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<!doctype html> <html lang="en"> <head> <meta charset="utf-8"> <title>UDP / Datagram Sockets Node.js v0.10.35 Manual & Documentation</title> <link rel="stylesheet" href="assets/style.css"> <link rel="stylesheet" href="assets/sh.css"> <link rel="canonical" href="http://nodejs.org/api/dgram.html"> <script type="text/javascript" src="//use.typekit.net/mse5tqx.js"></script> <script type="text/javascript">try{Typekit.load();}catch(e){}</script> </head> <body class="alt apidoc int docs" id="docs"> <div id="nav"> <img id="logo" src="assets/logo.svg" alt="node.js"> <ul> <li><a href="http://nodejs.org">Home</a></li> <li><a href="http://nodejs.org/download/">Downloads</a></li> <li class="active"><a href="http://nodejs.org/documentation/">Docs</a></li> <li><a href="http://nodejs.org/community/">Community</a></li> <li><a href="http://nodejs.org/about/">About</a></li> <li><a href="http://jobs.nodejs.org">Jobs</a></li> <li><a href="http://blog.nodejs.org">Blog</a></li> </ul> </div> <div id="content-wrap"> <div id="content" class="clearfix"> <div id="column2" class="interior">  <ul class="docs-nav"> <li><a href="http://nodejs.org/documentation/">About Docs</a></li> <li><a href="http://nodejs.org/documentation/tutorials/">Tutorials</a></li> <li><a href="http://nodejs.org/documentation/contributing/">Contributing</a></li> <li><a href="http://nodejs.org/documentation/localization/">Localization</a></li> <li class="active"><a href="http://nodejs.org/api/">API Docs</a></li> </ul> </div> <div id="column1" class="interior"> <header> <h1>Node.js v0.10.35 Manual & Documentation</h1> <div id="gtoc"> <p> <a href="index.html" name="toc">Index</a> | <a href="all.html">View on single page</a> | <a href="dgram.json">View as JSON</a> </p> </div> <hr> </header> <div id="toc"> <h2>Table of Contents</h2> <ul> <li><a href="#dgram_udp_datagram_sockets">UDP / Datagram Sockets</a><ul> <li><a href="#dgram_dgram_createsocket_type_callback">dgram.createSocket(type, [callback])</a></li> <li><a href="#dgram_class_dgram_socket">Class: dgram.Socket</a><ul> <li><a href="#dgram_event_message">Event: 'message'</a></li> <li><a href="#dgram_event_listening">Event: 'listening'</a></li> <li><a href="#dgram_event_close">Event: 'close'</a></li> <li><a href="#dgram_event_error">Event: 'error'</a></li> <li><a href="#dgram_socket_send_buf_offset_length_port_address_callback">socket.send(buf, offset, length, port, address, [callback])</a></li> <li><a href="#dgram_socket_bind_port_address_callback">socket.bind(port, [address], [callback])</a></li> <li><a href="#dgram_socket_close">socket.close()</a></li> <li><a href="#dgram_socket_address">socket.address()</a></li> <li><a href="#dgram_socket_setbroadcast_flag">socket.setBroadcast(flag)</a></li> <li><a href="#dgram_socket_setttl_ttl">socket.setTTL(ttl)</a></li> <li><a href="#dgram_socket_setmulticastttl_ttl">socket.setMulticastTTL(ttl)</a></li> <li><a href="#dgram_socket_setmulticastloopback_flag">socket.setMulticastLoopback(flag)</a></li> <li><a href="#dgram_socket_addmembership_multicastaddress_multicastinterface">socket.addMembership(multicastAddress, [multicastInterface])</a></li> <li><a href="#dgram_socket_dropmembership_multicastaddress_multicastinterface">socket.dropMembership(multicastAddress, [multicastInterface])</a></li> <li><a href="#dgram_socket_unref">socket.unref()</a></li> <li><a href="#dgram_socket_ref">socket.ref()</a></li> </ul> </li> </ul> </li> </ul> </div> <div id="apicontent"> <h1>UDP / Datagram Sockets<span><a class="mark" href="#dgram_udp_datagram_sockets" id="dgram_udp_datagram_sockets">#</a></span></h1> <pre class="api_stability_3">Stability: 3 - Stable</pre> <p>Datagram sockets are available through <code>require('dgram')</code>. </p> <p>Important note: the behavior of <code>dgram.Socket#bind()</code> has changed in v0.10 and is always asynchronous now. If you have code that looks like this: </p> <pre><code>var s = dgram.createSocket('udp4'); s.bind(1234); s.addMembership('224.0.0.114');</code></pre> <p>You have to change it to this: </p> <pre><code>var s = dgram.createSocket('udp4'); s.bind(1234, function() { s.addMembership('224.0.0.114'); });</code></pre> <h2>dgram.createSocket(type, [callback])<span><a class="mark" href="#dgram_dgram_createsocket_type_callback" id="dgram_dgram_createsocket_type_callback">#</a></span></h2> <div class="signature"><ul> <li><code>type</code> String. Either 'udp4' or 'udp6'</li> <li><code>callback</code> Function. Attached as a listener to <code>message</code> events. Optional</li> <li>Returns: Socket object</li> </div></ul> <p>Creates a datagram Socket of the specified types. Valid types are <code>udp4</code> and <code>udp6</code>. </p> <p>Takes an optional callback which is added as a listener for <code>message</code> events. </p> <p>Call <code>socket.bind</code> if you want to receive datagrams. <code>socket.bind()</code> will bind to the "all interfaces" address on a random port (it does the right thing for both <code>udp4</code> and <code>udp6</code> sockets). You can then retrieve the address and port with <code>socket.address().address</code> and <code>socket.address().port</code>. </p> <h2>Class: dgram.Socket<span><a class="mark" href="#dgram_class_dgram_socket" id="dgram_class_dgram_socket">#</a></span></h2> <p>The dgram Socket class encapsulates the datagram functionality. It should be created via <code>dgram.createSocket(type, [callback])</code>. </p> <h3>Event: 'message'<span><a class="mark" href="#dgram_event_message" id="dgram_event_message">#</a></span></h3> <div class="signature"><ul> <li><code>msg</code> Buffer object. The message</li> <li><code>rinfo</code> Object. Remote address information</li> </div></ul> <p>Emitted when a new datagram is available on a socket. <code>msg</code> is a <code>Buffer</code> and <code>rinfo</code> is an object with the sender's address information and the number of bytes in the datagram. </p> <h3>Event: 'listening'<span><a class="mark" href="#dgram_event_listening" id="dgram_event_listening">#</a></span></h3> <p>Emitted when a socket starts listening for datagrams. This happens as soon as UDP sockets are created. </p> <h3>Event: 'close'<span><a class="mark" href="#dgram_event_close" id="dgram_event_close">#</a></span></h3> <p>Emitted when a socket is closed with <code>close()</code>. No new <code>message</code> events will be emitted on this socket. </p> <h3>Event: 'error'<span><a class="mark" href="#dgram_event_error" id="dgram_event_error">#</a></span></h3> <div class="signature"><ul> <li><code>exception</code> Error object</li> </div></ul> <p>Emitted when an error occurs. </p> <h3>socket.send(buf, offset, length, port, address, [callback])<span><a class="mark" href="#dgram_socket_send_buf_offset_length_port_address_callback" id="dgram_socket_send_buf_offset_length_port_address_callback">#</a></span></h3> <div class="signature"><ul> <li><code>buf</code> Buffer object. Message to be sent</li> <li><code>offset</code> Integer. Offset in the buffer where the message starts.</li> <li><code>length</code> Integer. Number of bytes in the message.</li> <li><code>port</code> Integer. Destination port.</li> <li><code>address</code> String. Destination hostname or IP address.</li> <li><code>callback</code> Function. Called when the message has been sent. Optional.</li> </div></ul> <p>For UDP sockets, the destination port and address must be specified. A string may be supplied for the <code>address</code> parameter, and it will be resolved with DNS. </p> <p>If the address is omitted or is an empty string, <code>'0.0.0.0'</code> or <code>'::0'</code> 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. </p> <p>If the socket has not been previously bound with a call to <code>bind</code>, it gets assigned a random port number and is bound to the "all interfaces" address (<code>'0.0.0.0'</code> for <code>udp4</code> sockets, <code>'::0'</code> for <code>udp6</code> sockets.) </p> <p>An optional callback may be specified to detect DNS errors or for determining when it's safe to reuse the <code>buf</code> 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. </p> <p>Example of sending a UDP packet to a random port on <code>localhost</code>; </p> <pre><code>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(); });</code></pre> <p><strong>A Note about UDP datagram size</strong> </p> <p>The maximum size of an <code>IPv4/v6</code> datagram depends on the <code>MTU</code> (<em>Maximum Transmission Unit</em>) and on the <code>Payload Length</code> field size. </p> <ul> <li><p>The <code>Payload Length</code> field is <code>16 bits</code> 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.</p> </li> <li><p>The <code>MTU</code> is the largest size a given link layer technology can support for datagrams. For any link, <code>IPv4</code> mandates a minimum <code>MTU</code> of <code>68</code> octets, while the recommended <code>MTU</code> for IPv4 is <code>576</code> (typically recommended as the <code>MTU</code> for dial-up type applications), whether they arrive whole or in fragments.</p> <p>For <code>IPv6</code>, the minimum <code>MTU</code> is <code>1280</code> octets, however, the mandatory minimum fragment reassembly buffer size is <code>1500</code> octets. The value of <code>68</code> octets is very small, since most current link layer technologies have a minimum <code>MTU</code> of <code>1500</code> (like Ethernet).</p> </li> </ul> <p>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) <code>MTU</code> won't work (the packet gets silently dropped, without informing the source that the data did not reach its intended recipient). </p> <h3>socket.bind(port, [address], [callback])<span><a class="mark" href="#dgram_socket_bind_port_address_callback" id="dgram_socket_bind_port_address_callback">#</a></span></h3> <div class="signature"><ul> <li><code>port</code> Integer</li> <li><code>address</code> String, Optional</li> <li><code>callback</code> Function with no parameters, Optional. Callback when binding is done.</li> </div></ul> <p>For UDP sockets, listen for datagrams on a named <code>port</code> and optional <code>address</code>. If <code>address</code> is not specified, the OS will try to listen on all addresses. After binding is done, a "listening" event is emitted and the <code>callback</code>(if specified) is called. Specifying both a "listening" event listener and <code>callback</code> is not harmful but not very useful. </p> <p>A bound datagram socket keeps the node process running to receive datagrams. </p> <p>If binding fails, an "error" event is generated. In rare case (e.g. binding a closed socket), an <code>Error</code> may be thrown by this method. </p> <p>Example of a UDP server listening on port 41234: </p> <pre><code>var dgram = require("dgram"); var server = dgram.createSocket("udp4"); server.on("error", function (err) { console.log("server error:\n" + err.stack); server.close(); }); 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</code></pre> <h3>socket.close()<span><a class="mark" href="#dgram_socket_close" id="dgram_socket_close">#</a></span></h3> <p>Close the underlying socket and stop listening for data on it. </p> <h3>socket.address()<span><a class="mark" href="#dgram_socket_address" id="dgram_socket_address">#</a></span></h3> <p>Returns an object containing the address information for a socket. For UDP sockets, this object will contain <code>address</code> , <code>family</code> and <code>port</code>. </p> <h3>socket.setBroadcast(flag)<span><a class="mark" href="#dgram_socket_setbroadcast_flag" id="dgram_socket_setbroadcast_flag">#</a></span></h3> <div class="signature"><ul> <li><code>flag</code> Boolean</li> </div></ul> <p>Sets or clears the <code>SO_BROADCAST</code> socket option. When this option is set, UDP packets may be sent to a local interface's broadcast address. </p> <h3>socket.setTTL(ttl)<span><a class="mark" href="#dgram_socket_setttl_ttl" id="dgram_socket_setttl_ttl">#</a></span></h3> <div class="signature"><ul> <li><code>ttl</code> Integer</li> </div></ul> <p>Sets the <code>IP_TTL</code> 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. </p> <p>The argument to <code>setTTL()</code> is a number of hops between 1 and 255. The default on most systems is 64. </p> <h3>socket.setMulticastTTL(ttl)<span><a class="mark" href="#dgram_socket_setmulticastttl_ttl" id="dgram_socket_setmulticastttl_ttl">#</a></span></h3> <div class="signature"><ul> <li><code>ttl</code> Integer</li> </div></ul> <p>Sets the <code>IP_MULTICAST_TTL</code> 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. </p> <p>The argument to <code>setMulticastTTL()</code> is a number of hops between 0 and 255. The default on most systems is 1. </p> <h3>socket.setMulticastLoopback(flag)<span><a class="mark" href="#dgram_socket_setmulticastloopback_flag" id="dgram_socket_setmulticastloopback_flag">#</a></span></h3> <div class="signature"><ul> <li><code>flag</code> Boolean</li> </div></ul> <p>Sets or clears the <code>IP_MULTICAST_LOOP</code> socket option. When this option is set, multicast packets will also be received on the local interface. </p> <h3>socket.addMembership(multicastAddress, [multicastInterface])<span><a class="mark" href="#dgram_socket_addmembership_multicastaddress_multicastinterface" id="dgram_socket_addmembership_multicastaddress_multicastinterface">#</a></span></h3> <div class="signature"><ul> <li><code>multicastAddress</code> String</li> <li><code>multicastInterface</code> String, Optional</li> </div></ul> <p>Tells the kernel to join a multicast group with <code>IP_ADD_MEMBERSHIP</code> socket option. </p> <p>If <code>multicastInterface</code> is not specified, the OS will try to add membership to all valid interfaces. </p> <h3>socket.dropMembership(multicastAddress, [multicastInterface])<span><a class="mark" href="#dgram_socket_dropmembership_multicastaddress_multicastinterface" id="dgram_socket_dropmembership_multicastaddress_multicastinterface">#</a></span></h3> <div class="signature"><ul> <li><code>multicastAddress</code> String</li> <li><code>multicastInterface</code> String, Optional</li> </div></ul> <p>Opposite of <code>addMembership</code> - tells the kernel to leave a multicast group with <code>IP_DROP_MEMBERSHIP</code> 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. </p> <p>If <code>multicastInterface</code> is not specified, the OS will try to drop membership to all valid interfaces. </p> <h3>socket.unref()<span><a class="mark" href="#dgram_socket_unref" id="dgram_socket_unref">#</a></span></h3> <p>Calling <code>unref</code> 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 <code>unref</code>d calling <code>unref</code> again will have no effect. </p> <h3>socket.ref()<span><a class="mark" href="#dgram_socket_ref" id="dgram_socket_ref">#</a></span></h3> <p>Opposite of <code>unref</code>, calling <code>ref</code> on a previously <code>unref</code>d socket will <em>not</em> let the program exit if it's the only socket left (the default behavior). 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