<?xml version="1.0" encoding="utf-8" ?>
<!DOCTYPE erlref SYSTEM "erlref.dtd">

<erlref>
  <header>
    <copyright>
      <year>1997</year><year>2018</year>
      <holder>Ericsson AB. All Rights Reserved.</holder>
    </copyright>
    <legalnotice>
      Licensed under the Apache License, Version 2.0 (the "License");
      you may not use this file except in compliance with the License.
      You may obtain a copy of the License at
 
          http://www.apache.org/licenses/LICENSE-2.0

      Unless required by applicable law or agreed to in writing, software
      distributed under the License is distributed on an "AS IS" BASIS,
      WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
      See the License for the specific language governing permissions and
      limitations under the License.
    
    </legalnotice>

    <title>gen_udp</title>
    <prepared>tony@erix.ericsson.se</prepared>
    <docno></docno>
    <date>1997-12-03</date>
    <rev>A</rev>
  </header>
  <module since="">gen_udp</module>
  <modulesummary>Interface to UDP sockets.</modulesummary>
  <description>
    <p>This module provides functions for communicating
      with sockets using the UDP protocol.</p>
  </description>

  <datatypes>
    <datatype>
      <name name="option"/>
    </datatype>
    <datatype>
      <name name="option_name"/>
    </datatype>
    <datatype>
      <name>socket()</name>
      <desc>
        <p>As returned by
          <seealso marker="#open/1"><c>open/1,2</c></seealso>.</p>
      </desc>
    </datatype>
  </datatypes>

  <funcs>
    <func>
      <name name="close" arity="1" since=""/>
      <fsummary>Close a UDP socket.</fsummary>
      <desc>
        <p>Closes a UDP socket.</p>
      </desc>
    </func>

    <func>
      <name name="controlling_process" arity="2" since=""/>
      <fsummary>Change controlling process of a socket.</fsummary>
      <desc>
        <p>Assigns a new controlling process <c><anno>Pid</anno></c> to
          <c><anno>Socket</anno></c>. The controlling process is the process
          that receives messages from the socket. If called by any other
          process than the current controlling process,
          <c>{error, not_owner}</c> is returned. If the process identified
          by <c><anno>Pid</anno></c> is not an existing local pid,
          <c>{error, badarg}</c> is returned. <c>{error, badarg}</c> may also
          be returned in some cases when <c><anno>Socket</anno></c> is closed
          during the execution of this function.</p>
      </desc>
    </func>

    <func>
      <name name="open" arity="1" since=""/>
      <name name="open" arity="2" since=""/>
      <fsummary>Associate a UDP port number with the process calling it.</fsummary>
      <desc>
        <p>Associates a UDP port number (<c><anno>Port</anno></c>) with the
          calling process.</p>
        <p>The following options are available:</p>
        <taglist>
          <tag><c>list</c></tag>
          <item><p>Received <c>Packet</c> is delivered as a list.</p></item>
          <tag><c>binary</c></tag>
          <item><p>Received <c>Packet</c> is delivered as a binary.</p></item>
          <tag><c>{ip, Address}</c></tag>
          <item><p>If the host has many network interfaces, this option
            specifies which one to use.</p></item>
          <tag><c>{ifaddr, Address}</c></tag>
          <item><p>Same as <c>{ip, Address}</c>. If the host has many
            network interfaces, this option specifies which one to
            use.</p></item>
          <tag><c>{fd, integer() >= 0}</c></tag>
          <item><p>If a socket has somehow been opened without using
            <c>gen_udp</c>, use this option to pass the file descriptor
            for it. If <c><anno>Port</anno></c> is not set to <c>0</c> and/or
            <c>{ip, ip_address()}</c> is combined with this option, the
            <c>fd</c> is bound to the specified interface and port after it is
            being opened. If these options are not specified, it is assumed that
            the <c>fd</c> is already bound appropriately.</p></item>
          <tag><c>inet6</c></tag>
          <item><p>Sets up the socket for IPv6.</p></item>
          <tag><c>inet</c></tag>
          <item><p>Sets up the socket for IPv4.</p></item>
	  <tag><c>local</c></tag>
	  <item>
            <p>
	      Sets up a Unix Domain Socket. See
	      <seealso marker="inet#type-local_address">
		<c>inet:local_address()</c>
	      </seealso>
	    </p>
          </item>
          <tag><c>{udp_module, module()}</c></tag>
          <item><p>Overrides which callback module is used. Defaults to
            <c>inet_udp</c> for IPv4 and <c>inet6_udp</c> for IPv6.</p></item>
          <tag><c>{multicast_if, Address}</c></tag>
          <item><p>Sets the local device for a multicast socket.</p></item>
          <tag><c>{multicast_loop, true | false}</c></tag>
          <item><p>When <c>true</c>, sent multicast packets are looped back to
            the local sockets.</p></item>
          <tag><c>{multicast_ttl, Integer}</c></tag>
          <item><p>Option <c>multicast_ttl</c> changes the time-to-live (TTL)
            for outgoing multicast datagrams to control the scope of the
            multicasts.</p>
            <p>Datagrams with a TTL of 1 are not forwarded beyond the local
              network. Defaults to <c>1</c>.</p></item>
          <tag><c>{add_membership, {MultiAddress, InterfaceAddress}}</c></tag>
          <item><p>Joins a multicast group.</p></item>
          <tag><c>{drop_membership, {MultiAddress, InterfaceAddress}}</c></tag>
          <item><p>Leaves a multicast group.</p></item>
          <tag><c>Opt</c></tag>
          <item><p>See
            <seealso marker="inet#setopts/2"><c>inet:setopts/2</c></seealso>.
            </p></item>
        </taglist>
        <p>The returned socket <c><anno>Socket</anno></c> is used to send
          packets from this port with
          <seealso marker="#send/4"><c>send/4</c></seealso>.
          When UDP packets arrive
          at the opened port, if the socket is in an active mode, the packets
          are delivered as messages to the controlling process:</p>
        <code type="none">
{udp, Socket, IP, InPortNo, Packet} % Without ancillary data
{udp, Socket, IP, InPortNo, AncData, Packet} % With ancillary data
	</code>
	<p>
	  The message contains an <c>AncData</c> field
	  if any of the socket
	  <seealso marker="#type-option">options</seealso>
	  <seealso marker="inet#option-recvtos"><c>recvtos</c></seealso>,
	  <seealso marker="inet#option-recvtclass"><c>recvtclass</c></seealso>
	  or
	  <seealso marker="inet#option-recvttl"><c>recvttl</c></seealso>
	  are active, otherwise it does not.
	</p>
	<p>
	</p>
        <p>If the socket is not in an active mode, data can be
          retrieved through the
          <seealso marker="#recv/2"><c>recv/2,3</c></seealso> calls.
          Notice that arriving UDP packets that are longer than
          the receive buffer option specifies can be truncated
          without warning.</p>
        <p>When a socket in <c>{active, N}</c> mode (see
          <seealso marker="inet#setopts/2"><c>inet:setopts/2</c></seealso>
          for details), transitions to passive (<c>{active, false}</c>) mode,
          the controlling process is notified by a message of the following
          form:</p>
        <code type="none">
{udp_passive, Socket}</code>
        <p><c>IP</c> and <c>InPortNo</c> define the address from which
          <c>Packet</c> comes. <c>Packet</c> is a list of bytes if
          option <c>list</c> is specified. <c>Packet</c> is a
          binary if option <c>binary</c> is specified.</p>
        <p>Default value for the receive buffer option is
          <c>{recbuf, 8192}</c>.</p>
        <p>If <c><anno>Port</anno> == 0</c>, the underlying OS assigns a free
          UDP port, use
          <seealso marker="inet#port/1"><c>inet:port/1</c></seealso>
          to retrieve it.</p>
      </desc>
    </func>

    <func>
      <name name="recv" arity="2" since=""/>
      <name name="recv" arity="3" since=""/>
      <fsummary>Receive a packet from a passive socket.</fsummary>
      <desc>
        <p>
	  Receives a packet from a socket in passive mode. Optional parameter
          <c><anno>Timeout</anno></c> specifies a time-out in milliseconds.
          Defaults to <c>infinity</c>.
	</p>
	<p>
	  If any of the socket
	  <seealso marker="#type-option">options</seealso>
	  <seealso marker="inet#option-recvtos"><c>recvtos</c></seealso>,
	  <seealso marker="inet#option-recvtclass"><c>recvtclass</c></seealso>
	  or
	  <seealso marker="inet#option-recvttl"><c>recvttl</c></seealso>
	  are active, the <c><anno>RecvData</anno></c> tuple contains an
	  <c><anno>AncData</anno></c> field,
	  otherwise it does not.
	</p>
      </desc>
    </func>

    <func>
      <name name="send" arity="3" since="OTP 21.3.8.4"/>
      <fsummary>Send a packet.</fsummary>
      <desc>
        <p>
	  Sends a packet to the specified <c><anno>Destination</anno></c>.
	</p>
	<p>
	  This function is equivalent to
	  <seealso marker="#send-4-AncData"><c>send(<anno>Socket</anno>, <anno>Destination</anno>, [], <anno>Packet</anno>)</c></seealso>.
	</p>
      </desc>
    </func>

    <func>
      <name name="send" arity="4" clause_i="1" since=""/>
      <fsummary>Send a packet.</fsummary>
      <desc>
        <p>
	  Sends a packet to the specified <c><anno>Host</anno></c>
	  and <c><anno>Port</anno></c>.
	</p>
	<p>
	  This clause is equivalent to
	  <seealso marker="#send/5"><c>send(<anno>Socket</anno>, <anno>Host</anno>, <anno>Port</anno>, [], <anno>Packet</anno>)</c></seealso>.
	</p>
      </desc>
    </func>

    <func>
      <name name="send" arity="4" clause_i="2" anchor="send-4-AncData" since="OTP 21.3.8.4"/>
      <fsummary>Send a packet.</fsummary>
      <desc>
        <p>
	  Sends a packet to the specified <c><anno>Destination</anno></c>
	  with ancillary data <c><anno>AncData</anno></c>.
	</p>
	<note>
	  <p>
	    The ancillary data <c><anno>AncData</anno></c>
	    contains options that for this single message
	    override the default options for the socket,
	    an operation that may not be supported on all platforms,
	    and if so return <c>{error, einval}</c>.
	    Using more than one of an ancillary data item type
	    may also not be supported.
	    <c><anno>AncData</anno> =:= []</c> is always supported.
	  </p>
	</note>
      </desc>
    </func>

    <func>
      <name name="send" arity="4" clause_i="3" since="OTP 21.3.8.4"/>
      <fsummary>Send a packet.</fsummary>
      <desc>
        <p>
	  Sends a packet to the specified <c><anno>Destination</anno></c>.
	  Since <c><anno>Destination</anno></c> is complete,
	  <c><anno>PortZero</anno></c> is redundant and has to be <c>0</c>.
	</p>
	<p>
	  This is a legacy clause mostly for
	  <c><anno>Destination</anno> = {local, Binary}</c>
	  where <c><anno>PortZero</anno></c> is superfluous.
	  It is equivalent to
	  <seealso marker="#send-4-AncData"><c>send(<anno>Socket</anno>, <anno>Destination</anno>, [], <anno>Packet</anno>)</c></seealso>, the clause right above here.
	</p>
      </desc>
    </func>

    <func>
      <name name="send" arity="5" since="OTP 21.3.8.4"/>
      <fsummary>Send a packet.</fsummary>
      <desc>
        <p>
	  Sends a packet to the specified <c><anno>Host</anno></c>
	  and <c><anno>Port</anno></c>,
	  with ancillary data <c><anno>AncData</anno></c>.
	</p>
	<p>
	  Argument <c><anno>Host</anno></c> can be
	  a hostname or a socket address,
	  and <c><anno>Port</anno></c> can be a port number
	  or a service name atom.
	  These are resolved into a <c>Destination</c> and after that
	  this function is equivalent to
	  <seealso marker="#send-4-AncData"><c>send(<anno>Socket</anno>, Destination, <anno>AncData</anno>, <anno>Packet</anno>)</c></seealso>, read there about ancillary data.
	</p>
      </desc>
    </func>
  </funcs>
</erlref>

