Net | Node.js v13.14.0 Documentation (original) (raw)

Net#

The net module provides an asynchronous network API for creating stream-based TCP or IPC servers (net.createServer()) and clients (net.createConnection()).

It can be accessed using:

const net = require('net');

IPC Support#

The net module supports IPC with named pipes on Windows, and Unix domain sockets on other operating systems.

Identifying paths for IPC connections#

net.connect(), net.createConnection(), server.listen() andsocket.connect() take a path parameter to identify IPC endpoints.

On Unix, the local domain is also known as the Unix domain. The path is a filesystem pathname. It gets truncated to an OS-dependent length ofsizeof(sockaddr_un.sun_path) - 1. Typical values are 107 bytes on Linux and 103 bytes on macOS. If a Node.js API abstraction creates the Unix domain socket, it will unlink the Unix domain socket as well. For example,net.createServer() may create a Unix domain socket andserver.close() will unlink it. But if a user creates the Unix domain socket outside of these abstractions, the user will need to remove it. The same applies when a Node.js API creates a Unix domain socket but the program then crashes. In short, a Unix domain socket 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 how it might look, the pipe namespace is flat. Pipes will_not persist. They are removed when the last reference to them is closed. Unlike Unix domain sockets, Windows will close and remove the pipe when the owning process exits.

JavaScript string escaping requires paths to be specified with extra backslash escaping such as:

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

Class: net.Server#

Added in: v0.1.90

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

new net.Server([options][, connectionListener])#

net.Server is an EventEmitter with the following events:

Event: 'close'#

Added in: v0.5.0

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

Event: 'connection'#

Added in: v0.1.90

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

Event: 'error'#

Added in: v0.1.90

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

Event: 'listening'#

Added in: v0.1.90

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

server.address()#

Added in: v0.1.90

Returns the bound address, the address family name, and port of the server as reported by the operating system if listening on an IP socket (useful to find which port was assigned when getting an OS-assigned address):{ port: 12346, family: 'IPv4', address: '127.0.0.1' }.

For a server listening on a pipe or Unix domain socket, the name is returned as a string.

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

// Grab an arbitrary unused port.
server.listen(() => {
  console.log('opened server on', server.address());
});

server.address() returns null before the 'listening' event has been emitted or after calling server.close().

server.close([callback])#

Added in: v0.1.90

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#

Added in: v0.2.0Deprecated since: v0.9.7

The number of concurrent connections on the server.

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

server.getConnections(callback)#

Added in: v0.9.7

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()#

Start a server listening for connections. A net.Server can be a TCP or an IPC server depending on what it listens to.

Possible signatures:

This function is asynchronous. When the server starts listening, the'listening' event will be emitted. The last parameter callbackwill be added as a listener for the 'listening' event.

All listen() methods can take a backlog parameter to specify 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 somaxconnon Linux. The default value of this parameter is 511 (not 512).

All net.Socket are set to SO_REUSEADDR (see socket(7) for details).

The server.listen() method can be called again if and only if there was an error during the first server.listen() call or server.close() has been called. Otherwise, an ERR_SERVER_ALREADY_LISTEN error will be thrown.

One of the most common errors raised when listening is EADDRINUSE. This happens when another server is already listening on the requestedport/path/handle. One way to handle this would be to retry after a certain amount of time:

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

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

Added in: v0.5.10

Start a server listening for connections on a given handle that has already been bound to a port, a Unix domain socket, or a Windows named pipe.

The handle object can be either a server, a socket (anything with an underlying _handle member), or an object with an fd member that is a valid file descriptor.

Listening on a file descriptor is not supported on Windows.

server.listen(options[, callback])#

If port is specified, it behaves the same as server.listen([port[, host[, backlog]]][, callback]). Otherwise, if path is specified, it behaves the same asserver.listen(path[, backlog][, callback]). If none of them is specified, an error will be thrown.

If exclusive is false (default), then cluster workers will use the same underlying handle, allowing connection handling duties to be shared. Whenexclusive 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
});

Starting an IPC server as root may cause the server path to be inaccessible for unprivileged users. Using readableAll and writableAll will make the server accessible for all users.

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

Added in: v0.1.90

Start an IPC server listening for connections on the given path.

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

Added in: v0.1.90

Start a TCP server listening for connections on the given port and host.

If port is omitted or is 0, the operating system will assign an arbitrary unused port, which can be retrieved by using server.address().portafter the 'listening' event has been emitted.

If host is omitted, the server will accept connections on theunspecified IPv6 address (::) when IPv6 is available, or theunspecified IPv4 address (0.0.0.0) otherwise.

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).

server.listening#

Added in: v5.7.0

server.maxConnections#

Added in: v0.2.0

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()#

Added in: v0.9.1

Opposite of unref(), calling ref() on a previously unrefed server will_not_ let the program exit if it's the only server left (the default behavior). If the server is refed calling ref() again will have no effect.

server.unref()#

Added in: v0.9.1

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 unrefed callingunref() again will have no effect.

Class: net.Socket#

Added in: v0.3.4

This class is an abstraction of a TCP socket or a streaming IPC endpoint (uses named pipes on Windows, and Unix domain sockets otherwise). It is also an EventEmitter.

A net.Socket can be created by the user and used directly to interact with a server. For example, it is returned by net.createConnection(), so the user can use it to talk to the server.

It can also be created by Node.js and passed to the user when a connection is received. For example, it is passed to the listeners of a'connection' event emitted on a net.Server, so the user can use it to interact with the client.

new net.Socket([options])#

Added in: v0.3.4

Creates a new socket object.

The newly created socket can be either a TCP socket or a streaming IPCendpoint, depending on what it connect() to.

Event: 'close'#

Added in: v0.1.90

Emitted once the socket is fully closed. The argument hadError is a boolean which says if the socket was closed due to a transmission error.

Event: 'connect'#

Added in: v0.1.90

Emitted when a socket connection is successfully established. See net.createConnection().

Event: 'data'#

Added in: v0.1.90

Emitted when data is received. The argument data will be a Buffer orString. Encoding of data is set by socket.setEncoding().

The data will be lost if there is no listener when a Socketemits a 'data' event.

Event: 'drain'#

Added in: v0.1.90

Emitted when the write buffer becomes empty. Can be used to throttle uploads.

See also: the return values of socket.write().

Event: 'end'#

Added in: v0.1.90

Emitted when the other end of the socket sends a FIN packet, thus ending the readable side of the socket.

By default (allowHalfOpen is false) the socket will send a FIN packet back and destroy its file descriptor once it has written out its pending write queue. However, if allowHalfOpen is set to true, the socket will not automatically end() its writable side, allowing the user to write arbitrary amounts of data. The user must callend() explicitly to close the connection (i.e. sending a FIN packet back).

Event: 'error'#

Added in: v0.1.90

Emitted when an error occurs. The 'close' event will be called directly following this event.

Event: 'lookup'#

Emitted after resolving the host name but before connecting. Not applicable to Unix sockets.

Event: 'ready'#

Added in: v9.11.0

Emitted when a socket is ready to be used.

Triggered immediately after 'connect'.

Event: 'timeout'#

Added in: v0.1.90

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().

socket.address()#

Added in: v0.1.90

Returns the bound address, the address family name and port of the socket as reported by the operating system:{ port: 12346, family: 'IPv4', address: '127.0.0.1' }

socket.bufferSize#

Added in: v0.3.8

This property shows the number of characters buffered for writing. The buffer may contain strings whose length after encoding is not yet known. So this number is only an approximation of the number of bytes in the buffer.

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.js will internally queue up the data written to a socket and send it out over the wire when it is possible.

The consequence of this internal buffering is that memory may grow. Users who experience large or growing bufferSize should attempt to "throttle" the data flows in their program withsocket.pause() and socket.resume().

socket.bytesRead#

Added in: v0.5.3

The amount of received bytes.

socket.bytesWritten#

Added in: v0.5.3

The amount of bytes sent.

socket.connect()#

Initiate a connection on a given socket.

Possible signatures:

This function is asynchronous. When the connection is established, the'connect' event will be emitted. If there is a problem connecting, instead of a 'connect' event, an 'error' event will be emitted with the error passed to the 'error' listener. The last parameter connectListener, if supplied, will be added as a listener for the 'connect' event once.

socket.connect(options[, connectListener])#

Initiate a connection on a given socket. Normally this method is not needed, the socket should be created and opened with net.createConnection(). Use this only when implementing a custom Socket.

For TCP connections, available options are:

For IPC connections, available options are:

For both types, available options include:

Following is an example of a client using the onread option:

const net = require('net');
net.connect({
  port: 80,
  onread: {
    // Reuses a 4KiB Buffer for every read from the socket.
    buffer: Buffer.alloc(4 * 1024),
    callback: function(nread, buf) {
      // Received data is available in `buf` from 0 to `nread`.
      console.log(buf.toString('utf8', 0, nread));
    }
  }
});

socket.connect(path[, connectListener])#

Initiate an IPC connection on the given socket.

Alias tosocket.connect(options[, connectListener])called with { path: path } as options.

socket.connect(port[, host][, connectListener])#

Added in: v0.1.90

Initiate a TCP connection on the given socket.

Alias tosocket.connect(options[, connectListener])called with {port: port, host: host} as options.

socket.connecting#

Added in: v6.1.0

If true,socket.connect(options[, connectListener]) was called and has not yet finished. It will stay true until the socket becomes connected, then it is set to false and the 'connect' event is emitted. Note that thesocket.connect(options[, connectListener])callback is a listener for the 'connect' event.

socket.destroy([error])#

Added in: v0.1.90

Ensures that no more I/O activity happens on this socket. Destroys the stream and closes the connection.

See writable.destroy() for further details.

socket.destroyed#

See writable.destroyed for further details.

socket.end([data[, encoding]][, callback])#

Added in: v0.1.90

Half-closes the socket. i.e., it sends a FIN packet. It is possible the server will still send some data.

See writable.end() for further details.

socket.localAddress#

Added in: v0.9.6

The string representation of the local IP address the remote client is connecting on. For example, in a server listening on '0.0.0.0', if a client connects on '192.168.1.1', the value of socket.localAddress would be'192.168.1.1'.

socket.localPort#

Added in: v0.9.6

The numeric representation of the local port. For example, 80 or 21.

socket.pause()#

Pauses the reading of data. That is, 'data' events will not be emitted. Useful to throttle back an upload.

socket.pending#

Added in: v11.2.0

This is true if the socket is not connected yet, either because .connect()has not yet been called or because it is still in the process of connecting (see socket.connecting).

socket.ref()#

Added in: v0.9.1

Opposite of unref(), calling ref() on a previously unrefed socket will_not_ let the program exit if it's the only socket left (the default behavior). If the socket is refed calling ref again will have no effect.

socket.remoteAddress#

Added in: v0.5.10

The string representation of the remote IP address. For example,'74.125.127.100' or '2001:4860:a005::68'. Value may be undefined if the socket is destroyed (for example, if the client disconnected).

socket.remoteFamily#

Added in: v0.11.14

The string representation of the remote IP family. 'IPv4' or 'IPv6'.

socket.remotePort#

Added in: v0.5.10

The numeric representation of the remote port. For example, 80 or 21.

socket.resume()#

Resumes reading after a call to socket.pause().

socket.setEncoding([encoding])#

Added in: v0.1.90

Set the encoding for the socket as a Readable Stream. Seereadable.setEncoding() for more information.

socket.setKeepAlive([enable][, initialDelay])#

Added in: v0.1.92

Enable/disable keep-alive functionality, and optionally set the initial delay before the first keepalive probe is sent on an idle socket.

Set initialDelay (in milliseconds) to set the delay between the last data packet received and the first keepalive probe. Setting 0 forinitialDelay will leave the value unchanged from the default (or previous) setting.

socket.setNoDelay([noDelay])#

Added in: v0.1.90

Enable/disable the use of Nagle's algorithm.

When a TCP connection is created, it will have Nagle's algorithm enabled.

Nagle's algorithm delays data before it is sent via the network. It attempts to optimize throughput at the expense of latency.

Passing true for noDelay or not passing an argument will disable Nagle's algorithm for the socket. Passing false for noDelay will enable Nagle's algorithm.

socket.setTimeout(timeout[, callback])#

Added in: v0.1.90

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 callsocket.end() or socket.destroy() to end the connection.

socket.setTimeout(3000);
socket.on('timeout', () => {
  console.log('socket timeout');
  socket.end();
});

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.unref()#

Added in: v0.9.1

Calling unref() on a socket will allow the program to exit if this is the only active socket in the event system. If the socket is already unrefed callingunref() again will have no effect.

socket.write(data[, encoding][, callback])#

Added in: v0.1.90

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, which may not be immediately.

See Writable stream write() method for more information.

net.connect()#

Aliases tonet.createConnection().

Possible signatures:

net.connect(options[, connectListener])#

Added in: v0.7.0

Alias tonet.createConnection(options[, connectListener]).

net.connect(path[, connectListener])#

Added in: v0.1.90

Alias tonet.createConnection(path[, connectListener]).

net.connect(port[, host][, connectListener])#

Added in: v0.1.90

Alias tonet.createConnection(port[, host][, connectListener]).

net.createConnection()#

A factory function, which creates a new net.Socket, immediately initiates connection with socket.connect(), then returns the net.Socket that starts the connection.

When the connection is established, a 'connect' event will be emitted on the returned socket. The last parameter connectListener, if supplied, will be added as a listener for the 'connect' event once.

Possible signatures:

The net.connect() function is an alias to this function.

net.createConnection(options[, connectListener])#

Added in: v0.1.90

For available options, seenew net.Socket([options])and socket.connect(options[, connectListener]).

Additional options:

Following is an example of a client of the echo server described in the net.createServer() section:

const net = require('net');
const client = net.createConnection({ port: 8124 }, () => {
  // 'connect' listener.
  console.log('connected to server!');
  client.write('world!\r\n');
});
client.on('data', (data) => {
  console.log(data.toString());
  client.end();
});
client.on('end', () => {
  console.log('disconnected from server');
});

To connect on the socket /tmp/echo.sock:

const client = net.createConnection({ path: '/tmp/echo.sock' });

net.createConnection(path[, connectListener])#

Added in: v0.1.90

Initiates an IPC connection.

This function creates a new net.Socket with all options set to default, immediately initiates connection withsocket.connect(path[, connectListener]), then returns the net.Socket that starts the connection.

net.createConnection(port[, host][, connectListener])#

Added in: v0.1.90

Initiates a TCP connection.

This function creates a new net.Socket with all options set to default, immediately initiates connection withsocket.connect(port[, host][, connectListener]), then returns the net.Socket that starts the connection.

net.createServer([options][, connectionListener])#

Added in: v0.5.0

Creates a new TCP or IPC server.

If allowHalfOpen is set to true, when the other end of the socket sends a FIN packet, the server will only send a FIN packet back whensocket.end() is explicitly called, until then the connection is half-closed (non-readable but still writable). See 'end' event and RFC 1122 (section 4.2.2.13) for more information.

If pauseOnConnect is set to true, then the socket associated with each incoming connection will be paused, and no data will be read from its handle. This allows connections to be passed between processes without any data being read by the original process. To begin reading data from a paused socket, callsocket.resume().

The server can be a TCP server or an IPC server, depending on what itlisten() to.

Here is an example of an TCP echo server which listens for connections on port 8124:

const net = require('net');
const server = net.createServer((c) => {
  // 'connection' listener.
  console.log('client connected');
  c.on('end', () => {
    console.log('client disconnected');
  });
  c.write('hello\r\n');
  c.pipe(c);
});
server.on('error', (err) => {
  throw err;
});
server.listen(8124, () => {
  console.log('server bound');
});

Test this by using telnet:

$ telnet localhost 8124

To listen on the socket /tmp/echo.sock:

server.listen('/tmp/echo.sock', () => {
  console.log('server bound');
});

Use nc to connect to a Unix domain socket server:

$ nc -U /tmp/echo.sock

net.isIP(input)#

Added in: v0.3.0

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)#

Added in: v0.3.0

Returns true if input is a version 4 IP address, otherwise returns false.

net.isIPv6(input)#

Added in: v0.3.0

Returns true if input is a version 6 IP address, otherwise returns false.