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diff --git a/doc/api/dgram.md b/doc/api/dgram.md new file mode 100644 index 00000000000..1bb5155578d --- /dev/null +++ b/doc/api/dgram.md @@ -0,0 +1,426 @@ +# UDP / Datagram Sockets + + Stability: 2 - Stable + +<!-- name=dgram --> + +The `dgram` module provides an implementation of UDP Datagram sockets. + +```js +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', () => { + 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` 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' + +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} + +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 whenever a socket begins listening for +datagram messages. This occurs as soon as UDP sockets are created. + +### Event: 'message' + +* `msg` {Buffer} - The message +* `rinfo` {Object} - Remote 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: + +```js +socket.on('message', (msg, rinfo) => { + console.log('Received %d bytes from %s:%d\n', + msg.length, rinfo.address, rinfo.port); +}); +``` + +### socket.addMembership(multicastAddress[, multicastInterface]) + +* `multicastAddress` {String} +* `multicastInterface` {String}, Optional + +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` +properties. + +### socket.bind([port][, address][, callback]) + +* `port` {Number} - Integer, Optional +* `address` {String}, Optional +* `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 +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: + +```js +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', () => { + var address = server.address(); + console.log(`server listening ${address.address}:${address.port}`); +}); + +server.bind(41234); +// server listening 0.0.0.0:41234 +``` + +### socket.bind(options[, callback]) + +* `options` {Object} - Required. Supports the following properties: + * `port` {Number} - Required. + * `address` {String} - Optional. + * `exclusive` {Boolean} - Optional. +* `callback` {Function} - Optional. + +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. + +An example socket listening on an exclusive port is shown below. + +```js +socket.bind({ + address: 'localhost', + port: 8000, + exclusive: true +}); +``` + +### socket.close([callback]) + +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.dropMembership(multicastAddress[, multicastInterface]) + +* `multicastAddress` {String} +* `multicastInterface` {String}, Optional + +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.send(msg, [offset, length,] port, address[, callback]) + +* `msg` {Buffer|String|Array} Message to be sent +* `offset` {Number} Integer. Optional. Offset in the buffer where the message starts. +* `length` {Number} Integer. Optional. Number of bytes in the message. +* `port` {Number} Integer. Destination port. +* `address` {String} Destination hostname or IP address. +* `callback` {Function} Called when the message has been sent. Optional. + +Broadcasts a datagram on the socket. The destination `port` and `address` must +be specified. + +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 the `address` is not +specified or is an empty string, `'127.0.0.1'` or `'::1'` will be used instead. + +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. +Note that 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 if you specify one you would need to +specify the other. Also, they are supported only when the first +argument is a `Buffer`. + +Example of sending a UDP packet to a random port on `localhost`; + +```js +const dgram = require('dgram'); +const message = new Buffer('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 random port on `localhost`; + +```js +const dgram = require('dgram'); +const buf1 = new Buffer('Some '); +const buf2 = new Buffer('bytes'); +const client = dgram.createSocket('udp4'); +client.send([buf1, buf2], 41234, 'localhost', (err) => { + client.close(); +}); +``` + +Sending multiple buffers might be faster or slower depending on your +application and operating system: benchmark it. Usually it is faster. + +**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 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 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 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, like Ethernet, have a + minimum `MTU` 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. + +### 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. + +### socket.setMulticastTTL(ttl) + +* `ttl` {Number} 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 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` {Number} 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 argument to `socket.setTTL()` is a number of hops between 1 and 255. +The default on most systems is 64 but can vary. + +### socket.ref() + +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.unref() + +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. + +The `socket.unref()` method returns a reference to the socket so calls can be +chained. + +### 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: + +```js +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: + +```js +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: {dgram.Socket} + +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`. An optional `callback` function can be passed specified which is added +as a listener for `'message'` events. + +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`][]. + +### dgram.createSocket(type[, callback]) + +* `type` {String} - Either 'udp4' or 'udp6' +* `callback` {Function} - Attached as a listener to `'message'` events. + Optional +* Returns: {dgram.Socket} + +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. + +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.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 +[byte length]: buffer.html#buffer_class_method_buffer_bytelength_string_encoding |