Node.js v22.0.0-nightly202312285e6448310d documentation
- Node.js v22.0.0-nightly202312285e6448310d
-
►
Table of contents
- UDP/datagram sockets
- Class:
dgram.Socket
- Event:
'close'
- Event:
'connect'
- Event:
'error'
- Event:
'listening'
- Event:
'message'
socket.addMembership(multicastAddress[, multicastInterface])
socket.addSourceSpecificMembership(sourceAddress, groupAddress[, multicastInterface])
socket.address()
socket.bind([port][, address][, callback])
socket.bind(options[, callback])
socket.close([callback])
socket[Symbol.asyncDispose]()
socket.connect(port[, address][, callback])
socket.disconnect()
socket.dropMembership(multicastAddress[, multicastInterface])
socket.dropSourceSpecificMembership(sourceAddress, groupAddress[, multicastInterface])
socket.getRecvBufferSize()
socket.getSendBufferSize()
socket.getSendQueueSize()
socket.getSendQueueCount()
socket.ref()
socket.remoteAddress()
socket.send(msg[, offset, length][, port][, address][, callback])
socket.setBroadcast(flag)
socket.setMulticastInterface(multicastInterface)
socket.setMulticastLoopback(flag)
socket.setMulticastTTL(ttl)
socket.setRecvBufferSize(size)
socket.setSendBufferSize(size)
socket.setTTL(ttl)
socket.unref()
- Event:
node:dgram
module functions
- Class:
- UDP/datagram sockets
-
►
Index
- Assertion testing
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node:module
API - Modules: Packages
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- UDP/datagram
- URL
- Utilities
- V8
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- Worker threads
- Zlib
- ► Other versions
- ► Options
UDP/datagram sockets#
Source Code: lib/dgram.js
The node:dgram
module provides an implementation of UDP datagram sockets.
import dgram from 'node:dgram';
const server = dgram.createSocket('udp4');
server.on('error', (err) => {
console.error(`server error:\n${err.stack}`);
server.close();
});
server.on('message', (msg, rinfo) => {
console.log(`server got: ${msg} from ${rinfo.address}:${rinfo.port}`);
});
server.on('listening', () => {
const address = server.address();
console.log(`server listening ${address.address}:${address.port}`);
});
server.bind(41234);
// Prints: server listening 0.0.0.0:41234
const dgram = require('node:dgram');
const server = dgram.createSocket('udp4');
server.on('error', (err) => {
console.error(`server error:\n${err.stack}`);
server.close();
});
server.on('message', (msg, rinfo) => {
console.log(`server got: ${msg} from ${rinfo.address}:${rinfo.port}`);
});
server.on('listening', () => {
const address = server.address();
console.log(`server listening ${address.address}:${address.port}`);
});
server.bind(41234);
// Prints: server listening 0.0.0.0:41234
Class: dgram.Socket
#
- Extends: <EventEmitter>
Encapsulates the datagram functionality.
New instances of dgram.Socket
are created using dgram.createSocket()
.
The new
keyword is not to be used to create dgram.Socket
instances.
Event: 'close'
#
The 'close'
event is emitted after a socket is closed with close()
.
Once triggered, no new 'message'
events will be emitted on this socket.
Event: 'connect'
#
The 'connect'
event is emitted after a socket is associated to a remote
address as a result of a successful connect()
call.
Event: 'error'
#
exception
<Error>
The 'error'
event is emitted whenever any error occurs. The event handler
function is passed a single Error
object.
Event: 'listening'
#
The 'listening'
event is emitted once the dgram.Socket
is addressable and
can receive data. This happens either explicitly with socket.bind()
or
implicitly the first time data is sent using socket.send()
.
Until the dgram.Socket
is listening, the underlying system resources do not
exist and calls such as socket.address()
and socket.setTTL()
will fail.
Event: 'message'
#
The 'message'
event is emitted when a new datagram is available on a socket.
The event handler function is passed two arguments: msg
and rinfo
.
If the source address of the incoming packet is an IPv6 link-local
address, the interface name is added to the address
. For
example, a packet received on the en0
interface might have the
address field set to 'fe80::2618:1234:ab11:3b9c%en0'
, where '%en0'
is the interface name as a zone ID suffix.
socket.addMembership(multicastAddress[, multicastInterface])
#
Tells the kernel to join a multicast group at the given multicastAddress
and
multicastInterface
using the IP_ADD_MEMBERSHIP
socket option. If the
multicastInterface
argument is not specified, the operating system will choose
one interface and will add membership to it. To add membership to every
available interface, call addMembership
multiple times, once per interface.
When called on an unbound socket, this method will implicitly bind to a random port, listening on all interfaces.
When sharing a UDP socket across multiple cluster
workers, the
socket.addMembership()
function must be called only once or an
EADDRINUSE
error will occur:
import cluster from 'node:cluster';
import dgram from 'node:dgram';
if (cluster.isPrimary) {
cluster.fork(); // Works ok.
cluster.fork(); // Fails with EADDRINUSE.
} else {
const s = dgram.createSocket('udp4');
s.bind(1234, () => {
s.addMembership('224.0.0.114');
});
}
const cluster = require('node:cluster');
const dgram = require('node:dgram');
if (cluster.isPrimary) {
cluster.fork(); // Works ok.
cluster.fork(); // Fails with EADDRINUSE.
} else {
const s = dgram.createSocket('udp4');
s.bind(1234, () => {
s.addMembership('224.0.0.114');
});
}
socket.addSourceSpecificMembership(sourceAddress, groupAddress[, multicastInterface])
#
Tells the kernel to join a source-specific multicast channel at the given
sourceAddress
and groupAddress
, using the multicastInterface
with the
IP_ADD_SOURCE_MEMBERSHIP
socket option. If the multicastInterface
argument
is not specified, the operating system will choose one interface and will add
membership to it. To add membership to every available interface, call
socket.addSourceSpecificMembership()
multiple times, once per interface.
When called on an unbound socket, this method will implicitly bind to a random port, listening on all interfaces.
socket.address()
#
- Returns: <Object>
Returns an object containing the address information for a socket.
For UDP sockets, this object will contain address
, family
, and port
properties.
This method throws EBADF
if called on an unbound socket.
socket.bind([port][, address][, callback])
#
port
<integer>address
<string>callback
<Function> with no parameters. Called when binding is complete.
For UDP sockets, causes the dgram.Socket
to listen for datagram
messages on a named port
and optional address
. If port
is not
specified or is 0
, the operating system will attempt to bind to a
random port. If address
is not specified, the operating system will
attempt to listen on all addresses. Once binding is complete, a
'listening'
event is emitted and the optional callback
function is
called.
Specifying both a 'listening'
event listener and passing a
callback
to the socket.bind()
method is not harmful but not very
useful.
A bound datagram socket keeps the Node.js process running to receive datagram messages.
If binding fails, an 'error'
event is generated. In rare case (e.g.
attempting to bind with a closed socket), an Error
may be thrown.
Example of a UDP server listening on port 41234:
import dgram from 'node:dgram';
const server = dgram.createSocket('udp4');
server.on('error', (err) => {
console.error(`server error:\n${err.stack}`);
server.close();
});
server.on('message', (msg, rinfo) => {
console.log(`server got: ${msg} from ${rinfo.address}:${rinfo.port}`);
});
server.on('listening', () => {
const address = server.address();
console.log(`server listening ${address.address}:${address.port}`);
});
server.bind(41234);
// Prints: server listening 0.0.0.0:41234
const dgram = require('node:dgram');
const server = dgram.createSocket('udp4');
server.on('error', (err) => {
console.error(`server error:\n${err.stack}`);
server.close();
});
server.on('message', (msg, rinfo) => {
console.log(`server got: ${msg} from ${rinfo.address}:${rinfo.port}`);
});
server.on('listening', () => {
const address = server.address();
console.log(`server listening ${address.address}:${address.port}`);
});
server.bind(41234);
// Prints: server listening 0.0.0.0:41234
socket.bind(options[, callback])
#
options
<Object> Required. Supports the following properties:callback
<Function>
For UDP sockets, causes the dgram.Socket
to listen for datagram
messages on a named port
and optional address
that are passed as
properties of an options
object passed as the first argument. If
port
is not specified or is 0
, the operating system will attempt
to bind to a random port. If address
is not specified, the operating
system will attempt to listen on all addresses. Once binding is
complete, a 'listening'
event is emitted and the optional callback
function is called.
The options
object may contain a fd
property. When a fd
greater
than 0
is set, it will wrap around an existing socket with the given
file descriptor. In this case, the properties of port
and address
will be ignored.
Specifying both a 'listening'
event listener and passing a
callback
to the socket.bind()
method is not harmful but not very
useful.
The options
object may contain an additional exclusive
property that is
used when using dgram.Socket
objects with the cluster
module. When
exclusive
is set to false
(the default), cluster workers will use the same
underlying socket handle allowing connection handling duties to be shared.
When exclusive
is true
, however, the handle is not shared and attempted
port sharing results in an error.
A bound datagram socket keeps the Node.js process running to receive datagram messages.
If binding fails, an 'error'
event is generated. In rare case (e.g.
attempting to bind with a closed socket), an Error
may be thrown.
An example socket listening on an exclusive port is shown below.
socket.bind({
address: 'localhost',
port: 8000,
exclusive: true,
});
socket.close([callback])
#
callback
<Function> Called when the socket has been closed.
Close the underlying socket and stop listening for data on it. If a callback is
provided, it is added as a listener for the 'close'
event.
socket[Symbol.asyncDispose]()
#
Calls socket.close()
and returns a promise that fulfills when the
socket has closed.
socket.connect(port[, address][, callback])
#
port
<integer>address
<string>callback
<Function> Called when the connection is completed or on error.
Associates the dgram.Socket
to a remote address and port. Every
message sent by this handle is automatically sent to that destination. Also,
the socket will only receive messages from that remote peer.
Trying to call connect()
on an already connected socket will result
in an ERR_SOCKET_DGRAM_IS_CONNECTED
exception. If address
is not
provided, '127.0.0.1'
(for udp4
sockets) or '::1'
(for udp6
sockets)
will be used by default. Once the connection is complete, a 'connect'
event
is emitted and the optional callback
function is called. In case of failure,
the callback
is called or, failing this, an 'error'
event is emitted.
socket.disconnect()
#
A synchronous function that disassociates a connected dgram.Socket
from
its remote address. Trying to call disconnect()
on an unbound or already
disconnected socket will result in an ERR_SOCKET_DGRAM_NOT_CONNECTED
exception.
socket.dropMembership(multicastAddress[, multicastInterface])
#
Instructs the kernel to leave a multicast group at multicastAddress
using the
IP_DROP_MEMBERSHIP
socket option. This method is automatically called by the
kernel when the socket is closed or the process terminates, so most apps will
never have reason to call this.
If multicastInterface
is not specified, the operating system will attempt to
drop membership on all valid interfaces.
socket.dropSourceSpecificMembership(sourceAddress, groupAddress[, multicastInterface])
#
Instructs the kernel to leave a source-specific multicast channel at the given
sourceAddress
and groupAddress
using the IP_DROP_SOURCE_MEMBERSHIP
socket option. This method is automatically called by the kernel when the
socket is closed or the process terminates, so most apps will never have
reason to call this.
If multicastInterface
is not specified, the operating system will attempt to
drop membership on all valid interfaces.
socket.getRecvBufferSize()
#
- Returns: <number> the
SO_RCVBUF
socket receive buffer size in bytes.
This method throws ERR_SOCKET_BUFFER_SIZE
if called on an unbound socket.
socket.getSendBufferSize()
#
- Returns: <number> the
SO_SNDBUF
socket send buffer size in bytes.
This method throws ERR_SOCKET_BUFFER_SIZE
if called on an unbound socket.
socket.getSendQueueSize()
#
- Returns: <number> Number of bytes queued for sending.
socket.getSendQueueCount()
#
- Returns: <number> Number of send requests currently in the queue awaiting to be processed.
socket.ref()
#
- Returns: <dgram.Socket>
By default, binding a socket will cause it to block the Node.js process from
exiting as long as the socket is open. The socket.unref()
method can be used
to exclude the socket from the reference counting that keeps the Node.js
process active. The socket.ref()
method adds the socket back to the reference
counting and restores the default behavior.
Calling socket.ref()
multiples times will have no additional effect.
The socket.ref()
method returns a reference to the socket so calls can be
chained.
socket.remoteAddress()
#
- Returns: <Object>
Returns an object containing the address
, family
, and port
of the remote
endpoint. This method throws an ERR_SOCKET_DGRAM_NOT_CONNECTED
exception
if the socket is not connected.
socket.send(msg[, offset, length][, port][, address][, callback])
#
msg
<Buffer> | <TypedArray> | <DataView> | <string> | <Array> Message to be sent.offset
<integer> Offset in the buffer where the message starts.length
<integer> Number of bytes in the message.port
<integer> Destination port.address
<string> Destination host name or IP address.callback
<Function> Called when the message has been sent.
Broadcasts a datagram on the socket.
For connectionless sockets, the destination port
and address
must be
specified. Connected sockets, on the other hand, will use their associated
remote endpoint, so the port
and address
arguments must not be set.
The msg
argument contains the message to be sent.
Depending on its type, different behavior can apply. If msg
is a Buffer
,
any TypedArray
or a DataView
,
the offset
and length
specify the offset within the Buffer
where the
message begins and the number of bytes in the message, respectively.
If msg
is a String
, then it is automatically converted to a Buffer
with 'utf8'
encoding. With messages that
contain multi-byte characters, offset
and length
will be calculated with
respect to byte length and not the character position.
If msg
is an array, offset
and length
must not be specified.
The address
argument is a string. If the value of address
is a host name,
DNS will be used to resolve the address of the host. If address
is not
provided or otherwise nullish, '127.0.0.1'
(for udp4
sockets) or '::1'
(for udp6
sockets) will be used by default.
If the socket has not been previously bound with a call to bind
, the socket
is assigned a random port number and is bound to the "all interfaces" address
('0.0.0.0'
for udp4
sockets, '::0'
for udp6
sockets.)
An optional callback
function may be specified to as a way of reporting
DNS errors or for determining when it is safe to reuse the buf
object.
DNS lookups delay the time to send for at least one tick of the
Node.js event loop.
The only way to know for sure that the datagram has been sent is by using a
callback
. If an error occurs and a callback
is given, the error will be
passed as the first argument to the callback
. If a callback
is not given,
the error is emitted as an 'error'
event on the socket
object.
Offset and length are optional but both must be set if either are used.
They are supported only when the first argument is a Buffer
, a TypedArray
,
or a DataView
.
This method throws ERR_SOCKET_BAD_PORT
if called on an unbound socket.
Example of sending a UDP packet to a port on localhost
;
import dgram from 'node:dgram';
import { Buffer } from 'node:buffer';
const message = Buffer.from('Some bytes');
const client = dgram.createSocket('udp4');
client.send(message, 41234, 'localhost', (err) => {
client.close();
});
const dgram = require('node:dgram');
const { Buffer } = require('node:buffer');
const message = Buffer.from('Some bytes');
const client = dgram.createSocket('udp4');
client.send(message, 41234, 'localhost', (err) => {
client.close();
});
Example of sending a UDP packet composed of multiple buffers to a port on
127.0.0.1
;
import dgram from 'node:dgram';
import { Buffer } from 'node:buffer';
const buf1 = Buffer.from('Some ');
const buf2 = Buffer.from('bytes');
const client = dgram.createSocket('udp4');
client.send([buf1, buf2], 41234, (err) => {
client.close();
});
const dgram = require('node:dgram');
const { Buffer } = require('node:buffer');
const buf1 = Buffer.from('Some ');
const buf2 = Buffer.from('bytes');
const client = dgram.createSocket('udp4');
client.send([buf1, buf2], 41234, (err) => {
client.close();
});
Sending multiple buffers might be faster or slower depending on the application and operating system. Run benchmarks to determine the optimal strategy on a case-by-case basis. Generally speaking, however, sending multiple buffers is faster.
Example of sending a UDP packet using a socket connected to a port on
localhost
:
import dgram from 'node:dgram';
import { Buffer } from 'node:buffer';
const message = Buffer.from('Some bytes');
const client = dgram.createSocket('udp4');
client.connect(41234, 'localhost', (err) => {
client.send(message, (err) => {
client.close();
});
});
const dgram = require('node:dgram');
const { Buffer } = require('node:buffer');
const message = Buffer.from('Some bytes');
const client = dgram.createSocket('udp4');
client.connect(41234, 'localhost', (err) => {
client.send(message, (err) => {
client.close();
});
});
Note about UDP datagram size#
The maximum size of an IPv4/v6 datagram depends on the MTU
(Maximum Transmission Unit) and on the Payload Length
field size.
-
The
Payload Length
field is 16 bits wide, which means that a normal payload cannot exceed 64K octets including the internet header and data (65,507 bytes = 65,535 − 8 bytes UDP header − 20 bytes IP header); this is generally true for loopback interfaces, but such long datagram messages are impractical for most hosts and networks. -
The
MTU
is the largest size a given link layer technology can support for datagram messages. For any link, IPv4 mandates a minimumMTU
of 68 octets, while the recommendedMTU
for IPv4 is 576 (typically recommended as theMTU
for dial-up type applications), whether they arrive whole or in fragments.For IPv6, the minimum
MTU
is 1280 octets. However, the mandatory minimum fragment reassembly buffer size is 1500 octets. The value of 68 octets is very small, since most current link layer technologies, like Ethernet, have a minimumMTU
of 1500.
It is impossible to know in advance the MTU of each link through which
a packet might travel. Sending a datagram greater than the receiver MTU
will
not work because the packet will get silently dropped without informing the
source that the data did not reach its intended recipient.
socket.setBroadcast(flag)
#
flag
<boolean>
Sets or clears the SO_BROADCAST
socket option. When set to true
, UDP
packets may be sent to a local interface's broadcast address.
This method throws EBADF
if called on an unbound socket.
socket.setMulticastInterface(multicastInterface)
#
multicastInterface
<string>
All references to scope in this section are referring to
IPv6 Zone Indices, which are defined by RFC 4007. In string form, an IP
with a scope index is written as 'IP%scope'
where scope is an interface name
or interface number.
Sets the default outgoing multicast interface of the socket to a chosen
interface or back to system interface selection. The multicastInterface
must
be a valid string representation of an IP from the socket's family.
For IPv4 sockets, this should be the IP configured for the desired physical interface. All packets sent to multicast on the socket will be sent on the interface determined by the most recent successful use of this call.
For IPv6 sockets, multicastInterface
should include a scope to indicate the
interface as in the examples that follow. In IPv6, individual send
calls can
also use explicit scope in addresses, so only packets sent to a multicast
address without specifying an explicit scope are affected by the most recent
successful use of this call.
This method throws EBADF
if called on an unbound socket.
Example: IPv6 outgoing multicast interface#
On most systems, where scope format uses the interface name:
const socket = dgram.createSocket('udp6');
socket.bind(1234, () => {
socket.setMulticastInterface('::%eth1');
});
On Windows, where scope format uses an interface number:
const socket = dgram.createSocket('udp6');
socket.bind(1234, () => {
socket.setMulticastInterface('::%2');
});
Example: IPv4 outgoing multicast interface#
All systems use an IP of the host on the desired physical interface:
const socket = dgram.createSocket('udp4');
socket.bind(1234, () => {
socket.setMulticastInterface('10.0.0.2');
});
Call results#
A call on a socket that is not ready to send or no longer open may throw a Not
running Error
.
If multicastInterface
can not be parsed into an IP then an EINVAL
System Error
is thrown.
On IPv4, if multicastInterface
is a valid address but does not match any
interface, or if the address does not match the family then
a System Error
such as EADDRNOTAVAIL
or EPROTONOSUP
is thrown.
On IPv6, most errors with specifying or omitting scope will result in the socket continuing to use (or returning to) the system's default interface selection.
A socket's address family's ANY address (IPv4 '0.0.0.0'
or IPv6 '::'
) can be
used to return control of the sockets default outgoing interface to the system
for future multicast packets.
socket.setMulticastLoopback(flag)
#
flag
<boolean>
Sets or clears the IP_MULTICAST_LOOP
socket option. When set to true
,
multicast packets will also be received on the local interface.
This method throws EBADF
if called on an unbound socket.
socket.setMulticastTTL(ttl)
#
ttl
<integer>
Sets the IP_MULTICAST_TTL
socket option. While TTL generally stands for
"Time to Live", in this context it specifies the number of IP hops that a
packet is allowed to travel through, specifically for multicast traffic. Each
router or gateway that forwards a packet decrements the TTL. If the TTL is
decremented to 0 by a router, it will not be forwarded.
The ttl
argument may be between 0 and 255. The default on most systems is 1
.
This method throws EBADF
if called on an unbound socket.
socket.setRecvBufferSize(size)
#
size
<integer>
Sets the SO_RCVBUF
socket option. Sets the maximum socket receive buffer
in bytes.
This method throws ERR_SOCKET_BUFFER_SIZE
if called on an unbound socket.
socket.setSendBufferSize(size)
#
size
<integer>
Sets the SO_SNDBUF
socket option. Sets the maximum socket send buffer
in bytes.
This method throws ERR_SOCKET_BUFFER_SIZE
if called on an unbound socket.
socket.setTTL(ttl)
#
ttl
<integer>
Sets the IP_TTL
socket option. While TTL generally stands for "Time to Live",
in this context it specifies the number of IP hops that a packet is allowed to
travel through. Each router or gateway that forwards a packet decrements the
TTL. If the TTL is decremented to 0 by a router, it will not be forwarded.
Changing TTL values is typically done for network probes or when multicasting.
The ttl
argument may be between 1 and 255. The default on most systems
is 64.
This method throws EBADF
if called on an unbound socket.
socket.unref()
#
- Returns: <dgram.Socket>
By default, binding a socket will cause it to block the Node.js process from
exiting as long as the socket is open. The socket.unref()
method can be used
to exclude the socket from the reference counting that keeps the Node.js
process active, allowing the process to exit even if the socket is still
listening.
Calling socket.unref()
multiple times will have no additional effect.
The socket.unref()
method returns a reference to the socket so calls can be
chained.
node:dgram
module functions#
dgram.createSocket(options[, callback])
#
options
<Object> Available options are:type
<string> The family of socket. Must be either'udp4'
or'udp6'
. Required.reuseAddr
<boolean> Whentrue
socket.bind()
will reuse the address, even if another process has already bound a socket on it. Default:false
.ipv6Only
<boolean> Settingipv6Only
totrue
will disable dual-stack support, i.e., binding to address::
won't make0.0.0.0
be bound. Default:false
.recvBufferSize
<number> Sets theSO_RCVBUF
socket value.sendBufferSize
<number> Sets theSO_SNDBUF
socket value.lookup
<Function> Custom lookup function. Default:dns.lookup()
.signal
<AbortSignal> An AbortSignal that may be used to close a socket.
callback
<Function> Attached as a listener for'message'
events. Optional.- Returns: <dgram.Socket>
Creates a dgram.Socket
object. Once the socket is created, calling
socket.bind()
will instruct the socket to begin listening for datagram
messages. When address
and port
are not passed to socket.bind()
the
method will bind the socket to the "all interfaces" address on a random port
(it does the right thing for both udp4
and udp6
sockets). The bound address
and port can be retrieved using socket.address().address
and
socket.address().port
.
If the signal
option is enabled, calling .abort()
on the corresponding
AbortController
is similar to calling .close()
on the socket:
const controller = new AbortController();
const { signal } = controller;
const server = dgram.createSocket({ type: 'udp4', signal });
server.on('message', (msg, rinfo) => {
console.log(`server got: ${msg} from ${rinfo.address}:${rinfo.port}`);
});
// Later, when you want to close the server.
controller.abort();
dgram.createSocket(type[, callback])
#
type
<string> Either'udp4'
or'udp6'
.callback
<Function> Attached as a listener to'message'
events.- Returns: <dgram.Socket>
Creates a dgram.Socket
object of the specified type
.
Once the socket is created, calling socket.bind()
will instruct the
socket to begin listening for datagram messages. When address
and port
are
not passed to socket.bind()
the method will bind the socket to the "all
interfaces" address on a random port (it does the right thing for both udp4
and udp6
sockets). The bound address and port can be retrieved using
socket.address().address
and socket.address().port
.