Node.js v26.11.1 documentation
- Node.js v26.11.1
- Table of contents
- Net
- IPC support
- Class:
net.BlockListblockList.addAddress(address[, type])blockList.addAddresses(addresses[, type])blockList.addCIDR(cidr)blockList.addCIDRs(cidrs)blockList.addRange(start, end[, type])blockList.addSubnet(net, prefix[, type])blockList.check(address[, type])blockList.clear()blockList.fromJSON(value)BlockList.isBlockList(value)BlockList.PRIVATE_RANGESblockList.removeAddress(address[, type])blockList.removeCIDR(cidr)blockList.removeRange(start, end[, type])blockList.removeSubnet(net, prefix[, type])blockList.rulesblockList.sizeblockList.toJSON()
- Class:
net.SocketAddress - Class:
net.Servernew net.Server([options][, connectionListener])- Event:
'close' - Event:
'connection' - Event:
'error' - Event:
'listening' - Event:
'drop' server.address()server.close([callback])server[Symbol.asyncDispose]()server.getConnections(callback)server.listen()server.listeningserver.maxConnectionsserver.dropMaxConnectionserver.ref()server.unref()
- Class:
net.Socket- Transferring TCP handles to other threads
new net.Socket([options])- Event:
'close' - Event:
'connect' - Event:
'connectionAttempt' - Event:
'connectionAttemptFailed' - Event:
'connectionAttemptTimeout' - Event:
'data' - Event:
'drain' - Event:
'end' - Event:
'error' - Event:
'lookup' - Event:
'ready' - Event:
'timeout' socket.address()socket.autoSelectFamilyAttemptedAddressessocket.bufferSizesocket.bytesReadsocket.bytesWrittensocket.connect()socket.connectingsocket.destroy([error])socket.destroyedsocket.destroySoon()socket.end([data[, encoding]][, callback])socket.localAddresssocket.localPortsocket.localFamilysocket.pause()socket.pendingsocket.ref()socket.remoteAddresssocket.remoteFamilysocket.remotePortsocket.serversocket.resetAndDestroy()socket.resume()socket.setEncoding([encoding])socket.setKeepAlive()socket.setNoDelay([noDelay])socket.setTimeout(timeout[, callback])socket.getTypeOfService()socket.setTypeOfService(tos)socket.timeoutsocket.unref()socket.write(data[, encoding][, callback])socket.readyState
- Class:
net.BoundSocket net.connect()net.createConnection()net.createServer([options][, connectionListener])net.getDefaultAutoSelectFamily()net.setDefaultAutoSelectFamily(value)net.getDefaultAutoSelectFamilyAttemptTimeout()net.setDefaultAutoSelectFamilyAttemptTimeout(value)net.isIP(input)net.isIPv4(input)net.isIPv6(input)
- Net
- Index
- About this documentation
- Usage and example
- Assertion testing
- Asynchronous context tracking
- Async hooks
- Benchmark runner
- Buffer
- C++ addons
- C/C++ addons with Node-API
- C++ embedder API
- Child processes
- Cluster
- Command-line options
- Console
- Crypto
- Debugger
- Deprecated APIs
- Diagnostics Channel
- DNS
- Domain
- Environment Variables
- Errors
- Events
- File system
- FFI
- Globals
- HTTP
- HTTP/2
- HTTPS
- Inspector
- Internationalization
- Iterable Streams API
- Modules: CommonJS modules
- Modules: ECMAScript modules
- Modules:
node:moduleAPI - Modules: Packages
- Modules: TypeScript
- Net
- OS
- Path
- Performance hooks
- Permissions
- Process
- Punycode
- Query strings
- Readline
- REPL
- Report
- Single executable applications
- SQLite
- Stream
- String decoder
- Test runner
- Timers
- TLS/SSL
- Trace events
- TTY
- UDP/datagram
- URL
- Utilities
- V8
- Virtual File System
- VM
- WASI
- Web Crypto API
- Web Streams API
- Worker threads
- Zlib
- Other versions
- Options
Net#
Stability: 2 - Stable
The node: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:
import net from 'node:net';const net = require('node:net');
IPC support#
The node: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(), 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.
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.BlockList#
The BlockList object can be used with some network APIs to specify rules for
disabling inbound or outbound access to specific IP addresses, IP ranges, or
IP subnets.
blockList.addAddress(address[, type])#
Adds a rule to block the given IP address.
blockList.addAddresses(addresses[, type])#
addressestype'ipv4'or'ipv6'. Default:'ipv4'.
Adds multiple address rules to the block list in a single operation.
This is more efficient than calling blockList.addAddress() repeatedly
when adding a large number of individual addresses, as the addresses
are inserted under a single internal lock acquisition.
blockList.addCIDR(cidr)#
Adds a subnet rule using CIDR notation. The address family is automatically
detected from the address (IPv6 if the address contains ':', IPv4
otherwise). This is equivalent to calling blockList.addSubnet() with
the parsed network address, prefix length, and family.
blockList.addCIDRs(cidrs)#
Adds multiple subnet rules using CIDR notation in a single call. The address
family for each entry is automatically detected. This is equivalent to
calling blockList.addCIDR() for each element of the array.
blockList.addRange(start, end[, type])#
startendtype'ipv4'or'ipv6'. Default:'ipv4'.
Adds a rule to block a range of IP addresses from start (inclusive) to
end (inclusive).
blockList.addSubnet(net, prefix[, type])#
netprefix0and32. For IPv6, this must be between0and128.type'ipv4'or'ipv6'. Default:'ipv4'.
Adds a rule to block a range of IP addresses specified as a subnet mask.
blockList.check(address[, type])#
Returns true if the given IP address matches any of the rules added to the
BlockList.
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
blockList.clear()#
Clears all rules from the BlockList.
blockList.fromJSON(value)#
Stability: 1.2 - Release candidate
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));
valueBlocklist.rules
BlockList.isBlockList(value)#
BlockList.PRIVATE_RANGES#
A frozen array of CIDR strings representing private, loopback, and link-local
IP address ranges. This can be passed to blockList.addCIDRs() to quickly
populate a blocklist with all non-routable address ranges.
The included ranges are:
10.0.0.0/8— RFC 1918 private IPv4172.16.0.0/12— RFC 1918 private IPv4192.168.0.0/16— RFC 1918 private IPv4127.0.0.0/8— IPv4 loopback::1/128— IPv6 loopback169.254.0.0/16— IPv4 link-localfe80::/10— IPv6 link-localfc00::/7— IPv6 unique local (ULA)
const blockList = new net.BlockList();
blockList.addCIDRs(net.BlockList.PRIVATE_RANGES);
console.log(blockList.check('10.0.0.1')); // Prints: true
console.log(blockList.check('127.0.0.1')); // Prints: true
console.log(blockList.check('8.8.8.8')); // Prints: false
blockList.removeAddress(address[, type])#
Removes a rule that was previously added with blockList.addAddress(). The
address must match exactly the value used when the rule was added. If the
specified address does not exist, this is a no-op.
blockList.removeCIDR(cidr)#
Removes a subnet rule using CIDR notation. The address family is automatically
detected from the address. This is equivalent to calling
blockList.removeSubnet() with the parsed network address, prefix length,
and family. If the specified subnet does not exist, this is a no-op.
blockList.removeRange(start, end[, type])#
startendtype'ipv4'or'ipv6'. Default:'ipv4'.
Removes a rule that was previously added with blockList.addRange(). The start
and end addresses must match exactly the values used when the rule was added.
If the specified range does not exist, this is a no-op.
blockList.removeSubnet(net, prefix[, type])#
netprefix0and32. For IPv6, this must be between0and128.type'ipv4'or'ipv6'. Default:'ipv4'.
Removes a rule that was previously added with blockList.addSubnet(). The
network address and prefix must match exactly the values used when the rule was
added. If the specified subnet does not exist, this is a no-op.
blockList.rules#
The list of rules added to the blocklist.
blockList.size#
The number of rules in the blocklist. This is equivalent to
blockList.rules.length but does not allocate the rules array.
blockList.toJSON()#
Stability: 1.2 - Release candidate
- Returns Blocklist.rules
Class: net.SocketAddress#
new net.SocketAddress([options])#
socketaddress.address#
socketaddress.family#
socketaddress.flowlabel#
socketaddress.port#
SocketAddress.parse(input)#
Class: net.Server#
This class is used to create a TCP or IPC server.
A listening TCP net.Server can be transferred to a worker thread by listing it
in the transferList of a worker_threads postMessage() call. This moves
the underlying listening socket to the receiving thread, where it resumes
accepting connections. See Transferring TCP handles to other threads.
new net.Server([options][, connectionListener])#
optionsSeenet.createServer([options][, connectionListener]).connectionListener'connection'event.- Returns:
net.Server is an EventEmitter with the following events:
Event: 'close'#
Emitted when the server closes. If connections exist, this event is not emitted until all connections are ended.
Event: 'connection'#
Emitted when a new connection is made. socket is an instance of
net.Socket.
Event: '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().
Event: 'drop'#
When the number of connections reaches the threshold of server.maxConnections,
the server will drop new connections and emit 'drop' event instead. If it is a
TCP server, the argument is as follows, otherwise the argument is undefined.
server.address()#
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])#
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[Symbol.asyncDispose]()#
Calls server.close() and returns a promise that fulfills when the
server has closed.
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()#
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 serversserver.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.
One of the most common errors raised when listening is EADDRINUSE.
This happens when another server is already listening on the requested
port/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.error('Address in use, retrying...');
setTimeout(() => {
server.close();
server.listen(PORT, HOST);
}, 1000);
}
});
server.listen(handle[, backlog][, callback])#
handlebacklogserver.listen()functionscallback- Returns:
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).
Listening on a file descriptor is not supported on Windows.
server.listen(options[, callback])#
optionsRequired. Supports the following properties:backlogserver.listen()functions.exclusivefalsehandleBoundSocket. The server adopts the already-bound socket and listens on it, ignoringhost,port, andpath. Adoption consumes the bound socket (see ownership transfer).hostipv6Onlyipv6Onlytotruewill disable dual-stack support, i.e., binding to host::won't make0.0.0.0be bound. Default:false.reusePortreusePorttotrueallows 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.pathportis specified. See Identifying paths for IPC connections.portreadableAllfalse.signalwritableAllfalse.
callback- Returns:
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.
Using the
signaloption to destroy a long-lived server as a resource cleanup mechanism is deprecated. Thesignaloption remains appropriate for cancellation, externally propagated aborts, and timeouts. See DEP0209.
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,
});
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.
If the signal option is enabled, calling .abort() on the corresponding
AbortController is similar to calling .close() on the server:
const controller = new AbortController();
server.listen({
host: 'localhost',
port: 80,
signal: controller.signal,
});
// Later, when you want to close the server.
controller.abort();
server.listen(path[, backlog][, callback])#
pathbacklogserver.listen()functions.callback- Returns:
Start an IPC server listening for connections on the given path.
server.listen([port[, host[, backlog]]][, callback])#
porthostbacklogserver.listen()functions.callback- Returns:
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.
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#
server.maxConnections#
When the number of connections reaches the server.maxConnections threshold:
-
If the process is not running in cluster mode, Node.js will close the connection.
-
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.dropMaxConnectiontotrue.
It is not recommended to use this option once a socket has been sent to a child
with child_process.fork().
server.dropMaxConnection#
Set this property to true to begin closing connections once the number of connections reaches the server.maxConnections threshold. This setting is only effective in cluster mode.
server.ref()#
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()#
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 calling
unref() again will have no effect.
Class: net.Socket#
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.
Transferring TCP handles to other threads#
A connected TCP net.Socket can be moved to another thread by listing it in the
transferList of a worker_threads postMessage() call. After the
transfer, the source socket is destroyed on the sending thread (further use
fails with ERR_STREAM_DESTROYED rather than silently dropping data), and the
socket continues to work on the receiving thread. This makes it possible to
accept connections on one thread and distribute them across a pool of worker
threads, for example to build a node:cluster-like model on top of worker
threads.
The socket must be a freshly accepted or created TCP connection: it must still
be attached to a live handle, must not be connecting or destroyed, and must not
have started reading or have buffered data. Otherwise postMessage() throws
ERR_WORKER_HANDLE_NOT_TRANSFERABLE. Only TCP sockets are supported.
const net = require('node:net');
const { Worker } = require('node:worker_threads');
// worker.js receives `{ socket }` messages and handles each connection.
const worker = new Worker('./worker.js');
const server = net.createServer((socket) => {
// Hand the freshly accepted connection off to the worker thread.
worker.postMessage({ socket }, [socket]);
});
server.listen(8000);
A listening net.Server can be transferred the same way, which moves the
listening socket itself (and its pending accept queue) to the receiving thread.
An un-adopted TCP BoundSocket can also be transferred, which moves the
bound (but not yet listening or connected) socket. This allows a port to be
reserved synchronously on one thread and adopted by a server or outgoing
connection on another. Pipe binds are not transferable. After the transfer, the
source BoundSocket behaves as if it had been adopted: address(), fd() and
close() throw ERR_SOCKET_HANDLE_ADOPTED.
new net.Socket([options])#
optionsAvailable options are:allowHalfOpenfalse, then the socket will automatically end the writable side when the readable side ends. Seenet.createServer()and the'end'event for details. Default:false.blockListblockListcan be used for disabling outbound access to specific IP addresses, IP ranges, or IP subnets.fdhandleBoundSocket. A subsequentsocket.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).keepAlivetrue, it enables keep-alive functionality on the socket immediately after the connection is established, similarly on what is done insocket.setKeepAlive(). Default:false.keepAliveInitialDelay0.noDelaytrue, it disables the use of Nagle's algorithm immediately after the socket is established. Default:false.onreadIf specified, incoming data is stored in a singlebufferand passed to the suppliedcallbackwhen 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 likepause()andresume()will also behave as expected.buffercallbackbufferand a reference tobuffer. Returnfalsefrom this function to implicitlypause()the socket. This function will be executed in the global context.
readablefdis passed, otherwise ignored. Default:false.signaltypeOfServicewritablefdis passed, otherwise ignored. Default:false.
- Returns:
Creates a new socket object.
The newly created socket can be either a TCP socket or a streaming IPC
endpoint, depending on what it connect() to.
Event: 'close'#
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'#
Emitted when a socket connection is successfully established.
See net.createConnection().
Event: 'connectionAttempt'#
ipportfamily6for IPv6 or4for IPv4.
Emitted when a new connection attempt is started. This may be emitted multiple times
if the family autoselection algorithm is enabled in socket.connect(options).
Event: 'connectionAttemptFailed'#
ipportfamily6for IPv6 or4for IPv4.error
Emitted when a connection attempt failed. This may be emitted multiple times
if the family autoselection algorithm is enabled in socket.connect(options).
Event: 'connectionAttemptTimeout'#
ipportfamily6for IPv6 or4for IPv4.
Emitted when a connection attempt timed out. This is only emitted (and may be
emitted multiple times) if the family autoselection algorithm is enabled
in socket.connect(options).
Event: 'data'#
Emitted when data is received. The argument data will be a Buffer or
String. Encoding of data is set by socket.setEncoding().
The data will be lost if there is no listener when a Socket
emits a 'data' event.
Event: 'drain'#
Emitted when the write buffer becomes empty. Can be used to throttle uploads.
See also: the return values of socket.write().
Event: 'end'#
Emitted when the other end of the socket signals the end of transmission, thus ending the readable side of the socket.
By default (allowHalfOpen is false) the socket will send an end of
transmission 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 call
end() explicitly to close the connection (i.e. sending a
FIN packet back).
Event: 'error'#
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.
errdns.lookup().addressfamilydns.lookup().host
Event: 'ready'#
Emitted when a socket is ready to be used.
Triggered immediately after 'connect'.
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().
socket.address()#
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.autoSelectFamilyAttemptedAddresses#
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.
Each address is a string in the form of $IP:$PORT. If the connection was successful,
then the last address is the one that the socket is currently connected to.
socket.bufferSize#
Stability: 0 - Deprecated: Use writable.writableLength instead.
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 with
socket.pause() and socket.resume().
socket.bytesRead#
The amount of received bytes.
socket.bytesWritten#
The amount of bytes sent.
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:
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.
This function should only be used for reconnecting a socket after
'close' has been emitted or otherwise it may lead to undefined
behavior.
socket.connect(options[, connectListener])#
optionsconnectListenersocket.connect()methods. Will be added as a listener for the'connect'event once.- Returns:
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:
autoSelectFamilytrue, it enables a family autodetection algorithm that loosely implements section 5 of RFC 8305. Thealloption passed to lookup is set totrueand 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 theautoSelectFamilyAttemptTimeoutoption before timing out and trying the next address. Ignored if thefamilyoption is not0or iflocalAddressis set. Connection errors are not emitted if at least one connection succeeds. If all connections attempts fails, a singleAggregateErrorwith all failed attempts is emitted. Default:net.getDefaultAutoSelectFamily().autoSelectFamilyAttemptTimeoutautoSelectFamilyoption. If set to a positive integer less than10, then the value10will be used instead. Default:net.getDefaultAutoSelectFamilyAttemptTimeout().family4,6, or0. The value0indicates that both IPv4 and IPv6 addresses are allowed. Default:0.hintsdns.lookup()hints.host'localhost'.localAddresslocalPortlookupdns.lookup().port
For IPC connections, available options are:
path
socket.connect(path[, connectListener])#
pathconnectListenersocket.connect()methods. Will be added as a listener for the'connect'event once.- Returns:
Initiate an IPC connection on the given socket.
Alias to
socket.connect(options[, connectListener])
called with { path: path } as options.
socket.connect(port[, host][, connectListener])#
porthostconnectListenersocket.connect()methods. Will be added as a listener for the'connect'event once.- Returns:
Initiate a TCP connection on the given socket.
Alias to
socket.connect(options[, connectListener])
called with {port: port, host: host} as options.
socket.connecting#
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 the
socket.connect(options[, connectListener])
callback is a listener for the 'connect' event.
socket.destroy([error])#
Ensures that no more I/O activity happens on the current connection. Destroys the stream and closes the connection.
See writable.destroy() for further details.
socket.destroyed#
- Type:
See writable.destroyed for further details.
socket.destroySoon()#
Destroys the socket after all data is written. If the 'finish' event was
already emitted the socket is destroyed immediately. If the socket is still
writable it implicitly calls socket.end().
socket.end([data[, encoding]][, callback])#
dataencodingstring. Default:'utf8'.callback- Returns:
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#
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#
The numeric representation of the local port. For example, 80 or 21.
socket.localFamily#
The string representation of the local IP family. 'IPv4' or 'IPv6'.
socket.pause()#
Pauses the reading of data. That is, 'data' events will not be emitted.
Useful to throttle back an upload.
socket.pending#
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()#
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#
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#
The string representation of the remote IP family. 'IPv4' or 'IPv6'. Value may be undefined if
the socket is destroyed (for example, if the client disconnected).
socket.remotePort#
The numeric representation of the remote port. For example, 80 or 21. Value may be undefined if
the socket is destroyed (for example, if the client disconnected).
socket.server#
Reference to the server that accepted the socket. This is null for sockets
that were not accepted by a server.
socket.resetAndDestroy()#
Close the TCP connection by sending an RST packet and destroy the stream.
If this TCP socket is in connecting status, it will send an RST packet and destroy this TCP socket once it is connected.
Otherwise, it will call socket.destroy with an ERR_SOCKET_CLOSED Error.
If this is not a TCP socket (for example, a pipe), calling this method will immediately throw an ERR_INVALID_HANDLE_TYPE Error.
socket.resume()#
Resumes reading after a call to socket.pause().
socket.setEncoding([encoding])#
Set the encoding for the socket as a Readable Stream. See
readable.setEncoding() for more information.
socket.setKeepAlive()#
Enable/disable keep-alive functionality, and optionally configure the keepalive probe timing. Returns the socket itself.
Possible signatures:
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. For example,
setting initialDelay to 400 will result in a TCP_KEEPIDLE of 0
seconds (since 400 / 1000 rounds down to 0).
Enabling the keep-alive functionality will set the following socket options:
SO_KEEPALIVE=1TCP_KEEPIDLE=initialDelay / 1000TCP_KEEPCNT=countTCP_KEEPINTVL=interval / 1000
On Windows versions older than build 1709, keep-alive is configured through
SIO_KEEPALIVE_VALS, which has no probe-count field, so count is ignored on
those platforms.
socket.setKeepAlive([options])#
Configure keep-alive using an options object. See socket.setKeepAlive()
for a description of each property.
socket.setKeepAlive({ enable: true, initialDelay: 1000, interval: 1000, count: 10 });
socket.setKeepAlive([enable][, initialDelay][, interval][, count])#
enablefalseinitialDelay0interval1000count10- Returns:
Configure keep-alive using positional arguments. See
socket.setKeepAlive() for a description of each argument.
socket.setNoDelay([noDelay])#
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])#
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();
});
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.getTypeOfService()#
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.
On some platforms (e.g., Linux), certain TOS/ECN bits may be masked or ignored, and behavior can differ between IPv4 and IPv6 or dual-stack sockets. Callers should verify platform-specific semantics.
socket.setTypeOfService(tos)#
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.
On some platforms (e.g., Linux), certain TOS/ECN bits may be masked or ignored, and behavior can differ between IPv4 and IPv6 or dual-stack sockets. Callers should verify platform-specific semantics.
socket.timeout#
The socket timeout in milliseconds as set by socket.setTimeout().
It is undefined if a timeout has not been set.
socket.unref()#
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 calling
unref() again will have no effect.
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, which may not be immediately.
See Writable stream write() method for more
information.
socket.readyState#
This property represents the state of the connection as a string.
- If the socket is connecting,
socket.readyStateisopening. - If the socket is readable and writable, it is
open. - If the socket is readable and not writable, it is
readOnly. - If the socket is not readable and writable, it is
writeOnly. - Otherwise, it is
closed.
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.
A BoundSocket binds either a TCP endpoint (host or port) or a
Unix domain/named-pipe endpoint (path); the two are mutually exclusive. For a
path, the file system entry is reserved in the constructor, so conflicts such
as EADDRINUSE throw synchronously exactly as a TCP bind does. On Linux a
leading '\0' in path selects the abstract namespace (no file system entry);
an abstract path on any other platform throws ERR_INVALID_ARG_VALUE.
Adoption transfers ownership of the socket; afterwards address() and close()
throw ERR_SOCKET_HANDLE_ADOPTED. A handle that is never adopted must be
closed to avoid leaking the socket. Closing a pipe BoundSocket removes its
file system entry; abstract and TCP binds have none to remove.
When a pipe BoundSocket bound to a source path is adopted as a client, that
path is reported as the socket's localAddress once it connects.
An un-adopted TCP BoundSocket can be moved to another thread by listing it in
the transferList of a worker_threads postMessage() call, see
Transferring TCP handles to other threads. It can likewise be sent to a
child process as the sendHandle argument of subprocess.send(). In both
cases the source is left in the adopted state. Pipe binds cannot be moved
either way.
When an adopted BoundSocket connects to a numeric IP literal, connect(2) is
issued synchronously, so socket.localAddress is resolved once
socket.connect() returns. Connection failures are still reported via a
deferred 'error' event.
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.
new net.BoundSocket([options])#
optionshost'0.0.0.0', or'::'whenipv6Onlyistrue.port0requests an OS-assigned ephemeral port. Default:0.ipv6OnlyIPV6_V6ONLY, disabling dual-stack support so the socket binds IPv6 only. Only meaningful for IPv6 binds. Default:false.reusePortSO_REUSEPORT, allowing multiple sockets to bind the same address and port for kernel-level load balancing. Support is platform-dependent. Default:false.path'\0'selects the Linux abstract namespace. Mutually exclusive withhost,port,ipv6Only, andreusePort; combining them throwsERR_INVALID_ARG_VALUE.
boundSocket.address()#
- Returns:
|address,family, andportproperties, asserver.address()returns. For a pipe bind, the bound path string, asserver.address()returns for a pipe server.
Returns the bound local address. When bound with port: 0, port is the
OS-assigned ephemeral port.
boundSocket.isPipe#
true when the socket was bound with a path (a Unix domain socket or Windows
named pipe), false for a TCP bind. The getter's presence on
net.BoundSocket.prototype also serves as a capability probe for path
support.
boundSocket.fd()#
- Returns:
-1on platforms that do not expose one for sockets (such as Windows).
Returns the file descriptor of the bound socket. Ownership remains with the
BoundSocket, so the descriptor must not be closed by the caller. The
descriptor is only available before the handle is adopted; afterwards it belongs
to the adopting net.Server or net.Socket and fd() throws
ERR_SOCKET_HANDLE_ADOPTED.
boundSocket.close()#
Releases the bound socket. Only needed when the handle is never adopted.
boundSocket[Symbol.dispose]()#
Closes the handle if it has not been adopted or closed; otherwise a no-op.
net.connect()#
Aliases to
net.createConnection().
Possible signatures:
net.connect(options[, connectListener])net.connect(path[, connectListener])for IPC connections.net.connect(port[, host][, connectListener])for TCP connections.
net.connect(options[, connectListener])#
net.connect(path[, connectListener])#
net.connect(port[, host][, connectListener])#
Alias to
net.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:
net.createConnection(options[, connectListener])net.createConnection(path[, connectListener])for IPC connections.net.createConnection(port[, host][, connectListener])for TCP connections.
The net.connect() function is an alias to this function.
net.createConnection(options[, connectListener])#
optionsRequired. Will be passed to both thenew net.Socket([options])call and thesocket.connect(options[, connectListener])method.connectListenernet.createConnection()functions. If supplied, will be added as a listener for the'connect'event on the returned socket once.- Returns:
For available options, see
new net.Socket([options])
and socket.connect(options[, connectListener]).
Additional options:
handleBoundSocketused as the connection's source binding, honoring its local address and port. Adoption consumes the bound socket (see ownership transfer).timeoutsocket.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'); });
To connect on the socket /tmp/echo.sock:
const client = net.createConnection({ path: '/tmp/echo.sock' });
Following is an example of a client using the port and onread
option. In this case, the onread option will be only used to call
new net.Socket([options]) and the port option will be used to
call socket.connect(options[, connectListener]).
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)); }, }, });
net.createConnection(path[, connectListener])#
pathsocket.connect(path[, connectListener]). See Identifying paths for IPC connections.connectListenernet.createConnection()functions, an "once" listener for the'connect'event on the initiating socket. Will be passed tosocket.connect(path[, connectListener]).- Returns:
Initiates an IPC connection.
This function creates a new net.Socket with all options set to default,
immediately initiates connection with
socket.connect(path[, connectListener]),
then returns the net.Socket that starts the connection.
net.createConnection(port[, host][, connectListener])#
portsocket.connect(port[, host][, connectListener]).hostsocket.connect(port[, host][, connectListener]). Default:'localhost'.connectListenernet.createConnection()functions, an "once" listener for the'connect'event on the initiating socket. Will be passed tosocket.connect(port[, host][, connectListener]).- Returns:
Initiates a TCP connection.
This function creates a new net.Socket with all options set to default,
immediately initiates connection with
socket.connect(port[, host][, connectListener]),
then returns the net.Socket that starts the connection.
net.createServer([options][, connectionListener])#
-
allowHalfOpenfalse, then the socket will automatically end the writable side when the readable side ends. Default:false.highWaterMarknet.Sockets'readableHighWaterMarkandwritableHighWaterMark. Default: Seestream.getDefaultHighWaterMark().keepAlivetrue, it enables keep-alive functionality on the socket immediately after a new incoming connection is received, similarly on what is done insocket.setKeepAlive(). Default:false.keepAliveInitialDelay0.noDelaytrue, it disables the use of Nagle's algorithm immediately after a new incoming connection is received. Default:false.pauseOnConnectfalse.blockListblockListcan 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'connection'event.
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 packet is received, a FIN packet 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'); });
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.getDefaultAutoSelectFamily()#
Gets the current default value of the autoSelectFamily option of socket.connect(options).
The initial default value is true, unless the command line option
--no-network-family-autoselection is provided.
net.setDefaultAutoSelectFamily(value)#
Sets the default value of the autoSelectFamily option of socket.connect(options).
net.getDefaultAutoSelectFamilyAttemptTimeout()#
Gets the current default value of the autoSelectFamilyAttemptTimeout option of socket.connect(options).
The initial default value is 500 or the value specified via the command line
option --network-family-autoselection-attempt-timeout.
net.setDefaultAutoSelectFamilyAttemptTimeout(value)#
Sets the default value of the autoSelectFamilyAttemptTimeout option of socket.connect(options).
net.isIP(input)#
Returns 6 if input is an IPv6 address, including an IPv4-mapped IPv6 address.
Returns 4 if input is an IPv4 address in dot-decimal notation with no
leading zeroes. Otherwise, returns 0.
net.isIP('::1'); // returns 6
net.isIP('::ffff:127.0.0.1'); // 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
net.isIPv4(input)#
Returns true if input is an IPv4 address in dot-decimal notation with no
leading zeroes. Otherwise, returns false.
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
net.isIPv6(input)#
Returns true if input is an IPv6 address, including an IPv4-mapped IPv6 address.
Otherwise, returns false.
net.isIPv6('::1'); // returns true
net.isIPv6('::ffff:127.0.0.1'); // returns true
net.isIPv6('fhqwhgads'); // returns false