@ -4,50 +4,62 @@
<!-- name=dgram -->
Datagram sockets are available through `require('dgram')` .
The `dgram` module provides an implementation of UDP Datagram sockets .
Important note: the behavior of [`dgram.Socket#bind()`][] has changed in v0.10
and is always asynchronous now. If you have code that looks like this:
const dgram = require('dgram');
const server = dgram.createSocket('udp4');
const s = dgram.createSocket('udp4');
s.bind(1234);
s.addMembership('224.0.0.114');
server.on('error', (err) => {
console.log(`server error:\n${err.stack}`);
server.close();
});
You have to change it to this:
server.on('message', (msg, rinfo) => {
console.log(`server got: ${msg} from ${rinfo.address}:${rinfo.port}`);
});
const s = dgram.createSocket('udp4');
s.bind(1234, () => {
s.addMembership('224.0.0.114' );
server.on('listening', () => {
var address = server.address();
console.log(`server listening ${address.address}:${address.port}` );
});
server.bind(41234);
// server listening 0.0.0.0:41234
## Class: dgram.Socket
The dgram Socket class encapsulates the datagram functionality. It
should be created via [`dgram.createSocket(...)`][]
The `dgram.Socket` object is an [`EventEmitter`][] that 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'
Emitted after a socket is closed with [`close()`][]. No new `'message'` events will be emitted
on this socket.
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: 'error'
* `exception` Error object
Emitted when an error occurs.
The `'error'` event is emitted whenever any error occurs. The event handler
function is passed a single Error object.
### Event: 'listening'
Emitted when a socket starts listening for datagrams. This happens as soon as UDP sockets
are created.
The `'listening'` event is emitted whenever a socket begins listening for
datagram messages. This occurs as soon as UDP sockets are created.
### Event: 'message'
* `msg` Buffer object. The message
* `rinfo` Object. Remote address information
Emitted when a new datagram is available on a socket. `msg` is a `Buffer` and
`rinfo` is an object with the sender's address information:
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` . The
`msg` argument is a [`Buffer`][] and `rinfo` is an object with the sender's
address information provided by the `address` , `family` and `port` properties:
socket.on('message', (msg, rinfo) => {
console.log('Received %d bytes from %s:%d\n',
@ -59,41 +71,44 @@ Emitted when a new datagram is available on a socket. `msg` is a `Buffer` and
* `multicastAddress` String
* `multicastInterface` String, Optional
Tells the kernel to join a multicast group with `IP_ADD_MEMBERSHIP` socket option.
If `multicastInterface` is not specified, the OS will try to add membership to all valid
interfaces.
Tells the kernel to join a multicast group at the given `multicastAddress`
using the `IP_ADD_MEMBERSHIP` socket option. If the `multicastInterface`
argument is not specified, the operating system will try to add membership to
all valid networking interfaces.
### socket.address()
Returns an object containing the address information for a socket. For UDP sockets,
this object will contain `address` , `family` and `port` .
Returns an object containing the address information for a socket.
For UDP sockets, this object will contain `address` , `family` and `port`
properties.
### socket.bind([port][, address][, callback])
### [ socket.bind([port][, address][, callback])]
* `port` Integer, Optional
* `address` String, Optional
* `callback` Function with no parameters, Optional. Callback when
binding is done.
For UDP sockets, listen for datagrams on a named `port` and optional
`address` . If `port` is not specified, the OS will try to bind to a random
port. If `address` is not specified, the OS will try to listen on
all addresses. After binding is done, a `'listening'` event is emitted
and the `callback` (if specified) is called. Specifying both a
`'listening'` event listener and `callback` is not harmful but not very
* `callback` Function with no parameters, Optional. 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, 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.
Note that 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
datagrams.
datagram message s.
If binding fails, an `'error'` event is generated. In rare case (e.g.
binding a closed socket), an [`Error`][] may be thrown by this method .
attempting to bind with a closed socket), an [`Error`][] may be thrown .
Example of a UDP server listening on port 41234:
const dgram = require('dgram');
const server = dgram.createSocket('udp4');
server.on('error', (err) => {
@ -121,15 +136,22 @@ Example of a UDP server listening on port 41234:
* `exclusive` {Boolean} - Optional.
* `callback` {Function} - Optional.
The `port` and `address` properties of `options` , as well as the optional
callback function, behave as they do on a call to
[`socket.bind(port, \[address\], \[callback\])`][].
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, 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 an additional `exclusive` property that is
use 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.
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.
An example socket listening on an exclusive port is shown below.
socket.bind({
address: 'localhost',
@ -147,13 +169,13 @@ provided, it is added as a listener for the [`'close'`][] event.
* `multicastAddress` String
* `multicastInterface` String, Optional
Opposite of [`addMembership()`][] - tells the kernel to leave a multicast group with
`IP_DROP_MEMBERSHIP` socket option. This is automatically called by the kernel
when the socket is closed or process terminates, so most apps will never need to call
this.
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 OS will try to drop membership to all valid
interfaces.
If `multicastInterface` is not specified, the operating system will attempt to
drop membership on all valid interfaces.
### socket.send(buf, offset, length, port, address[, callback])
@ -164,26 +186,35 @@ interfaces.
* `address` String. Destination hostname or IP address.
* `callback` Function. Called when the message has been sent. Optional.
For UDP sockets, the destination port and address must be specified. A string
may be supplied for the `address` parameter, and it will be resolved with DNS .
Broadcasts a datagram on the socket. The destination `port` and `address` must
be specified .
If the address is omitted or is an empty string, `'0.0.0.0'` or `'::0'` is used
instead. Depending on the network configuration, those defaults may or may not
work; it's best to be explicit about the destination address.
The `buf` argument is a [`Buffer`] object containing the message. The `offset`
and `length` specify the offset within the `Buffer` where the message begins
and the number of bytes in the message, respectively. With messages that
contain multi-byte characters, `offset` and `length` will be calculated with
respect to [byte length][] and not the character position.
If the socket has not been previously bound with a call to `bind` , it gets
assigned a random port number and is bound to the "all interfaces" address
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 the `address` is not
specified or is an empty string, `'0.0.0.0'` or `'::0'` will be used instead.
It is possible, depending on the network configuration, that these defaults
may not work; accordingly, it is best to be explicit about the destination
address.
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 may be specified to detect DNS errors or for determining
when it's safe to reuse the `buf` object. Note that DNS lookups delay the time
to send for at least one tick. 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 the first argument to the callback. If a callback is
not given, the error is emitted as an `'error'` event on the `socket` object.
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.
Note that DNS lookups delay the time to send for at least one tick of the
Node.js event loop.
With consideration for multi-byte characters, `offset` and `length` will
be calculated with respect to [byte length][] and not the character position.
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.
Example of sending a UDP packet to a random port on `localhost` ;
@ -196,103 +227,137 @@ Example of sending a UDP packet to a random port on `localhost`;
**A 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 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 be larger than 64K octets including internet header and data
- The `Payload Length` field is `16 bits` wide, which means that a normal
payload 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 datagrams
are impractical for most hosts and networks.
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 datagrams.
For any link, `IPv4` mandates a minimum `MTU` of `68` octets, while the recommended `MTU`
for IPv4 is `576` (typically recommended as the `MTU` for dial-up type applications),
whether they arrive whole or in fragments.
- The `MTU` is the largest size a given link layer technology can support for
datagram messages. For any link, `IPv4` mandates a minimum `MTU` of `68`
octets, while the recommended `MTU` for IPv4 is `576` (typically recommended
as the `MTU` 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 have
a minimum `MTU` of `1500` (like Ethernet) .
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
minimum `MTU` of `1500` .
Note that it' s impossible to know in advance the MTU of each link through which
a packet might travel, and that generally sending a datagram greater than
the (receiver) `MTU` won't work (the packet gets silently dropped, without
informing the source that the data did not reach its intended recipient) .
It i s 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 this option is set, UDP packets
may be sent to a local interface's broadcast address.
Sets or clears the `SO_BROADCAST` socket option. When set to `true` , UDP
packets may be sent to a local interface's broadcast address.
### socket.setMulticastLoopback(flag)
* `flag` Boolean
Sets or clears the `IP_MULTICAST_LOOP` socket option. When this option is set, multicast
packets will also be received on the local interface.
Sets or clears the `IP_MULTICAST_LOOP` socket option. When set to `true` ,
multicast packets will also be received on the local interface.
### socket.setMulticastTTL(ttl)
* `ttl` Integer
Sets the `IP_MULTICAST_TTL` socket option. TTL stands for "Time to Live", but in this
context it specifies the number of IP hops that a packet is allowed to go 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.
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 argument to `setMulticastTTL()` is a number of hops between 0 and 255. The default on most
systems is 1.
The argument passed to to `socket. setMulticastTTL()` is a number of hops
between 0 and 255. The default on most systems is ` 1` but can vary
### socket.setTTL(ttl)
* `ttl` Integer
Sets the `IP_TTL` socket option. TTL stands for "Time to Live", but in this context it
specifies the number of IP hops that a packet is allowed to go 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.
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 argument to `setTTL()` is a number of hops between 1 and 255. The default
on most systems is 64.
The argument to `socket.s etTTL()` is a number of hops between 1 and 255.
The default on most systems is 64 but can vary .
### socket.ref()
Opposite of `unref` , calling `ref` on a previously `unref` d socket will *not*
let the program exit if it's the only socket left (the default behavior). If
the socket is `ref` d calling `ref` again will have no effect.
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.
Returns `socket` .
The `socket.ref()` method returns a reference to the socket so calls can be
chained.
### 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 `unref` d calling
`unref` again will have no effect.
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 addition effect.
Returns `socket` .
The `socket.unref()` method returns a reference to the socket so calls can be
chained.
## dgram.createSocket(options[, callback])
### Change to asynchronous `socket.bind()` behavior
As of Node.js v0.10, [`dgram.Socket#bind()`][] changed to an asynchronous
execution model. Legacy code that assumes synchronous behavior, as in the
following example:
const s = dgram.createSocket('udp4');
s.bind(1234);
s.addMembership('224.0.0.114');
Must be changed to pass a callback function to the [`dgram.Socket#bind()`][]
function:
const s = dgram.createSocket('udp4');
s.bind(1234, () => {
s.addMembership('224.0.0.114');
});
## `dgram` module functions
### dgram.createSocket(options[, callback])
* `options` Object
* `callback` Function. Attached as a listener to `'message'` events.
* Returns: Socket object
The `options` object should contain a `type` field of either `udp4` or `udp6`
and an optional boolean `reuseAddr` field.
Creates a `dgram.Socket` object. The `options` argument is an object that
should contain a `type` field of either `udp4` or `udp6` and an optional
boolean `reuseAddr` field.
When `reuseAddr` is `true` [`socket.bind()`][] will reuse the address, even if
another process has already bound a socket on it. `reuseAddr` defaults to
`false` .
`false` . An optional `callback` function can be passed specified which is added
as a listener for `'message'` events.
Takes an optional callback which is added as a listener for `'message'` events.
Call [`socket.bind()`][] if you want to receive datagrams. [`socket.bind()`][] will
bind to the "all interfaces" address on a random port (it does the right thing
for both `udp4` and `udp6` sockets). You can then retrieve the address and port
with [`socket.address().address`][] and [`socket.address().port`][].
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 "a ll
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`][].
## dgram.createSocket(type[, callback])
@ -301,24 +366,26 @@ with [`socket.address().address`][] and [`socket.address().port`][].
Optional
* Returns: Socket object
Creates a datagram Socket of the specified types. Valid types are `udp4`
and `udp6` .
Takes an optional callback which is added as a listener for `'message'` events.
Creates a `dgram.Socket` object of the specified `type` . The `type` argument
can be either `udp4` or `udp6` . An optional `callback` function can be passed
which is added as a listener for `'message'` events.
Call [`socket.bind()`][] if you want to receive datagrams. [`socket.bind()`][] will
bind to the "all interfaces" address on a random port (it does the right thing
for both `udp4` and `udp6` sockets). You can then retrieve the address and port
with [`socket.address().address`][] and [`socket.address().port`][].
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`][].
[`EventEmitter`]: events.html
[`Buffer`]: buffer.html
[`'close'`]: #dgram_event_close
[`addMembership()`]: #dgram_socket_addmembership_multicastaddress_multicastinterface
[`close()`]: #dgram_socket_close_callback
[`dgram.createSocket(... )`]: #dgram_dgram_createsocket_options_callback
[`dgram.createSocket()`]: #dgram_dgram_createsocket_options_callback
[`dgram.Socket#bind()`]: #dgram_socket_bind_options_callback
[`Error`]: errors.html#errors_class_error
[`socket.address().address`]: #dgram_socket_address
[`socket.address().port`]: #dgram_socket_address
[`socket.bind()`]: #dgram_socket_bind_port_address_callback
[`socket.bind(port, \[address\], \[callback\])`]: #dgram_socket_bind_port_address_callback
[byte length]: buffer.html#buffer_class_method_buffer_bytelength_string_encoding
James M Snell
9 years ago
Jeremiah Senkpiel