Node.js v0.8.24 Manual & Documentation
Table of Contents
- UDP / Datagram Sockets
- dgram.createSocket(type, [callback])
- Class: Socket
- Event: 'message'
- Event: 'listening'
- Event: 'close'
- Event: 'error'
- dgram.send(buf, offset, length, port, address, [callback])
- dgram.bind(port, [address])
- dgram.close()
- dgram.address()
- dgram.setBroadcast(flag)
- dgram.setTTL(ttl)
- dgram.setMulticastTTL(ttl)
- dgram.setMulticastLoopback(flag)
- dgram.addMembership(multicastAddress, [multicastInterface])
- dgram.dropMembership(multicastAddress, [multicastInterface])
UDP / Datagram Sockets#
Stability: 3 - Stable
Datagram sockets are available through require('dgram')
.
dgram.createSocket(type, [callback])#
type
String. Either 'udp4' or 'udp6'callback
Function. Attached as a listener tomessage
events. 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.
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
.
Class: Socket#
The dgram Socket class encapsulates the datagram functionality. It
should be created via dgram.createSocket(type, [callback])
.
Event: 'message'#
msg
Buffer object. The messagerinfo
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 and the number of bytes in the datagram.
Event: 'listening'#
Emitted when a socket starts listening for datagrams. This happens as soon as UDP sockets are created.
Event: 'close'#
Emitted when a socket is closed with close()
. No new message
events will be emitted
on this socket.
Event: 'error'#
exception
Error object
Emitted when an error occurs.
dgram.send(buf, offset, length, port, address, [callback])#
buf
Buffer object. Message to be sentoffset
Integer. Offset in the buffer where the message starts.length
Integer. Number of bytes in the message.port
Integer. destination portaddress
String. destination IPcallback
Function. Callback when message is done being delivered. Optional.
For UDP sockets, the destination port and IP address must be specified. A string
may be supplied for the address
parameter, and it will be resolved with DNS. An
optional callback may be specified to detect any DNS errors and when buf
may be
re-used. Note that DNS lookups will delay the time that a send takes place, at
least until the next tick. The only way to know for sure that a send has taken place
is to use the callback.
If the socket has not been previously bound with a call to bind
, it's
assigned a random port number and bound to the "all interfaces" address
(0.0.0.0 for udp4
sockets, ::0 for udp6
sockets).
Example of sending a UDP packet to a random port on localhost
;
var dgram = require('dgram');
var message = new Buffer("Some bytes");
var client = dgram.createSocket("udp4");
client.send(message, 0, message.length, 41234, "localhost", function(err, bytes) {
client.close();
});
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
Payload Length
field is16 bits
wide, which means that a normal payload cannot be larger than 64K octets including 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.The
MTU
is the largest size a given link layer technology can support for datagrams. For any link,IPv4
mandates a minimumMTU
of68
octets, while the recommendedMTU
for IPv4 is576
(typically recommended as theMTU
for dial-up type applications), whether they arrive whole or in fragments.For
IPv6
, the minimumMTU
is1280
octets, however, the mandatory minimum fragment reassembly buffer size is1500
octets. The value of68
octets is very small, since most current link layer technologies have a minimumMTU
of1500
(like Ethernet).
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).
dgram.bind(port, [address])#
port
Integeraddress
String, Optional
For UDP sockets, listen for datagrams on a named port
and optional address
. If
address
is not specified, the OS will try to listen on all addresses.
Example of a UDP server listening on port 41234:
var dgram = require("dgram");
var server = dgram.createSocket("udp4");
server.on("message", function (msg, rinfo) {
console.log("server got: " + msg + " from " +
rinfo.address + ":" + rinfo.port);
});
server.on("listening", function () {
var address = server.address();
console.log("server listening " +
address.address + ":" + address.port);
});
server.bind(41234);
// server listening 0.0.0.0:41234
dgram.close()#
Close the underlying socket and stop listening for data on it.
dgram.address()#
Returns an object containing the address information for a socket. For UDP sockets,
this object will contain address
, family
and port
.
dgram.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.
dgram.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.
The argument to setTTL()
is a number of hops between 1 and 255. The default on most
systems is 64.
dgram.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.
The argument to setMulticastTTL()
is a number of hops between 0 and 255. The default on most
systems is 1.
dgram.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.
dgram.addMembership(multicastAddress, [multicastInterface])#
multicastAddress
StringmulticastInterface
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.
dgram.dropMembership(multicastAddress, [multicastInterface])#
multicastAddress
StringmulticastInterface
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.
If multicastInterface
is not specified, the OS will try to drop membership to all valid
interfaces.