Table of Contents

• Net
  • Class: net.Server
    • Event: 'close'
    • Event: 'connection'
    • Event: 'error'
    • Event: 'listening'
    • server.address()
    • server.close([callback])
    • server.connections
    • server.getConnections(callback)
    • server.listen(handle[, backlog][, callback])
    • server.listen(options[, callback])
    • server.listen(path[, backlog][, callback])
    • server.listen([port][, hostname][, backlog][, callback])
    • server.listening
    • server.maxConnections
    • server.ref()
    • server.unref()
  • Class: net.Socket
    • new net.Socket([options])
    • Event: 'close'
    • Event: 'connect'
    • Event: 'data'
    • Event: 'drain'
    • Event: 'end'
    • Event: 'error'
    • Event: 'lookup'
    • Event: 'timeout'
    • socket.address()
    • socket.bufferSize
    • socket.bytesRead
    • socket.bytesWritten
    • socket.connect(options[, connectListener])
    • socket.connect(path[, connectListener])
    • socket.connect(port[, host][, connectListener])
    • socket.connecting
    • socket.destroy([exception])
    • socket.destroyed
    • socket.end([data][, encoding])
    • socket.localAddress
    • socket.localPort
    • socket.pause()
    • socket.ref()
    • socket.remoteAddress
    • socket.remoteFamily
    • socket.remotePort
    • socket.resume()
    • socket.setEncoding([encoding])
    • socket.setKeepAlive([enable][, initialDelay])
    • socket.setNoDelay([noDelay])
    • socket.setTimeout(timeout[, callback])
    • socket.unref()
    • socket.write(data[, encoding][, callback])
  • net.connect(options[, connectListener])
  • net.connect(path[, connectListener])
  • net.connect(port[, host][, connectListener])
  • net.createConnection(options[, connectListener])
  • net.createConnection(path[, connectListener])
  • net.createConnection(port[, host][, connectListener])
  • net.createServer([options][, connectionListener])
  • net.isIP(input)
  • net.isIPv4(input)
  • net.isIPv6(input)

Net#

Stability: 2 - Stable

The net module provides you with an asynchronous network wrapper. It contains functions for creating both servers and clients (called streams). You can include this module with require('net');.

Class: net.Server#

This class is used to create a TCP or local server.

net.Server is an EventEmitter with the following events:

Event: 'close'#

Emitted when the server closes. Note that if connections exist, this event is not emitted until all connections are ended.

Event: 'connection'#

• <net.Socket> The connection object

Emitted when a new connection is made. socket is an instance of net.Socket.

Event: 'error'#

• <Error>

Emitted when an error occurs. Unlike net.Socket, the 'close' event will not be emitted directly following this event unless server.close() is manually called. See the example in discussion of server.listen().

Event: 'listening'#

Emitted when the server has been bound after calling server.listen.

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 getting an OS-assigned address. Returns an object with port, family, and address properties: { port: 12346, family: 'IPv4', address: '127.0.0.1' }

Example:

const server = net.createServer((socket) => {
  socket.end('goodbye\n');
}).on('error', (err) => {
  // handle errors here
  throw err;
});

// grab a random port.
server.listen(() => {
  console.log('opened server on', server.address());
});

Don't call server.address() until the 'listening' event has been emitted.

server.close([callback])#

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. The optional callback will be called once the 'close' event occurs. Unlike that event, it will be called with an Error as its only argument if the server was not open when it was closed.

server.connections#

Stability: 0 - Deprecated: Use server.getConnections() instead.

The number of concurrent connections on the server.

This becomes null when sending a socket to a child with child_process.fork(). To poll forks and get current number of active connections use asynchronous server.getConnections instead.

server.getConnections(callback)#

Asynchronously get the number of concurrent connections on the server. Works when sockets were sent to forks.

Callback should take two arguments err and count.

server.listen(handle[, backlog][, callback])#

• handle <Object>
• backlog <number>
• callback <Function>

The handle object can be set to either a server or socket (anything with an underlying _handle member), or a {fd: <n>} object.

This will cause the server to accept connections on the specified handle, but it is presumed that the file descriptor or handle has already been bound to a port or domain socket.

Listening on a file descriptor is not supported on Windows.

This function is asynchronous. When the server has been bound, 'listening' event will be emitted. The last parameter callback will be added as a listener for the 'listening' event.

The parameter backlog behaves the same as in server.listen([port][, hostname][, backlog][, callback]).

server.listen(options[, callback])#

• options <Object> - Required. Supports the following properties:
  • port <number> - Optional.
  • host <string> - Optional.
  • backlog <number> - Optional.
  • path <string> - Optional.
  • exclusive <boolean> - Optional.
• callback <Function> - Optional.

The port, host, and backlog properties of options, as well as the optional callback function, behave as they do on a call to server.listen([port][, hostname][, backlog][, callback]). Alternatively, the path option can be used to specify a UNIX socket.

If exclusive is false (default), then cluster workers will use the same underlying handle, allowing connection handling duties to be shared. When exclusive is true, the handle is not shared, and attempted port sharing results in an error. An example which listens on an exclusive port is shown below.

server.listen({
  host: 'localhost',
  port: 80,
  exclusive: true
});

Note: The server.listen() method may be called multiple times. Each subsequent call will re-open the server using the provided options.

server.listen(path[, backlog][, callback])#

• path <string>
• backlog <number>
• callback <Function>

Start a local 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 callback will be added as a listener for the 'listening' event.

On UNIX, the local domain is usually known as the UNIX domain. The path is a filesystem path name. It gets truncated to sizeof(sockaddr_un.sun_path) bytes, decreased by 1. It varies on different operating system between 91 and 107 bytes. The typical values are 107 on Linux and 103 on OS X. The path is subject to the same naming conventions and permissions checks as would be done on file creation, will be visible in the filesystem, and will persist until unlinked.

On Windows, the local domain is implemented using a named pipe. The path must refer to an entry in \\?\pipe\ or \\.\pipe\. Any characters are permitted, but the latter may do some processing of pipe names, such as resolving .. sequences. Despite appearances, the pipe name space is flat. Pipes will not persist, they are removed when the last reference to them is closed. Do not forget JavaScript string escaping requires paths to be specified with double-backslashes, such as:

net.createServer().listen(
    path.join('\\\\?\\pipe', process.cwd(), 'myctl'));

The parameter backlog behaves the same as in server.listen([port][, hostname][, backlog][, callback]).

Note: The server.listen() method may be called multiple times. Each subsequent call will re-open the server using the provided options.

server.listen([port][, hostname][, backlog][, callback])#

Begin accepting connections on the specified port and hostname. If the hostname is omitted, the server will accept connections on the unspecified IPv6 address (::) when IPv6 is available, or the unspecified IPv4 address (0.0.0.0) otherwise.

Note: in most operating systems, listening to the unspecified IPv6 address (::) may cause the net.Server to also listen on the unspecified IPv4 address (0.0.0.0).

Omit the port argument, or use a port value of 0, to have the operating system assign a random port, which can be retrieved by using server.address().port after the 'listening' event has been emitted.

Backlog is the maximum length of the queue of pending connections. The actual length will be determined by the OS through sysctl settings such as tcp_max_syn_backlog and somaxconn on Linux. The default value of this parameter is 511 (not 512).

This function is asynchronous. When the server has been bound, 'listening' event will be emitted. The last parameter callback will be added as a 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:

server.on('error', (e) => {
  if (e.code == 'EADDRINUSE') {
    console.log('Address in use, retrying...');
    setTimeout(() => {
      server.close();
      server.listen(PORT, HOST);
    }, 1000);
  }
});

(Note: All sockets in Node.js are set SO_REUSEADDR.)

Note: The server.listen() method may be called multiple times. Each subsequent call will re-open the server using the provided options.

server.listening#

A Boolean indicating whether or not the server is listening for connections.

server.maxConnections#

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

It is not recommended to use this option once a socket has been sent to a child with child_process.fork().

server.ref()#

Opposite of unref, calling ref on a previously unrefd server will not let the program exit if it's the only server left (the default behavior). If the server is refd calling ref again will have no effect.

Returns server.

server.unref()#

Calling unref on a server will allow the program to exit if this is the only active server in the event system. If the server is already unrefd calling unref again will have no effect.

Returns server.

Class: net.Socket#

This object is an abstraction of a TCP or local 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.js 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,
  allowHalfOpen: false,
  readable: false,
  writable: false
}

fd allows you to specify the existing file descriptor of socket. Set readable and/or writable to true to allow reads and/or writes on this socket (NOTE: Works only when fd is passed). About allowHalfOpen, refer to