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<?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>[email protected]</prepared>
<docno></docno>
<date>1997-12-03</date>
<rev>A</rev>
</header>
<module>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"/>
<fsummary>Close a UDP socket.</fsummary>
<desc>
<p>Closes a UDP socket.</p>
</desc>
</func>
<func>
<name name="controlling_process" arity="2"/>
<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"/>
<name name="open" arity="2"/>
<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"/>
<name name="recv" arity="3"/>
<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="4"/>
<fsummary>Send a packet.</fsummary>
<desc>
<p>
Sends a packet to the specified address and port. Argument
<c><anno>Address</anno></c> can be a hostname or a socket address.
</p>
</desc>
</func>
</funcs>
</erlref>
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