# Dgram : UDP network module

This module provides dgram operations compatible with Node.js.

User can use the following code to import the dgram module.

var dgram = require('dgram');

# Support

The following shows dgram module APIs available for each permissions.

# Dgram.Socket Class

# dgram.createSocket(options[, callback])

• options {Object} Options.
• callback {Function} Attached as a listener for 'message' events. Optional.
• Returns: {Object} dgram.Socket object.

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.

options can contain the following members:

• type {String} The family of socket. Must be either 'udp4' or 'udp6'. Required.
• fd {Integer} Use this file descriptor to create.
• reuseAddr {Boolean} When true socket.bind() will reuse the address, even if another process has already bound a socket on it. default: false.
• ipv6Only {Boolean} Setting ipv6Only to true will disable dual-stack support, i.e., binding to address :: won't make 0.0.0.0 be bound. default: false.
• recvBufferSize {Integer} Sets the SO_RCVBUF socket value.
• sendBufferSize {Integer} Sets the SO_SNDBUF socket value.
• lookup {Function} Custom lookup function. default: dns.lookup(hostname[, domain], callback).

# Example

var socket = dgram.createSocket({ type: 'udp4' });

# dgram.createSocket(type[, callback])

• type {String} The family of socket. Must be either 'udp4' or 'udp6'.
• callback {Function} Attached as a listener for 'message' events. Optional.
• Returns: {Object} Dgram socket object.

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.

# Example

var socket = dgram.createSocket('udp4');

# Dgram.Socket Object

# 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.

# Example

var socket = dgram.createSocket('udp4');
socket.close();

# socket.bind([port][, address][, callback])

• port {Integer} Port.
• address {String} Local address.
• 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 JSRE 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 3333:

# Example

const dgram = require('dgram');
const server = dgram.createSocket('udp4');

server.on('error', (err) => {
  console.log(`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(3333);
// Prints: server listening 0.0.0.0:3333

# socket.bind(options[, callback])

• options {Object} Binding options.
• 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 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.

options can contain the following members:

• port {Integer} Port.
• address {String} Local address.
• fd {Integer} Change file descriptor to socket file.

The options object may contain a fd property. When a fd greater or equal 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.

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

socket.bind({
  address: 'localhost',
  port: 8000
});

# socket.connect(port[, address][, callback])

• port {Integer} Port.
• address {String} Local address.
• 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. 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.

# Example

socket.connect(8000);

# socket.disconnect()

A synchronous function that disassociates a connected dgram.Socket from its remote address.

# socket.address()

• Returns: {Object} This socket address info.

Returns an object containing the address information for a socket. For UDP sockets, this object will contain address, family and port properties.

# Example

console.log('udp on port:', socket.address().port);

# socket.remoteAddress()

• Returns: {Object} This socket remote address info.

Returns an object containing the address, family, and port of the remote endpoint.

# socket.send(msg[, offset, length][, port][, address][, callback])

• msg {Buffer | 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 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 falsy, '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 JSRE 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.

# Example

• Example of sending a UDP packet to a port on localhost;

const dgram = require('dgram');
const message = Buffer.from('Some bytes');
const client = dgram.createSocket('udp4');

client.send(message, 3333, 'localhost', (err) => {
  client.close();
});

• Example of sending a UDP packet composed of multiple buffers to a port on 127.0.0.1;

const dgram = require('dgram');
const buf1 = Buffer.from('Some ');
const buf2 = Buffer.from('bytes');
const client = dgram.createSocket('udp4');

client.send([buf1, buf2], 3333, (err) => {
  client.close();
});

• Example of sending a UDP packet using a socket connected to a port on localhost:

const dgram = require('dgram');
const message = Buffer.from('Some bytes');
const client = dgram.createSocket('udp4');

client.connect(3333, 'localhost', (err) => {
  client.send(message, (err) => {
    client.close();
  });
});

# socket.setTTL(timeToLive)

• timeToLive {Integer} IP TTL: 0 ~ 255.
• Returns: {Boolean} Whether the operation was successful.

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.

# socket.bindToDevice([ifname])

• ifname {String} Network interface name. default: all network interface.
• Returns: {Boolean} Whether the operation was successful.

The socket.bindToDevice() function binds the network sending and receiving to the specified network interface, and the data packet is only allowed to be sent and received using this network interface.

# Example

socket.bindToDevice('en1');

# socket.setBroadcast(enable)

• enable {Boolean} Whether to enable broadcast.
• Returns: {Boolean} Whether the operation was successful.

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.getRecvBufferSize()

• Returns: {Integer} Receive buffer size, negative on error.

Get current receive buffer size in bytes.

# socket.getSendBufferSize()

• Returns: {Integer} Send buffer size, negative on error.

Get current send buffer size in bytes.

# socket.setRecvBufferSize(size)

• size {Integer} Receive buffer size. Must be between 1024bytes and 16Mbytes.
• Returns: {Boolean} Whether the operation was successful.

Set current receive buffer size in bytes.

# socket.setSendBufferSize(size)

• size {Integer} Send buffer size. Must be between 1024bytes and 16Mbytes.
• Returns: {Boolean} Whether the operation was successful.

Set current send buffer size in bytes.

# socket.ref()

• Returns: {Object} This dgram.Socket object.

This object reference, the system will not recycle this object.

# socket.unref()

• Returns: {Object} This dgram.Socket object.

This object unreference.

# socket.setMulticastInterface(multicastInterface)

• multicastInterface {String} Multicast network interface name.
• Returns: {Boolean} Whether the operation was successful.

Set the specified udp multicast network interface.

# Example

socket.setMulticastInterface('wl3');

# socket.setMulticastTTL(timeToLive)

• timeToLive {Integer} IP TTL: 0 ~ 255.
• Returns: {Boolean} Whether the operation was successful.

Changes the specified udp TTL value of the multicast IP header.

# Example

socket.setMulticastTTL(8);

# socket.setMulticastLoop(enable)

• enable {Boolean} Whether to enable multicast loop.
• Returns: {Boolean} Whether the operation was successful.

Set the specified udp whether to allow multicast loop.

# Example

socket.setMulticastLoop(false);

# socket.addMembership(multicastAddr[, multicastInterface])

• multicastAddr {String} Multicast address.
• multicastInterface {String} Multicast network interface name. default: all interface.
• Returns: {Boolean} Whether the operation was successful.

Use the socket.addMembership() to join an multicast group on a interface.

# Example

socket.addMembership('224.0.1.222', 'en1');

# socket.addSourceSpecificMembership(sourceAddress, groupAddress[, multicastInterface])

• sourceAddress {String} Source address
• groupAddress {String} Multicast address.
• multicastInterface {String} Multicast network interface name. default: all interface.
• Returns: {Boolean} Whether the operation was successful.

Use the socket.addSourceSpecificMembership() to join an multicast group on a interface.

# Example

socket.addSourceSpecificMembership('192.168.1.1', '224.0.1.222', 'en1');

# socket.dropMembership(multicastAddr[, multicastInterface[, sourceAddr]])

• multicastAddr {String} Multicast address.
• multicastInterface {String} Multicast network interface name. default: all interface.
• Returns: {Boolean} Whether the operation was successful.

Use the socket.dropMembership() to leave an multicast group on a interface.

# Example

socket.dropMembership('224.0.1.222', 'en1');

# socket.dropSourceSpecificMembership(sourceAddress, groupAddress[, multicastInterface])

• sourceAddress {String} Source address
• groupAddress {String} Multicast address.
• multicastInterface {String} Multicast network interface name. default: all interface.
• Returns: {Boolean} Whether the operation was successful.

Use the socket.dropSourceSpecificMembership() to leave an multicast group on a interface.

# Example

socket.dropSourceSpecificMembership('192.168.1.1', '224.0.1.222', 'en1');