Node.js v26.5.0 documentation

Net#

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

import net from 'node:net';
const net = require('node:net');
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IPC support#

Support binding to abstract Unix domain socket path like \0abstract. We can bind '\0' for Node.js < v20.4.0.

Identifying paths for IPC connections#

net.connect(), net.createConnection(), server.listen(), and socket.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 file system pathname. It will throw an error when the length of pathname is greater than the length of sizeof(sockaddr_un.sun_path). 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 and server.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 file system and will persist until unlinked. On Linux, You can use Unix abstract socket by adding \0 to the beginning of the path, such as \0abstract. The path to the Unix abstract socket is not visible in the file system and it will disappear automatically when all open references to the socket are closed.

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.

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

blockList.addAddress(address[, type])#

• address <string> | <net.SocketAddress> An IPv4 or IPv6 address.
• type <string> Either 'ipv4' or 'ipv6'. Default: 'ipv4'.

blockList.addRange(start, end[, type])#

• start <string> | <net.SocketAddress> The starting IPv4 or IPv6 address in the range.
• end <string> | <net.SocketAddress> The ending IPv4 or IPv6 address in the range.
• type <string> Either 'ipv4' or 'ipv6'. Default: 'ipv4'.

blockList.addSubnet(net, prefix[, type])#

• net <string> | <net.SocketAddress> The network IPv4 or IPv6 address.
• prefix <number> The number of CIDR prefix bits. For IPv4, this must be a value between 0 and 32. For IPv6, this must be between 0 and 128.
• type <string> Either 'ipv4' or 'ipv6'. Default: 'ipv4'.

blockList.check(address[, type])#

• address <string> | <net.SocketAddress> The IP address to check
• type <string> Either 'ipv4' or 'ipv6'. Default: 'ipv4'.
• Returns: <boolean>

const blockList = new net.BlockList();
blockList.addAddress('123.123.123.123');
blockList.addRange('10.0.0.1', '10.0.0.10');
blockList.addSubnet('8592:757c:efae:4e45::', 64, 'ipv6');

console.log(blockList.check('123.123.123.123'));  // Prints: true
console.log(blockList.check('10.0.0.3'));  // Prints: true
console.log(blockList.check('222.111.111.222'));  // Prints: false

// IPv6 notation for IPv4 addresses works:
console.log(blockList.check('::ffff:7b7b:7b7b', 'ipv6')); // Prints: true
console.log(blockList.check('::ffff:123.123.123.123', 'ipv6')); // Prints: true
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blockList.rules#

• Type: <string>[]

const blockList = new net.BlockList();
const data = [
  'Subnet: IPv4 192.168.1.0/24',
  'Address: IPv4 10.0.0.5',
  'Range: IPv4 192.168.2.1-192.168.2.10',
  'Range: IPv4 10.0.0.1-10.0.0.10',
];
blockList.fromJSON(data);
blockList.fromJSON(JSON.stringify(data));
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Class: net.Server#

• Extends: <EventEmitter>

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

• options <Object> See net.createServer([options][, connectionListener]).
• connectionListener <Function> Automatically set as a listener for the 'connection' event.
• Returns: <net.Server>

Event: 'close'#

Event: 'connection'#

• Type: <net.Socket> The connection object

Event: 'error'#

• Type: <Error>

Event: 'listening'#

Event: 'drop'#

• data <Object> The argument passed to event listener.
  • localAddress <string> Local address.
  • localPort <number> Local port.
  • localFamily <string> Local family.
  • remoteAddress <string> Remote address.
  • remotePort <number> Remote port.
  • remoteFamily <string> Remote IP family. 'IPv4' or 'IPv6'.

server.address()#

The family property now returns a number instead of a string.

• Returns: <Object> | <string> | <null>

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());
});
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server.close([callback])#

• callback <Function> Called when the server is closed.
• Returns: <net.Server>

server[Symbol.asyncDispose]()#

No longer experimental.

server.getConnections(callback)#

• callback <Function>
• Returns: <net.Server>

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

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:

• server.listen(handle[, backlog][, callback])
• server.listen(options[, callback])
• server.listen(path[, backlog][, callback]) for IPC servers
• server.listen([port[, host[, backlog]]][, callback]) for TCP servers

This function is asynchronous. When the server starts listening, the 'listening' event will be emitted. The last parameter callback will 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 somaxconn on 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.

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

• handle <Object>
• backlog <number> Common parameter of server.listen() functions
• callback <Function>
• Returns: <net.Server>

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), a BoundSocket, or an object with an fd member that is a valid file descriptor.

When handle is a BoundSocket, the server adopts the already-bound socket and starts listening on it. Adoption consumes the bound socket (see ownership transfer).

server.listen(options[, callback])#

The ipv6Only option is supported.

• options <Object> Required. Supports the following properties:
  • backlog <number> Common parameter of server.listen() functions.
  • exclusive <boolean> Default: false
  • handle <net.BoundSocket> A pre-bound BoundSocket. The server adopts the already-bound socket and listens on it, ignoring host, port, and path. Adoption consumes the bound socket (see ownership transfer).
  • host <string>
  • ipv6Only <boolean> For TCP servers, setting ipv6Only to true will disable dual-stack support, i.e., binding to host :: won't make 0.0.0.0 be bound. Default: false.
  • reusePort <boolean> For TCP servers, setting reusePort to true allows multiple sockets on the same host to bind to the same port. Incoming connections are distributed by the operating system to listening sockets. This option is available only on some platforms, such as Linux 3.9+, DragonFlyBSD 3.6+, FreeBSD 12.0+, Solaris 11.4, and AIX 7.2.5+. On unsupported platforms, this option raises an error. Default: false.
  • path <string> Will be ignored if port is specified. See Identifying paths for IPC connections.
  • port <number>
  • readableAll <boolean> For IPC servers makes the pipe readable for all users. Default: false.
  • signal <AbortSignal> An AbortSignal that may be used to close a listening server.
  • writableAll <boolean> For IPC servers makes the pipe writable for all users. Default: false.
• callback <Function> functions.
• Returns: <net.Server>

If handle is specified, the server adopts that pre-bound socket. Otherwise, if port is specified, it behaves the same as server.listen([port[, host[, backlog]]][, callback]). Otherwise, if path is specified, it behaves the same as server.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. 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,
});
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When exclusive is true and the underlying handle is shared, it is possible that several workers query a handle with different backlogs. In this case, the first backlog passed to the master process will be used.

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.

const controller = new AbortController();
server.listen({
  host: 'localhost',
  port: 80,
  signal: controller.signal,
});
// Later, when you want to close the server.
controller.abort();
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server.listen(path[, backlog][, callback])#

• path <string> Path the server should listen to. See Identifying paths for IPC connections.
• backlog <number> Common parameter of server.listen() functions.
• callback <Function>.
• Returns: <net.Server>

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

• port <number>
• host <string>
• backlog <number> Common parameter of server.listen() functions.
• callback <Function>.
• Returns: <net.Server>

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().port after the 'listening' event has been emitted.

If host 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.

server.maxConnections#

Setting maxConnections to 0 drops all the incoming connections. Previously, it was interpreted as Infinity.

• Type: <integer>

When the number of connections reaches the server.maxConnections threshold:

1. If the process is not running in cluster mode, Node.js will close the connection.

2. If the process is running in cluster mode, Node.js will, by default, route the connection to another worker process. To close the connection instead, set server.dropMaxConnection to true.

server.dropMaxConnection#

• Type: <boolean>

server.ref()#

• Returns: <net.Server>

server.unref()#

• Returns: <net.Server>

Class: net.Socket#

• Extends: <stream.Duplex>

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.

new net.Socket([options])#

Added onread option.

• options <Object> Available options are:
  • allowHalfOpen <boolean> If set to false, then the socket will automatically end the writable side when the readable side ends. See net.createServer() and the 'end' event for details. Default: false.
  • blockList <net.BlockList> blockList can be used for disabling outbound access to specific IP addresses, IP ranges, or IP subnets.
  • fd <number> If specified, wrap around an existing socket with the given file descriptor, otherwise a new socket will be created.
  • handle <net.BoundSocket> If specified, wrap around the bound socket from a BoundSocket. A subsequent socket.connect() uses the bound socket as the connection's source binding (honoring the bound local address and port). Adoption consumes the bound socket (see ownership transfer).
  • keepAlive <boolean> If set to true, it enables keep-alive functionality on the socket immediately after the connection is established, similarly on what is done in socket.setKeepAlive(). Default: false.
  • keepAliveInitialDelay <number> If set to a positive number, it sets the initial delay before the first keepalive probe is sent on an idle socket. Default: 0.
  • noDelay <boolean> If set to true, it disables the use of Nagle's algorithm immediately after the socket is established. Default: false.
  • onread <Object> If specified, incoming data is stored in a single buffer and passed to the supplied callback when data arrives on the socket. This will cause the streaming functionality to not provide any data. The socket will emit events like 'error', 'end', and 'close' as usual. Methods like pause() and resume() will also behave as expected.
    • buffer <Buffer> | <Uint8Array> | <Function> Either a reusable chunk of memory to use for storing incoming data or a function that returns such.
    • callback <Function> This function is called for every chunk of incoming data. Two arguments are passed to it: the number of bytes written to buffer and a reference to buffer. Return false from this function to implicitly pause() the socket. This function will be executed in the global context.
  • readable <boolean> Allow reads on the socket when an fd is passed, otherwise ignored. Default: false.
  • signal <AbortSignal> An Abort signal that may be used to destroy the socket.
  • typeOfService <number> The initial Type of Service (TOS) value.
  • writable <boolean> Allow writes on the socket when an fd is passed, otherwise ignored. Default: false.
• Returns: <net.Socket>

Creates a new socket object.

Event: 'close'#

• hadError <boolean> true if the socket had a transmission error.

Event: 'connect'#

Event: 'connectionAttempt'#

• ip <string> The IP which the socket is attempting to connect to.
• port <number> The port which the socket is attempting to connect to.
• family <number> The family of the IP. It can be 6 for IPv6 or 4 for IPv4.

Event: 'connectionAttemptFailed'#

• ip <string> The IP which the socket attempted to connect to.
• port <number> The port which the socket attempted to connect to.
• family <number> The family of the IP. It can be 6 for IPv6 or 4 for IPv4.
• error <Error> The error associated with the failure.

Event: 'connectionAttemptTimeout'#

• ip <string> The IP which the socket attempted to connect to.
• port <number> The port which the socket attempted to connect to.
• family <number> The family of the IP. It can be 6 for IPv6 or 4 for IPv4.

Event: 'data'#

• Type: <Buffer> | <string>

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

Event: 'drain'#

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

Event: 'end'#

Emitted when the other end of the socket signals the end of transmission, thus ending the readable side of the socket.

Event: 'error'#

• Type: <Error>

Event: 'lookup'#

The host parameter is supported now.

• err <Error> | <null> The error object. See dns.lookup().
• address <string> The IP address.
• family <number> | <null> The address type. See dns.lookup().
• host <string> The host name.

Event: 'ready'#

Emitted when a socket is ready to be used.

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.

socket.address()#

The family property now returns a number instead of a string.

• Returns: <Object>

socket.autoSelectFamilyAttemptedAddresses#

• Type: <string>[]

This property is only present if the family autoselection algorithm is enabled in socket.connect(options) and it is an array of the addresses that have been attempted.

socket.bufferSize#

• Type: <integer>

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.

socket.bytesRead#

• Type: <integer>

socket.bytesWritten#

• Type: <integer>

socket.connect()#

Initiate a connection on a given socket.

Possible signatures:

• socket.connect(options[, connectListener])
• socket.connect(path[, connectListener]) for IPC connections.
• socket.connect(port[, host][, connectListener]) for TCP connections.
• Returns: <net.Socket> The socket itself.

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])#

The hints option is supported now.

• options <Object>
• connectListener <Function> Common parameter of socket.connect() methods. Will be added as a listener for the 'connect' event once.
• Returns: <net.Socket> The socket itself.

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:

• autoSelectFamily <boolean>: If set to true, it enables a family autodetection algorithm that loosely implements section 5 of RFC 8305. The all option passed to lookup is set to true and the sockets attempts to connect to all obtained IPv6 and IPv4 addresses, in sequence, until a connection is established. The first returned AAAA address is tried first, then the first returned A address, then the second returned AAAA address and so on. Each connection attempt (but the last one) is given the amount of time specified by the autoSelectFamilyAttemptTimeout option before timing out and trying the next address. Ignored if the family option is not 0 or if localAddress is set. Connection errors are not emitted if at least one connection succeeds. If all connections attempts fails, a single AggregateError with all failed attempts is emitted. Default: net.getDefaultAutoSelectFamily().
• autoSelectFamilyAttemptTimeout <number>: The amount of time in milliseconds to wait for a connection attempt to finish before trying the next address when using the autoSelectFamily option. If set to a positive integer less than 10, then the value 10 will be used instead. Default: net.getDefaultAutoSelectFamilyAttemptTimeout().
• family <number>: Version of IP stack. Must be 4, 6, or 0. The value 0 indicates that both IPv4 and IPv6 addresses are allowed. Default: 0.
• hints <number> Optional dns.lookup() hints.
• host <string> Host the socket should connect to. Default: 'localhost'.
• localAddress <string> Local address the socket should connect from.
• localPort <number> Local port the socket should connect from.
• lookup <Function> Custom lookup function. Default: dns.lookup().
• port <number> Required. Port the socket should connect to.

• path <string> Required. Path the client should connect to. See Identifying paths for IPC connections. If provided, the TCP-specific options above are ignored.

socket.connect(path[, connectListener])#

• path <string> Path the client should connect to. See Identifying paths for IPC connections.
• connectListener <Function> Common parameter of socket.connect() methods. Will be added as a listener for the 'connect' event once.
• Returns: <net.Socket> The socket itself.

Initiate an IPC connection on the given socket.

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

• port <number> Port the client should connect to.
• host <string> Host the client should connect to.
• connectListener <Function> Common parameter of socket.connect() methods. Will be added as a listener for the 'connect' event once.
• Returns: <net.Socket> The socket itself.

Initiate a TCP connection on the given socket.

socket.connecting#

• Type: <boolean>

socket.destroy([error])#

• error <Object>
• Returns: <net.Socket>

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

socket.destroyed#

• Type: <boolean> Indicates if the connection is destroyed or not. Once a connection is destroyed no further data can be transferred using it.

socket.destroySoon()#

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

• data <string> | <Buffer> | <Uint8Array>
• encoding <string> Only used when data is string. Default: 'utf8'.
• callback <Function> Optional callback for when the socket is finished.
• Returns: <net.Socket> The socket itself.

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

socket.localAddress#

• Type: <string>

socket.localPort#

• Type: <integer>

socket.localFamily#

• Type: <string>

socket.pause()#

• Returns: <net.Socket> The socket itself.

socket.pending#

• Type: <boolean>

socket.ref()#

• Returns: <net.Socket> The socket itself.

socket.remoteAddress#

• Type: <string>

socket.remoteFamily#

• Type: <string>

socket.remotePort#

• Type: <integer>

socket.resetAndDestroy()#

• Returns: <net.Socket>

socket.resume()#

• Returns: <net.Socket> The socket itself.

socket.setEncoding([encoding])#

• encoding <string>
• Returns: <net.Socket> The socket itself.

socket.setKeepAlive()#

Enable/disable keep-alive functionality, and optionally configure the keepalive probe timing. Returns the socket itself.

Possible signatures:

• socket.setKeepAlive([options])
• socket.setKeepAlive([enable][, initialDelay][, interval][, count])

Enabling keep-alive sets 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 for initialDelay will leave the value unchanged from the default (or previous) setting.

Set interval (in milliseconds) to set the delay between successive keepalive probes once they begin (TCP_KEEPINTVL). Set count to the number of unacknowledged probes sent before the connection is dropped (TCP_KEEPCNT). Both are only applied when keep-alive is enabled. Omitting interval or count uses the defaults of 1000 ms and 10. As with initialDelay, a non-positive interval or count leaves the corresponding system default unchanged.

initialDelay and interval are specified in milliseconds but the underlying socket options are configured in whole seconds; the values are divided by 1000 and rounded down before being applied.

Enabling the keep-alive functionality will set the following socket options:

• SO_KEEPALIVE=1
• TCP_KEEPIDLE=initialDelay / 1000
• TCP_KEEPCNT=count
• TCP_KEEPINTVL=interval / 1000

socket.setKeepAlive([options])#

• options <Object>
  • enable <boolean> Default: false
  • initialDelay <number> Default: 0
  • interval <number> Default: 1000
  • count <number> Default: 10
• Returns: <net.Socket> The socket itself.

socket.setKeepAlive({ enable: true, initialDelay: 1000, interval: 1000, count: 10 });
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socket.setKeepAlive([enable][, initialDelay][, interval][, count])#

New defaults for TCP_KEEPCNT and TCP_KEEPINTVL socket options were added.

• enable <boolean> Default: false
• initialDelay <number> Default: 0
• interval <number> Default: 1000
• count <number> Default: 10
• Returns: <net.Socket> The socket itself.

socket.setNoDelay([noDelay])#

• noDelay <boolean> Default: true
• Returns: <net.Socket> The socket itself.

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.

socket.setTimeout(timeout[, callback])#

Passing an invalid callback to the callback argument now throws ERR_INVALID_ARG_TYPE instead of ERR_INVALID_CALLBACK.

• timeout <number>
• callback <Function>
• Returns: <net.Socket> The socket itself.

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

socket.setTimeout(3000);
socket.on('timeout', () => {
  console.log('socket timeout');
  socket.end();
});
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If timeout is 0, then the existing idle timeout is disabled.

socket.getTypeOfService()#

• Returns: <integer> The current TOS value.

Returns the current Type of Service (TOS) field for IPv4 packets or Traffic Class for IPv6 packets for this socket.

setTypeOfService() may be called before the socket is connected; the value will be cached and applied when the socket establishes a connection. getTypeOfService() will return the currently set value even before connection.

socket.setTypeOfService(tos)#

• tos <integer> The TOS value to set (0-255).
• Returns: <net.Socket> The socket itself.

Sets the Type of Service (TOS) field for IPv4 packets or Traffic Class for IPv6 Packets sent from this socket. This can be used to prioritize network traffic.

setTypeOfService() may be called before the socket is connected; the value will be cached and applied when the socket establishes a connection. getTypeOfService() will return the currently set value even before connection.

socket.timeout#

• Type: <number> | <undefined>

socket.unref()#

• Returns: <net.Socket> The socket itself.

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

• data <string> | <Buffer> | <Uint8Array>
• encoding <string> Only used when data is string. Default: utf8.
• callback <Function>
• Returns: <boolean>

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.

socket.readyState#

• Type: <string>

• If the stream is connecting socket.readyState is opening.
• If the stream is readable and writable, it is open.
• If the stream is readable and not writable, it is readOnly.
• If the stream is not readable and writable, it is writeOnly.

Class: net.BoundSocket#

Allows for the synchronous creation of a pre-bound socket, that can be passed to listen() or new net.Socket() later on. For listen() this enables synchronous port reservation, while for new net.Socket(), it allows control over the local egress port/IP, via bind(2) semantics.

import net from 'node:net';

const bound = new net.BoundSocket();
const { port } = bound.address();
console.log(`Reserved port ${port} for server`);

const server = net.createServer();
server.listen(bound); // Adopt as a server, or pass to new net.Socket() instead.
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boundSocket.address()#

• Returns: <Object> An object with address, family, and port properties, as server.address() returns.

boundSocket.fd()#

• Returns: <integer> The underlying OS file descriptor, or -1 on platforms that do not expose one for sockets (such as Windows).

boundSocket.close()#

boundSocket[Symbol.dispose]()#

net.connect()#

Aliases to net.createConnection().

• net.connect(options[, connectListener])
• net.connect(path[, connectListener]) for IPC connections.
• net.connect(port[, host][, connectListener]) for TCP connections.

net.connect(options[, connectListener])#

• options <Object>
• connectListener <Function>
• Returns: <net.Socket>

net.connect(path[, connectListener])#

• path <string>
• connectListener <Function>
• Returns: <net.Socket>

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

• port <number>
• host <string>
• connectListener <Function>
• Returns: <net.Socket>

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:

• net.createConnection(options[, connectListener])
• net.createConnection(path[, connectListener]) for IPC connections.
• net.createConnection(port[, host][, connectListener]) for TCP connections.

net.createConnection(options[, connectListener])#

• options <Object> Required. Will be passed to both the new net.Socket([options]) call and the socket.connect(options[, connectListener]) method.
• connectListener <Function> Common parameter of the net.createConnection() functions. If supplied, will be added as a listener for the 'connect' event on the returned socket once.
• Returns: <net.Socket> The newly created socket used to start the connection.

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

Additional options:

• handle <net.BoundSocket> A pre-bound BoundSocket used as the connection's source binding, honoring its local address and port. Adoption consumes the bound socket (see ownership transfer).
• timeout <number> If set, will be used to call socket.setTimeout(timeout) after the socket is created, but before it starts the connection.

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

import net from 'node: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');
});
const net = require('node: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');
});
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To connect on the socket /tmp/echo.sock:

const client = net.createConnection({ path: '/tmp/echo.sock' });
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import net from 'node:net';
import { Buffer } from 'node:buffer';
net.createConnection({
  port: 8124,
  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));
    },
  },
});
const net = require('node:net');
net.createConnection({
  port: 8124,
  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));
    },
  },
});
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net.createConnection(path[, connectListener])#

• path <string> Path the socket should connect to. Will be passed to socket.connect(path[, connectListener]). See Identifying paths for IPC connections.
• connectListener <Function> Common parameter of the net.createConnection() functions, an "once" listener for the 'connect' event on the initiating socket. Will be passed to socket.connect(path[, connectListener]).
• Returns: <net.Socket> The newly created socket used to start the connection.

Initiates an IPC connection.

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

• port <number> Port the socket should connect to. Will be passed to socket.connect(port[, host][, connectListener]).
• host <string> Host the socket should connect to. Will be passed to socket.connect(port[, host][, connectListener]). Default: 'localhost'.
• connectListener <Function> Common parameter of the net.createConnection() functions, an "once" listener for the 'connect' event on the initiating socket. Will be passed to socket.connect(port[, host][, connectListener]).
• Returns: <net.Socket> The newly created socket used to start the connection.

Initiates a TCP connection.

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

The noDelay, keepAlive, and keepAliveInitialDelay options are supported now.

• options <Object>

  • allowHalfOpen <boolean> If set to false, then the socket will automatically end the writable side when the readable side ends. Default: false.
  • highWaterMark <number> Optionally overrides all net.Sockets' readableHighWaterMark and writableHighWaterMark. Default: See stream.getDefaultHighWaterMark().
  • keepAlive <boolean> If set to true, it enables keep-alive functionality on the socket immediately after a new incoming connection is received, similarly on what is done in socket.setKeepAlive(). Default: false.
  • keepAliveInitialDelay <number> If set to a positive number, it sets the initial delay before the first keepalive probe is sent on an idle socket. Default: 0.
  • noDelay <boolean> If set to true, it disables the use of Nagle's algorithm immediately after a new incoming connection is received. Default: false.
  • pauseOnConnect <boolean> Indicates whether the socket should be paused on incoming connections. Default: false.
  • blockList <net.BlockList> blockList can be used for disabling inbound access to specific IP addresses, IP ranges, or IP subnets. This does not work if the server is behind a reverse proxy, NAT, etc. because the address checked against the block list is the address of the proxy, or the one specified by the NAT.

• connectionListener <Function> Automatically set as a listener for the 'connection' event.

• Returns: <net.Server>

Creates a new TCP or IPC server.

If allowHalfOpen is set to true, when the other end of the socket signals the end of transmission, the server will only send back the end of transmission when socket.end() is explicitly called. For example, in the context of TCP, when a FIN packed is received, a FIN packed is sent back only when socket.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, call socket.resume().

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

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

import net from 'node: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');
});
const net = require('node: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');
});
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Test this by using telnet:

telnet localhost 8124
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To listen on the socket /tmp/echo.sock:

server.listen('/tmp/echo.sock', () => {
  console.log('server bound');
});
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nc -U /tmp/echo.sock
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net.getDefaultAutoSelectFamily()#

• Returns: <boolean> The current default value of the autoSelectFamily option.

net.setDefaultAutoSelectFamily(value)#

• value <boolean> The new default value. The initial default value is true, unless the command line option --no-network-family-autoselection is provided.

net.getDefaultAutoSelectFamilyAttemptTimeout()#

• Returns: <number> The current default value of the autoSelectFamilyAttemptTimeout option.

net.setDefaultAutoSelectFamilyAttemptTimeout(value)#

• value <number> The new default value, which must be a positive number. If the number is less than 10, the value 10 is used instead. The initial default value is 250 or the value specified via the command line option --network-family-autoselection-attempt-timeout.

net.isIP(input)#

• input <string>
• Returns: <integer>

net.isIP('::1'); // returns 6
net.isIP('127.0.0.1'); // returns 4
net.isIP('127.000.000.001'); // returns 0
net.isIP('127.0.0.1/24'); // returns 0
net.isIP('fhqwhgads'); // returns 0
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net.isIPv4(input)#

• input <string>
• Returns: <boolean>

net.isIPv4('127.0.0.1'); // returns true
net.isIPv4('127.000.000.001'); // returns false
net.isIPv4('127.0.0.1/24'); // returns false
net.isIPv4('fhqwhgads'); // returns false
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net.isIPv6(input)#

• input <string>
• Returns: <boolean>

Returns true if input is an IPv6 address. Otherwise, returns false.

net.isIPv6('::1'); // returns true
net.isIPv6('fhqwhgads'); // returns false
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