, and .json files are parsed as JSON text files. .node files are interpreted as compiled addon modules loaded with dlopen.

A module prefixed with '/' is an absolute path to the file. For example, require('/home/marco/foo.js') will load the file at /home/marco/foo.js.

A module prefixed with './' is relative to the file calling require(). That is, circle.js must be in the same directory as foo.js for require('./circle') to find it.

Without a leading '/' or './' to indicate a file, the module is either a "core module" or is loaded from a node_modules folder.

If the given path does not exist, require() will throw an Error with its code property set to 'MODULE_NOT_FOUND'.

Loading from node_modules Folders#

If the module identifier passed to require() is not a native module, and does not begin with '/', '../', or './', then node starts at the parent directory of the current module, and adds /node_modules, and attempts to load the module from that location.

If it is not found there, then it moves to the parent directory, and so on, until the root of the tree is reached.

For example, if the file at '/home/ry/projects/foo.js' called require('bar.js'), then node would look in the following locations, in this order:

  • /home/ry/projects/node_modules/bar.js
  • /home/ry/node_modules/bar.js
  • /home/node_modules/bar.js
  • /node_modules/bar.js

This allows programs to localize their dependencies, so that they do not clash.

Folders as Modules#

It is convenient to organize programs and libraries into self-contained directories, and then provide a single entry point to that library. There are three ways in which a folder may be passed to require() as an argument.

The first is to create a package.json file in the root of the folder, which specifies a main module. An example package.json file might look like this: 

{ "name" : "some-library",
  "main" : "./lib/some-library.js" }

If this was in a folder at ./some-library, then require('./some-library') would attempt to load ./some-library/lib/some-library.js.

This is the extent of Node's awareness of package.json files.

If there is no package.json file present in the directory, then node will attempt to load an index.js or index.node file out of that directory. For example, if there was no package.json file in the above example, then require('./some-library') would attempt to load:

  • ./some-library/index.js
  • ./some-library/index.node

Caching#

Modules are cached after the first time they are loaded. This means (among other things) that every call to require('foo') will get exactly the same object returned, if it would resolve to the same file.

Multiple calls to require('foo') may not cause the module code to be executed multiple times. This is an important feature. With it, "partially done" objects can be returned, thus allowing transitive dependencies to be loaded even when they would cause cycles.

If you want to have a module execute code multiple times, then export a function, and call that function.

Module Caching Caveats#

Modules are cached based on their resolved filename. Since modules may resolve to a different filename based on the location of the calling module (loading from node_modules folders), it is not a guarantee that require('foo') will always return the exact same object, if it would resolve to different files.

The module Object#

  • {Object}

In each module, the module free variable is a reference to the object representing the current module. In particular module.exports is the same as the exports object. module isn't actually a global but rather local to each module.

module.exports#

  • Object

The exports object is created by the Module system. Sometimes this is not acceptable, many want their module to be an instance of some class. To do this assign the desired export object to module.exports. For example suppose we were making a module called a.js 

var EventEmitter = require('events').EventEmitter;

module.exports = new EventEmitter();

// Do some work, and after some time emit
// the 'ready' event from the module itself.
setTimeout(function() {
  module.exports.emit('ready');
}, 1000);

Then in another file we could do 

var a = require('./a');
a.on('ready', function() {
  console.log('module a is ready');
});

Note that assignment to module.exports must be done immediately. It cannot be done in any callbacks. This does not work:

x.js: 

setTimeout(function() {
  module.exports = { a: "hello" };
}, 0);

y.js: 

var x = require('./x');
console.log(x.a);

module.require(id)#

  • id String
  • Return: Object exports from the resolved module

The module.require method provides a way to load a module as if require() was called from the original module.

Note that in order to do this, you must get a reference to the module object. Since require() returns the exports, and the module is typically only available within a specific module's code, it must be explicitly exported in order to be used.

module.id#

  • String

The identifier for the module. Typically this is the fully resolved filename.

module.filename#

  • String

The fully resolved filename to the module.

module.loaded#

  • Boolean

Whether or not the module is done loading, or is in the process of loading.

module.parent#

  • Module Object

The module that required this one.

module.children#

  • Array

The module objects required by this one.

All Together...#

To get the exact filename that will be loaded when require() is called, use the require.resolve() function.

Putting together all of the above, here is the high-level algorithm in pseudocode of what require.resolve does: 

require(X) from module at path Y
1. If X is a core module,
   a. return the core module
   b. STOP
2. If X begins with './' or '/' or '../'
   a. LOAD_AS_FILE(Y + X)
   b. LOAD_AS_DIRECTORY(Y + X)
3. LOAD_NODE_MODULES(X, dirname(Y))
4. THROW "not found"

LOAD_AS_FILE(X)
1. If X is a file, load X as JavaScript text.  STOP
2. If X.js is a file, load X.js as JavaScript text.  STOP
3. If X.node is a file, load X.node as binary addon.  STOP

LOAD_AS_DIRECTORY(X)
1. If X/package.json is a file,
   a. Parse X/package.json, and look for "main" field.
   b. let M = X + (json main field)
   c. LOAD_AS_FILE(M)
2. If X/index.js is a file, load X/index.js as JavaScript text.  STOP
3. If X/index.node is a file, load X/index.node as binary addon.  STOP

LOAD_NODE_MODULES(X, START)
1. let DIRS=NODE_MODULES_PATHS(START)
2. for each DIR in DIRS:
   a. LOAD_AS_FILE(DIR/X)
   b. LOAD_AS_DIRECTORY(DIR/X)

NODE_MODULES_PATHS(START)
1. let PARTS = path split(START)
2. let ROOT = index of first instance of "node_modules" in PARTS, or 0
3. let I = count of PARTS - 1
4. let DIRS = []
5. while I > ROOT,
   a. if PARTS[I] = "node_modules" CONTINUE
   c. DIR = path join(PARTS[0 .. I] + "node_modules")
   b. DIRS = DIRS + DIR
   c. let I = I - 1
6. return DIRS

Loading from the global folders#

If the NODE_PATH environment variable is set to a colon-delimited list of absolute paths, then node will search those paths for modules if they are not found elsewhere. (Note: On Windows, NODE_PATH is delimited by semicolons instead of colons.)

Additionally, node will search in the following locations:

  • 1: $HOME/.node_modules
  • 2: $HOME/.node_libraries
  • 3: $PREFIX/lib/node

Where $HOME is the user's home directory, and $PREFIX is node's configured installPrefix.

These are mostly for historic reasons. You are highly encouraged to place your dependencies locally in node_modules folders. They will be loaded faster, and more reliably.

Accessing the main module#

When a file is run directly from Node, require.main is set to its module. That means that you can determine whether a file has been run directly by testing 

require.main === module

For a file foo.js, this will be true if run via node foo.js, but false if run by require('./foo').

Because module provides a filename property (normally equivalent to __filename), the entry point of the current application can be obtained by checking require.main.filename.

Addenda: Package Manager Tips#

The semantics of Node's require() function were designed to be general enough to support a number of sane directory structures. Package manager programs such as dpkg, rpm, and npm will hopefully find it possible to build native packages from Node modules without modification.

Below we give a suggested directory structure that could work:

Let's say that we wanted to have the folder at /usr/lib/node/<some-package>/<some-version> hold the contents of a specific version of a package.

Packages can depend on one another. In order to install package foo, you may have to install a specific version of package bar. The bar package may itself have dependencies, and in some cases, these dependencies may even collide or form cycles.

Since Node looks up the realpath of any modules it loads (that is, resolves symlinks), and then looks for their dependencies in the node_modules folders as described above, this situation is very simple to resolve with the following architecture:

  • /usr/lib/node/foo/1.2.3/ - Contents of the foo package, version 1.2.3.
  • /usr/lib/node/bar/4.3.2/ - Contents of the bar package that foo depends on.
  • /usr/lib/node/foo/1.2.3/node_modules/bar - Symbolic link to /usr/lib/node/bar/4.3.2/.
  • /usr/lib/node/bar/4.3.2/node_modules/* - Symbolic links to the packages that bar depends on.

Thus, even if a cycle is encountered, or if there are dependency conflicts, every module will be able to get a version of its dependency that it can use.

When the code in the foo package does require('bar'), it will get the version that is symlinked into /usr/lib/node/foo/1.2.3/node_modules/bar. Then, when the code in the bar package calls require('quux'), it'll get the version that is symlinked into /usr/lib/node/bar/4.3.2/node_modules/quux.

Furthermore, to make the module lookup process even more optimal, rather than putting packages directly in /usr/lib/node, we could put them in /usr/lib/node_modules/<name>/<version>. Then node will not bother looking for missing dependencies in /usr/node_modules or /node_modules.

In order to make modules available to the node REPL, it might be useful to also add the /usr/lib/node_modules folder to the $NODE_PATH environment variable. Since the module lookups using node_modules folders are all relative, and based on the real path of the files making the calls to require(), the packages themselves can be anywhere.

Addons#

Addons are dynamically linked shared objects. They can provide glue to C and C++ libraries. The API (at the moment) is rather complex, involving knowledge of several libraries:

  • V8 JavaScript, a C++ library. Used for interfacing with JavaScript: creating objects, calling functions, etc. Documented mostly in the v8.h header file (deps/v8/include/v8.h in the Node source tree), which is also available online.

  • libuv, C event loop library. Anytime one needs to wait for a file descriptor to become readable, wait for a timer, or wait for a signal to received one will need to interface with libuv. That is, if you perform any I/O, libuv will need to be used.

  • Internal Node libraries. Most importantly is the node::ObjectWrap class which you will likely want to derive from.

  • Others. Look in deps/ for what else is available.

Node statically compiles all its dependencies into the executable. When compiling your module, you don't need to worry about linking to any of these libraries.

Hello world#

To get started let's make a small Addon which is the C++ equivalent of the following Javascript code: 

exports.hello = function() { return 'world'; };

First we create a file hello.cc: 

#include <node.h>
#include <v8.h>

using namespace v8;

Handle<Value> Method(const Arguments& args) {
  HandleScope scope;
  return scope.Close(String::New("world"));
}

void init(Handle<Object> target) {
  target->Set(String::NewSymbol("hello"),
      FunctionTemplate::New(Method)->GetFunction());
}
NODE_MODULE(hello, init)

Note that all Node addons must export an initialization function: 

void Initialize (Handle<Object> target);
NODE_MODULE(module_name, Initialize)

There is no semi-colon after NODE_MODULE as it's not a function (see node.h).

The module_name needs to match the filename of the final binary (minus the .node suffix).

The source code needs to be built into hello.node, the binary Addon. To do this we create a file called binding.gyp which describes the configuration to build your module in a JSON-like format. This file gets compiled by node-gyp. 

{
  "targets": [
    {
      "target_name": "hello",
      "sources": [ "hello.cc" ]
    }
  ]
}

The next step is to generate the appropriate project build files for the current platform. Use node-gyp configure for that.

Now you will have either a Makefile (on Unix platforms) or a vcxproj file (on Windows) in the build/ directory. Next invoke the node-gyp build command.

Now you have your compiled .node bindings file! The compiled bindings end up in build/Release/.

You can now use the binary addon in a Node project hello.js by pointing require to the recently built hello.node module: 

var addon = require('./build/Release/hello');

console.log(addon.hello()); // 'world'

Please see patterns below for further information or

https://github.com/arturadib/node-qt for an example in production.

Addon patterns#

Below are some addon patterns to help you get started. Consult the online v8 reference for help with the various v8 calls, and v8's Embedder's Guide for an explanation of several concepts used such as handles, scopes, function templates, etc.

In order to use these examples you need to compile them using node-gyp. Create the following binding.gyp file: 

{
  "targets": [
    {
      "target_name": "addon",
      "sources": [ "addon.cc" ]
    }
  ]
}

In cases where there is more than one .cc file, simply add the file name to the sources array, e.g.: 

"sources": ["addon.cc", "myexample.cc"]

Now that you have your binding.gyp ready, you can configure and build the addon: 

$ node-gyp configure build

Function arguments#

The following pattern illustrates how to read arguments from JavaScript function calls and return a result. This is the main and only needed source addon.cc: 

#define BUILDING_NODE_EXTENSION
#include <node.h>

using namespace v8;

Handle<Value> Add(const Arguments& args) {
  HandleScope scope;

  if (args.Length() < 2) {
    ThrowException(Exception::TypeError(String::New("Wrong number of arguments")));
    return scope.Close(Undefined());
  }

  if (!args[0]->IsNumber() || !args[1]->IsNumber()) {
    ThrowException(Exception::TypeError(String::New("Wrong arguments")));
    return scope.Close(Undefined());
  }

  Local<Number> num = Number::New(args[0]->NumberValue() +
      args[1]->NumberValue());
  return scope.Close(num);
}

void Init(Handle<Object> target) {
  target->Set(String::NewSymbol("add"),
      FunctionTemplate::New(Add)->GetFunction());
}

NODE_MODULE(addon, Init)

You can test it with the following JavaScript snippet: 

var addon = require('./build/Release/addon');

console.log( 'This should be eight:', addon.add(3,5) );

Callbacks#

You can pass JavaScript functions to a C++ function and execute them from there. Here's addon.cc: 

#define BUILDING_NODE_EXTENSION
#include <node.h>

using namespace v8;

Handle<Value> RunCallback(const Arguments& args) {
  HandleScope scope;

  Local<Function> cb = Local<Function>::Cast(args[0]);
  const unsigned argc = 1;
  Local<Value> argv[argc] = { Local<Value>::New(String::New("hello world")) };
  cb->Call(Context::GetCurrent()->Global(), argc, argv);

  return scope.Close(Undefined());
}

void Init(Handle<Object> target) {
  target->Set(String::NewSymbol("runCallback"),
      FunctionTemplate::New(RunCallback)->GetFunction());
}

NODE_MODULE(addon, Init)

To test it run the following JavaScript snippet: 

var addon = require('./build/Release/addon');

addon.runCallback(function(msg){
  console.log(msg); // 'hello world'
});

Object factory#

You can create and return new objects from within a C++ function with this addon.cc pattern, which returns an object with property msg that echoes the string passed to createObject(): 

#define BUILDING_NODE_EXTENSION
#include <node.h>

using namespace v8;

Handle<Value> CreateObject(const Arguments& args) {
  HandleScope scope;

  Local<Object> obj = Object::New();
  obj->Set(String::NewSymbol("msg"), args[0]->ToString());

  return scope.Close(obj);
}

void Init(Handle<Object> target) {
  target->Set(String::NewSymbol("createObject"),
      FunctionTemplate::New(CreateObject)->GetFunction());
}

NODE_MODULE(addon, Init)

To test it in JavaScript: 

var addon = require('./build/Release/addon');

var obj1 = addon.createObject('hello');
var obj2 = addon.createObject('world');
console.log(obj1.msg+' '+obj2.msg); // 'hello world'

Function factory#

This pattern illustrates how to create and return a JavaScript function that wraps a C++ function: 

#define BUILDING_NODE_EXTENSION
#include <node.h>

using namespace v8;

Handle<Value> MyFunction(const Arguments& args) {
  HandleScope scope;
  return scope.Close(String::New("hello world"));
}

Handle<Value> CreateFunction(const Arguments& args) {
  HandleScope scope;

  Local<FunctionTemplate> tpl = FunctionTemplate::New(MyFunction);
  Local<Function> fn = tpl->GetFunction();
  fn->SetName(String::NewSymbol("theFunction")); // omit this to make it anonymous

  return scope.Close(fn);
}

void Init(Handle<Object> target) {
  target->Set(String::NewSymbol("createFunction"),
      FunctionTemplate::New(CreateFunction)->GetFunction());
}

NODE_MODULE(addon, Init)

To test: 

var addon = require('./build/Release/addon');

var fn = addon.createFunction();
console.log(fn()); // 'hello world'

Wrapping C++ objects#

Here we will create a wrapper for a C++ object/class MyObject that can be instantiated in JavaScript through the new operator. First prepare the main module addon.cc: 

#define BUILDING_NODE_EXTENSION
#include <node.h>
#include "myobject.h"

using namespace v8;

void InitAll(Handle<Object> target) {
  MyObject::Init(target);
}

NODE_MODULE(addon, InitAll)

Then in myobject.h make your wrapper inherit from node::ObjectWrap: 

#ifndef MYOBJECT_H
#define MYOBJECT_H

#include <node.h>

class MyObject : public node::ObjectWrap {
 public:
  static void Init(v8::Handle<v8::Object> target);

 private:
  MyObject();
  ~MyObject();

  static v8::Handle<v8::Value> New(const v8::Arguments& args);
  static v8::Handle<v8::Value> PlusOne(const v8::Arguments& args);
  double counter_;
};

#endif

And in myobject.cc implement the various methods that you want to expose. Here we expose the method plusOne by adding it to the constructor's prototype: 

#define BUILDING_NODE_EXTENSION
#include <node.h>
#include "myobject.h"

using namespace v8;

MyObject::MyObject() {};
MyObject::~MyObject() {};

void MyObject::Init(Handle<Object> target) {
  // Prepare constructor template
  Local<FunctionTemplate> tpl = FunctionTemplate::New(New);
  tpl->SetClassName(String::NewSymbol("MyObject"));
  tpl->InstanceTemplate()->SetInternalFieldCount(1);
  // Prototype
  tpl->PrototypeTemplate()->Set(String::NewSymbol("plusOne"),
      FunctionTemplate::New(PlusOne)->GetFunction());

  Persistent<Function> constructor = Persistent<Function>::New(tpl->GetFunction());
  target->Set(String::NewSymbol("MyObject"), constructor);
}

Handle<Value> MyObject::New(const Arguments& args) {
  HandleScope scope;

  MyObject* obj = new MyObject();
  obj->counter_ = args[0]->IsUndefined() ? 0 : args[0]->NumberValue();
  obj->Wrap(args.This());

  return args.This();
}

Handle<Value> MyObject::PlusOne(const Arguments& args) {
  HandleScope scope;

  MyObject* obj = ObjectWrap::Unwrap<MyObject>(args.This());
  obj->counter_ += 1;

  return scope.Close(Number::New(obj->counter_));
}

Test it with: 

var addon = require('./build/Release/addon');

var obj = new addon.MyObject(10);
console.log( obj.plusOne() ); // 11
console.log( obj.plusOne() ); // 12
console.log( obj.plusOne() ); // 13

Factory of wrapped objects#

This is useful when you want to be able to create native objects without explicitly instantiating them with the new operator in JavaScript, e.g. 

var obj = addon.createObject();
// instead of:
// var obj = new addon.Object();

Let's register our createObject method in addon.cc: 

#define BUILDING_NODE_EXTENSION
#include <node.h>
#include "myobject.h"

using namespace v8;

Handle<Value> CreateObject(const Arguments& args) {
  HandleScope scope;
  return scope.Close(MyObject::NewInstance(args));
}

void InitAll(Handle<Object> target) {
  MyObject::Init();

  target->Set(String::NewSymbol("createObject"),
      FunctionTemplate::New(CreateObject)->GetFunction());
}

NODE_MODULE(addon, InitAll)

In myobject.h we now introduce the static method NewInstance that takes care of instantiating the object (i.e. it does the job of new in JavaScript): 

#define BUILDING_NODE_EXTENSION
#ifndef MYOBJECT_H
#define MYOBJECT_H

#include <node.h>

class MyObject : public node::ObjectWrap {
 public:
  static void Init();
  static v8::Handle<v8::Value> NewInstance(const v8::Arguments& args);

 private:
  MyObject();
  ~MyObject();

  static v8::Persistent<v8::Function> constructor;
  static v8::Handle<v8::Value> New(const v8::Arguments& args);
  static v8::Handle<v8::Value> PlusOne(const v8::Arguments& args);
  double counter_;
};

#endif

The implementation is similar to the above in myobject.cc: 

#define BUILDING_NODE_EXTENSION
#include <node.h>
#include "myobject.h"

using namespace v8;

MyObject::MyObject() {};
MyObject::~MyObject() {};

Persistent<Function> MyObject::constructor;

void MyObject::Init() {
  // Prepare constructor template
  Local<FunctionTemplate> tpl = FunctionTemplate::New(New);
  tpl->SetClassName(String::NewSymbol("MyObject"));
  tpl->InstanceTemplate()->SetInternalFieldCount(1);
  // Prototype
  tpl->PrototypeTemplate()->Set(String::NewSymbol("plusOne"),
      FunctionTemplate::New(PlusOne)->GetFunction());

  constructor = Persistent<Function>::New(tpl->GetFunction());
}

Handle<Value> MyObject::New(const Arguments& args) {
  HandleScope scope;

  MyObject* obj = new MyObject();
  obj->counter_ = args[0]->IsUndefined() ? 0 : args[0]->NumberValue();
  obj->Wrap(args.This());

  return args.This();
}

Handle<Value> MyObject::NewInstance(const Arguments& args) {
  HandleScope scope;

  const unsigned argc = 1;
  Handle<Value> argv[argc] = { args[0] };
  Local<Object> instance = constructor->NewInstance(argc, argv);

  return scope.Close(instance);
}

Handle<Value> MyObject::PlusOne(const Arguments& args) {
  HandleScope scope;

  MyObject* obj = ObjectWrap::Unwrap<MyObject>(args.This());
  obj->counter_ += 1;

  return scope.Close(Number::New(obj->counter_));
}

Test it with: 

var addon = require('./build/Release/addon');

var obj = addon.createObject(10);
console.log( obj.plusOne() ); // 11
console.log( obj.plusOne() ); // 12
console.log( obj.plusOne() ); // 13

var obj2 = addon.createObject(20);
console.log( obj2.plusOne() ); // 21
console.log( obj2.plusOne() ); // 22
console.log( obj2.plusOne() ); // 23

Passing wrapped objects around#

In addition to wrapping and returning C++ objects, you can pass them around by unwrapping them with Node's node::ObjectWrap::Unwrap helper function. In the following addon.cc we introduce a function add() that can take on two MyObject objects: 

#define BUILDING_NODE_EXTENSION
#include <node.h>
#include "myobject.h"

using namespace v8;

Handle<Value> CreateObject(const Arguments& args) {
  HandleScope scope;
  return scope.Close(MyObject::NewInstance(args));
}

Handle<Value> Add(const Arguments& args) {
  HandleScope scope;

  MyObject* obj1 = node::ObjectWrap::Unwrap<MyObject>(
      args[0]->ToObject());
  MyObject* obj2 = node::ObjectWrap::Unwrap<MyObject>(
      args[1]->ToObject());

  double sum = obj1->Val() + obj2->Val();
  return scope.Close(Number::New(sum));
}

void InitAll(Handle<Object> target) {
  MyObject::Init();

  target->Set(String::NewSymbol("createObject"),
      FunctionTemplate::New(CreateObject)->GetFunction());

  target->Set(String::NewSymbol("add"),
      FunctionTemplate::New(Add)->GetFunction());
}

NODE_MODULE(addon, InitAll)

To make things interesting we introduce a public method in myobject.h so we can probe private values after unwrapping the object: 

#define BUILDING_NODE_EXTENSION
#ifndef MYOBJECT_H
#define MYOBJECT_H

#include <node.h>

class MyObject : public node::ObjectWrap {
 public:
  static void Init();
  static v8::Handle<v8::Value> NewInstance(const v8::Arguments& args);
  double Val() const { return val_; }

 private:
  MyObject();
  ~MyObject();

  static v8::Persistent<v8::Function> constructor;
  static v8::Handle<v8::Value> New(const v8::Arguments& args);
  double val_;
};

#endif

The implementation of myobject.cc is similar as before: 

#define BUILDING_NODE_EXTENSION
#include <node.h>
#include "myobject.h"

using namespace v8;

MyObject::MyObject() {};
MyObject::~MyObject() {};

Persistent<Function> MyObject::constructor;

void MyObject::Init() {
  // Prepare constructor template
  Local<FunctionTemplate> tpl = FunctionTemplate::New(New);
  tpl->SetClassName(String::NewSymbol("MyObject"));
  tpl->InstanceTemplate()->SetInternalFieldCount(1);

  constructor = Persistent<Function>::New(tpl->GetFunction());
}

Handle<Value> MyObject::New(const Arguments& args) {
  HandleScope scope;

  MyObject* obj = new MyObject();
  obj->val_ = args[0]->IsUndefined() ? 0 : args[0]->NumberValue();
  obj->Wrap(args.This());

  return args.This();
}

Handle<Value> MyObject::NewInstance(const Arguments& args) {
  HandleScope scope;

  const unsigned argc = 1;
  Handle<Value> argv[argc] = { args[0] };
  Local<Object> instance = constructor->NewInstance(argc, argv);

  return scope.Close(instance);
}

Test it with: 

var addon = require('./build/Release/addon');

var obj1 = addon.createObject(10);
var obj2 = addon.createObject(20);
var result = addon.add(obj1, obj2);

console.log(result); // 30

process#

The process object is a global object and can be accessed from anywhere. It is an instance of EventEmitter.

Event: 'exit'#

Emitted when the process is about to exit. This is a good hook to perform constant time checks of the module's state (like for unit tests). The main event loop will no longer be run after the 'exit' callback finishes, so timers may not be scheduled.

Example of listening for exit: 

process.on('exit', function () {
  process.nextTick(function () {
   console.log('This will not run');
  });
  console.log('About to exit.');
});

Event: 'uncaughtException'#

Emitted when an exception bubbles all the way back to the event loop. If a listener is added for this exception, the default action (which is to print a stack trace and exit) will not occur.

Example of listening for uncaughtException: 

process.on('uncaughtException', function (err) {
  console.log('Caught exception: ' + err);
});

setTimeout(function () {
  console.log('This will still run.');
}, 500);

// Intentionally cause an exception, but don't catch it.
nonexistentFunc();
console.log('This will not run.');

Note that uncaughtException is a very crude mechanism for exception handling. Using try / catch in your program will give you more control over your program's flow. Especially for server programs that are designed to stay running forever, uncaughtException can be a useful safety mechanism.

Signal Events#

Emitted when the processes receives a signal. See sigaction(2) for a list of standard POSIX signal names such as SIGINT, SIGUSR1, etc.

Example of listening for SIGINT: 

// Start reading from stdin so we don't exit.
process.stdin.resume();

process.on('SIGINT', function () {
  console.log('Got SIGINT.  Press Control-D to exit.');
});

An easy way to send the SIGINT signal is with Control-C in most terminal programs.

process.stdout#

A Writable Stream to stdout.

Example: the definition of console.log 

console.log = function (d) {
  process.stdout.write(d + '\n');
};

process.stderr and process.stdout are unlike other streams in Node in that writes to them are usually blocking. They are blocking in the case that they refer to regular files or TTY file descriptors. In the case they refer to pipes, they are non-blocking like other streams.

process.stderr#

A writable stream to stderr.

process.stderr and process.stdout are unlike other streams in Node in that writes to them are usually blocking. They are blocking in the case that they refer to regular files or TTY file descriptors. In the case they refer to pipes, they are non-blocking like other streams.

process.stdin#

A Readable Stream for stdin. The stdin stream is paused by default, so one must call process.stdin.resume() to read from it.

Example of opening standard input and listening for both events: 

process.stdin.resume();
process.stdin.setEncoding('utf8');

process.stdin.on('data', function (chunk) {
  process.stdout.write('data: ' + chunk);
});

process.stdin.on('end', function () {
  process.stdout.write('end');
});

process.argv#

An array containing the command line arguments. The first element will be 'node', the second element will be the name of the JavaScript file. The next elements will be any additional command line arguments. 

// print process.argv
process.argv.forEach(function (val, index, array) {
  console.log(index + ': ' + val);
});

This will generate: 

$ node process-2.js one two=three four
0: node
1: /Users/mjr/work/node/process-2.js
2: one
3: two=three
4: four

process.execPath#

This is the absolute pathname of the executable that started the process.

Example: 

/usr/local/bin/node

process.abort()#

This causes node to emit an abort. This will cause node to exit and generate a core file.

process.chdir(directory)#

Changes the current working directory of the process or throws an exception if that fails. 

console.log('Starting directory: ' + process.cwd());
try {
  process.chdir('/tmp');
  console.log('New directory: ' + process.cwd());
}
catch (err) {
  console.log('chdir: ' + err);
}

process.cwd()#

Returns the current working directory of the process. 

console.log('Current directory: ' + process.cwd());

process.env#

An object containing the user environment. See environ(7).

process.exit([code])#

Ends the process with the specified code. If omitted, exit uses the 'success' code 0.

To exit with a 'failure' code: 

process.exit(1);

The shell that executed node should see the exit code as 1.

process.getgid()#

Gets the group identity of the process. (See getgid(2).) This is the numerical group id, not the group name. 

console.log('Current gid: ' + process.getgid());

process.setgid(id)#

Sets the group identity of the process. (See setgid(2).) This accepts either a numerical ID or a groupname string. If a groupname is specified, this method blocks while resolving it to a numerical ID. 

console.log('Current gid: ' + process.getgid());
try {
  process.setgid(501);
  console.log('New gid: ' + process.getgid());
}
catch (err) {
  console.log('Failed to set gid: ' + err);
}

process.getuid()#

Gets the user identity of the process. (See getuid(2).) This is the numerical userid, not the username. 

console.log('Current uid: ' + process.getuid());

process.setuid(id)#

Sets the user identity of the process. (See setuid(2).) This accepts either a numerical ID or a username string. If a username is specified, this method blocks while resolving it to a numerical ID. 

console.log('Current uid: ' + process.getuid());
try {
  process.setuid(501);
  console.log('New uid: ' + process.getuid());
}
catch (err) {
  console.log('Failed to set uid: ' + err);
}

process.version#

A compiled-in property that exposes NODE_VERSION. 

console.log('Version: ' + process.version);

process.versions#

A property exposing version strings of node and its dependencies. 

console.log(process.versions);

Will output: 

{ node: '0.4.12',
  v8: '3.1.8.26',
  ares: '1.7.4',
  ev: '4.4',
  openssl: '1.0.0e-fips' }

process.config#

An Object containing the JavaScript representation of the configure options that were used to compile the current node executable. This is the same as the "config.gypi" file that was produced when running the ./configure script.

An example of the possible output looks like: 

{ target_defaults:
   { cflags: [],
     default_configuration: 'Release',
     defines: [],
     include_dirs: [],
     libraries: [] },
  variables:
   { host_arch: 'x64',
     node_install_npm: 'true',
     node_install_waf: 'true',
     node_prefix: '',
     node_shared_v8: 'false',
     node_shared_zlib: 'false',
     node_use_dtrace: 'false',
     node_use_openssl: 'true',
     node_use_system_openssl: 'false',
     strict_aliasing: 'true',
     target_arch: 'x64',
     v8_use_snapshot: 'true' } }

process.installPrefix#

A compiled-in property that exposes NODE_PREFIX. 

console.log('Prefix: ' + process.installPrefix);

process.kill(pid, [signal])#

Send a signal to a process. pid is the process id and signal is the string describing the signal to send. Signal names are strings like 'SIGINT' or 'SIGUSR1'. If omitted, the signal will be 'SIGTERM'. See kill(2) for more information.

Note that just because the name of this function is process.kill, it is really just a signal sender, like the kill system call. The signal sent may do something other than kill the target process.

Example of sending a signal to yourself: 

process.on('SIGHUP', function () {
  console.log('Got SIGHUP signal.');
});

setTimeout(function () {
  console.log('Exiting.');
  process.exit(0);
}, 100);

process.kill(process.pid, 'SIGHUP');

process.pid#

The PID of the process. 

console.log('This process is pid ' + process.pid);

process.title#

Getter/setter to set what is displayed in 'ps'.

process.arch#

What processor architecture you're running on: 'arm', 'ia32', or 'x64'. 

console.log('This processor architecture is ' + process.arch);

process.platform#

What platform you're running on. 'linux2', 'darwin', etc. 

console.log('This platform is ' + process.platform);

process.memoryUsage()#

Returns an object describing the memory usage of the Node process measured in bytes. 

var util = require('util');

console.log(util.inspect(process.memoryUsage()));

This will generate: 

{ rss: 4935680,
  heapTotal: 1826816,
  heapUsed: 650472 }

heapTotal and heapUsed refer to V8's memory usage.

process.nextTick(callback)#

On the next loop around the event loop call this callback. This is not a simple alias to setTimeout(fn, 0), it's much more efficient. 

process.nextTick(function () {
  console.log('nextTick callback');
});

process.umask([mask])#

Sets or reads the process's file mode creation mask. Child processes inherit the mask from the parent process. Returns the old mask if mask argument is given, otherwise returns the current mask. 

var oldmask, newmask = 0644;

oldmask = process.umask(newmask);
console.log('Changed umask from: ' + oldmask.toString(8) +
            ' to ' + newmask.toString(8));

process.uptime()#

Number of seconds Node has been running.

process.hrtime()#

Returns the current high-resolution real time in a [seconds, nanoseconds] tuple Array. It is relative to an arbitrary time in the past. It is not related to the time of day and therefore not subject to clock drift. The primary use is for measuring performance between intervals.

You may pass in the result of a previous call to process.hrtime() to get a diff reading, useful for benchmarks and measuring intervals: 

var t = process.hrtime();
// [ 1800216, 927643717 ]

setTimeout(function () {
  t = process.hrtime(t);
  // [ 1, 6962306 ]

  console.log('benchmark took %d seconds and %d nanoseconds', t[0], t[1]);
  // benchmark took 1 seconds and 6962306 nanoseconds
}, 1000);

util#

Stability: 5 - Locked

These functions are in the module 'util'. Use require('util') to access them.

util.format()#

Returns a formatted string using the first argument as a printf-like format.

The first argument is a string that contains zero or more placeholders. Each placeholder is replaced with the converted value from its corresponding argument. Supported placeholders are:

  • %s - String.
  • %d - Number (both integer and float).
  • %j - JSON.
  • % - single percent sign ('%'). This does not consume an argument.

If the placeholder does not have a corresponding argument, the placeholder is not replaced. 

util.format('%s:%s', 'foo'); // 'foo:%s'

If there are more arguments than placeholders, the extra arguments are converted to strings with util.inspect() and these strings are concatenated, delimited by a space. 

util.format('%s:%s', 'foo', 'bar', 'baz'); // 'foo:bar baz'

If the first argument is not a format string then util.format() returns a string that is the concatenation of all its arguments separated by spaces. Each argument is converted to a string with util.inspect(). 

util.format(1, 2, 3); // '1 2 3'

util.debug(string)#

A synchronous output function. Will block the process and output string immediately to stderr. 

require('util').debug('message on stderr');

util.log(string)#

Output with timestamp on stdout. 

require('util').log('Timestamped message.');

util.inspect(object, [showHidden], [depth], [colors])#

Return a string representation of object, which is useful for debugging.

If showHidden is true, then the object's non-enumerable properties will be shown too. Defaults to false.

If depth is provided, it tells inspect how many times to recurse while formatting the object. This is useful for inspecting large complicated objects.

The default is to only recurse twice. To make it recurse indefinitely, pass in null for depth.

If colors is true, the output will be styled with ANSI color codes. Defaults to false.

Example of inspecting all properties of the util object: 

var util = require('util');

console.log(util.inspect(util, true, null));

util.isArray(object)#

Returns true if the given "object" is an Array. false otherwise. 

var util = require('util');

util.isArray([])
  // true
util.isArray(new Array)
  // true
util.isArray({})
  // false

util.isRegExp(object)#

Returns true if the given "object" is a RegExp. false otherwise. 

var util = require('util');

util.isRegExp(/some regexp/)
  // true
util.isRegExp(new RegExp('another regexp'))
  // true
util.isRegExp({})
  // false

util.isDate(object)#

Returns true if the given "object" is a Date. false otherwise. 

var util = require('util');

util.isDate(new Date())
  // true
util.isDate(Date())
  // false (without 'new' returns a String)
util.isDate({})
  // false

util.isError(object)#

Returns true if the given "object" is an Error. false otherwise. 

var util = require('util');

util.isError(new Error())
  // true
util.isError(new TypeError())
  // true
util.isError({ name: 'Error', message: 'an error occurred' })
  // false

util.pump(readableStream, writableStream, [callback])#

Experimental

Read the data from readableStream and send it to the writableStream. When writableStream.write(data) returns false readableStream will be paused until the drain event occurs on the writableStream. callback gets an error as its only argument and is called when writableStream is closed or when an error occurs.

util.inherits(constructor, superConstructor)#

Inherit the prototype methods from one constructor into another. The prototype of constructor will be set to a new object created from superConstructor.

As an additional convenience, superConstructor will be accessible through the constructor.super_ property. 

var util = require("util");
var events = require("events");

function MyStream() {
    events.EventEmitter.call(this);
}

util.inherits(MyStream, events.EventEmitter);

MyStream.prototype.write = function(data) {
    this.emit("data", data);
}

var stream = new MyStream();

console.log(stream instanceof events.EventEmitter); // true
console.log(MyStream.super_ === events.EventEmitter); // true

stream.on("data", function(data) {
    console.log('Received data: "' + data + '"');
})
stream.write("It works!"); // Received data: "It works!"

Events#

Stability: 4 - API Frozen

Many objects in Node emit events: a net.Server emits an event each time a peer connects to it, a fs.readStream emits an event when the file is opened. All objects which emit events are instances of events.EventEmitter. You can access this module by doing: require("events");

Typically, event names are represented by a camel-cased string, however, there aren't any strict restrictions on that, as any string will be accepted.

Functions can then be attached to objects, to be executed when an event is emitted. These functions are called listeners.

Class: events.EventEmitter#

To access the EventEmitter class, require('events').EventEmitter.

When an EventEmitter instance experiences an error, the typical action is to emit an 'error' event. Error events are treated as a special case in node. If there is no listener for it, then the default action is to print a stack trace and exit the program.

All EventEmitters emit the event 'newListener' when new listeners are added.

emitter.addListener(event, listener)#

emitter.on(event, listener)#

Adds a listener to the end of the listeners array for the specified event. 

server.on('connection', function (stream) {
  console.log('someone connected!');
});

emitter.once(event, listener)#

Adds a one time listener for the event. This listener is invoked only the next time the event is fired, after which it is removed. 

server.once('connection', function (stream) {
  console.log('Ah, we have our first user!');
});

emitter.removeListener(event, listener)#

Remove a listener from the listener array for the specified event. Caution: changes array indices in the listener array behind the listener. 

var callback = function(stream) {
  console.log('someone connected!');
};
server.on('connection', callback);
// ...
server.removeListener('connection', callback);

emitter.removeAllListeners([event])#

Removes all listeners, or those of the specified event.

emitter.setMaxListeners(n)#

By default EventEmitters will print a warning if more than 10 listeners are added for a particular event. This is a useful default which helps finding memory leaks. Obviously not all Emitters should be limited to 10. This function allows that to be increased. Set to zero for unlimited.

emitter.listeners(event)#

Returns an array of listeners for the specified event. This array can be manipulated, e.g. to remove listeners. 

server.on('connection', function (stream) {
  console.log('someone connected!');
});
console.log(util.inspect(server.listeners('connection'))); // [ [Function] ]

emitter.emit(event, [arg1], [arg2], [...])#

Execute each of the listeners in order with the supplied arguments.

Event: 'newListener'#

  • event String The event name
  • listener Function The event handler function

This event is emitted any time someone adds a new listener.

Domain#

Stability: 1 - Experimental

Domains provide a way to handle multiple different IO operations as a single group. If any of the event emitters or callbacks registered to a domain emit an error event, or throw an error, then the domain object will be notified, rather than losing the context of the error in the process.on('uncaughtException') handler, or causing the program to exit with an error code.

This feature is new in Node version 0.8. It is a first pass, and is expected to change significantly in future versions. Please use it and provide feedback.

Due to their experimental nature, the Domains features are disabled unless the domain module is loaded at least once. No domains are created or registered by default. This is by design, to prevent adverse effects on current programs. It is expected to be enabled by default in future Node.js versions.

Additions to Error objects#

Any time an Error object is routed through a domain, a few extra fields are added to it.

  • error.domain The domain that first handled the error.
  • error.domain_emitter The event emitter that emitted an 'error' event with the error object.
  • error.domain_bound The callback function which was bound to the domain, and passed an error as its first argument.
  • error.domain_thrown A boolean indicating whether the error was thrown, emitted, or passed to a bound callback function.

Implicit Binding#

If domains are in use, then all new EventEmitter objects (including Stream objects, requests, responses, etc.) will be implicitly bound to the active domain at the time of their creation.

Additionally, callbacks passed to lowlevel event loop requests (such as to fs.open, or other callback-taking methods) will automatically be bound to the active domain. If they throw, then the domain will catch the error.

In order to prevent excessive memory usage, Domain objects themselves are not implicitly added as children of the active domain. If they were, then it would be too easy to prevent request and response objects from being properly garbage collected.

If you want to nest Domain objects as children of a parent Domain, then you must explicitly add them, and then dispose of them later.

Implicit binding routes thrown errors and 'error' events to the Domain's error event, but does not register the EventEmitter on the Domain, so domain.dispose() will not shut down the EventEmitter. Implicit binding only takes care of thrown errors and 'error' events.

domain.create()#

  • return: Domain

Returns a new Domain object.

Class: Domain#

The Domain class encapsulates the functionality of routing errors and uncaught exceptions to the active Domain object.

Domain is a child class of EventEmitter. To handle the errors that it catches, listen to its error event.

domain.members#

  • Array

An array of timers and event emitters that have been explicitly added to the domain.

domain.add(emitter)#

  • emitter EventEmitter | Timer emitter or timer to be added to the domain

Explicitly adds an emitter to the domain. If any event handlers called by the emitter throw an error, or if the emitter emits an error event, it will be routed to the domain's error event, just like with implicit binding.

This also works with timers that are returned from setInterval and setTimeout. If their callback function throws, it will be caught by the domain 'error' handler.

If the Timer or EventEmitter was already bound to a domain, it is removed from that one, and bound to this one instead.

domain.remove(emitter)#

  • emitter EventEmitter | Timer emitter or timer to be removed from the domain

The opposite of domain.add(emitter). Removes domain handling from the specified emitter.

domain.bind(cb)#

  • cb Function The callback function
  • return: Function The bound function

The returned function will be a wrapper around the supplied callback function. When the returned function is called, any errors that are thrown will be routed to the domain's error event.

Example#

var d = domain.create();

function readSomeFile(filename, cb) {
  fs.readFile(filename, d.bind(function(er, data) {
    // if this throws, it will also be passed to the domain
    return cb(er, JSON.parse(data));
  }));
}

d.on('error', function(er) {
  // an error occurred somewhere.
  // if we throw it now, it will crash the program
  // with the normal line number and stack message.
});

domain.intercept(cb)#

  • cb Function The callback function
  • return: Function The intercepted function

This method is almost identical to domain.bind(cb). However, in addition to catching thrown errors, it will also intercept Error objects sent as the first argument to the function.

In this way, the common if (er) return cb(er); pattern can be replaced with a single error handler in a single place.

Example#

var d = domain.create();

function readSomeFile(filename, cb) {
  fs.readFile(filename, d.intercept(function(er, data) {
    // if this throws, it will also be passed to the domain
    // additionally, we know that 'er' will always be null,
    // so the error-handling logic can be moved to the 'error'
    // event on the domain instead of being repeated throughout
    // the program.
    return cb(er, JSON.parse(data));
  }));
}

d.on('error', function(er) {
  // an error occurred somewhere.
  // if we throw it now, it will crash the program
  // with the normal line number and stack message.
});

domain.dispose()#

The dispose method destroys a domain, and makes a best effort attempt to clean up any and all IO that is associated with the domain. Streams are aborted, ended, closed, and/or destroyed. Timers are cleared. Explicitly bound callbacks are no longer called. Any error events that are raised as a result of this are ignored.

The intention of calling dispose is generally to prevent cascading errors when a critical part of the Domain context is found to be in an error state.

Note that IO might still be performed. However, to the highest degree possible, once a domain is disposed, further errors from the emitters in that set will be ignored. So, even if some remaining actions are still in flight, Node.js will not communicate further about them.

Buffer#

Stability: 3 - Stable

Pure Javascript is Unicode friendly but not nice to binary data. When dealing with TCP streams or the file system, it's necessary to handle octet streams. Node has several strategies for manipulating, creating, and consuming octet streams.

Raw data is stored in instances of the Buffer class. A Buffer is similar to an array of integers but corresponds to a raw memory allocation outside the V8 heap. A Buffer cannot be resized.

The Buffer class is a global, making it very rare that one would need to ever require('buffer').

Converting between Buffers and JavaScript string objects requires an explicit encoding method. Here are the different string encodings.

  • 'ascii' - for 7 bit ASCII data only. This encoding method is very fast, and will strip the high bit if set. Note that this encoding converts a null character ('\0' or '\u0000') into 0x20 (character code of a space). If you want to convert a null character into 0x00, you should use 'utf8'.

  • 'utf8' - Multi byte encoded Unicode characters. Many web pages and other document formats use UTF-8.

  • 'ucs2' - 2-bytes, little endian encoded Unicode characters. It can encode only BMP(Basic Multilingual Plane, U+0000 - U+FFFF).

  • 'base64' - Base64 string encoding.

  • 'binary' - A way of encoding raw binary data into strings by using only the first 8 bits of each character. This encoding method is deprecated and should be avoided in favor of Buffer objects where possible. This encoding will be removed in future versions of Node.

  • 'hex' - Encode each byte as two hexidecimal characters.

Class: Buffer#

The Buffer class is a global type for dealing with binary data directly. It can be constructed in a variety of ways.

new Buffer(size)#

  • size Number

Allocates a new buffer of size octets.

new Buffer(array)#

  • array Array

Allocates a new buffer using an array of octets.

new Buffer(str, [encoding])#

  • str String - string to encode.
  • encoding String - encoding to use, Optional.

Allocates a new buffer containing the given str. encoding defaults to 'utf8'.

buf.write(string, [offset], [length], [encoding])#

  • string String - data to be written to buffer
  • offset Number, Optional, Default: 0
  • length Number, Optional
  • encoding String, Optional, Default: 'utf8'

Writes string to the buffer at offset using the given encoding. offset defaults to 0, encoding defaults to 'utf8'. length is the number of bytes to write. Returns number of octets written. If buffer did not contain enough space to fit the entire string, it will write a partial amount of the string. length defaults to buffer.length - offset. The method will not write partial characters. 

buf = new Buffer(256);
len = buf.write('\u00bd + \u00bc = \u00be', 0);
console.log(len + " bytes: " + buf.toString('utf8', 0, len));

The number of characters written (which may be different than the number of bytes written) is set in Buffer._charsWritten and will be overwritten the next time buf.write() is called.

buf.toString([encoding], [start], [end])#

  • encoding String, Optional, Default: 'utf8'
  • start Number, Optional, Default: 0
  • end Number, Optional

Decodes and returns a string from buffer data encoded with encoding (defaults to 'utf8') beginning at start (defaults to 0) and ending at end (defaults to buffer.length).

See buffer.write() example, above.

buf[index]#

Get and set the octet at index. The values refer to individual bytes, so the legal range is between 0x00 and 0xFF hex or 0 and 255.

Example: copy an ASCII string into a buffer, one byte at a time: 

str = "node.js";
buf = new Buffer(str.length);

for (var i = 0; i < str.length ; i++) {
  buf[i] = str.charCodeAt(i);
}

console.log(buf);

// node.js

Class Method: Buffer.isBuffer(obj)#

  • obj Object
  • Return: Boolean

Tests if obj is a Buffer.

Class Method: Buffer.byteLength(string, [encoding])#

  • string String
  • encoding String, Optional, Default: 'utf8'
  • Return: Number

Gives the actual byte length of a string. encoding defaults to 'utf8'. This is not the same as String.prototype.length since that returns the number of characters in a string.

Example: 

str = '\u00bd + \u00bc = \u00be';

console.log(str + ": " + str.length + " characters, " +
  Buffer.byteLength(str, 'utf8') + " bytes");

// ½ + ¼ = ¾: 9 characters, 12 bytes

buf.length#

  • Number

The size of the buffer in bytes. Note that this is not necessarily the size of the contents. length refers to the amount of memory allocated for the buffer object. It does not change when the contents of the buffer are changed. 

buf = new Buffer(1234);

console.log(buf.length);
buf.write("some string", 0, "ascii");
console.log(buf.length);

// 1234
// 1234

buf.copy(targetBuffer, [targetStart], [sourceStart], [sourceEnd])#

  • targetBuffer Buffer object - Buffer to copy into
  • targetStart Number, Optional, Default: 0
  • sourceStart Number, Optional, Default: 0
  • sourceEnd Number, Optional, Default: 0

Does copy between buffers. The source and target regions can be overlapped. targetStart and sourceStart default to 0. sourceEnd defaults to buffer.length.

Example: build two Buffers, then copy buf1 from byte 16 through byte 19 into buf2, starting at the 8th byte in buf2. 

buf1 = new Buffer(26);
buf2 = new Buffer(26);

for (var i = 0 ; i < 26 ; i++) {
  buf1[i] = i + 97; // 97 is ASCII a
  buf2[i] = 33; // ASCII !
}

buf1.copy(buf2, 8, 16, 20);
console.log(buf2.toString('ascii', 0, 25));

// !!!!!!!!qrst!!!!!!!!!!!!!

buf.slice([start], [end])#

  • start Number, Optional, Default: 0
  • end Number, Optional, Default: 0

Returns a new buffer which references the same memory as the old, but offset and cropped by the start (defaults to 0) and end (defaults to buffer.length) indexes.

Modifying the new buffer slice will modify memory in the original buffer!

Example: build a Buffer with the ASCII alphabet, take a slice, then modify one byte from the original Buffer. 

var buf1 = new Buffer(26);

for (var i = 0 ; i < 26 ; i++) {
  buf1[i] = i + 97; // 97 is ASCII a
}

var buf2 = buf1.slice(0, 3);
console.log(buf2.toString('ascii', 0, buf2.length));
buf1[0] = 33;
console.log(buf2.toString('ascii', 0, buf2.length));

// abc
// !bc

buf.readUInt8(offset, [noAssert])#

  • offset Number
  • noAssert Boolean, Optional, Default: false
  • Return: Number

Reads an unsigned 8 bit integer from the buffer at the specified offset.

Set noAssert to true to skip validation of offset. This means that offset may be beyond the end of the buffer. Defaults to false.

Example: 

var buf = new Buffer(4);

buf[0] = 0x3;
buf[1] = 0x4;
buf[2] = 0x23;
buf[3] = 0x42;

for (ii = 0; ii < buf.length; ii++) {
  console.log(buf.readUInt8(ii));
}

// 0x3
// 0x4
// 0x23
// 0x42

buf.readUInt16LE(offset, [noAssert])#

buf.readUInt16BE(offset, [noAssert])#

  • offset Number
  • noAssert Boolean, Optional, Default: false
  • Return: Number

Reads an unsigned 16 bit integer from the buffer at the specified offset with specified endian format.

Set noAssert to true to skip validation of offset. This means that offset may be beyond the end of the buffer. Defaults to false.

Example: 

var buf = new Buffer(4);

buf[0] = 0x3;
buf[1] = 0x4;
buf[2] = 0x23;
buf[3] = 0x42;

console.log(buf.readUInt16BE(0));
console.log(buf.readUInt16LE(0));
console.log(buf.readUInt16BE(1));
console.log(buf.readUInt16LE(1));
console.log(buf.readUInt16BE(2));
console.log(buf.readUInt16LE(2));

// 0x0304
// 0x0403
// 0x0423
// 0x2304
// 0x2342
// 0x4223

buf.readUInt32LE(offset, [noAssert])#

buf.readUInt32BE(offset, [noAssert])#

  • offset Number
  • noAssert Boolean, Optional, Default: false
  • Return: Number

Reads an unsigned 32 bit integer from the buffer at the specified offset with specified endian format.

Set noAssert to true to skip validation of offset. This means that offset may be beyond the end of the buffer. Defaults to false.

Example: 

var buf = new Buffer(4);

buf[0] = 0x3;
buf[1] = 0x4;
buf[2] = 0x23;
buf[3] = 0x42;

console.log(buf.readUInt32BE(0));
console.log(buf.readUInt32LE(0));

// 0x03042342
// 0x42230403

buf.readInt8(offset, [noAssert])#

  • offset Number
  • noAssert Boolean, Optional, Default: false
  • Return: Number

Reads a signed 8 bit integer from the buffer at the specified offset.

Set noAssert to true to skip validation of offset. This means that offset may be beyond the end of the buffer. Defaults to false.

Works as buffer.readUInt8, except buffer contents are treated as two's complement signed values.

buf.readInt16LE(offset, [noAssert])#

buf.readInt16BE(offset, [noAssert])#

  • offset Number
  • noAssert Boolean, Optional, Default: false
  • Return: Number

Reads a signed 16 bit integer from the buffer at the specified offset with specified endian format.

Set noAssert to true to skip validation of offset. This means that offset may be beyond the end of the buffer. Defaults to false.

Works as buffer.readUInt16*, except buffer contents are treated as two's complement signed values.

buf.readInt32LE(offset, [noAssert])#

buf.readInt32BE(offset, [noAssert])#

  • offset Number
  • noAssert Boolean, Optional, Default: false
  • Return: Number

Reads a signed 32 bit integer from the buffer at the specified offset with specified endian format.

Set noAssert to true to skip validation of offset. This means that offset may be beyond the end of the buffer. Defaults to false.

Works as buffer.readUInt32*, except buffer contents are treated as two's complement signed values.

buf.readFloatLE(offset, [noAssert])#

buf.readFloatBE(offset, [noAssert])#

  • offset Number
  • noAssert Boolean, Optional, Default: false
  • Return: Number

Reads a 32 bit float from the buffer at the specified offset with specified endian format.

Set noAssert to true to skip validation of offset. This means that offset may be beyond the end of the buffer. Defaults to false.

Example: 

var buf = new Buffer(4);

buf[0] = 0x00;
buf[1] = 0x00;
buf[2] = 0x80;
buf[3] = 0x3f;

console.log(buf.readFloatLE(0));

// 0x01

buf.readDoubleLE(offset, [noAssert])#

buf.readDoubleBE(offset, [noAssert])#

  • offset Number
  • noAssert Boolean, Optional, Default: false
  • Return: Number

Reads a 64 bit double from the buffer at the specified offset with specified endian format.

Set noAssert to true to skip validation of offset. This means that offset may be beyond the end of the buffer. Defaults to false.

Example: 

var buf = new Buffer(8);

buf[0] = 0x55;
buf[1] = 0x55;
buf[2] = 0x55;
buf[3] = 0x55;
buf[4] = 0x55;
buf[5] = 0x55;
buf[6] = 0xd5;
buf[7] = 0x3f;

console.log(buf.readDoubleLE(0));

// 0.3333333333333333

buf.writeUInt8(value, offset, [noAssert])#

  • value Number
  • offset Number
  • noAssert Boolean, Optional, Default: false

Writes value to the buffer at the specified offset. Note, value must be a valid unsigned 8 bit integer.

Set noAssert to true to skip validation of value and offset. This means that value may be too large for the specific function and offset may be beyond the end of the buffer leading to the values being silently dropped. This should not be used unless you are certain of correctness. Defaults to false.

Example: 

var buf = new Buffer(4);
buf.writeUInt8(0x3, 0);
buf.writeUInt8(0x4, 1);
buf.writeUInt8(0x23, 2);
buf.writeUInt8(0x42, 3);

console.log(buf);

// <Buffer 03 04 23 42>

buf.writeUInt16LE(value, offset, [noAssert])#

buf.writeUInt16BE(value, offset, [noAssert])#

  • value Number
  • offset Number
  • noAssert Boolean, Optional, Default: false

Writes value to the buffer at the specified offset with specified endian format. Note, value must be a valid unsigned 16 bit integer.

Set noAssert to true to skip validation of value and offset. This means that value may be too large for the specific function and offset may be beyond the end of the buffer leading to the values being silently dropped. This should not be used unless you are certain of correctness. Defaults to false.

Example: 

var buf = new Buffer(4);
buf.writeUInt16BE(0xdead, 0);
buf.writeUInt16BE(0xbeef, 2);

console.log(buf);

buf.writeUInt16LE(0xdead, 0);
buf.writeUInt16LE(0xbeef, 2);

console.log(buf);

// <Buffer de ad be ef>
// <Buffer ad de ef be>

buf.writeUInt32LE(value, offset, [noAssert])#

buf.writeUInt32BE(value, offset, [noAssert])#

  • value Number
  • offset Number
  • noAssert Boolean, Optional, Default: false

Writes value to the buffer at the specified offset with specified endian format. Note, value must be a valid unsigned 32 bit integer.

Set noAssert to true to skip validation of value and offset. This means that value may be too large for the specific function and offset may be beyond the end of the buffer leading to the values being silently dropped. This should not be used unless you are certain of correctness. Defaults to false.

Example: 

var buf = new Buffer(4);
buf.writeUInt32BE(0xfeedface, 0);

console.log(buf);

buf.writeUInt32LE(0xfeedface, 0);

console.log(buf);

// <Buffer fe ed fa ce>
// <Buffer ce fa ed fe>

buf.writeInt8(value, offset, [noAssert])#

  • value Number
  • offset Number
  • noAssert Boolean, Optional, Default: false

Writes value to the buffer at the specified offset. Note, value must be a valid signed 8 bit integer.

Set noAssert to true to skip validation of value and offset. This means that value may be too large for the specific function and offset may be beyond the end of the buffer leading to the values being silently dropped. This should not be used unless you are certain of correctness. Defaults to false.

Works as buffer.writeUInt8, except value is written out as a two's complement signed integer into buffer.

buf.writeInt16LE(value, offset, [noAssert])#

buf.writeInt16BE(value, offset, [noAssert])#

  • value Number
  • offset Number
  • noAssert Boolean, Optional, Default: false

Writes value to the buffer at the specified offset with specified endian format. Note, value must be a valid signed 16 bit integer.

Set noAssert to true to skip validation of value and offset. This means that value may be too large for the specific function and offset may be beyond the end of the buffer leading to the values being silently dropped. This should not be used unless you are certain of correctness. Defaults to false.

Works as buffer.writeUInt16*, except value is written out as a two's complement signed integer into buffer.

buf.writeInt32LE(value, offset, [noAssert])#

buf.writeInt32BE(value, offset, [noAssert])#

  • value Number
  • offset Number
  • noAssert Boolean, Optional, Default: false

Writes value to the buffer at the specified offset with specified endian format. Note, value must be a valid signed 32 bit integer.

Set noAssert to true to skip validation of value and offset. This means that value may be too large for the specific function and offset may be beyond the end of the buffer leading to the values being silently dropped. This should not be used unless you are certain of correctness. Defaults to false.

Works as buffer.writeUInt32*, except value is written out as a two's complement signed integer into buffer.

buf.writeFloatLE(value, offset, [noAssert])#

buf.writeFloatBE(value, offset, [noAssert])#

  • value Number
  • offset Number
  • noAssert Boolean, Optional, Default: false

Writes value to the buffer at the specified offset with specified endian format. Note, value must be a valid 32 bit float.

Set noAssert to true to skip validation of value and offset. This means that value may be too large for the specific function and offset may be beyond the end of the buffer leading to the values being silently dropped. This should not be used unless you are certain of correctness. Defaults to false.

Example: 

var buf = new Buffer(4);
buf.writeFloatBE(0xcafebabe, 0);

console.log(buf);

buf.writeFloatLE(0xcafebabe, 0);

console.log(buf);

// <Buffer 4f 4a fe bb>
// <Buffer bb fe 4a 4f>

buf.writeDoubleLE(value, offset, [noAssert])#

buf.writeDoubleBE(value, offset, [noAssert])#

  • value Number
  • offset Number
  • noAssert Boolean, Optional, Default: false

Writes value to the buffer at the specified offset with specified endian format. Note, value must be a valid 64 bit double.

Set noAssert to true to skip validation of value and offset. This means that value may be too large for the specific function and offset may be beyond the end of the buffer leading to the values being silently dropped. This should not be used unless you are certain of correctness. Defaults to false.

Example: 

var buf = new Buffer(8);
buf.writeDoubleBE(0xdeadbeefcafebabe, 0);

console.log(buf);

buf.writeDoubleLE(0xdeadbeefcafebabe, 0);

console.log(buf);

// <Buffer 43 eb d5 b7 dd f9 5f d7>
// <Buffer d7 5f f9 dd b7 d5 eb 43>

buf.fill(value, [offset], [end])#

  • value
  • offset Number, Optional
  • end Number, Optional

Fills the buffer with the specified value. If the offset (defaults to 0) and end (defaults to buffer.length) are not given it will fill the entire buffer. 

var b = new Buffer(50);
b.fill("h");

buffer.INSPECT_MAX_BYTES#

  • Number, Default: 50

How many bytes will be returned when buffer.inspect() is called. This can be overridden by user modules.

Note that this is a property on the buffer module returned by require('buffer'), not on the Buffer global, or a buffer instance.

Class: SlowBuffer#

This class is primarily for internal use. JavaScript programs should use Buffer instead of using SlowBuffer.

In order to avoid the overhead of allocating many C++ Buffer objects for small blocks of memory in the lifetime of a server, Node allocates memory in 8Kb (8192 byte) chunks. If a buffer is smaller than this size, then it will be backed by a parent SlowBuffer object. If it is larger than this, then Node will allocate a SlowBuffer slab for it directly.

Stream#

Stability: 2 - Unstable

A stream is an abstract interface implemented by various objects in Node. For example a request to an HTTP server is a stream, as is stdout. Streams are readable, writable, or both. All streams are instances of EventEmitter.

You can load up the Stream base class by doing require('stream').

Readable Stream#

A Readable Stream has the following methods, members, and events.

Event: 'data'#

function (data) { }

The 'data' event emits either a Buffer (by default) or a string if setEncoding() was used.

Note that the data will be lost if there is no listener when a Readable Stream emits a 'data' event.

Event: 'end'#

function () { }

Emitted when the stream has received an EOF (FIN in TCP terminology). Indicates that no more 'data' events will happen. If the stream is also writable, it may be possible to continue writing.

Event: 'error'#

function (exception) { }

Emitted if there was an error receiving data.

Event: 'close'#

function () { }

Emitted when the underlying file descriptor has been closed. Not all streams will emit this. (For example, an incoming HTTP request will not emit 'close'.)

stream.readable#

A boolean that is true by default, but turns false after an 'error' occurred, the stream came to an 'end', or destroy() was called.

stream.setEncoding(encoding)#

Makes the data event emit a string instead of a Buffer. encoding can be 'utf8', 'ascii', or 'base64'.

stream.pause()#

Issues an advisory signal to the underlying communication layer, requesting that no further data be sent until resume() is called.

Note that, due to the advisory nature, certain streams will not be paused immediately, and so 'data' events may be emitted for some indeterminate period of time even after pause() is called. You may wish to buffer such 'data' events.

stream.resume()#

Resumes the incoming 'data' events after a pause().

stream.destroy()#

Closes the underlying file descriptor. Stream will not emit any more events.

stream.destroySoon()#

After the write queue is drained, close the file descriptor.

stream.pipe(destination, [options])#

This is a Stream.prototype method available on all Streams.

Connects this read stream to destination WriteStream. Incoming data on this stream gets written to destination. The destination and source streams are kept in sync by pausing and resuming as necessary.

This function returns the destination stream.

Emulating the Unix cat command: 

process.stdin.resume();
process.stdin.pipe(process.stdout);

By default end() is called on the destination when the source stream emits end, so that destination is no longer writable. Pass { end: false } as options to keep the destination stream open.

This keeps process.stdout open so that "Goodbye" can be written at the end. 

process.stdin.resume();

process.stdin.pipe(process.stdout, { end: false });

process.stdin.on("end", function() {
  process.stdout.write("Goodbye\n");
});

Writable Stream#

A Writable Stream has the following methods, members, and events.

Event: 'drain'#

function () { }

After a write() method returned false, this event is emitted to indicate that it is safe to write again.

Event: 'error'#

function (exception) { }

Emitted on error with the exception exception.

Event: 'close'#

function () { }

Emitted when the underlying file descriptor has been closed.

Event: 'pipe'#

function (src) { }

Emitted when the stream is passed to a readable stream's pipe method.

stream.writable#

A boolean that is true by default, but turns false after an 'error' occurred or end() / destroy() was called.

stream.write(string, [encoding], [fd])#

Writes string with the given encoding to the stream. Returns true if the string has been flushed to the kernel buffer. Returns false to indicate that the kernel buffer is full, and the data will be sent out in the future. The 'drain' event will indicate when the kernel buffer is empty again. The encoding defaults to 'utf8'.

If the optional fd parameter is specified, it is interpreted as an integral file descriptor to be sent over the stream. This is only supported for UNIX streams, and is silently ignored otherwise. When writing a file descriptor in this manner, closing the descriptor before the stream drains risks sending an invalid (closed) FD.

stream.write(buffer)#

Same as the above except with a raw buffer.

stream.end()#

Terminates the stream with EOF or FIN. This call will allow queued write data to be sent before closing the stream.

stream.end(string, encoding)#

Sends string with the given encoding and terminates the stream with EOF or FIN. This is useful to reduce the number of packets sent.

stream.end(buffer)#

Same as above but with a buffer.

stream.destroy()#

Closes the underlying file descriptor. Stream will not emit any more events. Any queued write data will not be sent.

stream.destroySoon()#

After the write queue is drained, close the file descriptor. destroySoon() can still destroy straight away, as long as there is no data left in the queue for writes.

Crypto#

Stability: 3 - Stable

Use require('crypto') to access this module.

The crypto module requires OpenSSL to be available on the underlying platform. It offers a way of encapsulating secure credentials to be used as part of a secure HTTPS net or http connection.

It also offers a set of wrappers for OpenSSL's hash, hmac, cipher, decipher, sign and verify methods.

crypto.createCredentials(details)#

Creates a credentials object, with the optional details being a dictionary with keys:

  • key : A string holding the PEM encoded private key
  • passphrase : A string of passphrase for the private key
  • cert : A string holding the PEM encoded certificate
  • ca : Either a string or list of strings of PEM encoded CA certificates to trust.
  • crl : Either a string or list of strings of PEM encoded CRLs (Certificate Revocation List)
  • ciphers: A string describing the ciphers to use or exclude. Consult http://www.openssl.org/docs/apps/ciphers.html#CIPHER_LIST_FORMAT for details on the format.

If no 'ca' details are given, then node.js will use the default publicly trusted list of CAs as given in

http://mxr.mozilla.org/mozilla/source/security/nss/lib/ckfw/builtins/certdata.txt.

crypto.createHash(algorithm)#

Creates and returns a hash object, a cryptographic hash with the given algorithm which can be used to generate hash digests.

algorithm is dependent on the available algorithms supported by the version of OpenSSL on the platform. Examples are 'sha1', 'md5', 'sha256', 'sha512', etc. On recent releases, openssl list-message-digest-algorithms will display the available digest algorithms.

Example: this program that takes the sha1 sum of a file 

var filename = process.argv[2];
var crypto = require('crypto');
var fs = require('fs');

var shasum = crypto.createHash('sha1');

var s = fs.ReadStream(filename);
s.on('data', function(d) {
  shasum.update(d);
});

s.on('end', function() {
  var d = shasum.digest('hex');
  console.log(d + '  ' + filename);
});

Class: Hash#

The class for creating hash digests of data.

Returned by crypto.createHash.

hash.update(data, [input_encoding])#

Updates the hash content with the given data, the encoding of which is given in input_encoding and can be 'utf8', 'ascii' or 'binary'. Defaults to 'binary'. This can be called many times with new data as it is streamed.

hash.digest([encoding])#

Calculates the digest of all of the passed data to be hashed. The encoding can be 'hex', 'binary' or 'base64'. Defaults to 'binary'.

Note: hash object can not be used after digest() method been called.

crypto.createHmac(algorithm, key)#

Creates and returns a hmac object, a cryptographic hmac with the given algorithm and key.

algorithm is dependent on the available algorithms supported by OpenSSL - see createHash above. key is the hmac key to be used.

Class: Hmac#

Class for creating cryptographic hmac content.

Returned by crypto.createHmac.

hmac.update(data)#

Update the hmac content with the given data. This can be called many times with new data as it is streamed.

hmac.digest([encoding])#

Calculates the digest of all of the passed data to the hmac. The encoding can be 'hex', 'binary' or 'base64'. Defaults to 'binary'.

Note: hmac object can not be used after digest() method been called.

crypto.createCipher(algorithm, password)#

Creates and returns a cipher object, with the given algorithm and password.

algorithm is dependent on OpenSSL, examples are 'aes192', etc. On recent releases, openssl list-cipher-algorithms will display the available cipher algorithms. password is used to derive key and IV, which must be 'binary' encoded string (See the Buffer section for more information).

crypto.createCipheriv(algorithm, key, iv)#

Creates and returns a cipher object, with the given algorithm, key and iv.

algorithm is the same as the createCipher(). key is a raw key used in algorithm. iv is an Initialization vector. key and iv must be 'binary' encoded string (See the Buffer section for more information).

Class: Cipher#

Class for encrypting data.

Returned by crypto.createCipher and crypto.createCipheriv.

cipher.update(data, [input_encoding], [output_encoding])#

Updates the cipher with data, the encoding of which is given in input_encoding and can be 'utf8', 'ascii' or 'binary'. Defaults to 'binary'.

The output_encoding specifies the output format of the enciphered data, and can be 'binary', 'base64' or 'hex'. Defaults to 'binary'.

Returns the enciphered contents, and can be called many times with new data as it is streamed.

cipher.final([output_encoding])#

Returns any remaining enciphered contents, with output_encoding being one of: 'binary', 'base64' or 'hex'. Defaults to 'binary'.

Note: cipher object can not be used after final() method been called.

cipher.setAutoPadding(auto_padding=true)#

You can disable automatic padding of the input data to block size. If auto_padding is false, the length of the entire input data must be a multiple of the cipher's block size or final will fail. Useful for non-standard padding, e.g. using 0x0 instead of PKCS padding. You must call this before cipher.final.

crypto.createDecipher(algorithm, password)#

Creates and returns a decipher object, with the given algorithm and key. This is the mirror of the createCipher() above.

crypto.createDecipheriv(algorithm, key, iv)#

Creates and returns a decipher object, with the given algorithm, key and iv. This is the mirror of the createCipheriv() above.

Class: Decipher#

Class for decrypting data.

Returned by crypto.createDecipher and crypto.createDecipheriv.

decipher.update(data, [input_encoding], [output_encoding])#

Updates the decipher with data, which is encoded in 'binary', 'base64' or 'hex'. Defaults to 'binary'.

The output_decoding specifies in what format to return the deciphered plaintext: 'binary', 'ascii' or 'utf8'. Defaults to 'binary'.

decipher.final([output_encoding])#

Returns any remaining plaintext which is deciphered, with output_encoding being one of: 'binary', 'ascii' or 'utf8'. Defaults to 'binary'.

Note: decipher object can not be used after final() method been called.

decipher.setAutoPadding(auto_padding=true)#

You can disable auto padding if the data has been encrypted without standard block padding to prevent decipher.final from checking and removing it. Can only work if the input data's length is a multiple of the ciphers block size. You must call this before streaming data to decipher.update.

crypto.createSign(algorithm)#

Creates and returns a signing object, with the given algorithm. On recent OpenSSL releases, openssl list-public-key-algorithms will display the available signing algorithms. Examples are 'RSA-SHA256'.

Class: Signer#

Class for generating signatures.

Returned by crypto.createSign.

signer.update(data)#

Updates the signer object with data. This can be called many times with new data as it is streamed.

signer.sign(private_key, [output_format])#

Calculates the signature on all the updated data passed through the signer. private_key is a string containing the PEM encoded private key for signing.

Returns the signature in output_format which can be 'binary', 'hex' or 'base64'. Defaults to 'binary'.

Note: signer object can not be used after sign() method been called.

crypto.createVerify(algorithm)#

Creates and returns a verification object, with the given algorithm. This is the mirror of the signing object above.

Class: Verify#

Class for verifying signatures.

Returned by crypto.createVerify.

verifier.update(data)#

Updates the verifier object with data. This can be called many times with new data as it is streamed.

verifier.verify(object, signature, [signature_format])#

Verifies the signed data by using the object and signature. object is a string containing a PEM encoded object, which can be one of RSA public key, DSA public key, or X.509 certificate. signature is the previously calculated signature for the data, in the signature_format which can be 'binary', 'hex' or 'base64'. Defaults to 'binary'.

Returns true or false depending on the validity of the signature for the data and public key.

Note: verifier object can not be used after verify() method been called.

crypto.createDiffieHellman(prime_length)#

Creates a Diffie-Hellman key exchange object and generates a prime of the given bit length. The generator used is 2.

crypto.createDiffieHellman(prime, [encoding])#

Creates a Diffie-Hellman key exchange object using the supplied prime. The generator used is 2. Encoding can be 'binary', 'hex', or 'base64'. Defaults to 'binary'.

Class: DiffieHellman#

The class for creating Diffie-Hellman key exchanges.

Returned by crypto.createDiffieHellman.

diffieHellman.generateKeys([encoding])#

Generates private and public Diffie-Hellman key values, and returns the public key in the specified encoding. This key should be transferred to the other party. Encoding can be 'binary', 'hex', or 'base64'. Defaults to 'binary'.

diffieHellman.computeSecret(other_public_key, [input_encoding], [output_encoding])#

Computes the shared secret using other_public_key as the other party's public key and returns the computed shared secret. Supplied key is interpreted using specified input_encoding, and secret is encoded using specified output_encoding. Encodings can be 'binary', 'hex', or 'base64'. The input encoding defaults to 'binary'. If no output encoding is given, the input encoding is used as output encoding.

diffieHellman.getPrime([encoding])#

Returns the Diffie-Hellman prime in the specified encoding, which can be 'binary', 'hex', or 'base64'. Defaults to 'binary'.

diffieHellman.getGenerator([encoding])#

Returns the Diffie-Hellman prime in the specified encoding, which can be 'binary', 'hex', or 'base64'. Defaults to 'binary'.

diffieHellman.getPublicKey([encoding])#

Returns the Diffie-Hellman public key in the specified encoding, which can be 'binary', 'hex', or 'base64'. Defaults to 'binary'.

diffieHellman.getPrivateKey([encoding])#

Returns the Diffie-Hellman private key in the specified encoding, which can be 'binary', 'hex', or 'base64'. Defaults to 'binary'.

diffieHellman.setPublicKey(public_key, [encoding])#

Sets the Diffie-Hellman public key. Key encoding can be 'binary', 'hex', or 'base64'. Defaults to 'binary'.

diffieHellman.setPrivateKey(public_key, [encoding])#

Sets the Diffie-Hellman private key. Key encoding can be 'binary', 'hex', or 'base64'. Defaults to 'binary'.

crypto.getDiffieHellman(group_name)#

Creates a predefined Diffie-Hellman key exchange object. The supported groups are: 'modp1', 'modp2', 'modp5' (defined in RFC 2412) and 'modp14', 'modp15', 'modp16', 'modp17', 'modp18' (defined in RFC 3526). The returned object mimics the interface of objects created by crypto.createDiffieHellman() above, but will not allow to change the keys (with diffieHellman.setPublicKey() for example). The advantage of using this routine is that the parties don't have to generate nor exchange group modulus beforehand, saving both processor and communication time.

Example (obtaining a shared secret): 

var crypto = require('crypto');
var alice = crypto.getDiffieHellman('modp5');
var bob = crypto.getDiffieHellman('modp5');

alice.generateKeys();
bob.generateKeys();

var alice_secret = alice.computeSecret(bob.getPublicKey(), 'binary', 'hex');
var bob_secret = bob.computeSecret(alice.getPublicKey(), 'binary', 'hex');

/* alice_secret and bob_secret should be the same */
console.log(alice_secret == bob_secret);

crypto.pbkdf2(password, salt, iterations, keylen, callback)#

Asynchronous PBKDF2 applies pseudorandom function HMAC-SHA1 to derive a key of given length from the given password, salt and iterations. The callback gets two arguments (err, derivedKey).

crypto.randomBytes(size, [callback])#

Generates cryptographically strong pseudo-random data. Usage: 

// async
crypto.randomBytes(256, function(ex, buf) {
  if (ex) throw ex;
  console.log('Have %d bytes of random data: %s', buf.length, buf);
});

// sync
try {
  var buf = crypto.randomBytes(256);
  console.log('Have %d bytes of random data: %s', buf.length, buf);
} catch (ex) {
  // handle error
}

TLS (SSL)#

Stability: 3 - Stable

Use require('tls') to access this module.

The tls module uses OpenSSL to provide Transport Layer Security and/or Secure Socket Layer: encrypted stream communication.

TLS/SSL is a public/private key infrastructure. Each client and each server must have a private key. A private key is created like this 

openssl genrsa -out ryans-key.pem 1024

All severs and some clients need to have a certificate. Certificates are public keys signed by a Certificate Authority or self-signed. The first step to getting a certificate is to create a "Certificate Signing Request" (CSR) file. This is done with: 

openssl req -new -key ryans-key.pem -out ryans-csr.pem

To create a self-signed certificate with the CSR, do this: 

openssl x509 -req -in ryans-csr.pem -signkey ryans-key.pem -out ryans-cert.pem

Alternatively you can send the CSR to a Certificate Authority for signing.

(TODO: docs on creating a CA, for now interested users should just look at test/fixtures/keys/Makefile in the Node source code)

Client-initiated renegotiation attack mitigation#

The TLS protocol lets the client renegotiate certain aspects of the TLS session. Unfortunately, session renegotiation requires a disproportional amount of server-side resources, which makes it a potential vector for denial-of-service attacks.

To mitigate this, renegotiations are limited to three times every 10 minutes. An error is emitted on the CleartextStream instance when the threshold is exceeded. The limits are configurable:

  • tls.CLIENT_RENEG_LIMIT: renegotiation limit, default is 3.

  • tls.CLIENT_RENEG_WINDOW: renegotiation window in seconds, default is

                           10 minutes.

Don't change the defaults unless you know what you are doing.

To test your server, connect to it with openssl s_client -connect address:port and tap R<CR> (that's the letter R followed by a carriage return) a few times.

NPN and SNI#

NPN (Next Protocol Negotiation) and SNI (Server Name Indication) are TLS handshake extensions allowing you:

  • NPN - to use one TLS server for multiple protocols (HTTP, SPDY)
  • SNI - to use one TLS server for multiple hostnames with different SSL certificates.

tls.createServer(options, [secureConnectionListener])#

Creates a new tls.Server. The connectionListener argument is automatically set as a listener for the secureConnection event. The options object has these possibilities:

  • key: A string or Buffer containing the private key of the server in PEM format. (Required)

  • passphrase: A string of passphrase for the private key.

  • cert: A string or Buffer containing the certificate key of the server in PEM format. (Required)

  • ca: An array of strings or Buffers of trusted certificates. If this is omitted several well known "root" CAs will be used, like VeriSign. These are used to authorize connections.

  • crl : Either a string or list of strings of PEM encoded CRLs (Certificate Revocation List)

  • ciphers: A string describing the ciphers to use or exclude. Consult http://www.openssl.org/docs/apps/ciphers.html#CIPHER_LIST_FORMAT for details on the format. To mitigate [BEAST attacks] (http://blog.ivanristic.com/2011/10/mitigating-the-beast-attack-on-tls.html), it is recommended that you use this option in conjunction with the honorCipherOrder option described below to prioritize the RC4 algorithm, since it is a non-CBC cipher. A recommended cipher list follows: ECDHE-RSA-AES256-SHA:AES256-SHA:RC4-SHA:RC4:HIGH:!MD5:!aNULL:!EDH:!AESGCM

  • honorCipherOrder : When choosing a cipher, use the server's preferences instead of the client preferences. Note that if SSLv2 is used, the server will send its list of preferences to the client, and the client chooses the cipher. Although, this option is disabled by default, it is recommended that you use this option in conjunction with the ciphers option to mitigate BEAST attacks.

  • requestCert: If true the server will request a certificate from clients that connect and attempt to verify that certificate. Default: false.

  • rejectUnauthorized: If true the server will reject any connection which is not authorized with the list of supplied CAs. This option only has an effect if requestCert is true. Default: false.

  • NPNProtocols: An array or Buffer of possible NPN protocols. (Protocols should be ordered by their priority).

  • SNICallback: A function that will be called if client supports SNI TLS extension. Only one argument will be passed to it: servername. And SNICallback should return SecureContext instance. (You can use crypto.createCredentials(...).context to get proper SecureContext). If SNICallback wasn't provided - default callback with high-level API will be used (see below).

  • sessionIdContext: A string containing a opaque identifier for session resumption. If requestCert is true, the default is MD5 hash value generated from command-line. Otherwise, the default is not provided.

Here is a simple example echo server: 

var tls = require('tls');
var fs = require('fs');

var options = {
  key: fs.readFileSync('server-key.pem'),
  cert: fs.readFileSync('server-cert.pem'),

  // This is necessary only if using the client certificate authentication.
  requestCert: true,

  // This is necessary only if the client uses the self-signed certificate.
  ca: [ fs.readFileSync('client-cert.pem') ]
};

var server = tls.createServer(options, function(cleartextStream) {
  console.log('server connected',
              cleartextStream.authorized ? 'authorized' : 'unauthorized');
  cleartextStream.write("welcome!\n");
  cleartextStream.setEncoding('utf8');
  cleartextStream.pipe(cleartextStream);
});
server.listen(8000, function() {
  console.log('server bound');
});

You can test this server by connecting to it with openssl s_client: 

openssl s_client -connect 127.0.0.1:8000

tls.connect(options, [secureConnectListener])#

tls.connect(port, [host], [options], [secureConnectListener])#

Creates a new client connection to the given port and host (old API) or options.port and options.host. (If host is omitted, it defaults to localhost.) options should be an object which specifies:

  • host: Host the client should connect to

  • port: Port the client should connect to

  • socket: Establish secure connection on a given socket rather than creating a new socket. If this option is specified, host and port are ignored.

  • key: A string or Buffer containing the private key of the client in PEM format.

  • passphrase: A string of passphrase for the private key.

  • cert: A string or Buffer containing the certificate key of the client in PEM format.

  • ca: An array of strings or Buffers of trusted certificates. If this is omitted several well known "root" CAs will be used, like VeriSign. These are used to authorize connections.

  • rejectUnauthorized: If true, the server certificate is verified against the list of supplied CAs. An 'error' event is emitted if verification fails. Default: false.

  • NPNProtocols: An array of string or Buffer containing supported NPN protocols. Buffer should have following format: 0x05hello0x05world, where first byte is next protocol name's length. (Passing array should usually be much simpler: ['hello', 'world'].)

  • servername: Servername for SNI (Server Name Indication) TLS extension.

The secureConnectListener parameter will be added as a listener for the 'secureConnect' event.

tls.connect() returns a CleartextStream object.

Here is an example of a client of echo server as described previously: 

var tls = require('tls');
var fs = require('fs');

var options = {
  // These are necessary only if using the client certificate authentication
  key: fs.readFileSync('client-key.pem'),
  cert: fs.readFileSync('client-cert.pem'),

  // This is necessary only if the server uses the self-signed certificate
  ca: [ fs.readFileSync('server-cert.pem') ]
};

var cleartextStream = tls.connect(8000, options, function() {
  console.log('client connected',
              cleartextStream.authorized ? 'authorized' : 'unauthorized');
  process.stdin.pipe(cleartextStream);
  process.stdin.resume();
});
cleartextStream.setEncoding('utf8');
cleartextStream.on('data', function(data) {
  console.log(data);
});
cleartextStream.on('end', function() {
  server.close();
});

tls.createSecurePair([credentials], [isServer], [requestCert], [rejectUnauthorized])#

Creates a new secure pair object with two streams, one of which reads/writes encrypted data, and one reads/writes cleartext data. Generally the encrypted one is piped to/from an incoming encrypted data stream, and the cleartext one is used as a replacement for the initial encrypted stream.

  • credentials: A credentials object from crypto.createCredentials( ... )

  • isServer: A boolean indicating whether this tls connection should be opened as a server or a client.

  • requestCert: A boolean indicating whether a server should request a certificate from a connecting client. Only applies to server connections.

  • rejectUnauthorized: A boolean indicating whether a server should automatically reject clients with invalid certificates. Only applies to servers with requestCert enabled.

tls.createSecurePair() returns a SecurePair object with cleartext and encrypted stream properties.

Class: SecurePair#

Returned by tls.createSecurePair.

Event: 'secure'#

The event is emitted from the SecurePair once the pair has successfully established a secure connection.

Similarly to the checking for the server 'secureConnection' event, pair.cleartext.authorized should be checked to confirm whether the certificate used properly authorized.

Class: tls.Server#

This class is a subclass of net.Server and has the same methods on it. Instead of accepting just raw TCP connections, this accepts encrypted connections using TLS or SSL.

Event: 'secureConnection'#

function (cleartextStream) {}

This event is emitted after a new connection has been successfully handshaked. The argument is a instance of CleartextStream. It has all the common stream methods and events.

cleartextStream.authorized is a boolean value which indicates if the client has verified by one of the supplied certificate authorities for the server. If cleartextStream.authorized is false, then cleartextStream.authorizationError is set to describe how authorization failed. Implied but worth mentioning: depending on the settings of the TLS server, you unauthorized connections may be accepted. cleartextStream.npnProtocol is a string containing selected NPN protocol. cleartextStream.servername is a string containing servername requested with SNI.

Event: 'clientError'#

function (exception) { }

When a client connection emits an 'error' event before secure connection is established - it will be forwarded here.

server.listen(port, [host], [callback])#

Begin accepting connections on the specified port and host. If the host is omitted, the server will accept connections directed to any IPv4 address (INADDR_ANY).

This function is asynchronous. The last parameter callback will be called when the server has been bound.

See net.Server for more information.

server.close()#

Stops the server from accepting new connections. This function is asynchronous, the server is finally closed when the server emits a 'close' event.

server.address()#

Returns the bound address, the address family name and port of the server as reported by the operating system. See net.Server.address() for more information.

server.addContext(hostname, credentials)#

Add secure context that will be used if client request's SNI hostname is matching passed hostname (wildcards can be used). credentials can contain key, cert and ca.

server.maxConnections#

Set this property to reject connections when the server's connection count gets high.

server.connections#

The number of concurrent connections on the server.

Class: tls.CleartextStream#

This is a stream on top of the Encrypted stream that makes it possible to read/write an encrypted data as a cleartext data.

This instance implements a duplex Stream interfaces. It has all the common stream methods and events.

A ClearTextStream is the clear member of a SecurePair object.

Event: 'secureConnect'#

This event is emitted after a new connection has been successfully handshaked. The listener will be called no matter if the server's certificate was authorized or not. It is up to the user to test cleartextStream.authorized to see if the server certificate was signed by one of the specified CAs. If cleartextStream.authorized === false then the error can be found in cleartextStream.authorizationError. Also if NPN was used - you can check cleartextStream.npnProtocol for negotiated protocol.

cleartextStream.authorized#

A boolean that is true if the peer certificate was signed by one of the specified CAs, otherwise false

cleartextStream.authorizationError#

The reason why the peer's certificate has not been verified. This property becomes available only when cleartextStream.authorized === false.

cleartextStream.getPeerCertificate()#

Returns an object representing the peer's certificate. The returned object has some properties corresponding to the field of the certificate.

Example: 

{ subject: 
   { C: 'UK',
     ST: 'Acknack Ltd',
     L: 'Rhys Jones',
     O: 'node.js',
     OU: 'Test TLS Certificate',
     CN: 'localhost' },
  issuer: 
   { C: 'UK',
     ST: 'Acknack Ltd',
     L: 'Rhys Jones',
     O: 'node.js',
     OU: 'Test TLS Certificate',
     CN: 'localhost' },
  valid_from: 'Nov 11 09:52:22 2009 GMT',
  valid_to: 'Nov  6 09:52:22 2029 GMT',
  fingerprint: '2A:7A:C2:DD:E5:F9:CC:53:72:35:99:7A:02:5A:71:38:52:EC:8A:DF' }

If the peer does not provide a certificate, it returns null or an empty object.

cleartextStream.getCipher()#

Returns an object representing the cipher name and the SSL/TLS protocol version of the current connection.

Example: { name: 'AES256-SHA', version: 'TLSv1/SSLv3' }

See SSL_CIPHER_get_name() and SSL_CIPHER_get_version() in http://www.openssl.org/docs/ssl/ssl.html#DEALING_WITH_CIPHERS for more information.

cleartextStream.address()#

Returns the bound address, the address family name and port of the underlying socket as reported by the operating system. Returns an object with three properties, e.g. { port: 12346, family: 'IPv4', address: '127.0.0.1' }

cleartextStream.remoteAddress#

The string representation of the remote IP address. For example, '74.125.127.100' or '2001:4860:a005::68'.

cleartextStream.remotePort#

The numeric representation of the remote port. For example, 443.

File System#

Stability: 3 - Stable

File I/O is provided by simple wrappers around standard POSIX functions. To use this module do require('fs'). All the methods have asynchronous and synchronous forms.

The asynchronous form always take a completion callback as its last argument. The arguments passed to the completion callback depend on the method, but the first argument is always reserved for an exception. If the operation was completed successfully, then the first argument will be null or undefined.

When using the synchronous form any exceptions are immediately thrown. You can use try/catch to handle exceptions or allow them to bubble up.

Here is an example of the asynchronous version: 

var fs = require('fs');

fs.unlink('/tmp/hello', function (err) {
  if (err) throw err;
  console.log('successfully deleted /tmp/hello');
});

Here is the synchronous version: 

var fs = require('fs');

fs.unlinkSync('/tmp/hello')
console.log('successfully deleted /tmp/hello');

With the asynchronous methods there is no guaranteed ordering. So the following is prone to error: 

fs.rename('/tmp/hello', '/tmp/world', function (err) {
  if (err) throw err;
  console.log('renamed complete');
});
fs.stat('/tmp/world', function (err, stats) {
  if (err) throw err;
  console.log('stats: ' + JSON.stringify(stats));
});

It could be that fs.stat is executed before fs.rename. The correct way to do this is to chain the callbacks. 

fs.rename('/tmp/hello', '/tmp/world', function (err) {
  if (err) throw err;
  fs.stat('/tmp/world', function (err, stats) {
    if (err) throw err;
    console.log('stats: ' + JSON.stringify(stats));
  });
});

In busy processes, the programmer is strongly encouraged to use the asynchronous versions of these calls. The synchronous versions will block the entire process until they complete--halting all connections.

Relative path to filename can be used, remember however that this path will be relative to process.cwd().

fs.rename(oldPath, newPath, [callback])#

Asynchronous rename(2). No arguments other than a possible exception are given to the completion callback.

fs.renameSync(oldPath, newPath)#

Synchronous rename(2).

fs.truncate(fd, len, [callback])#

Asynchronous ftruncate(2). No arguments other than a possible exception are given to the completion callback.

fs.truncateSync(fd, len)#

Synchronous ftruncate(2).

fs.chown(path, uid, gid, [callback])#

Asynchronous chown(2). No arguments other than a possible exception are given to the completion callback.

fs.chownSync(path, uid, gid)#

Synchronous chown(2).

fs.fchown(fd, uid, gid, [callback])#

Asynchronous fchown(2). No arguments other than a possible exception are given to the completion callback.

fs.fchownSync(fd, uid, gid)#

Synchronous fchown(2).

fs.lchown(path, uid, gid, [callback])#

Asynchronous lchown(2). No arguments other than a possible exception are given to the completion callback.

fs.lchownSync(path, uid, gid)#

Synchronous lchown(2).

fs.chmod(path, mode, [callback])#

Asynchronous chmod(2). No arguments other than a possible exception are given to the completion callback.

fs.chmodSync(path, mode)#

Synchronous chmod(2).

fs.fchmod(fd, mode, [callback])#

Asynchronous fchmod(2). No arguments other than a possible exception are given to the completion callback.

fs.fchmodSync(fd, mode)#

Synchronous fchmod(2).

fs.lchmod(path, mode, [callback])#

Asynchronous lchmod(2). No arguments other than a possible exception are given to the completion callback.

fs.lchmodSync(path, mode)#

Synchronous lchmod(2).

fs.stat(path, [callback])#

Asynchronous stat(2). The callback gets two arguments (err, stats) where stats is a fs.Stats object. See the fs.Stats section below for more information.

fs.lstat(path, [callback])#

Asynchronous lstat(2). The callback gets two arguments (err, stats) where stats is a fs.Stats object. lstat() is identical to stat(), except that if path is a symbolic link, then the link itself is stat-ed, not the file that it refers to.

fs.fstat(fd, [callback])#

Asynchronous fstat(2). The callback gets two arguments (err, stats) where stats is a fs.Stats object. fstat() is identical to stat(), except that the file to be stat-ed is specified by the file descriptor fd.

fs.statSync(path)#

Synchronous stat(2). Returns an instance of fs.Stats.

fs.lstatSync(path)#

Synchronous lstat(2). Returns an instance of fs.Stats.

fs.fstatSync(fd)#

Synchronous fstat(2). Returns an instance of fs.Stats.

fs.link(srcpath, dstpath, [callback])#

Asynchronous link(2). No arguments other than a possible exception are given to the completion callback.

fs.linkSync(srcpath, dstpath)#

Synchronous link(2).

fs.symlink(destination, path, [type], [callback])#

Asynchronous symlink(2). No arguments other than a possible exception are given to the completion callback. type argument can be either 'dir' or 'file' (default is 'file'). It is only used on Windows (ignored on other platforms).

fs.symlinkSync(destination, path, [type])#

Synchronous symlink(2).

fs.readlink(path, [callback])#

Asynchronous readlink(2). The callback gets two arguments (err, linkString).

fs.readlinkSync(path)#

Synchronous readlink(2). Returns the symbolic link's string value.

fs.realpath(path, [cache], callback)#

Asynchronous realpath(2). The callback gets two arguments (err, resolvedPath). May use process.cwd to resolve relative paths. cache is an object literal of mapped paths that can be used to force a specific path resolution or avoid additional fs.stat calls for known real paths.

Example: 

var cache = {'/etc':'/private/etc'};
fs.realpath('/etc/passwd', cache, function (err, resolvedPath) {
  if (err) throw err;
  console.log(resolvedPath);
});

fs.realpathSync(path, [cache])#

Synchronous realpath(2). Returns the resolved path.

fs.unlink(path, [callback])#

Asynchronous unlink(2). No arguments other than a possible exception are given to the completion callback.

fs.unlinkSync(path)#

Synchronous unlink(2).

fs.rmdir(path, [callback])#

Asynchronous rmdir(2). No arguments other than a possible exception are given to the completion callback.

fs.rmdirSync(path)#

Synchronous rmdir(2).

fs.mkdir(path, [mode], [callback])#

Asynchronous mkdir(2). No arguments other than a possible exception are given to the completion callback. mode defaults to 0777.

fs.mkdirSync(path, [mode])#

Synchronous mkdir(2).

fs.readdir(path, [callback])#

Asynchronous readdir(3). Reads the contents of a directory. The callback gets two arguments (err, files) where files is an array of the names of the files in the directory excluding '.' and '..'.

fs.readdirSync(path)#

Synchronous readdir(3). Returns an array of filenames excluding '.' and '..'.

fs.close(fd, [callback])#

Asynchronous close(2). No arguments other than a possible exception are given to the completion callback.

fs.closeSync(fd)#

Synchronous close(2).

fs.open(path, flags, [mode], [callback])#

Asynchronous file open. See open(2). flags can be:

  • 'r' - Open file for reading. An exception occurs if the file does not exist.

  • 'r+' - Open file for reading and writing. An exception occurs if the file does not exist.

  • 'w' - Open file for writing. The file is created (if it does not exist) or truncated (if it exists).

  • 'wx' - Like 'w' but opens the file in exclusive mode.

  • 'w+' - Open file for reading and writing. The file is created (if it does not exist) or truncated (if it exists).

  • 'wx+' - Like 'w+' but opens the file in exclusive mode.

  • 'a' - Open file for appending. The file is created if it does not exist.

  • 'ax' - Like 'a' but opens the file in exclusive mode.

  • 'a+' - Open file for reading and appending. The file is created if it does not exist.

  • 'ax+' - Like 'a+' but opens the file in exclusive mode.

mode defaults to 0666. The callback gets two arguments (err, fd).

Exclusive mode (O_EXCL) ensures that path is newly created. fs.open() fails if a file by that name already exists. On POSIX systems, symlinks are not followed. Exclusive mode may or may not work with network file systems.

fs.openSync(path, flags, [mode])#

Synchronous open(2).

fs.utimes(path, atime, mtime, [callback])#

fs.utimesSync(path, atime, mtime)#

Change file timestamps of the file referenced by the supplied path.

fs.futimes(fd, atime, mtime, [callback])#

fs.futimesSync(fd, atime, mtime)#

Change the file timestamps of a file referenced by the supplied file descriptor.

fs.fsync(fd, [callback])#

Asynchronous fsync(2). No arguments other than a possible exception are given to the completion callback.

fs.fsyncSync(fd)#

Synchronous fsync(2).

fs.write(fd, buffer, offset, length, position, [callback])#

Write buffer to the file specified by fd.

offset and length determine the part of the buffer to be written.

position refers to the offset from the beginning of the file where this data should be written. If position is null, the data will be written at the current position. See pwrite(2).

The callback will be given three arguments (err, written, buffer) where written specifies how many bytes were written from buffer.

Note that it is unsafe to use fs.write multiple times on the same file without waiting for the callback. For this scenario, fs.createWriteStream is strongly recommended.

fs.writeSync(fd, buffer, offset, length, position)#

Synchronous version of buffer-based fs.write(). Returns the number of bytes written.

fs.writeSync(fd, str, position, [encoding])#

Synchronous version of string-based fs.write(). encoding defaults to 'utf8'. Returns the number of bytes written.

fs.read(fd, buffer, offset, length, position, [callback])#

Read data from the file specified by fd.

buffer is the buffer that the data will be written to.

offset is offset within the buffer where writing will start.

length is an integer specifying the number of bytes to read.

position is an integer specifying where to begin reading from in the file. If position is null, data will be read from the current file position.

The callback is given the three arguments, (err, bytesRead, buffer).

fs.readSync(fd, buffer, offset, length, position)#

Synchronous version of buffer-based fs.read. Returns the number of bytesRead.

fs.readSync(fd, length, position, encoding)#

Synchronous version of string-based fs.read. Returns the number of bytesRead.

fs.readFile(filename, [encoding], [callback])#

Asynchronously reads the entire contents of a file. Example: 

fs.readFile('/etc/passwd', function (err, data) {
  if (err) throw err;
  console.log(data);
});

The callback is passed two arguments (err, data), where data is the contents of the file.

If no encoding is specified, then the raw buffer is returned.

fs.readFileSync(filename, [encoding])#

Synchronous version of fs.readFile. Returns the contents of the filename.

If encoding is specified then this function returns a string. Otherwise it returns a buffer.

fs.writeFile(filename, data, [encoding], [callback])#

Asynchronously writes data to a file, replacing the file if it already exists. data can be a string or a buffer. The encoding argument is ignored if data is a buffer. It defaults to 'utf8'.

Example: 

fs.writeFile('message.txt', 'Hello Node', function (err) {
  if (err) throw err;
  console.log('It\'s saved!');
});

fs.writeFileSync(filename, data, [encoding])#

The synchronous version of fs.writeFile.

fs.appendFile(filename, data, encoding='utf8', [callback])#

Asynchronously append data to a file, creating the file if it not yet exists. data can be a string or a buffer. The encoding argument is ignored if data is a buffer.

Example: 

fs.appendFile('message.txt', 'data to append', function (err) {
  if (err) throw err;
  console.log('The "data to append" was appended to file!');
});

fs.appendFileSync(filename, data, encoding='utf8')#

The synchronous version of fs.appendFile.

fs.watchFile(filename, [options], listener)#

Stability: 2 - Unstable.  Use fs.watch instead, if available.

Watch for changes on filename. The callback listener will be called each time the file is accessed.

The second argument is optional. The options if provided should be an object containing two members a boolean, persistent, and interval. persistent indicates whether the process should continue to run as long as files are being watched. interval indicates how often the target should be polled, in milliseconds. (On Linux systems with inotify, interval is ignored.) The default is { persistent: true, interval: 0 }.

The listener gets two arguments the current stat object and the previous stat object: 

fs.watchFile('message.text', function (curr, prev) {
  console.log('the current mtime is: ' + curr.mtime);
  console.log('the previous mtime was: ' + prev.mtime);
});

These stat objects are instances of fs.Stat.

If you want to be notified when the file was modified, not just accessed you need to compare curr.mtime and prev.mtime.

fs.unwatchFile(filename)#

Stability: 2 - Unstable.  Use fs.watch instead, if available.

Stop watching for changes on filename.

fs.watch(filename, [options], listener)#

Stability: 2 - Unstable.  Not available on all platforms.

Watch for changes on filename, where filename is either a file or a directory. The returned object is a fs.FSWatcher.

The second argument is optional. The options if provided should be an object containing a boolean member persistent, which indicates whether the process should continue to run as long as files are being watched. The default is { persistent: true }.

The listener callback gets two arguments (event, filename). event is either 'rename' or 'change', and filename is the name of the file which triggered the event.

Caveats#

The fs.watch API is not 100% consistent across platforms, and is unavailable in some situations.

Availability#

This feature depends on the underlying operating system providing a way to be notified of filesystem changes.

  • On Linux systems, this uses inotify.
  • On BSD systems (including OS X), this uses kqueue.
  • On SunOS systems (including Solaris and SmartOS), this uses event ports.
  • On Windows systems, this feature depends on ReadDirectoryChangesW.

If the underlying functionality is not available for some reason, then fs.watch will not be able to function. You can still use fs.watchFile, which uses stat polling, but it is slower and less reliable.

Filename Argument#

Providing filename argument in the callback is not supported on every platform (currently it's only supported on Linux and Windows). Even on supported platforms filename is not always guaranteed to be provided. Therefore, don't assume that filename argument is always provided in the callback, and have some fallback logic if it is null. 

fs.watch('somedir', function (event, filename) {
  console.log('event is: ' + event);
  if (filename) {
    console.log('filename provided: ' + filename);
  } else {
    console.log('filename not provided');
  }
});

fs.exists(path, [callback])#

Test whether or not the given path exists by checking with the file system. Then call the callback argument with either true or false. Example: 

fs.exists('/etc/passwd', function (exists) {
  util.debug(exists ? "it's there" : "no passwd!");
});

fs.existsSync(path)#

Synchronous version of fs.exists.

Class: fs.Stats#

Objects returned from fs.stat(), fs.lstat() and fs.fstat() and their synchronous counterparts are of this type.

  • stats.isFile()
  • stats.isDirectory()
  • stats.isBlockDevice()
  • stats.isCharacterDevice()
  • stats.isSymbolicLink() (only valid with fs.lstat())
  • stats.isFIFO()
  • stats.isSocket()

For a regular file util.inspect(stats) would return a string very similar to this: 

{ dev: 2114,
  ino: 48064969,
  mode: 33188,
  nlink: 1,
  uid: 85,
  gid: 100,
  rdev: 0,
  size: 527,
  blksize: 4096,
  blocks: 8,
  atime: Mon, 10 Oct 2011 23:24:11 GMT,
  mtime: Mon, 10 Oct 2011 23:24:11 GMT,
  ctime: Mon, 10 Oct 2011 23:24:11 GMT }

Please note that atime, mtime and ctime are instances of Date object and to compare the values of these objects you should use appropriate methods. For most general uses getTime() will return the number of milliseconds elapsed since 1 January 1970 00:00:00 UTC and this integer should be sufficient for any comparison, however there additional methods which can be used for displaying fuzzy information. More details can be found in the MDN JavaScript Reference page.

fs.createReadStream(path, [options])#

Returns a new ReadStream object (See Readable Stream).

options is an object with the following defaults: 

{ flags: 'r',
  encoding: null,
  fd: null,
  mode: 0666,
  bufferSize: 64 * 1024
}

options can include start and end values to read a range of bytes from the file instead of the entire file. Both start and end are inclusive and start at 0. The encoding can be 'utf8', 'ascii', or 'base64'.

An example to read the last 10 bytes of a file which is 100 bytes long: 

fs.createReadStream('sample.txt', {start: 90, end: 99});

Class: fs.ReadStream#

ReadStream is a Readable Stream.

Event: 'open'#

  • fd Integer file descriptor used by the ReadStream.

Emitted when the ReadStream's file is opened.

fs.createWriteStream(path, [options])#

Returns a new WriteStream object (See Writable Stream).

options is an object with the following defaults: 

{ flags: 'w',
  encoding: null,
  mode: 0666 }

options may also include a start option to allow writing data at some position past the beginning of the file. Modifying a file rather than replacing it may require a flags mode of r+ rather than the default mode w.

fs.WriteStream#

WriteStream is a Writable Stream.

Event: 'open'#

  • fd Integer file descriptor used by the WriteStream.

Emitted when the WriteStream's file is opened.

file.bytesWritten#

The number of bytes written so far. Does not include data that is still queued for writing.

Class: fs.FSWatcher#

Objects returned from fs.watch() are of this type.

watcher.close()#

Stop watching for changes on the given fs.FSWatcher.

Event: 'change'#

  • event String The type of fs change
  • filename String The filename that changed (if relevant/available)

Emitted when something changes in a watched directory or file. See more details in fs.watch.

Event: 'error'#

  • error Error object

Emitted when an error occurs.

Path#

Stability: 3 - Stable

This module contains utilities for handling and transforming file paths. Almost all these methods perform only string transformations. The file system is not consulted to check whether paths are valid.

Use require('path') to use this module. The following methods are provided:

path.normalize(p)#

Normalize a string path, taking care of '..' and '.' parts.

When multiple slashes are found, they're replaced by a single one; when the path contains a trailing slash, it is preserved. On windows backslashes are used.

Example: 

path.normalize('/foo/bar//baz/asdf/quux/..')
// returns
'/foo/bar/baz/asdf'

path.join([path1], [path2], [...])#

Join all arguments together and normalize the resulting path. Non-string arguments are ignored.

Example: 

path.join('/foo', 'bar', 'baz/asdf', 'quux', '..')
// returns
'/foo/bar/baz/asdf'

path.join('foo', {}, 'bar')
// returns
'foo/bar'

path.resolve([from ...], to)#

Resolves to to an absolute path.

If to isn't already absolute from arguments are prepended in right to left order, until an absolute path is found. If after using all from paths still no absolute path is found, the current working directory is used as well. The resulting path is normalized, and trailing slashes are removed unless the path gets resolved to the root directory. Non-string arguments are ignored.

Another way to think of it is as a sequence of cd commands in a shell. 

path.resolve('foo/bar', '/tmp/file/', '..', 'a/../subfile')

Is similar to: 

cd foo/bar
cd /tmp/file/
cd ..
cd a/../subfile
pwd

The difference is that the different paths don't need to exist and may also be files.

Examples: 

path.resolve('/foo/bar', './baz')
// returns
'/foo/bar/baz'

path.resolve('/foo/bar', '/tmp/file/')
// returns
'/tmp/file'

path.resolve('wwwroot', 'static_files/png/', '../gif/image.gif')
// if currently in /home/myself/node, it returns
'/home/myself/node/wwwroot/static_files/gif/image.gif'

path.relative(from, to)#

Solve the relative path from from to to.

At times we have two absolute paths, and we need to derive the relative path from one to the other. This is actually the reverse transform of path.resolve, which means we see that: 

path.resolve(from, path.relative(from, to)) == path.resolve(to)

Examples: 

path.relative('C:\\orandea\\test\\aaa', 'C:\\orandea\\impl\\bbb')
// returns
'..\\..\\impl\\bbb'

path.relative('/data/orandea/test/aaa', '/data/orandea/impl/bbb')
// returns
'../../impl/bbb'

path.dirname(p)#

Return the directory name of a path. Similar to the Unix dirname command.

Example: 

path.dirname('/foo/bar/baz/asdf/quux')
// returns
'/foo/bar/baz/asdf'

path.basename(p, [ext])#

Return the last portion of a path. Similar to the Unix basename command.

Example: 

path.basename('/foo/bar/baz/asdf/quux.html')
// returns
'quux.html'

path.basename('/foo/bar/baz/asdf/quux.html', '.html')
// returns
'quux'

path.extname(p)#

Return the extension of the path, from the last '.' to end of string in the last portion of the path. If there is no '.' in the last portion of the path or the first character of it is '.', then it returns an empty string. Examples: 

path.extname('index.html')
// returns
'.html'

path.extname('index.')
// returns
'.'

path.extname('index')
// returns
''

net#

Stability: 3 - Stable

The net module provides you with an asynchronous network wrapper. It contains methods for creating both servers and clients (called streams). You can include this module with require('net');

net.createServer([options], [connectionListener])#

Creates a new TCP server. The connectionListener argument is automatically set as a listener for the 'connection' event.

options is an object with the following defaults: 

{ allowHalfOpen: false
}

If allowHalfOpen is true, then the socket won't automatically send a FIN packet when the other end of the socket sends a FIN packet. The socket becomes non-readable, but still writable. You should call the end() method explicitly. See 'end' event for more information.

Here is an example of a echo server which listens for connections on port 8124: 

var net = require('net');
var server = net.createServer(function(c) { //'connection' listener
  console.log('server connected');
  c.on('end', function() {
    console.log('server disconnected');
  });
  c.write('hello\r\n');
  c.pipe(c);
});
server.listen(8124, function() { //'listening' listener
  console.log('server bound');
});

Test this by using telnet: 

telnet localhost 8124

To listen on the socket /tmp/echo.sock the third line from the last would just be changed to 

server.listen('/tmp/echo.sock', function() { //'listening' listener

Use nc to connect to a UNIX domain socket server: 

nc -U /tmp/echo.sock

net.connect(options, [connectionListener])#

net.createConnection(options, [connectionListener])#

Constructs a new socket object and opens the socket to the given location. When the socket is established, the 'connect' event will be emitted.

For TCP sockets, options argument should be an object which specifies:

  • port: Port the client should connect to (Required).

  • host: Host the client should connect to. Defaults to 'localhost'.

  • localAddress: Local interface to bind to for network connections.

For UNIX domain sockets, options argument should be an object which specifies:

  • path: Path the client should connect to (Required).

Common options are:

  • allowHalfOpen: if true, the socket won't automatically send a FIN packet when the other end of the socket sends a FIN packet. Defaults to false. See 'end' event for more information.

The connectListener parameter will be added as an listener for the 'connect' event.

Here is an example of a client of echo server as described previously: 

var net = require('net');
var client = net.connect({port: 8124},
    function() { //'connect' listener
  console.log('client connected');
  client.write('world!\r\n');
});
client.on('data', function(data) {
  console.log(data.toString());
  client.end();
});
client.on('end', function() {
  console.log('client disconnected');
});

To connect on the socket /tmp/echo.sock the second line would just be changed to 

var client = net.connect({path: '/tmp/echo.sock'},

net.connect(port, [host], [connectListener])#

net.createConnection(port, [host], [connectListener])#

Creates a TCP connection to port on host. If host is omitted, 'localhost' will be assumed. The connectListener parameter will be added as an listener for the 'connect' event.

net.connect(path, [connectListener])#

net.createConnection(path, [connectListener])#

Creates unix socket connection to path. The connectListener parameter will be added as an listener for the 'connect' event.

Class: net.Server#

This class is used to create a TCP or UNIX server. A server is a net.Socket that can listen for new incoming connections.

server.listen(port, [host], [listeningListener])#

Begin accepting connections on the specified port and host. If the host is omitted, the server will accept connections directed to any IPv4 address (INADDR_ANY). A port value of zero will assign a random port.

This function is asynchronous. When the server has been bound, 'listening' event will be emitted. the last parameter listeningListener will be added as an listener for the 'listening' event.

One issue some users run into is getting EADDRINUSE errors. This means that another server is already running on the requested port. One way of handling this would be to wait a second and then try again. This can be done with 

server.on('error', function (e) {
  if (e.code == 'EADDRINUSE') {
    console.log('Address in use, retrying...');
    setTimeout(function () {
      server.close();
      server.listen(PORT, HOST);
    }, 1000);
  }
});

(Note: All sockets in Node set SO_REUSEADDR already)

server.listen(path, [listeningListener])#

Start a UNIX socket server listening for connections on the given path.

This function is asynchronous. When the server has been bound, 'listening' event will be emitted. the last parameter listeningListener will be added as an listener for the 'listening' event.

server.close([cb])#

Stops the server from accepting new connections and keeps existing connections. This function is asynchronous, the server is finally closed when all connections are ended and the server emits a 'close' event. Optionally, you can pass a callback to listen for the 'close' event.

server.address()#

Returns the bound address, the address family name and port of the server as reported by the operating system. Useful to find which port was assigned when giving getting an OS-assigned address. Returns an object with three properties, e.g. { port: 12346, family: 'IPv4', address: '127.0.0.1' }

Example: 

var server = net.createServer(function (socket) {
  socket.end("goodbye\n");
});

// grab a random port.
server.listen(function() {
  address = server.address();
  console.log("opened server on %j", address);
});

Don't call server.address() until the 'listening' event has been emitted.

server.maxConnections#

Set this property to reject connections when the server's connection count gets high.

server.connections#

The number of concurrent connections on the server.

net.Server is an EventEmitter with the following events:

Event: 'listening'#

Emitted when the server has been bound after calling server.listen.

Event: 'connection'#

  • Socket object The connection object

Emitted when a new connection is made. socket is an instance of net.Socket.

Event: 'close'#

Emitted when the server closes. Note that if connections exist, this event is not emitted until all connections are ended.

Event: 'error'#

  • Error Object

Emitted when an error occurs. The 'close' event will be called directly following this event. See example in discussion of server.listen.

Class: net.Socket#

This object is an abstraction of a TCP or UNIX socket. net.Socket instances implement a duplex Stream interface. They can be created by the user and used as a client (with connect()) or they can be created by Node and passed to the user through the 'connection' event of a server.

new net.Socket([options])#

Construct a new socket object.

options is an object with the following defaults: 

{ fd: null
  type: null
  allowHalfOpen: false
}

fd allows you to specify the existing file descriptor of socket. type specified underlying protocol. It can be 'tcp4', 'tcp6', or 'unix'. About allowHalfOpen, refer to createServer() and 'end' event.

socket.connect(port, [host], [connectListener])#

socket.connect(path, [connectListener])#

Opens the connection for a given socket. If port and host are given, then the socket will be opened as a TCP socket, if host is omitted, localhost will be assumed. If a path is given, the socket will be opened as a unix socket to that path.

Normally this method is not needed, as net.createConnection opens the socket. Use this only if you are implementing a custom Socket or if a Socket is closed and you want to reuse it to connect to another server.

This function is asynchronous. When the 'connect' event is emitted the socket is established. If there is a problem connecting, the 'connect' event will not be emitted, the 'error' event will be emitted with the exception.

The connectListener parameter will be added as an listener for the 'connect' event.

socket.bufferSize#

net.Socket has the property that socket.write() always works. This is to help users get up and running quickly. The computer cannot always keep up with the amount of data that is written to a socket - the network connection simply might be too slow. Node will internally queue up the data written to a socket and send it out over the wire when it is possible. (Internally it is polling on the socket's file descriptor for being writable).

The consequence of this internal buffering is that memory may grow. This property shows the number of characters currently buffered to be written. (Number of characters is approximately equal to the number of bytes to be written, but the buffer may contain strings, and the strings are lazily encoded, so the exact number of bytes is not known.)

Users who experience large or growing bufferSize should attempt to "throttle" the data flows in their program with pause() and resume().

socket.setEncoding([encoding])#

Sets the encoding (either 'ascii', 'utf8', or 'base64') for data that is received. Defaults to null.

socket.write(data, [encoding], [callback])#

Sends data on the socket. The second parameter specifies the encoding in the case of a string--it defaults to UTF8 encoding.

Returns true if the entire data was flushed successfully to the kernel buffer. Returns false if all or part of the data was queued in user memory. 'drain' will be emitted when the buffer is again free.

The optional callback parameter will be executed when the data is finally written out - this may not be immediately.

socket.end([data], [encoding])#

Half-closes the socket. i.e., it sends a FIN packet. It is possible the server will still send some data.

If data is specified, it is equivalent to calling socket.write(data, encoding) followed by socket.end().

socket.destroy()#

Ensures that no more I/O activity happens on this socket. Only necessary in case of errors (parse error or so).

socket.pause()#

Pauses the reading of data. That is, 'data' events will not be emitted. Useful to throttle back an upload.

socket.resume()#

Resumes reading after a call to pause().

socket.setTimeout(timeout, [callback])#

Sets the socket to timeout after timeout milliseconds of inactivity on the socket. By default net.Socket do not have a timeout.

When an idle timeout is triggered the socket will receive a 'timeout' event but the connection will not be severed. The user must manually end() or destroy() the socket.

If timeout is 0, then the existing idle timeout is disabled.

The optional callback parameter will be added as a one time listener for the 'timeout' event.

socket.setNoDelay([noDelay])#

Disables the Nagle algorithm. By default TCP connections use the Nagle algorithm, they buffer data before sending it off. Setting true for noDelay will immediately fire off data each time socket.write() is called. noDelay defaults to true.

socket.setKeepAlive([enable], [initialDelay])#

Enable/disable keep-alive functionality, and optionally set the initial delay before the first keepalive probe is sent on an idle socket. enable defaults to false.

Set initialDelay (in milliseconds) to set the delay between the last data packet received and the first keepalive probe. Setting 0 for initialDelay will leave the value unchanged from the default (or previous) setting. Defaults to 0.

socket.address()#

Returns the bound address, the address family name and port of the socket as reported by the operating system. Returns an object with three properties, e.g. { port: 12346, family: 'IPv4', address: '127.0.0.1' }

socket.remoteAddress#

The string representation of the remote IP address. For example, '74.125.127.100' or '2001:4860:a005::68'.

socket.remotePort#

The numeric representation of the remote port. For example, 80 or 21.

socket.bytesRead#

The amount of received bytes.

socket.bytesWritten#

The amount of bytes sent.

net.Socket instances are EventEmitters with the following events:

Event: 'connect'#

Emitted when a socket connection is successfully established. See connect().

Event: 'data'#

  • Buffer object

Emitted when data is received. The argument data will be a Buffer or String. Encoding of data is set by socket.setEncoding(). (See the Readable Stream section for more information.)

Note that the data will be lost if there is no listener when a Socket emits a 'data' event.

Event: 'end'#

Emitted when the other end of the socket sends a FIN packet.

By default (allowHalfOpen == false) the socket will destroy its file descriptor once it has written out its pending write queue. However, by setting allowHalfOpen == true the socket will not automatically end() its side allowing the user to write arbitrary amounts of data, with the caveat that the user is required to end() their side now.

Event: 'timeout'#

Emitted if the socket times out from inactivity. This is only to notify that the socket has been idle. The user must manually close the connection.

See also: socket.setTimeout()

Event: 'drain'#

Emitted when the write buffer becomes empty. Can be used to throttle uploads.

See also: the return values of socket.write()

Event: 'error'#

  • Error object

Emitted when an error occurs. The 'close' event will be called directly following this event.

Event: 'close'#

  • had_error Boolean true if the socket had a transmission error

Emitted once the socket is fully closed. The argument had_error is a boolean which says if the socket was closed due to a transmission error.

net.isIP(input)#

Tests if input is an IP address. Returns 0 for invalid strings, returns 4 for IP version 4 addresses, and returns 6 for IP version 6 addresses.

net.isIPv4(input)#

Returns true if input is a version 4 IP address, otherwise returns false.

net.isIPv6(input)#

Returns true if input is a version 6 IP address, otherwise returns false.

UDP / Datagram Sockets#

Stability: 3 - Stable

Datagram sockets are available through require('dgram').

dgram.createSocket(type, [callback])#

  • type String. Either 'udp4' or 'udp6'
  • callback Function. Attached as a listener to message events. Optional
  • Returns: Socket object

Creates a datagram Socket of the specified types. Valid types are udp4 and udp6.

Takes an optional callback which is added as a listener for message events.

Call socket.bind if you want to receive datagrams. socket.bind() will bind to the "all interfaces" address on a random port (it does the right thing for both udp4 and udp6 sockets). You can then retrieve the address and port with socket.address().address and socket.address().port.

Class: Socket#

The dgram Socket class encapsulates the datagram functionality. It should be created via dgram.createSocket(type, [callback]).

Event: 'message'#

  • msg Buffer object. The message
  • rinfo Object. Remote address information

Emitted when a new datagram is available on a socket. msg is a Buffer and rinfo is an object with the sender's address information and the number of bytes in the datagram.

Event: 'listening'#

Emitted when a socket starts listening for datagrams. This happens as soon as UDP sockets are created.

Event: 'close'#

Emitted when a socket is closed with close(). No new message events will be emitted on this socket.

Event: 'error'#

  • exception Error object

Emitted when an error occurs.

dgram.send(buf, offset, length, port, address, [callback])#

  • buf Buffer object. Message to be sent
  • offset Integer. Offset in the buffer where the message starts.
  • length Integer. Number of bytes in the message.
  • port Integer. destination port
  • address String. destination IP
  • callback Function. Callback when message is done being delivered. Optional.

For UDP sockets, the destination port and IP address must be specified. A string may be supplied for the address parameter, and it will be resolved with DNS. An optional callback may be specified to detect any DNS errors and when buf may be re-used. Note that DNS lookups will delay the time that a send takes place, at least until the next tick. The only way to know for sure that a send has taken place is to use the callback.

If the socket has not been previously bound with a call to bind, it's assigned a random port number and bound to the "all interfaces" address (0.0.0.0 for udp4 sockets, ::0 for udp6 sockets).

Example of sending a UDP packet to a random port on localhost; 

var dgram = require('dgram');
var message = new Buffer("Some bytes");
var client = dgram.createSocket("udp4");
client.send(message, 0, message.length, 41234, "localhost", function(err, bytes) {
  client.close();
});

A Note about UDP datagram size

The maximum size of an IPv4/v6 datagram depends on the MTU (Maximum Transmission Unit) and on the Payload Length field size.

  • The Payload Length field is 16 bits wide, which means that a normal payload cannot be larger than 64K octets including internet header and data (65,507 bytes = 65,535 − 8 bytes UDP header − 20 bytes IP header); this is generally true for loopback interfaces, but such long datagrams are impractical for most hosts and networks.

  • The MTU is the largest size a given link layer technology can support for datagrams. For any link, IPv4 mandates a minimum MTU of 68 octets, while the recommended MTU for IPv4 is 576 (typically recommended as the MTU for dial-up type applications), whether they arrive whole or in fragments.

    For IPv6, the minimum MTU is 1280 octets, however, the mandatory minimum fragment reassembly buffer size is 1500 octets. The value of 68 octets is very small, since most current link layer technologies have a minimum MTU of 1500 (like Ethernet).

Note that it's impossible to know in advance the MTU of each link through which a packet might travel, and that generally sending a datagram greater than the (receiver) MTU won't work (the packet gets silently dropped, without informing the source that the data did not reach its intended recipient).

dgram.bind(port, [address])#

  • port Integer
  • address String, Optional

For UDP sockets, listen for datagrams on a named port and optional address. If address is not specified, the OS will try to listen on all addresses.

Example of a UDP server listening on port 41234: 

var dgram = require("dgram");

var server = dgram.createSocket("udp4");

server.on("message", function (msg, rinfo) {
  console.log("server got: " + msg + " from " +
    rinfo.address + ":" + rinfo.port);
});

server.on("listening", function () {
  var address = server.address();
  console.log("server listening " +
      address.address + ":" + address.port);
});

server.bind(41234);
// server listening 0.0.0.0:41234

dgram.close()#

Close the underlying socket and stop listening for data on it.

dgram.address()#

Returns an object containing the address information for a socket. For UDP sockets, this object will contain address and port.

dgram.setBroadcast(flag)#

  • flag Boolean

Sets or clears the SO_BROADCAST socket option. When this option is set, UDP packets may be sent to a local interface's broadcast address.

dgram.setTTL(ttl)#

  • ttl Integer

Sets the IP_TTL socket option. TTL stands for "Time to Live," but in this context it specifies the number of IP hops that a packet is allowed to go through. Each router or gateway that forwards a packet decrements the TTL. If the TTL is decremented to 0 by a router, it will not be forwarded. Changing TTL values is typically done for network probes or when multicasting.

The argument to setTTL() is a number of hops between 1 and 255. The default on most systems is 64.

dgram.setMulticastTTL(ttl)#

  • ttl Integer

Sets the IP_MULTICAST_TTL socket option. TTL stands for "Time to Live," but in this context it specifies the number of IP hops that a packet is allowed to go through, specifically for multicast traffic. Each router or gateway that forwards a packet decrements the TTL. If the TTL is decremented to 0 by a router, it will not be forwarded.

The argument to setMulticastTTL() is a number of hops between 0 and 255. The default on most systems is 1.

dgram.setMulticastLoopback(flag)#

  • flag Boolean

Sets or clears the IP_MULTICAST_LOOP socket option. When this option is set, multicast packets will also be received on the local interface.

dgram.addMembership(multicastAddress, [multicastInterface])#

  • multicastAddress String
  • multicastInterface String, Optional

Tells the kernel to join a multicast group with IP_ADD_MEMBERSHIP socket option.

If multicastInterface is not specified, the OS will try to add membership to all valid interfaces.

dgram.dropMembership(multicastAddress, [multicastInterface])#

  • multicastAddress String
  • multicastInterface String, Optional

Opposite of addMembership - tells the kernel to leave a multicast group with IP_DROP_MEMBERSHIP socket option. This is automatically called by the kernel when the socket is closed or process terminates, so most apps will never need to call this.

If multicastInterface is not specified, the OS will try to drop membership to all valid interfaces.

DNS#

Stability: 3 - Stable

Use require('dns') to access this module. All methods in the dns module use C-Ares except for dns.lookup which uses getaddrinfo(3) in a thread pool. C-Ares is much faster than getaddrinfo but the system resolver is more constant with how other programs operate. When a user does net.connect(80, 'google.com') or http.get({ host: 'google.com' }) the dns.lookup method is used. Users who need to do a large number of look ups quickly should use the methods that go through C-Ares.

Here is an example which resolves 'www.google.com' then reverse resolves the IP addresses which are returned. 

var dns = require('dns');

dns.resolve4('www.google.com', function (err, addresses) {
  if (err) throw err;

  console.log('addresses: ' + JSON.stringify(addresses));

  addresses.forEach(function (a) {
    dns.reverse(a, function (err, domains) {
      if (err) {
        console.log('reverse for ' + a + ' failed: ' +
          err.message);
      } else {
        console.log('reverse for ' + a + ': ' +
          JSON.stringify(domains));
      }
    });
  });
});

dns.lookup(domain, [family], callback)#

Resolves a domain (e.g. 'google.com') into the first found A (IPv4) or AAAA (IPv6) record. The family can be the integer 4 or 6. Defaults to null that indicates both Ip v4 and v6 address family.

The callback has arguments (err, address, family). The address argument is a string representation of a IP v4 or v6 address. The family argument is either the integer 4 or 6 and denotes the family of address (not necessarily the value initially passed to lookup).

dns.resolve(domain, [rrtype], callback)#

Resolves a domain (e.g. 'google.com') into an array of the record types specified by rrtype. Valid rrtypes are 'A' (IPV4 addresses, default), 'AAAA' (IPV6 addresses), 'MX' (mail exchange records), 'TXT' (text records), 'SRV' (SRV records), 'PTR' (used for reverse IP lookups), 'NS' (name server records) and 'CNAME' (canonical name records).

The callback has arguments (err, addresses). The type of each item in addresses is determined by the record type, and described in the documentation for the corresponding lookup methods below.

On error, err would be an instanceof Error object, where err.errno is one of the error codes listed below and err.message is a string describing the error in English.

dns.resolve4(domain, callback)#

The same as dns.resolve(), but only for IPv4 queries (A records). addresses is an array of IPv4 addresses (e.g. ['74.125.79.104', '74.125.79.105', '74.125.79.106']).

dns.resolve6(domain, callback)#

The same as dns.resolve4() except for IPv6 queries (an AAAA query).

dns.resolveMx(domain, callback)#

The same as dns.resolve(), but only for mail exchange queries (MX records).

addresses is an array of MX records, each with a priority and an exchange attribute (e.g. [{'priority': 10, 'exchange': 'mx.example.com'},...]).

dns.resolveTxt(domain, callback)#

The same as dns.resolve(), but only for text queries (TXT records). addresses is an array of the text records available for domain (e.g., ['v=spf1 ip4:0.0.0.0 ~all']).

dns.resolveSrv(domain, callback)#

The same as dns.resolve(), but only for service records (SRV records). addresses is an array of the SRV records available for domain. Properties of SRV records are priority, weight, port, and name (e.g., [{'priority': 10, {'weight': 5, 'port': 21223, 'name': 'service.example.com'}, ...]).

dns.reverse(ip, callback)#

Reverse resolves an ip address to an array of domain names.

The callback has arguments (err, domains).

dns.resolveNs(domain, callback)#

The same as dns.resolve(), but only for name server records (NS records). addresses is an array of the name server records available for domain (e.g., ['ns1.example.com', 'ns2.example.com']).

dns.resolveCname(domain, callback)#

The same as dns.resolve(), but only for canonical name records (CNAME records). addresses is an array of the canonical name records available for domain (e.g., ['bar.example.com']).

If there an an error, err will be non-null and an instanceof the Error object.

Each DNS query can return an error code.

  • dns.TEMPFAIL: timeout, SERVFAIL or similar.
  • dns.PROTOCOL: got garbled reply.
  • dns.NXDOMAIN: domain does not exists.
  • dns.NODATA: domain exists but no data of reqd type.
  • dns.NOMEM: out of memory while processing.
  • dns.BADQUERY: the query is malformed.

HTTP#

Stability: 3 - Stable

To use the HTTP server and client one must require('http').

The HTTP interfaces in Node are designed to support many features of the protocol which have been traditionally difficult to use. In particular, large, possibly chunk-encoded, messages. The interface is careful to never buffer entire requests or responses--the user is able to stream data.

HTTP message headers are represented by an object like this: 

{ 'content-length': '123',
  'content-type': 'text/plain',
  'connection': 'keep-alive',
  'accept': '*/*' }

Keys are lowercased. Values are not modified.

In order to support the full spectrum of possible HTTP applications, Node's HTTP API is very low-level. It deals with stream handling and message parsing only. It parses a message into headers and body but it does not parse the actual headers or the body.

http.createServer([requestListener])#

Returns a new web server object.

The requestListener is a function which is automatically added to the 'request' event.

Class: http.Server#

This is an EventEmitter with the following events:

Event: 'request'#

function (request, response) { }

Emitted each time there is a request. Note that there may be multiple requests per connection (in the case of keep-alive connections). request is an instance of http.ServerRequest and response is an instance of http.ServerResponse

Event: 'connection'#

function (socket) { }

When a new TCP stream is established. socket is an object of type net.Socket. Usually users will not want to access this event. The socket can also be accessed at request.connection.

Event: 'close'#

function () { }

Emitted when the server closes.

Event: 'checkContinue'#

function (request, response) { }

Emitted each time a request with an http Expect: 100-continue is received. If this event isn't listened for, the server will automatically respond with a 100 Continue as appropriate.

Handling this event involves calling response.writeContinue if the client should continue to send the request body, or generating an appropriate HTTP response (e.g., 400 Bad Request) if the client should not continue to send the request body.

Note that when this event is emitted and handled, the request event will not be emitted.

Event: 'connect'#

function (request, socket, head) { }

Emitted each time a client requests a http CONNECT method. If this event isn't listened for, then clients requesting a CONNECT method will have their connections closed.

  • request is the arguments for the http request, as it is in the request event.
  • socket is the network socket between the server and client.
  • head is an instance of Buffer, the first packet of the tunneling stream, this may be empty.

After this event is emitted, the request's socket will not have a data event listener, meaning you will need to bind to it in order to handle data sent to the server on that socket.

Event: 'upgrade'#

function (request, socket, head) { }

Emitted each time a client requests a http upgrade. If this event isn't listened for, then clients requesting an upgrade will have their connections closed.

  • request is the arguments for the http request, as it is in the request event.
  • socket is the network socket between the server and client.
  • head is an instance of Buffer, the first packet of the upgraded stream, this may be empty.

After this event is emitted, the request's socket will not have a data event listener, meaning you will need to bind to it in order to handle data sent to the server on that socket.

Event: 'clientError'#

function (exception) { }

If a client connection emits an 'error' event - it will forwarded here.

server.listen(port, [hostname], [callback])#

Begin accepting connections on the specified port and hostname. If the hostname is omitted, the server will accept connections directed to any IPv4 address (INADDR_ANY).

To listen to a unix socket, supply a filename instead of port and hostname.

This function is asynchronous. The last parameter callback will be added as a listener for the 'listening' event. See also net.Server.listen().

server.listen(path, [callback])#

Start a UNIX socket server listening for connections on the given path.

This function is asynchronous. The last parameter callback will be added as a listener for the 'listening' event. See also net.Server.listen().

server.close([cb])#

Stops the server from accepting new connections. See net.Server.close().

server.maxHeadersCount#

Limits maximum incoming headers count, equal to 1000 by default. If set to 0 - no limit will be applied.

Class: http.ServerRequest#

This object is created internally by a HTTP server -- not by the user -- and passed as the first argument to a 'request' listener.

The request implements the Readable Stream interface. This is an EventEmitter with the following events:

Event: 'data'#

function (chunk) { }

Emitted when a piece of the message body is received. The chunk is a string if an encoding has been set with request.setEncoding(), otherwise it's a Buffer.

Note that the data will be lost if there is no listener when a ServerRequest emits a 'data' event.

Event: 'end'#

function () { }

Emitted exactly once for each request. After that, no more 'data' events will be emitted on the request.

Event: 'close'#

function () { }

Indicates that the underlaying connection was terminated before response.end() was called or able to flush.

Just like 'end', this event occurs only once per request, and no more 'data' events will fire afterwards.

Note: 'close' can fire after 'end', but not vice versa.

request.method#

The request method as a string. Read only. Example: 'GET', 'DELETE'.

request.url#

Request URL string. This contains only the URL that is present in the actual HTTP request. If the request is: 

GET /status?name=ryan HTTP/1.1\r\n
Accept: text/plain\r\n
\r\n

Then request.url will be: 

'/status?name=ryan'

If you would like to parse the URL into its parts, you can use require('url').parse(request.url). Example: 

node> require('url').parse('/status?name=ryan')
{ href: '/status?name=ryan',
  search: '?name=ryan',
  query: 'name=ryan',
  pathname: '/status' }

If you would like to extract the params from the query string, you can use the require('querystring').parse function, or pass true as the second argument to require('url').parse. Example: 

node> require('url').parse('/status?name=ryan', true)
{ href: '/status?name=ryan',
  search: '?name=ryan',
  query: { name: 'ryan' },
  pathname: '/status' }

request.headers#

Read only.

request.trailers#

Read only; HTTP trailers (if present). Only populated after the 'end' event.

request.httpVersion#

The HTTP protocol version as a string. Read only. Examples: '1.1', '1.0'. Also request.httpVersionMajor is the first integer and request.httpVersionMinor is the second.

request.setEncoding([encoding])#

Set the encoding for the request body. Either 'utf8' or 'binary'. Defaults to null, which means that the 'data' event will emit a Buffer object..

request.pause()#

Pauses request from emitting events. Useful to throttle back an upload.

request.resume()#

Resumes a paused request.

request.connection#

The net.Socket object associated with the connection.

With HTTPS support, use request.connection.verifyPeer() and request.connection.getPeerCertificate() to obtain the client's authentication details.

Class: http.ServerResponse#

This object is created internally by a HTTP server--not by the user. It is passed as the second parameter to the 'request' event.

The response implements the Writable Stream interface. This is an EventEmitter with the following events:

Event: 'close'#

function () { }

Indicates that the underlaying connection was terminated before response.end() was called or able to flush.

response.writeContinue()#

Sends a HTTP/1.1 100 Continue message to the client, indicating that the request body should be sent. See the checkContinue event on Server.

response.writeHead(statusCode, [reasonPhrase], [headers])#

Sends a response header to the request. The status code is a 3-digit HTTP status code, like 404. The last argument, headers, are the response headers. Optionally one can give a human-readable reasonPhrase as the second argument.

Example: 

var body = 'hello world';
response.writeHead(200, {
  'Content-Length': body.length,
  'Content-Type': 'text/plain' });

This method must only be called once on a message and it must be called before response.end() is called.

If you call response.write() or response.end() before calling this, the implicit/mutable headers will be calculated and call this function for you.

Note: that Content-Length is given in bytes not characters. The above example works because the string 'hello world' contains only single byte characters. If the body contains higher coded characters then Buffer.byteLength() should be used to determine the number of bytes in a given encoding. And Node does not check whether Content-Length and the length of the body which has been transmitted are equal or not.

response.statusCode#

When using implicit headers (not calling response.writeHead() explicitly), this property controls the status code that will be send to the client when the headers get flushed.

Example: 

response.statusCode = 404;

After response header was sent to the client, this property indicates the status code which was sent out.

response.setHeader(name, value)#

Sets a single header value for implicit headers. If this header already exists in the to-be-sent headers, its value will be replaced. Use an array of strings here if you need to send multiple headers with the same name.

Example: 

response.setHeader("Content-Type", "text/html");

or 

response.setHeader("Set-Cookie", ["type=ninja", "language=javascript"]);

response.sendDate#

When true, the Date header will be automatically generated and sent in the response if it is not already present in the headers. Defaults to true.

This should only be disabled for testing; HTTP requires the Date header in responses.

response.getHeader(name)#

Reads out a header that's already been queued but not sent to the client. Note that the name is case insensitive. This can only be called before headers get implicitly flushed.

Example: 

var contentType = response.getHeader('content-type');

response.removeHeader(name)#

Removes a header that's queued for implicit sending.

Example: 

response.removeHeader("Content-Encoding");

response.write(chunk, [encoding])#

If this method is called and response.writeHead() has not been called, it will switch to implicit header mode and flush the implicit headers.

This sends a chunk of the response body. This method may be called multiple times to provide successive parts of the body.

chunk can be a string or a buffer. If chunk is a string, the second parameter specifies how to encode it into a byte stream. By default the encoding is 'utf8'.

Note: This is the raw HTTP body and has nothing to do with higher-level multi-part body encodings that may be used.

The first time response.write() is called, it will send the buffered header information and the first body to the client. The second time response.write() is called, Node assumes you're going to be streaming data, and sends that separately. That is, the response is buffered up to the first chunk of body.

response.addTrailers(headers)#

This method adds HTTP trailing headers (a header but at the end of the message) to the response.

Trailers will only be emitted if chunked encoding is used for the response; if it is not (e.g., if the request was HTTP/1.0), they will be silently discarded.

Note that HTTP requires the Trailer header to be sent if you intend to emit trailers, with a list of the header fields in its value. E.g., 

response.writeHead(200, { 'Content-Type': 'text/plain',
                          'Trailer': 'Content-MD5' });
response.write(fileData);
response.addTrailers({'Content-MD5': "7895bf4b8828b55ceaf47747b4bca667"});
response.end();

response.end([data], [encoding])#

This method signals to the server that all of the response headers and body has been sent; that server should consider this message complete. The method, response.end(), MUST be called on each response.

If data is specified, it is equivalent to calling response.write(data, encoding) followed by response.end().

http.request(options, callback)#

Node maintains several connections per server to make HTTP requests. This function allows one to transparently issue requests. options align with url.parse().

Options:

  • host: A domain name or IP address of the server to issue the request to. Defaults to 'localhost'.
  • hostname: To support url.parse() hostname is preferred over host
  • port: Port of remote server. Defaults to 80.
  • localAddress: Local interface to bind for network connections.
  • socketPath: Unix Domain Socket (use one of host:port or socketPath)
  • method: A string specifying the HTTP request method. Defaults to 'GET'.
  • path: Request path. Defaults to '/'. Should include query string if any. E.G. '/index.html?page=12'
  • headers: An object containing request headers.
  • auth: Basic authentication i.e. 'user:password' to compute an Authorization header.
  • agent: Controls Agent behavior. When an Agent is used request will default to Connection: keep-alive. Possible values:
    • undefined (default): use global Agent for this host and port.
    • Agent object: explicitly use the passed in Agent.
    • false: opts out of connection pooling with an Agent, defaults request to Connection: close.

http.request() returns an instance of the http.ClientRequest class. The ClientRequest instance is a writable stream. If one needs to upload a file with a POST request, then write to the ClientRequest object.

Example: 

var options = {
  host: 'www.google.com',
  port: 80,
  path: '/upload',
  method: 'POST'
};

var req = http.request(options, function(res) {
  console.log('STATUS: ' + res.statusCode);
  console.log('HEADERS: ' + JSON.stringify(res.headers));
  res.setEncoding('utf8');
  res.on('data', function (chunk) {
    console.log('BODY: ' + chunk);
  });
});

req.on('error', function(e) {
  console.log('problem with request: ' + e.message);
});

// write data to request body
req.write('data\n');
req.write('data\n');
req.end();

Note that in the example req.end() was called. With http.request() one must always call req.end() to signify that you're done with the request - even if there is no data being written to the request body.

If any error is encountered during the request (be that with DNS resolution, TCP level errors, or actual HTTP parse errors) an 'error' event is emitted on the returned request object.

There are a few special headers that should be noted.

  • Sending a 'Connection: keep-alive' will notify Node that the connection to the server should be persisted until the next request.

  • Sending a 'Content-length' header will disable the default chunked encoding.

  • Sending an 'Expect' header will immediately send the request headers. Usually, when sending 'Expect: 100-continue', you should both set a timeout and listen for the continue event. See RFC2616 Section 8.2.3 for more information.

  • Sending an Authorization header will override using the auth option to compute basic authentication.

http.get(options, callback)#

Since most requests are GET requests without bodies, Node provides this convenience method. The only difference between this method and http.request() is that it sets the method to GET and calls req.end() automatically.

Example: 

var options = {
  host: 'www.google.com',
  port: 80,
  path: '/index.html'
};

http.get(options, function(res) {
  console.log("Got response: " + res.statusCode);
}).on('error', function(e) {
  console.log("Got error: " + e.message);
});

Class: http.Agent#

In node 0.5.3+ there is a new implementation of the HTTP Agent which is used for pooling sockets used in HTTP client requests.

Previously, a single agent instance help the pool for single host+port. The current implementation now holds sockets for any number of hosts.

The current HTTP Agent also defaults client requests to using Connection:keep-alive. If no pending HTTP requests are waiting on a socket to become free the socket is closed. This means that node's pool has the benefit of keep-alive when under load but still does not require developers to manually close the HTTP clients using keep-alive.

Sockets are removed from the agent's pool when the socket emits either a "close" event or a special "agentRemove" event. This means that if you intend to keep one HTTP request open for a long time and don't want it to stay in the pool you can do something along the lines of: 

http.get(options, function(res) {
  // Do stuff
}).on("socket", function (socket) {
  socket.emit("agentRemove");
});

Alternatively, you could just opt out of pooling entirely using agent:false: 

http.get({host:'localhost', port:80, path:'/', agent:false}, function (res) {
  // Do stuff
})

agent.maxSockets#

By default set to 5. Determines how many concurrent sockets the agent can have open per host.

agent.sockets#

An object which contains arrays of sockets currently in use by the Agent. Do not modify.

agent.requests#

An object which contains queues of requests that have not yet been assigned to sockets. Do not modify.

http.globalAgent#

Global instance of Agent which is used as the default for all http client requests.

Class: http.ClientRequest#

This object is created internally and returned from http.request(). It represents an in-progress request whose header has already been queued. The header is still mutable using the setHeader(name, value), getHeader(name), removeHeader(name) API. The actual header will be sent along with the first data chunk or when closing the connection.

To get the response, add a listener for 'response' to the request object. 'response' will be emitted from the request object when the response headers have been received. The 'response' event is executed with one argument which is an instance of http.ClientResponse.

During the 'response' event, one can add listeners to the response object; particularly to listen for the 'data' event. Note that the 'response' event is called before any part of the response body is received, so there is no need to worry about racing to catch the first part of the body. As long as a listener for 'data' is added during the 'response' event, the entire body will be caught. 

// Good
request.on('response', function (response) {
  response.on('data', function (chunk) {
    console.log('BODY: ' + chunk);
  });
});

// Bad - misses all or part of the body
request.on('response', function (response) {
  setTimeout(function () {
    response.on('data', function (chunk) {
      console.log('BODY: ' + chunk);
    });
  }, 10);
});

Note: Node does not check whether Content-Length and the length of the body which has been transmitted are equal or not.

The request implements the Writable Stream interface. This is an EventEmitter with the following events:

Event 'response'#

function (response) { }

Emitted when a response is received to this request. This event is emitted only once. The response argument will be an instance of http.ClientResponse.

Options:

  • host: A domain name or IP address of the server to issue the request to.
  • port: Port of remote server.
  • socketPath: Unix Domain Socket (use one of host:port or socketPath)

Event: 'socket'#

function (socket) { }

Emitted after a socket is assigned to this request.

Event: 'connect'#

function (response, socket, head) { }

Emitted each time a server responds to a request with a CONNECT method. If this event isn't being listened for, clients receiving a CONNECT method will have their connections closed.

A client server pair that show you how to listen for the connect event. 

var http = require('http');
var net = require('net');
var url = require('url');

// Create an HTTP tunneling proxy
var proxy = http.createServer(function (req, res) {
  res.writeHead(200, {'Content-Type': 'text/plain'});
  res.end('okay');
});
proxy.on('connect', function(req, cltSocket, head) {
  // connect to an origin server
  var srvUrl = url.parse('http://' + req.url);
  var srvSocket = net.connect(srvUrl.port, srvUrl.hostname, function() {
    cltSocket.write('HTTP/1.1 200 Connection Established\r\n' +
                    'Proxy-agent: Node-Proxy\r\n' +
                    '\r\n');
    srvSocket.write(head);
    srvSocket.pipe(cltSocket);
    cltSocket.pipe(srvSocket);
  });
});

// now that proxy is running
proxy.listen(1337, '127.0.0.1', function() {

  // make a request to a tunneling proxy
  var options = {
    port: 1337,
    host: '127.0.0.1',
    method: 'CONNECT',
    path: 'www.google.com:80'
  };

  var req = http.request(options);
  req.end();

  req.on('connect', function(res, socket, head) {
    console.log('got connected!');

    // make a request over an HTTP tunnel
    socket.write('GET / HTTP/1.1\r\n' +
                 'Host: www.google.com:80\r\n' +
                 'Connection: close\r\n' +
                 '\r\n');
    socket.on('data', function(chunk) {
      console.log(chunk.toString());
    });
    socket.on('end', function() {
      proxy.close();
    });
  });
});

Event: 'upgrade'#

function (response, socket, head) { }

Emitted each time a server responds to a request with an upgrade. If this event isn't being listened for, clients receiving an upgrade header will have their connections closed.

A client server pair that show you how to listen for the upgrade event. 

var http = require('http');

// Create an HTTP server
var srv = http.createServer(function (req, res) {
  res.writeHead(200, {'Content-Type': 'text/plain'});
  res.end('okay');
});
srv.on('upgrade', function(req, socket, head) {
  socket.write('HTTP/1.1 101 Web Socket Protocol Handshake\r\n' +
               'Upgrade: WebSocket\r\n' +
               'Connection: Upgrade\r\n' +
               '\r\n');

  socket.pipe(socket); // echo back
});

// now that server is running
srv.listen(1337, '127.0.0.1', function() {

  // make a request
  var options = {
    port: 1337,
    host: '127.0.0.1',
    headers: {
      'Connection': 'Upgrade',
      'Upgrade': 'websocket'
    }
  };

  var req = http.request(options);
  req.end();

  req.on('upgrade', function(res, socket, upgradeHead) {
    console.log('got upgraded!');
    socket.end();
    process.exit(0);
  });
});

Event: 'continue'#

function () { }

Emitted when the server sends a '100 Continue' HTTP response, usually because the request contained 'Expect: 100-continue'. This is an instruction that the client should send the request body.

request.write(chunk, [encoding])#

Sends a chunk of the body. By calling this method many times, the user can stream a request body to a server--in that case it is suggested to use the ['Transfer-Encoding', 'chunked'] header line when creating the request.

The chunk argument should be a buffer or a string.

The encoding argument is optional and only applies when chunk is a string. Defaults to 'utf8'.

request.end([data], [encoding])#

Finishes sending the request. If any parts of the body are unsent, it will flush them to the stream. If the request is chunked, this will send the terminating '0\r\n\r\n'.

If data is specified, it is equivalent to calling request.write(data, encoding) followed by request.end().

request.abort()#

Aborts a request. (New since v0.3.8.)

request.setTimeout(timeout, [callback])#

Once a socket is assigned to this request and is connected socket.setTimeout(timeout, [callback]) will be called.

request.setNoDelay([noDelay])#

Once a socket is assigned to this request and is connected socket.setNoDelay(noDelay) will be called.

request.setSocketKeepAlive([enable], [initialDelay])#

Once a socket is assigned to this request and is connected socket.setKeepAlive(enable, [initialDelay]) will be called.

http.ClientResponse#

This object is created when making a request with http.request(). It is passed to the 'response' event of the request object.

The response implements the Readable Stream interface. This is an EventEmitter with the following events:

Event: 'data'#

function (chunk) { }

Emitted when a piece of the message body is received.

Note that the data will be lost if there is no listener when a ClientResponse emits a 'data' event.

Event: 'end'#

function () { }

Emitted exactly once for each message. No arguments. After emitted no other events will be emitted on the response.

Event: 'close'#

function (err) { }

Indicates that the underlaying connection was terminated before end event was emitted. See http.ServerRequest's 'close' event for more information.

response.statusCode#

The 3-digit HTTP response status code. E.G. 404.

response.httpVersion#

The HTTP version of the connected-to server. Probably either '1.1' or '1.0'. Also response.httpVersionMajor is the first integer and response.httpVersionMinor is the second.

response.headers#

The response headers object.

response.trailers#

The response trailers object. Only populated after the 'end' event.

response.setEncoding([encoding])#

Set the encoding for the response body. Either 'utf8', 'ascii', or 'base64'. Defaults to null, which means that the 'data' event will emit a Buffer object.

response.pause()#

Pauses response from emitting events. Useful to throttle back a download.

response.resume()#

Resumes a paused response.

HTTPS#

Stability: 3 - Stable

HTTPS is the HTTP protocol over TLS/SSL. In Node this is implemented as a separate module.

Class: https.Server#

This class is a subclass of tls.Server and emits events same as http.Server. See http.Server for more information.

https.createServer(options, [requestListener])#

Returns a new HTTPS web server object. The options is similar to tls.createServer(). The requestListener is a function which is automatically added to the 'request' event.

Example: 

// curl -k https://localhost:8000/
var https = require('https');
var fs = require('fs');

var options = {
  key: fs.readFileSync('test/fixtures/keys/agent2-key.pem'),
  cert: fs.readFileSync('test/fixtures/keys/agent2-cert.pem')
};

https.createServer(options, function (req, res) {
  res.writeHead(200);
  res.end("hello world\n");
}).listen(8000);

https.request(options, callback)#

Makes a request to a secure web server. All options from http.request() are valid.

Example: 

var https = require('https');

var options = {
  host: 'encrypted.google.com',
  port: 443,
  path: '/',
  method: 'GET'
};

var req = https.request(options, function(res) {
  console.log("statusCode: ", res.statusCode);
  console.log("headers: ", res.headers);

  res.on('data', function(d) {
    process.stdout.write(d);
  });
});
req.end();

req.on('error', function(e) {
  console.error(e);
});

The options argument has the following options

  • host: IP or domain of host to make request to. Defaults to 'localhost'.
  • port: port of host to request to. Defaults to 443.
  • path: Path to request. Default '/'.

  • method: HTTP request method. Default 'GET'.

  • host: A domain name or IP address of the server to issue the request to. Defaults to 'localhost'.

  • hostname: To support url.parse() hostname is preferred over host
  • port: Port of remote server. Defaults to 443.
  • method: A string specifying the HTTP request method. Defaults to 'GET'.
  • path: Request path. Defaults to '/'. Should include query string if any. E.G. '/index.html?page=12'
  • headers: An object containing request headers.
  • auth: Basic authentication i.e. 'user:password' to compute an Authorization header.
  • agent: Controls Agent behavior. When an Agent is used request will default to Connection: keep-alive. Possible values:
    • undefined (default): use globalAgent for this host and port.
    • Agent object: explicitly use the passed in Agent.
    • false: opts out of connection pooling with an Agent, defaults request to Connection: close.

The following options from tls.connect() can also be specified. However, a globalAgent silently ignores these.

  • key: Private key to use for SSL. Default null.
  • passphrase: A string of passphrase for the private key. Default null.
  • cert: Public x509 certificate to use. Default null.
  • ca: An authority certificate or array of authority certificates to check the remote host against.
  • ciphers: A string describing the ciphers to use or exclude. Consult http://www.openssl.org/docs/apps/ciphers.html#CIPHER_LIST_FORMAT for details on the format.
  • rejectUnauthorized: If true, the server certificate is verified against the list of supplied CAs. An 'error' event is emitted if verification fails. Verification happens at the connection level, before the HTTP request is sent. Default false.

In order to specify these options, use a custom Agent.

Example: 

var options = {
  host: 'encrypted.google.com',
  port: 443,
  path: '/',
  method: 'GET',
  key: fs.readFileSync('test/fixtures/keys/agent2-key.pem'),
  cert: fs.readFileSync('test/fixtures/keys/agent2-cert.pem')
};
options.agent = new https.Agent(options);

var req = https.request(options, function(res) {
  ...
}

Or does not use an Agent.

Example: 

var options = {
  host: 'encrypted.google.com',
  port: 443,
  path: '/',
  method: 'GET',
  key: fs.readFileSync('test/fixtures/keys/agent2-key.pem'),
  cert: fs.readFileSync('test/fixtures/keys/agent2-cert.pem'),
  agent: false
};

var req = https.request(options, function(res) {
  ...
}

https.get(options, callback)#

Like http.get() but for HTTPS.

Example: 

var https = require('https');

https.get({ host: 'encrypted.google.com', path: '/' }, function(res) {
  console.log("statusCode: ", res.statusCode);
  console.log("headers: ", res.headers);

  res.on('data', function(d) {
    process.stdout.write(d);
  });

}).on('error', function(e) {
  console.error(e);
});

Class: https.Agent#

An Agent object for HTTPS similar to http.Agent. See https.request() for more information.

https.globalAgent#

Global instance of https.Agent which is used as the default for all HTTPS client requests.

URL#

Stability: 3 - Stable

This module has utilities for URL resolution and parsing. Call require('url') to use it.

Parsed URL objects have some or all of the following fields, depending on whether or not they exist in the URL string. Any parts that are not in the URL string will not be in the parsed object. Examples are shown for the URL

'http://user:pass@host.com:8080/p/a/t/h?query=string#hash'

  • href: The full URL that was originally parsed. Both the protocol and host are lowercased.

    Example: 'http://user:pass@host.com:8080/p/a/t/h?query=string#hash'

  • protocol: The request protocol, lowercased.

    Example: 'http:'

  • host: The full lowercased host portion of the URL, including the port.

    Example: 'host.com:8080'

  • auth: The authentication information portion of a URL.

    Example: 'user:pass'

  • hostname: Just the lowercased hostname portion of the host.

    Example: 'host.com'

  • port: The port number portion of the host.

    Example: '8080'

  • pathname: The path section of the URL, that comes after the host and before the query, including the initial slash if present.

    Example: '/p/a/t/h'

  • search: The 'query string' portion of the URL, including the leading question mark.

    Example: '?query=string'

  • path: Concatenation of pathname and search.

    Example: '/p/a/t/h?query=string'

  • query: Either the 'params' portion of the query string, or a querystring-parsed object.

    Example: 'query=string' or {'query':'string'}

  • hash: The 'fragment' portion of the URL including the pound-sign.

    Example: '#hash'

The following methods are provided by the URL module:

url.parse(urlStr, [parseQueryString], [slashesDenoteHost])#

Take a URL string, and return an object.

Pass true as the second argument to also parse the query string using the querystring module. Defaults to false.

Pass true as the third argument to treat //foo/bar as { host: 'foo', pathname: '/bar' } rather than { pathname: '//foo/bar' }. Defaults to false.

url.format(urlObj)#

Take a parsed URL object, and return a formatted URL string.

  • href will be ignored.
  • protocolis treated the same with or without the trailing : (colon).
    • The protocols http, https, ftp, gopher, file will be postfixed with :// (colon-slash-slash).
    • All other protocols mailto, xmpp, aim, sftp, foo, etc will be postfixed with : (colon)
  • auth will only be used if host is absent.
  • hostname will only be used if host is absent.
  • port will only be used if host is absent.
  • host will be used in place of hostname and port
  • pathname is treated the same with or without the leading / (slash)
  • search will be used in place of query
  • query (object; see querystring) will only be used if search is absent.
  • search is treated the same with or without the leading ? (question mark)
  • hash is treated the same with or without the leading # (pound sign, anchor)

url.resolve(from, to)#

Take a base URL, and a href URL, and resolve them as a browser would for an anchor tag.

Query String#

Stability: 3 - Stable

This module provides utilities for dealing with query strings. It provides the following methods:

querystring.stringify(obj, [sep], [eq])#

Serialize an object to a query string. Optionally override the default separator ('&') and assignment ('=') characters.

Example: 

querystring.stringify({ foo: 'bar', baz: ['qux', 'quux'], corge: '' })
// returns
'foo=bar&baz=qux&baz=quux&corge='

querystring.stringify({foo: 'bar', baz: 'qux'}, ';', ':')
// returns
'foo:bar;baz:qux'

querystring.parse(str, [sep], [eq], [options])#

Deserialize a query string to an object. Optionally override the default separator ('&') and assignment ('=') characters.

Options object may contain maxKeys property (equal to 1000 by default), it'll be used to limit processed keys. Set it to 0 to remove key count limitation.

Example: 

querystring.parse('foo=bar&baz=qux&baz=quux&corge')
// returns
{ foo: 'bar', baz: ['qux', 'quux'], corge: '' }

querystring.escape#

The escape function used by querystring.stringify, provided so that it could be overridden if necessary.

querystring.unescape#

The unescape function used by querystring.parse, provided so that it could be overridden if necessary.

Readline#

Stability: 2 - Unstable

To use this module, do require('readline'). Readline allows reading of a stream (such as process.stdin) on a line-by-line basis.

Note that once you've invoked this module, your node program will not terminate until you've closed the interface. Here's how to allow your program to gracefully exit: 

var rl = require('readline');

var i = rl.createInterface({
  input: process.stdin,
  output: process.stdout
});

i.question("What do you think of node.js? ", function(answer) {
  // TODO: Log the answer in a database
  console.log("Thank you for your valuable feedback:", answer);

  i.close();
});

rl.createInterface(options)#

Creates a readline Interface instance. Accepts an "options" Object that takes the following values:

  • input - the readable stream to listen to (Required).

  • output - the writable stream to write readline data to (Required).

  • completer - an optional function that is used for Tab autocompletion. See below for an example of using this.

  • terminal - pass true if the input and output streams should be treated like a TTY, and have ANSI/VT100 escape codes written to it. Defaults to checking isTTY on the output stream upon instantiation.

The completer function is given a the current line entered by the user, and is supposed to return an Array with 2 entries:

  1. An Array with matching entries for the completion.

  2. The substring that was used for the matching.

Which ends up looking something like: [[substr1, substr2, ...], originalsubstring].

Also completer can be run in async mode if it accepts two arguments: 

function completer(linePartial, callback) {
  callback(null, [['123'], linePartial]);
}

createInterface is commonly used with process.stdin and process.stdout in order to accept user input: 

var readline = require('readline');
var rl = readline.createInterface({
  input: process.stdin,
  output: process.stdout
});

Once you have a readline instance, you most commonly listen for the "line" event.

If terminal is true for this instance then the output stream will get the best compatability if it defines an output.columns property, and fires a "resize" event on the output if/when the columns ever change (process.stdout does this automatically when it is a TTY).

Class: Interface#

The class that represents a readline interface with an input and output stream.

rl.setPrompt(prompt, length)#

Sets the prompt, for example when you run node on the command line, you see > , which is node's prompt.

rl.prompt()#

Readies readline for input from the user, putting the current setPrompt options on a new line, giving the user a new spot to write.

This will also resume the input stream used with createInterface if it has been paused.

rl.question(query, callback)#

Prepends the prompt with query and invokes callback with the user's response. Displays the query to the user, and then invokes callback with the user's response after it has been typed.

This will also resume the input stream used with createInterface if it has been paused.

Example usage: 

interface.question('What is your favorite food?', function(answer) {
  console.log('Oh, so your favorite food is ' + answer);
});

rl.pause()#

Pauses the readline input stream, allowing it to be resumed later if needed.

rl.resume()#

Resumes the readline input stream.

rl.close()#

Closes the Interface instance, relinquishing control on the input and output streams. The "close" event will also be emitted.

rl.write()#

Writes to output stream.

This will also resume the input stream if it has been paused.

Event: 'line'#

function (line) {}

Emitted whenever the input stream receives a \n, usually received when the user hits enter, or return. This is a good hook to listen for user input.

Example of listening for line: 

rl.on('line', function (cmd) {
  console.log('You just typed: '+cmd);
});

Event: 'pause'#

function () {}

Emitted whenever the input stream is paused.

Also emitted whenever the input stream is not paused and receives the SIGCONT event. (See events SIGTSTP and SIGCONT)

Example of listening for pause: 

rl.on('pause', function() {
  console.log('Readline paused.');
});

Event: 'resume'#

function () {}

Emitted whenever the input stream is resumed.

Example of listening for resume: 

rl.on('resume', function() {
  console.log('Readline resumed.');
});

Event: 'close'#

function () {}

Emitted when close() is called.

Also emitted when the input stream receives its "end" event. The Interface instance should be considered "finished" once this is emitted. For example, when the input stream receives ^D, respectively known as EOT.

This event is also called if there is no SIGINT event listener present when the input stream receives a ^C, respectively known as SIGINT.

Event: 'SIGINT'#

function () {}

Emitted whenever the input stream receives a ^C, respectively known as SIGINT. If there is no SIGINT event listener present when the input stream receives a SIGINT, pause will be triggered.

Example of listening for SIGINT: 

rl.on('SIGINT', function() {
  rl.question('Are you sure you want to exit?', function(answer) {
    if (answer.match(/^y(es)?$/i)) rl.pause();
  });
});

Event: 'SIGTSTP'#

function () {}

This does not work on Windows.

Emitted whenever the input stream receives a ^Z, respectively known as SIGTSTP. If there is no SIGTSTP event listener present when the input stream receives a SIGTSTP, the program will be sent to the background.

When the program is resumed with fg, the pause and SIGCONT events will be emitted. You can use either to resume the stream.

The pause and SIGCONT events will not be triggered if the stream was paused before the program was sent to the background.

Example of listening for SIGTSTP: 

rl.on('SIGTSTP', function() {
  // This will override SIGTSTP and prevent the program from going to the
  // background.
  console.log('Caught SIGTSTP.');
});

Event: 'SIGCONT'#

function () {}

This does not work on Windows.

Emitted whenever the input stream is sent to the background with ^Z, respectively known as SIGTSTP, and then continued with fg(1). This event only emits if the stream was not paused before sending the program to the background.

Example of listening for SIGCONT: 

rl.on('SIGCONT', function() {
  // `prompt` will automatically resume the stream
  rl.prompt();
});

Here's an example of how to use all these together to craft a tiny command line interface: 

var readline = require('readline'),
    rl = readline.createInterface(process.stdin, process.stdout);

rl.setPrompt('OHAI> ');
rl.prompt();

rl.on('line', function(line) {
  switch(line.trim()) {
    case 'hello':
      console.log('world!');
      break;
    default:
      console.log('Say what? I might have heard `' + line.trim() + '`');
      break;
  }
  rl.prompt();
}).on('close', function() {
  console.log('Have a great day!');
  process.exit(0);
});

REPL#

A Read-Eval-Print-Loop (REPL) is available both as a standalone program and easily includable in other programs. The REPL provides a way to interactively run JavaScript and see the results. It can be used for debugging, testing, or just trying things out.

By executing node without any arguments from the command-line you will be dropped into the REPL. It has simplistic emacs line-editing. 

mjr:~$ node
Type '.help' for options.
> a = [ 1, 2, 3];
[ 1, 2, 3 ]
> a.forEach(function (v) {
...   console.log(v);
...   });
1
2
3

For advanced line-editors, start node with the environmental variable NODE_NO_READLINE=1. This will start the main and debugger REPL in canonical terminal settings which will allow you to use with rlwrap.

For example, you could add this to your bashrc file: 

alias node="env NODE_NO_READLINE=1 rlwrap node"

repl.start(options)#

Returns and starts a REPLServer instance. Accepts an "options" Object that takes the following values:

  • prompt - the prompt and stream for all I/O. Defaults to > .

  • input - the readable stream to listen to. Defaults to process.stdin.

  • output - the writable stream to write readline data to. Defaults to process.stdout.

  • terminal - pass true if the stream should be treated like a TTY, and have ANSI/VT100 escape codes written to it. Defaults to checking isTTY on the output stream upon instantiation.

  • eval - function that will be used to eval each given line. Defaults to an async wrapper for eval(). See below for an example of a custom eval.

  • useColors - a boolean which specifies whether or not the writer function should output colors. If a different writer function is set then this does nothing. Defaults to the repl's terminal value.

  • useGlobal - if set to true, then the repl will use the global object, instead of running scripts in a separate context. Defaults to false.

  • ignoreUndefined - if set to true, then the repl will not output the return value of command if it's undefined. Defaults to false.

  • writer - the function to invoke for each command that gets evaluated which returns the formatting (including coloring) to display. Defaults to util.inspect.

You can use your own eval function if it has following signature: 

function eval(cmd, context, filename, callback) {
  callback(null, result);
}

Multiple REPLs may be started against the same running instance of node. Each will share the same global object but will have unique I/O.

Here is an example that starts a REPL on stdin, a Unix socket, and a TCP socket: 

var net = require("net"),
    repl = require("repl");

connections = 0;

repl.start({
  prompt: "node via stdin> ",
  input: process.stdin,
  output: process.stdout
});

net.createServer(function (socket) {
  connections += 1;
  repl.start({
    prompt: "node via Unix socket> ",
    input: socket,
    output: socket
  }).on('exit', function() {
    socket.end();
  })
}).listen("/tmp/node-repl-sock");

net.createServer(function (socket) {
  connections += 1;
  repl.start({
    prompt: "node via TCP socket> ",
    input: socket,
    output: socket
  }).on('exit', function() {
    socket.end();
  });
}).listen(5001);

Running this program from the command line will start a REPL on stdin. Other REPL clients may connect through the Unix socket or TCP socket. telnet is useful for connecting to TCP sockets, and socat can be used to connect to both Unix and TCP sockets.

By starting a REPL from a Unix socket-based server instead of stdin, you can connect to a long-running node process without restarting it.

For an example of running a "full-featured" (terminal) REPL over a net.Server and net.Socket instance, see: https://gist.github.com/2209310

For an example of running a REPL instance over curl(1), see: https://gist.github.com/2053342

Event: 'exit'#

function () {}

Emitted when the user exits the REPL in any of the defined ways. Namely, typing .exit at the repl, pressing Ctrl+C twice to signal SIGINT, or pressing Ctrl+D to signal "end" on the input stream.

Example of listening for exit: 

r.on('exit', function () {
  console.log('Got "exit" event from repl!');
  process.exit();
});

REPL Features#

Inside the REPL, Control+D will exit. Multi-line expressions can be input. Tab completion is supported for both global and local variables.

The special variable _ (underscore) contains the result of the last expression. 

> [ "a", "b", "c" ]
[ 'a', 'b', 'c' ]
> _.length
3
> _ += 1
4

The REPL provides access to any variables in the global scope. You can expose a variable to the REPL explicitly by assigning it to the context object associated with each REPLServer. For example: 

// repl_test.js
var repl = require("repl"),
    msg = "message";

repl.start().context.m = msg;

Things in the context object appear as local within the REPL: 

mjr:~$ node repl_test.js
> m
'message'

There are a few special REPL commands:

  • .break - While inputting a multi-line expression, sometimes you get lost or just don't care about completing it. .break will start over.
  • .clear - Resets the context object to an empty object and clears any multi-line expression.
  • .exit - Close the I/O stream, which will cause the REPL to exit.
  • .help - Show this list of special commands.
  • .save - Save the current REPL session to a file

    .save ./file/to/save.js

  • .load - Load a file into the current REPL session.

    .load ./file/to/load.js

The following key combinations in the REPL have these special effects:

  • <ctrl>C - Similar to the .break keyword. Terminates the current command. Press twice on a blank line to forcibly exit.
  • <ctrl>D - Similar to the .exit keyword.

Executing JavaScript#

Stability: 3 - Stable

You can access this module with: 

var vm = require('vm');

JavaScript code can be compiled and run immediately or compiled, saved, and run later.

vm.runInThisContext(code, [filename])#

vm.runInThisContext() compiles code, runs it and returns the result. Running code does not have access to local scope. filename is optional, it's used only in stack traces.

Example of using vm.runInThisContext and eval to run the same code: 

var localVar = 123,
    usingscript, evaled,
    vm = require('vm');

usingscript = vm.runInThisContext('localVar = 1;',
  'myfile.vm');
console.log('localVar: ' + localVar + ', usingscript: ' +
  usingscript);
evaled = eval('localVar = 1;');
console.log('localVar: ' + localVar + ', evaled: ' +
  evaled);

// localVar: 123, usingscript: 1
// localVar: 1, evaled: 1

vm.runInThisContext does not have access to the local scope, so localVar is unchanged. eval does have access to the local scope, so localVar is changed.

In case of syntax error in code, vm.runInThisContext emits the syntax error to stderr and throws an exception.

vm.runInNewContext(code, [sandbox], [filename])#

vm.runInNewContext compiles code, then runs it in sandbox and returns the result. Running code does not have access to local scope. The object sandbox will be used as the global object for code. sandbox and filename are optional, filename is only used in stack traces.

Example: compile and execute code that increments a global variable and sets a new one. These globals are contained in the sandbox. 

var util = require('util'),
    vm = require('vm'),
    sandbox = {
      animal: 'cat',
      count: 2
    };

vm.runInNewContext('count += 1; name = "kitty"', sandbox, 'myfile.vm');
console.log(util.inspect(sandbox));

// { animal: 'cat', count: 3, name: 'kitty' }

Note that running untrusted code is a tricky business requiring great care. To prevent accidental global variable leakage, vm.runInNewContext is quite useful, but safely running untrusted code requires a separate process.

In case of syntax error in code, vm.runInNewContext emits the syntax error to stderr and throws an exception.

vm.runInContext(code, context, [filename])#

vm.runInContext compiles code, then runs it in context and returns the result. A (V8) context comprises a global object, together with a set of built-in objects and functions. Running code does not have access to local scope and the global object held within context will be used as the global object for code. filename is optional, it's used only in stack traces.

Example: compile and execute code in a existing context. 

var util = require('util'),
    vm = require('vm'),
    initSandbox = {
      animal: 'cat',
      count: 2
    },
    context = vm.createContext(initSandbox);

vm.runInContext('count += 1; name = "CATT"', context, 'myfile.vm');
console.log(util.inspect(context));

// { animal: 'cat', count: 3, name: 'CATT' }

Note that createContext will perform a shallow clone of the supplied sandbox object in order to initialise the global object of the freshly constructed context.

Note that running untrusted code is a tricky business requiring great care. To prevent accidental global variable leakage, vm.runInContext is quite useful, but safely running untrusted code requires a separate process.

In case of syntax error in code, vm.runInContext emits the syntax error to stderr and throws an exception.

vm.createContext([initSandbox])#

vm.createContext creates a new context which is suitable for use as the 2nd argument of a subsequent call to vm.runInContext. A (V8) context comprises a global object together with a set of build-in objects and functions. The optional argument initSandbox will be shallow-copied to seed the initial contents of the global object used by the context.

vm.createScript(code, [filename])#

createScript compiles code but does not run it. Instead, it returns a vm.Script object representing this compiled code. This script can be run later many times using methods below. The returned script is not bound to any global object. It is bound before each run, just for that run. filename is optional, it's only used in stack traces.

In case of syntax error in code, createScript prints the syntax error to stderr and throws an exception.

Class: Script#

A class for running scripts. Returned by vm.createScript.

script.runInThisContext()#

Similar to vm.runInThisContext but a method of a precompiled Script object. script.runInThisContext runs the code of script and returns the result. Running code does not have access to local scope, but does have access to the global object (v8: in actual context).

Example of using script.runInThisContext to compile code once and run it multiple times: 

var vm = require('vm');

globalVar = 0;

var script = vm.createScript('globalVar += 1', 'myfile.vm');

for (var i = 0; i < 1000 ; i += 1) {
  script.runInThisContext();
}

console.log(globalVar);

// 1000

script.runInNewContext([sandbox])#

Similar to vm.runInNewContext a method of a precompiled Script object. script.runInNewContext runs the code of script with sandbox as the global object and returns the result. Running code does not have access to local scope. sandbox is optional.

Example: compile code that increments a global variable and sets one, then execute this code multiple times. These globals are contained in the sandbox. 

var util = require('util'),
    vm = require('vm'),
    sandbox = {
      animal: 'cat',
      count: 2
    };

var script = vm.createScript('count += 1; name = "kitty"', 'myfile.vm');

for (var i = 0; i < 10 ; i += 1) {
  script.runInNewContext(sandbox);
}

console.log(util.inspect(sandbox));

// { animal: 'cat', count: 12, name: 'kitty' }

Note that running untrusted code is a tricky business requiring great care. To prevent accidental global variable leakage, script.runInNewContext is quite useful, but safely running untrusted code requires a separate process.

Child Process#

Stability: 3 - Stable

Node provides a tri-directional popen(3) facility through the child_process module.

It is possible to stream data through a child's stdin, stdout, and stderr in a fully non-blocking way.

To create a child process use require('child_process').spawn() or require('child_process').fork(). The semantics of each are slightly different, and explained below.

Class: ChildProcess#

ChildProcess is an EventEmitter.

Child processes always have three streams associated with them. child.stdin, child.stdout, and child.stderr. These may be shared with the stdio streams of the parent process, or they may be separate stream objects which can be piped to and from.

The ChildProcess class is not intended to be used directly. Use the spawn() or fork() methods to create a Child Process instance.

Event: 'exit'#

  • code Number the exit code, if it exited normally.
  • signal String the signal passed to kill the child process, if it was killed by the parent.

This event is emitted after the child process ends. If the process terminated normally, code is the final exit code of the process, otherwise null. If the process terminated due to receipt of a signal, signal is the string name of the signal, otherwise null.

Note that the child process stdio streams might still be open.

See waitpid(2).

Event: 'close'#

This event is emitted when the stdio streams of a child process have all terminated. This is distinct from 'exit', since multiple processes might share the same stdio streams.

Event: 'disconnect'#

This event is emitted after using the .disconnect() method in the parent or in the child. After disconnecting it is no longer possible to send messages. An alternative way to check if you can send messages is to see if the child.connected property is true.

child.stdin#

  • Stream object

A Writable Stream that represents the child process's stdin. Closing this stream via end() often causes the child process to terminate.

If the child stdio streams are shared with the parent, then this will not be set.

child.stdout#

  • Stream object

A Readable Stream that represents the child process's stdout.

If the child stdio streams are shared with the parent, then this will not be set.

child.stderr#

  • Stream object

A Readable Stream that represents the child process's stderr.

If the child stdio streams are shared with the parent, then this will not be set.

child.pid#

  • Integer

The PID of the child process.

Example: 

var spawn = require('child_process').spawn,
    grep  = spawn('grep', ['ssh']);

console.log('Spawned child pid: ' + grep.pid);
grep.stdin.end();

child.kill([signal])#

  • signal String

Send a signal to the child process. If no argument is given, the process will be sent 'SIGTERM'. See signal(7) for a list of available signals. 

var spawn = require('child_process').spawn,
    grep  = spawn('grep', ['ssh']);

grep.on('exit', function (code, signal) {
  console.log('child process terminated due to receipt of signal '+signal);
});

// send SIGHUP to process
grep.kill('SIGHUP');

Note that while the function is called kill, the signal delivered to the child process may not actually kill it. kill really just sends a signal to a process.

See kill(2)

child.send(message, [sendHandle])#

  • message Object
  • sendHandle Handle object

Send a message (and, optionally, a handle object) to a child process.

See child_process.fork() for details.

child_process.spawn(command, [args], [options])#

  • command String The command to run
  • args Array List of string arguments
  • options Object
    • cwd String Current working directory of the child process
    • customFds Array Deprecated File descriptors for the child to use for stdio. (See below)
    • env Object Environment key-value pairs
    • setsid Boolean
  • return: ChildProcess object

Launches a new process with the given command, with command line arguments in args. If omitted, args defaults to an empty Array.

The third argument is used to specify additional options, which defaults to: 

{ cwd: undefined,
  env: process.env
}

cwd allows you to specify the working directory from which the process is spawned. Use env to specify environment variables that will be visible to the new process.

Example of running ls -lh /usr, capturing stdout, stderr, and the exit code: 

var util  = require('util'),
    spawn = require('child_process').spawn,
    ls    = spawn('ls', ['-lh', '/usr']);

ls.stdout.on('data', function (data) {
  console.log('stdout: ' + data);
});

ls.stderr.on('data', function (data) {
  console.log('stderr: ' + data);
});

ls.on('exit', function (code) {
  console.log('child process exited with code ' + code);
});

Example: A very elaborate way to run 'ps ax | grep ssh' 

var util  = require('util'),
    spawn = require('child_process').spawn,
    ps    = spawn('ps', ['ax']),
    grep  = spawn('grep', ['ssh']);

ps.stdout.on('data', function (data) {
  grep.stdin.write(data);
});

ps.stderr.on('data', function (data) {
  console.log('ps stderr: ' + data);
});

ps.on('exit', function (code) {
  if (code !== 0) {
    console.log('ps process exited with code ' + code);
  }
  grep.stdin.end();
});

grep.stdout.on('data', function (data) {
  console.log(data);
});

grep.stderr.on('data', function (data) {
  console.log('grep stderr: ' + data);
});

grep.on('exit', function (code) {
  if (code !== 0) {
    console.log('grep process exited with code ' + code);
  }
});

Example of checking for failed exec: 

var spawn = require('child_process').spawn,
    child = spawn('bad_command');

child.stderr.setEncoding('utf8');
child.stderr.on('data', function (data) {
  if (/^execvp\(\)/.test(data)) {
    console.log('Failed to start child process.');
  }
});

Note that if spawn receives an empty options object, it will result in spawning the process with an empty environment rather than using process.env. This due to backwards compatibility issues with a deprecated API.

There is a deprecated option called customFds which allows one to specify specific file descriptors for the stdio of the child process. This API was not portable to all platforms and therefore removed. With customFds it was possible to hook up the new process' [stdin, stdout, stderr] to existing streams; -1 meant that a new stream should be created. Use at your own risk.

There are several internal options. In particular stdinStream, stdoutStream, stderrStream. They are for INTERNAL USE ONLY. As with all undocumented APIs in Node, they should not be used.

See also: child_process.exec() and child_process.fork()

child_process.exec(command, [options], callback)#

  • command String The command to run, with space-separated arguments
  • options Object
    • cwd String Current working directory of the child process
    • customFds Array Deprecated File descriptors for the child to use for stdio. (See below)
    • env Object Environment key-value pairs
    • setsid Boolean
    • encoding String (Default: 'utf8')
    • timeout Number (Default: 0)
    • maxBuffer Number (Default: 200*1024)
    • killSignal String (Default: 'SIGTERM')
  • callback Function called with the output when process terminates
    • code Integer Exit code
    • stdout Buffer
    • stderr Buffer
  • Return: ChildProcess object

Runs a command in a shell and buffers the output. 

var util = require('util'),
    exec = require('child_process').exec,
    child;

child = exec('cat *.js bad_file | wc -l',
  function (error, stdout, stderr) {
    console.log('stdout: ' + stdout);
    console.log('stderr: ' + stderr);
    if (error !== null) {
      console.log('exec error: ' + error);
    }
});

The callback gets the arguments (error, stdout, stderr). On success, error will be null. On error, error will be an instance of Error and err.code will be the exit code of the child process, and err.signal will be set to the signal that terminated the process.

There is a second optional argument to specify several options. The default options are 

{ encoding: 'utf8',
  timeout: 0,
  maxBuffer: 200*1024,
  killSignal: 'SIGTERM',
  cwd: null,
  env: null }

If timeout is greater than 0, then it will kill the child process if it runs longer than timeout milliseconds. The child process is killed with killSignal (default: 'SIGTERM'). maxBuffer specifies the largest amount of data allowed on stdout or stderr - if this value is exceeded then the child process is killed.

child_process.execFile(file, args, options, callback)#

  • file String The filename of the program to run
  • args Array List of string arguments
  • options Object
    • cwd String Current working directory of the child process
    • customFds Array Deprecated File descriptors for the child to use for stdio. (See below)
    • env Object Environment key-value pairs
    • setsid Boolean
    • encoding String (Default: 'utf8')
    • timeout Number (Default: 0)
    • maxBuffer Number (Default: 200*1024)
    • killSignal String (Default: 'SIGTERM')
  • callback Function called with the output when process terminates
    • code Integer Exit code
    • stdout Buffer
    • stderr Buffer
  • Return: ChildProcess object

This is similar to child_process.exec() except it does not execute a subshell but rather the specified file directly. This makes it slightly leaner than child_process.exec. It has the same options.

child_process.fork(modulePath, [args], [options])#

  • modulePath String The module to run in the child
  • args Array List of string arguments
  • options Object
    • cwd String Current working directory of the child process
    • customFds Array Deprecated File descriptors for the child to use for stdio. (See below)
    • env Object Environment key-value pairs
    • setsid Boolean
    • encoding String (Default: 'utf8')
    • timeout Number (Default: 0)
  • callback Function called with the output when process terminates
    • code Integer Exit code
    • stdout Buffer
    • stderr Buffer
  • Return: ChildProcess object

This is a special case of the spawn() functionality for spawning Node processes. In addition to having all the methods in a normal ChildProcess instance, the returned object has a communication channel built-in. The channel is written to with child.send(message, [sendHandle]) and messages are received by a 'message' event on the child.

For example: 

var cp = require('child_process');

var n = cp.fork(__dirname + '/sub.js');

n.on('message', function(m) {
  console.log('PARENT got message:', m);
});

n.send({ hello: 'world' });

And then the child script, 'sub.js' might look like this: 

process.on('message', function(m) {
  console.log('CHILD got message:', m);
});

process.send({ foo: 'bar' });

In the child the process object will have a send() method, and process will emit objects each time it receives a message on its channel.

There is a special case when sending a {cmd: 'NODE_foo'} message. All messages containing a NODE_ prefix in its cmd property will not be emitted in the message event, since they are internal messages used by node core. Messages containing the prefix are emitted in the internalMessage event, you should by all means avoid using this feature, it may change without warranty.

By default the spawned Node process will have the stdout, stderr associated with the parent's. To change this behavior set the silent property in the options object to true.

These child Nodes are still whole new instances of V8. Assume at least 30ms startup and 10mb memory for each new Node. That is, you cannot create many thousands of them.

The sendHandle option to child.send() is for sending a handle object to another process. Child will receive the handle as as second argument to the message event. Here is an example of sending a handle: 

var server = require('net').createServer();
var child = require('child_process').fork(__dirname + '/child.js');
// Open up the server object and send the handle.
server.listen(1337, function() {
  child.send({ server: true }, server._handle);
});

Here is an example of receiving the server handle and sharing it between processes: 

process.on('message', function(m, serverHandle) {
  if (serverHandle) {
    var server = require('net').createServer();
    server.listen(serverHandle);
  }
});

To close the IPC connection between parent and child use the child.disconnect() method. This allows the child to exit gracefully since there is no IPC channel keeping it alive. When calling this method the disconnect event will be emitted in both parent and child, and the connected flag will be set to false. Please note that you can also call process.disconnect() in the child process.

Assert#

Stability: 5 - Locked

This module is used for writing unit tests for your applications, you can access it with require('assert').

assert.fail(actual, expected, message, operator)#

Throws an exception that displays the values for actual and expected separated by the provided operator.

assert(value, message), assert.ok(value, [message])#

Tests if value is truthy, it is equivalent to assert.equal(true, !!value, message);

assert.equal(actual, expected, [message])#

Tests shallow, coercive equality with the equal comparison operator ( == ).

assert.notEqual(actual, expected, [message])#

Tests shallow, coercive non-equality with the not equal comparison operator ( != ).

assert.deepEqual(actual, expected, [message])#

Tests for deep equality.

assert.notDeepEqual(actual, expected, [message])#

Tests for any deep inequality.

assert.strictEqual(actual, expected, [message])#

Tests strict equality, as determined by the strict equality operator ( === )

assert.notStrictEqual(actual, expected, [message])#

Tests strict non-equality, as determined by the strict not equal operator ( !== )

assert.throws(block, [error], [message])#

Expects block to throw an error. error can be constructor, regexp or validation function.

Validate instanceof using constructor: 

assert.throws(
  function() {
    throw new Error("Wrong value");
  },
  Error
);

Validate error message using RegExp: 

assert.throws(
  function() {
    throw new Error("Wrong value");
  },
  /value/
);

Custom error validation: 

assert.throws(
  function() {
    throw new Error("Wrong value");
  },
  function(err) {
    if ( (err instanceof Error) && /value/.test(err) ) {
      return true;
    }
  },
  "unexpected error"
);

assert.doesNotThrow(block, [error], [message])#

Expects block not to throw an error, see assert.throws for details.

assert.ifError(value)#

Tests if value is not a false value, throws if it is a true value. Useful when testing the first argument, error in callbacks.

TTY#

Stability: 2 - Unstable

The tty module houses the tty.ReadStream and tty.WriteStream classes. In most cases, you will not need to use this module directly.

When node detects that it is being run inside a TTY context, then process.stdin will be a tty.ReadStream instance and process.stdout will be a tty.WriteStream instance. The preferred way to check if node is being run in a TTY context is to check process.stdout.isTTY: 

$ node -p -e "Boolean(process.stdout.isTTY)"
true
$ node -p -e "Boolean(process.stdout.isTTY)" | cat
false

tty.isatty(fd)#

Returns true or false depending on if the fd is associated with a terminal.

tty.setRawMode(mode)#

Deprecated. Use tty.ReadStream#setRawMode() (i.e. process.stdin.setRawMode()) instead.

Class: ReadStream#

A net.Socket subclass that represents the readable portion of a tty. In normal circumstances, process.stdin will be the only tty.ReadStream instance in any node program (only when isatty(0) is true).

rs.isRaw#

A Boolean that is initialized to false. It represents the current "raw" state of the tty.ReadStream instance.

rs.setRawMode(mode)#

mode should be true or false. This sets the properties of the tty.ReadStream to act either as a raw device or default. isRaw will be set to the resulting mode.

Class WriteStream#

A net.Socket subclass that represents the writable portion of a tty. In normal circumstances, process.stdout will be the only tty.WriteStream instance ever created (and only when isatty(1) is true).

ws.columns#

A Number that gives the number of columns the TTY currently has. This property gets updated on "resize" events.

ws.rows#

A Number that gives the number of rows the TTY currently has. This property gets updated on "resize" events.

Event: 'resize'#

function () {}

Emitted by refreshSize() when either of the columns or rows properties has changed. 

process.stdout.on('resize', function() {
  console.log('screen size has changed!');
  console.log(process.stdout.columns + 'x' + process.stdout.rows);
});

Zlib#

Stability: 3 - Stable

You can access this module with: 

var zlib = require('zlib');

This provides bindings to Gzip/Gunzip, Deflate/Inflate, and DeflateRaw/InflateRaw classes. Each class takes the same options, and is a readable/writable Stream.

Examples#

Compressing or decompressing a file can be done by piping an fs.ReadStream into a zlib stream, then into an fs.WriteStream. 

var gzip = zlib.createGzip();
var fs = require('fs');
var inp = fs.createReadStream('input.txt');
var out = fs.createWriteStream('input.txt.gz');

inp.pipe(gzip).pipe(out);

Compressing or decompressing data in one step can be done by using the convenience methods. 

var input = '.................................';
zlib.deflate(input, function(err, buffer) {
  if (!err) {
    console.log(buffer.toString('base64'));
  }
});

var buffer = new Buffer('eJzT0yMAAGTvBe8=', 'base64');
zlib.unzip(buffer, function(err, buffer) {
  if (!err) {
    console.log(buffer.toString());
  }
});

To use this module in an HTTP client or server, use the accept-encoding on requests, and the content-encoding header on responses.

Note: these examples are drastically simplified to show the basic concept. Zlib encoding can be expensive, and the results ought to be cached. See Memory Usage Tuning below for more information on the speed/memory/compression tradeoffs involved in zlib usage. 

// client request example
var zlib = require('zlib');
var http = require('http');
var fs = require('fs');
var request = http.get({ host: 'izs.me',
                         path: '/',
                         port: 80,
                         headers: { 'accept-encoding': 'gzip,deflate' } });
request.on('response', function(response) {
  var output = fs.createWriteStream('izs.me_index.html');

  switch (response.headers['content-encoding']) {
    // or, just use zlib.createUnzip() to handle both cases
    case 'gzip':
      response.pipe(zlib.createGunzip()).pipe(output);
      break;
    case 'deflate':
      response.pipe(zlib.createInflate()).pipe(output);
      break;
    default:
      response.pipe(output);
      break;
  }
});

// server example
// Running a gzip operation on every request is quite expensive.
// It would be much more efficient to cache the compressed buffer.
var zlib = require('zlib');
var http = require('http');
var fs = require('fs');
http.createServer(function(request, response) {
  var raw = fs.createReadStream('index.html');
  var acceptEncoding = request.headers['accept-encoding'];
  if (!acceptEncoding) {
    acceptEncoding = '';
  }

  // Note: this is not a conformant accept-encoding parser.
  // See http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.3
  if (acceptEncoding.match(/\bdeflate\b/)) {
    response.writeHead(200, { 'content-encoding': 'deflate' });
    raw.pipe(zlib.createDeflate()).pipe(response);
  } else if (acceptEncoding.match(/\bgzip\b/)) {
    response.writeHead(200, { 'content-encoding': 'gzip' });
    raw.pipe(zlib.createGzip()).pipe(response);
  } else {
    response.writeHead(200, {});
    raw.pipe(response);
  }
}).listen(1337);

Constants#

All of the constants defined in zlib.h are also defined on require('zlib'). They are described in more detail in the zlib documentation. See http://zlib.net/manual.html#Constants for more details.

zlib.createGzip([options])#

Returns a new Gzip object with an options.

zlib.createGunzip([options])#

Returns a new Gunzip object with an options.

zlib.createDeflate([options])#

Returns a new Deflate object with an options.

zlib.createInflate([options])#

Returns a new Inflate object with an options.

zlib.createDeflateRaw([options])#

Returns a new DeflateRaw object with an options.

zlib.createInflateRaw([options])#

Returns a new InflateRaw object with an options.

zlib.createUnzip([options])#

Returns a new Unzip object with an options.

Class: zlib.Gzip#

Compress data using gzip.

Class: zlib.Gunzip#

Decompress a gzip stream.

Class: zlib.Deflate#

Compress data using deflate.

Class: zlib.Inflate#

Decompress a deflate stream.

Class: zlib.DeflateRaw#

Compress data using deflate, and do not append a zlib header.

Class: zlib.InflateRaw#

Decompress a raw deflate stream.

Class: zlib.Unzip#

Decompress either a Gzip- or Deflate-compressed stream by auto-detecting the header.

Convenience Methods#

All of these take a string or buffer as the first argument, and call the supplied callback with callback(error, result). The compression/decompression engine is created using the default settings in all convenience methods. To supply different options, use the zlib classes directly.

zlib.deflate(buf, callback)#

Compress a string with Deflate.

zlib.deflateRaw(buf, callback)#

Compress a string with DeflateRaw.

zlib.gzip(buf, callback)#

Compress a string with Gzip.

zlib.gunzip(buf, callback)#

Decompress a raw Buffer with Gunzip.

zlib.inflate(buf, callback)#

Decompress a raw Buffer with Inflate.

zlib.inflateRaw(buf, callback)#

Decompress a raw Buffer with InflateRaw.

zlib.unzip(buf, callback)#

Decompress a raw Buffer with Unzip.

Options#

Each class takes an options object. All options are optional. (The convenience methods use the default settings for all options.)

Note that some options are only relevant when compressing, and are ignored by the decompression classes.

  • chunkSize (default: 16*1024)
  • windowBits
  • level (compression only)
  • memLevel (compression only)
  • strategy (compression only)
  • dictionary (deflate/inflate only, empty dictionary by default)

See the description of deflateInit2 and inflateInit2 at

http://zlib.net/manual.html#Advanced for more information on these.

Memory Usage Tuning#

From zlib/zconf.h, modified to node's usage:

The memory requirements for deflate are (in bytes): 

(1 << (windowBits+2)) +  (1 << (memLevel+9))

that is: 128K for windowBits=15 + 128K for memLevel = 8 (default values) plus a few kilobytes for small objects.

For example, if you want to reduce the default memory requirements from 256K to 128K, set the options to: 

{ windowBits: 14, memLevel: 7 }

Of course this will generally degrade compression (there's no free lunch).

The memory requirements for inflate are (in bytes) 

1 << windowBits

that is, 32K for windowBits=15 (default value) plus a few kilobytes for small objects.

This is in addition to a single internal output slab buffer of size chunkSize, which defaults to 16K.

The speed of zlib compression is affected most dramatically by the level setting. A higher level will result in better compression, but will take longer to complete. A lower level will result in less compression, but will be much faster.

In general, greater memory usage options will mean that node has to make fewer calls to zlib, since it'll be able to process more data in a single write operation. So, this is another factor that affects the speed, at the cost of memory usage.

os#

Stability: 4 - API Frozen

Provides a few basic operating-system related utility functions.

Use require('os') to access this module.

os.hostname()#

Returns the hostname of the operating system.

os.type()#

Returns the operating system name.

os.platform()#

Returns the operating system platform.

os.arch()#

Returns the operating system CPU architecture.

os.release()#

Returns the operating system release.

os.uptime()#

Returns the system uptime in seconds.

os.loadavg()#

Returns an array containing the 1, 5, and 15 minute load averages.

os.totalmem()#

Returns the total amount of system memory in bytes.

os.freemem()#

Returns the amount of free system memory in bytes.

os.cpus()#

Returns an array of objects containing information about each CPU/core installed: model, speed (in MHz), and times (an object containing the number of CPU ticks spent in: user, nice, sys, idle, and irq).

Example inspection of os.cpus: 

[ { model: 'Intel(R) Core(TM) i7 CPU         860  @ 2.80GHz',
    speed: 2926,
    times:
     { user: 252020,
       nice: 0,
       sys: 30340,
       idle: 1070356870,
       irq: 0 } },
  { model: 'Intel(R) Core(TM) i7 CPU         860  @ 2.80GHz',
    speed: 2926,
    times:
     { user: 306960,
       nice: 0,
       sys: 26980,
       idle: 1071569080,
       irq: 0 } },
  { model: 'Intel(R) Core(TM) i7 CPU         860  @ 2.80GHz',
    speed: 2926,
    times:
     { user: 248450,
       nice: 0,
       sys: 21750,
       idle: 1070919370,
       irq: 0 } },
  { model: 'Intel(R) Core(TM) i7 CPU         860  @ 2.80GHz',
    speed: 2926,
    times:
     { user: 256880,
       nice: 0,
       sys: 19430,
       idle: 1070905480,
       irq: 20 } },
  { model: 'Intel(R) Core(TM) i7 CPU         860  @ 2.80GHz',
    speed: 2926,
    times:
     { user: 511580,
       nice: 20,
       sys: 40900,
       idle: 1070842510,
       irq: 0 } },
  { model: 'Intel(R) Core(TM) i7 CPU         860  @ 2.80GHz',
    speed: 2926,
    times:
     { user: 291660,
       nice: 0,
       sys: 34360,
       idle: 1070888000,
       irq: 10 } },
  { model: 'Intel(R) Core(TM) i7 CPU         860  @ 2.80GHz',
    speed: 2926,
    times:
     { user: 308260,
       nice: 0,
       sys: 55410,
       idle: 1071129970,
       irq: 880 } },
  { model: 'Intel(R) Core(TM) i7 CPU         860  @ 2.80GHz',
    speed: 2926,
    times:
     { user: 266450,
       nice: 1480,
       sys: 34920,
       idle: 1072572010,
       irq: 30 } } ]

os.networkInterfaces()#

Get a list of network interfaces: 

{ lo0: 
   [ { address: '::1', family: 'IPv6', internal: true },
     { address: 'fe80::1', family: 'IPv6', internal: true },
     { address: '127.0.0.1', family: 'IPv4', internal: true } ],
  en1: 
   [ { address: 'fe80::cabc:c8ff:feef:f996', family: 'IPv6',
       internal: false },
     { address: '10.0.1.123', family: 'IPv4', internal: false } ],
  vmnet1: [ { address: '10.99.99.254', family: 'IPv4', internal: false } ],
  vmnet8: [ { address: '10.88.88.1', family: 'IPv4', internal: false } ],
  ppp0: [ { address: '10.2.0.231', family: 'IPv4', internal: false } ] }

os.EOL#

A constant defining the appropriate End-of-line marker for the operating system.

Debugger#

Stability: 3 - Stable

V8 comes with an extensive debugger which is accessible out-of-process via a simple TCP protocol. Node has a built-in client for this debugger. To use this, start Node with the debug argument; a prompt will appear: 

% node debug myscript.js
< debugger listening on port 5858
connecting... ok
break in /home/indutny/Code/git/indutny/myscript.js:1
  1 x = 5;
  2 setTimeout(function () {
  3   debugger;
debug>

Node's debugger client doesn't support the full range of commands, but simple step and inspection is possible. By putting the statement debugger; into the source code of your script, you will enable a breakpoint.

For example, suppose myscript.js looked like this: 

// myscript.js
x = 5;
setTimeout(function () {
  debugger;
  console.log("world");
}, 1000);
console.log("hello");

Then once the debugger is run, it will break on line 4. 

% node debug myscript.js
< debugger listening on port 5858
connecting... ok
break in /home/indutny/Code/git/indutny/myscript.js:1
  1 x = 5;
  2 setTimeout(function () {
  3   debugger;
debug> cont
< hello
break in /home/indutny/Code/git/indutny/myscript.js:3
  1 x = 5;
  2 setTimeout(function () {
  3   debugger;
  4   console.log("world");
  5 }, 1000);
debug> next
break in /home/indutny/Code/git/indutny/myscript.js:4
  2 setTimeout(function () {
  3   debugger;
  4   console.log("world");
  5 }, 1000);
  6 console.log("hello");
debug> repl
Press Ctrl + C to leave debug repl
> x
5
> 2+2
4
debug> next
< world
break in /home/indutny/Code/git/indutny/myscript.js:5
  3   debugger;
  4   console.log("world");
  5 }, 1000);
  6 console.log("hello");
  7
debug> quit
%

The repl command allows you to evaluate code remotely. The next command steps over to the next line. There are a few other commands available and more to come. Type help to see others.

Watchers#

You can watch expression and variable values while debugging your code. On every breakpoint each expression from the watchers list will be evaluated in the current context and displayed just before the breakpoint's source code listing.

To start watching an expression, type watch("my_expression"). watchers prints the active watchers. To remove a watcher, type unwatch("my_expression").

Commands reference#

Stepping#

  • cont, c - Continue execution
  • next, n - Step next
  • step, s - Step in
  • out, o - Step out
  • pause - Pause running code (like pause button in Developer TOols)

Breakpoints#

  • setBreakpoint(), sb() - Set breakpoint on current line
  • setBreakpoint(line), sb(line) - Set breakpoint on specific line
  • setBreakpoint('fn()'), sb(...) - Set breakpoint on a first statement in functions body
  • setBreakpoint('script.js', 1), sb(...) - Set breakpoint on first line of script.js
  • clearBreakpoint, cb(...) - Clear breakpoint

Info#

  • backtrace, bt - Print backtrace of current execution frame
  • list(5) - List scripts source code with 5 line context (5 lines before and after)
  • watch(expr) - Add expression to watch list
  • unwatch(expr) - Remove expression from watch list
  • watchers - List all watchers and their values (automatically listed on each breakpoint)
  • repl - Open debugger's repl for evaluation in debugging script's context

Execution control#

  • run - Run script (automatically runs on debugger's start)
  • restart - Restart script
  • kill - Kill script

Various#

  • scripts - List all loaded scripts
  • version - Display v8's version

Advanced Usage#

The V8 debugger can be enabled and accessed either by starting Node with the --debug command-line flag or by signaling an existing Node process with SIGUSR1.

Cluster#

Stability: 1 - Experimental

A single instance of Node runs in a single thread. To take advantage of multi-core systems the user will sometimes want to launch a cluster of Node processes to handle the load.

The cluster module allows you to easily create a network of processes that all share server ports. 

var cluster = require('cluster');
var http = require('http');
var numCPUs = require('os').cpus().length;

if (cluster.isMaster) {
  // Fork workers.
  for (var i = 0; i < numCPUs; i++) {
    cluster.fork();
  }

  cluster.on('exit', function(worker) {
    console.log('worker ' + worker.pid + ' died');
  });
} else {
  // Workers can share any TCP connection
  // In this case its a HTTP server
  http.createServer(function(req, res) {
    res.writeHead(200);
    res.end("hello world\n");
  }).listen(8000);
}

Running node will now share port 8000 between the workers: 

% node server.js
Worker 2438 online
Worker 2437 online

This feature was introduced recently, and may change in future versions. Please try it out and provide feedback.

cluster.settings#

  • Object
    • exec String file path to worker file. (Default=__filename)
    • args Array string arguments passed to worker. (Default=process.argv.slice(2))
    • silent Boolean whether or not to send output to parent's stdio. (Default=false)

All settings set by the .setupMaster is stored in this settings object. This object is not supposed to be change or set manually, by you.

cluster.isMaster#

  • Boolean

True if the process is a master. This is determined by the process.env.NODE_UNIQUE_ID. If process.env.NODE_UNIQUE_ID is undefined, then isMaster is true.

cluster.isWorker#

  • Boolean

This boolean flag is true if the process is a worker forked from a master. If the process.env.NODE_UNIQUE_ID is set to a value, then isWorker is true.

Event: 'fork'#

  • worker Worker object

When a new worker is forked the cluster module will emit a 'fork' event. This can be used to log worker activity, and create you own timeout. 

var timeouts = [];
var errorMsg = function () {
  console.error("Something must be wrong with the connection ...");
});

cluster.on('fork', function (worker) {
  timeouts[worker.uniqueID] = setTimeout(errorMsg, 2000);
});
cluster.on('listening', function (worker) {
  clearTimeout(timeouts[worker.uniqueID]);
});
cluster.on('exit', function (worker) {
  clearTimeout(timeouts[worker.uniqueID]);
  errorMsg();
});

Event: 'online'#

  • worker Worker object

After forking a new worker, the worker should respond with a online message. When the master receives a online message it will emit such event. The difference between 'fork' and 'online' is that fork is emitted when the master tries to fork a worker, and 'online' is emitted when the worker is being executed. 

cluster.on('online', function (worker) {
  console.log("Yay, the worker responded after it was forked");
});

Event: 'listening'#

  • worker Worker object

When calling listen() from a worker, a 'listening' event is automatically assigned to the server instance. When the server is listening a message is send to the master where the 'listening' event is emitted. 

cluster.on('listening', function (worker) {
  console.log("We are now connected");
});

Event: 'disconnect'#

  • worker Worker object

When a workers IPC channel has disconnected this event is emitted. This will happen when the worker dies, usually after calling .destroy().

When calling .disconnect(), there may be a delay between the disconnect and exit events. This event can be used to detect if the process is stuck in a cleanup or if there are long-living connections. 

cluster.on('disconnect', function(worker) {
  console.log('The worker #' + worker.uniqueID + ' has disconnected');
});

Event: 'exit'#

  • worker Worker object

When any of the workers die the cluster module will emit the 'exit' event. This can be used to restart the worker by calling fork() again. 

cluster.on('exit', function(worker) {
  console.log('worker ' + worker.pid + ' died. restart...');
  cluster.fork();
});

Event: 'setup'#

  • worker Worker object

When the .setupMaster() function has been executed this event emits. If .setupMaster() was not executed before fork() this function will call .setupMaster() with no arguments.

cluster.setupMaster([settings])#

  • settings Object
    • exec String file path to worker file. (Default=__filename)
    • args Array string arguments passed to worker. (Default=process.argv.slice(2))
    • silent Boolean whether or not to send output to parent's stdio. (Default=false)

The setupMaster is used to change the default 'fork' behavior. It takes one option object argument.

Example: 

var cluster = require("cluster");
cluster.setupMaster({
  exec : "worker.js",
  args : ["--use", "https"],
  silent : true
});
cluster.autoFork();

cluster.fork([env])#

  • env Object Key/value pairs to add to child process environment.
  • return Worker object

Spawn a new worker process. This can only be called from the master process.

cluster.settings#

  • Object
    • exec String file path to worker file. Default: __filename
    • args Array string arguments passed to worker. (Default=process.argv.slice(2))
    • silent Boolean whether or not to send output to parent's stdio. (Default=false)

All settings set by the .setupMaster is stored in this settings object. This object is not supposed to be change or set manually.

cluster.disconnect([callback])#

  • callback Function called when all workers are disconnected and handlers are closed

When calling this method, all workers will commit a graceful suicide. When they are disconnected all internal handlers will be closed, allowing the master process to die graceful if no other event is waiting.

The method takes an optional callback argument which will be called when finished.

cluster.workers#

  • Object

In the cluster all living worker objects are stored in this object by there uniqueID as the key. This makes it easy to loop through all living workers. 

// Go through all workers
function eachWorker(callback) {
  for (var uniqueID in cluster.workers) {
    callback(cluster.workers[uniqueID]);
  }
}
eachWorker(function (worker) {
  worker.send('big announcement to all workers');
});

Should you wish to reference a worker over a communication channel, using the worker's uniqueID is the easiest way to find the worker. 

socket.on('data', function (uniqueID) {
  var worker = cluster.workers[uniqueID];
});

Class: Worker#

A Worker object contains all public information and method about a worker. In the master it can be obtained using cluster.workers. In a worker it can be obtained using cluster.worker.

worker.uniqueID#

  • String

Each new worker is given its own unique id, this id is stored in the uniqueID.

While a worker is alive, this is the key that indexes it in cluster.workers

worker.process#

  • ChildProcess object

All workers are created using child_process.fork(), the returned object from this function is stored in process.

See: Child Process module

worker.suicide#

  • Boolean

This property is a boolean. It is set when a worker dies after calling .destroy() or immediately after calling the .disconnect() method. Until then it is undefined.

worker.send(message, [sendHandle])#

  • message Object
  • sendHandle Handle object

This function is equal to the send methods provided by child_process.fork(). In the master you should use this function to send a message to a specific worker. However in a worker you can also use process.send(message), since this is the same function.

This example will echo back all messages from the master: 

if (cluster.isMaster) {
  var worker = cluster.fork();
  worker.send('hi there');

} else if (cluster.isWorker) {
  process.on('message', function (msg) {
    process.send(msg);
  });
}

worker.destroy()#

This function will kill the worker, and inform the master to not spawn a new worker. The boolean suicide lets you distinguish between voluntary and accidental exit. 

cluster.on('exit', function (worker) {
  if (worker.suicide === true) {
    console.log('Oh, it was just suicide\' – no need to worry').
  }
});

// destroy worker
worker.destroy();

Worker.disconnect()#

When calling this function the worker will no longer accept new connections, but they will be handled by any other listening worker. Existing connection will be allowed to exit as usual. When no more connections exist, the IPC channel to the worker will close allowing it to die graceful. When the IPC channel is closed the disconnect event will emit, this is then followed by the exit event, there is emitted when the worker finally die.

Because there might be long living connections, it is useful to implement a timeout. This example ask the worker to disconnect and after 2 seconds it will destroy the server. An alternative wound be to execute worker.destroy() after 2 seconds, but that would normally not allow the worker to do any cleanup if needed. 

if (cluster.isMaster) {
  var worker = cluser.fork();
  var timeout;

  worker.on('listening', function () {
    worker.disconnect();
    timeout = setTimeout(function () {
      worker.send('force kill');
    }, 2000);
  });

  worker.on('disconnect', function () {
    clearTimeout(timeout);
  });

} else if (cluster.isWorker) {
  var net = require('net');
  var server = net.createServer(function (socket) {
    // connection never end
  });

  server.listen(8000);

  server.on('close', function () {
    // cleanup
  });

  process.on('message', function (msg) {
    if (msg === 'force kill') {
      server.destroy();
    }
  });
}

Event: 'message'#

  • message Object

This event is the same as the one provided by child_process.fork(). In the master you should use this event, however in a worker you can also use process.on('message')

As an example, here is a cluster that keeps count of the number of requests in the master process using the message system: 

var cluster = require('cluster');
var http = require('http');

if (cluster.isMaster) {

  // Keep track of http requests
  var numReqs = 0;
  setInterval(function() {
    console.log("numReqs =", numReqs);
  }, 1000);

  // Count requestes
  var messageHandler = function (msg) {
    if (msg.cmd && msg.cmd == 'notifyRequest') {
      numReqs += 1;
    }
  };

  // Start workers and listen for messages containing notifyRequest
  cluster.autoFork();
  Object.keys(cluster.workers).forEach(function (uniqueID) {
    cluster.workers[uniqueID].on('message', messageHandler);
  });

} else {

  // Worker processes have a http server.
  http.Server(function(req, res) {
    res.writeHead(200);
    res.end("hello world\n");

    // notify master about the request
    process.send({ cmd: 'notifyRequest' });
  }).listen(8000);
}

Event: 'online'#

  • worker Worker object

Same as the cluster.on('online') event, but emits only when the state change on the specified worker. 

cluster.fork().on('online', function (worker) {
  // Worker is online
};

Event: 'listening'#

  • worker Worker object

Same as the cluster.on('listening') event, but emits only when the state change on the specified worker. 

cluster.fork().on('listening', function (worker) {
  // Worker is listening
};

Event: 'disconnect'#

  • worker Worker object

Same as the cluster.on('disconnect') event, but emits only when the state change on the specified worker. 

cluster.fork().on('disconnect', function (worker) {
  // Worker has disconnected
};

Event: 'exit'#

  • worker Worker object

Same as the cluster.on('exit') event, but emits only when the state change on the specified worker. 

cluster.fork().on('exit', function (worker) {
  // Worker has died
};

Appendix 1 - Third Party Modules#

There are many third party modules for Node. At the time of writing, August 2010, the master repository of modules is the wiki page.

This appendix is intended as a SMALL guide to new-comers to help them quickly find what are considered to be quality modules. It is not intended to be a complete list. There may be better more complete modules found elsewhere.

Patches to this list are welcome.