path: root/erts/doc/src/socket.xml

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

<erlref>
  <header>
    <copyright>
      <year>2018</year><year>2019</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>socket</title>
    <prepared></prepared>
    <docno></docno>
    <date></date>
    <rev></rev>
    <file>socket.xml</file>
  </header>
  <module since="OTP 22.0">socket</module>
  <modulesummary>Socket interface.</modulesummary>
  <description>
    <p>This module provides an API for the socket interface.
    It is used to create, delete and manipulate sockets,
    send and receive data.</p>
    <p>The idea is that it shall be as "close as possible" to the OS
    level socket interface. The only significant addition is that some of
    the functions,
    e.g. <seealso marker="#recv/3"><c>recv/3</c></seealso>, 
    has a timeout argument. </p>
    <note>
      <p>Some functions allow for an <i>asynchronous</i> call.
      This is achieved by setting the <c>Timeout</c> argument to
      <c>nowait</c>. For instance, if calling the
      <seealso marker="#recv_async"><c>recv/3</c></seealso>
      function with Timeout set to <c>nowait</c> (<c>recv(Sock, 0, nowait)</c>)
      when there is actually nothing to read, it will return with
      <c>{select, </c>
      <seealso marker="#type-select_info"><c>SelectInfo</c></seealso><c>}</c>
      (<c>SelectInfo</c> contains the
      <seealso marker="socket#type-select_ref">SelectRef</seealso>).
      When data eventually arrives a 'select' message
      will be sent to the caller: </p>
      <taglist>
	<!-- NOTE THAT THE EMPTY TAG IS INTENTIONAL -->
	<tag></tag>
	<item><c>{'$socket', socket(), select, SelectRef}</c></item>
      </taglist>
      <p>The caller can now make another
      call to the recv function and now expect data.</p>
      <p>Note that all other users are <em>locked out</em> until the
      'current user' has called the function (recv in this case).</p>
      <p>Another message the user must be prepared for (when making asynchronous
      calls) is the <c>abort</c> message:</p>
      <taglist>
	<!-- NOTE THAT THE EMPTY TAG IS INTENTIONAL -->
	<tag></tag>
	<item><c>{'$socket', socket(), abort, Info}</c></item>
      </taglist>
      <p>This message indicates
      that the (asynchronous) operation has been aborted.
      If, for instance, the socket has been closed (by another process),
      <c>Info</c> will be <c>{SelectRef, closed}</c>. </p>
    </note>
    <note>
      <p>There is currently <em>no</em> support for Windows. </p>
      <p>Support for IPv6 has been implemented but <em>not</em> tested. </p>
      <p>SCTP has only been partly implemented (and not tested). </p>
    </note>
  </description>

  <datatypes>
    <datatype>
      <name name="domain"/>
    </datatype>
    <datatype>
      <name name="type"/>
    </datatype>
    <datatype>
      <name name="protocol"/>
    </datatype>
    <datatype>
      <name>socket()</name>
      <desc><p>As returned by
        <seealso marker="#open/2"><c>open/2,3,4</c></seealso> and
        <seealso marker="#accept/1"><c>accept/1,2</c></seealso>.</p>
      </desc>
    </datatype>
    <datatype>
      <name name="select_tag"/>
      <desc>
	<p>A tag that describes the (select) operation.</p>
      </desc>
    </datatype>
    <datatype>
      <name name="select_ref"/>
      <desc>
	<p>A reference that uniquely identifies the (select) operation.</p>
      </desc>
    </datatype>
    <datatype>
      <name name="select_info"/>
    </datatype>
    <datatype>
      <name name="socket_counters"/>
    </datatype>
    <datatype>
      <name name="socket_counter"/>
    </datatype>
    <datatype>
      <name name="socket_info"/>
    </datatype>
    <datatype>
      <name name="ip4_address"/>
    </datatype>
    <datatype>
      <name name="ip6_address"/>
    </datatype>
    <datatype>
      <name name="ip_address"/>
    </datatype>
    <datatype>
      <name name="sockaddr"/>
    </datatype>
    <datatype>
      <name name="sockaddr_in4"/>
    </datatype>
    <datatype>
      <name name="sockaddr_in6"/>
    </datatype>
    <datatype>
      <name name="sockaddr_un"/>
    </datatype>
    <datatype>
      <name name="port_number"/>
    </datatype>
    <datatype>
      <name name="in6_flow_info"/>
    </datatype>
    <datatype>
      <name name="in6_scope_id"/>
    </datatype>
    <datatype>
      <name name="accept_flags"/>
    </datatype>
    <datatype>
      <name name="accept_flag"/>
    </datatype>
    <datatype>
      <name name="send_flags"/>
    </datatype>
    <datatype>
      <name name="send_flag"/>
    </datatype>
    <datatype>
      <name name="recv_flags"/>
    </datatype>
    <datatype>
      <name name="recv_flag"/>
    </datatype>
    <datatype>
      <name name="shutdown_how"/>
    </datatype>
    <datatype>
      <name name="sockopt_level"/>
    </datatype>
    <datatype>
      <name name="otp_socket_option"/>
    </datatype>
    <datatype>
      <name name="socket_option"/>
    </datatype>
    <datatype>
      <name name="ip_socket_option"/>
    </datatype>
    <datatype>
      <name name="ipv6_socket_option"/>
    </datatype>
    <datatype>
      <name name="tcp_socket_option"/>
    </datatype>
    <datatype>
      <name name="udp_socket_option"/>
    </datatype>
    <datatype>
      <name name="sctp_socket_option"/>
    </datatype>
    <datatype>
      <name name="timeval"/>
    </datatype>
    <datatype>
      <name name="ip_tos"/>
    </datatype>
    <datatype>
      <name name="ip_mreq"/>
    </datatype>
    <datatype>
      <name name="ip_mreq_source"/>
    </datatype>
    <datatype>
      <name name="ip_pmtudisc"/>
    </datatype>
    <datatype>
      <name name="ip_msfilter_mode"/>
    </datatype>
    <datatype>
      <name name="ip_msfilter"/>
    </datatype>
    <datatype>
      <name name="ip_pktinfo"/>
    </datatype>
    <datatype>
      <name name="ipv6_mreq"/>
    </datatype>
    <datatype>
      <name name="ipv6_pmtudisc"/>
    </datatype>
    <datatype>
      <name name="ipv6_pktinfo"/>
    </datatype>
    <datatype>
      <name name="sctp_assoc_id"/>
    </datatype>
    <datatype>
      <name name="sctp_sndrcvinfo"/>
    </datatype>
    <datatype>
      <name name="sctp_event_subscribe"/>
    </datatype>
    <datatype>
      <name name="sctp_assocparams"/>
    </datatype>
    <datatype>
      <name name="sctp_initmsg"/>
    </datatype>
    <datatype>
      <name name="sctp_rtoinfo"/>
    </datatype>
    <datatype>
      <name name="msghdr_flag"/>
    </datatype>
    <datatype>
      <name name="msghdr_flags"/>
    </datatype>
    <datatype>
      <name name="msghdr"/>
    </datatype>
    <datatype>
      <name name="cmsghdr_level"/>
    </datatype>
    <datatype>
      <name name="cmsghdr_type"/>
    </datatype>
    <!--
    <datatype>
      <name name="cmsghdr_data"/>
    </datatype>
    -->
    <datatype>
      <name name="cmsghdr_recv"/>
    </datatype>
    <datatype>
      <name name="cmsghdr_send"/>
    </datatype>
    <datatype>
      <name name="uint8"/>
    </datatype>
    <datatype>
      <name name="uint16"/>
    </datatype>
    <datatype>
      <name name="uint20"/>
    </datatype>
    <datatype>
      <name name="uint32"/>
    </datatype>
    <datatype>
      <name name="int32"/>
    </datatype>
    <datatype>
      <name name="supports_options_socket"/>
    </datatype>
    <datatype>
      <name name="supports_options_ip"/>
    </datatype>
    <datatype>
      <name name="supports_options_ipv6"/>
    </datatype>
    <datatype>
      <name name="supports_options_tcp"/>
    </datatype>
    <datatype>
      <name name="supports_options_udp"/>
    </datatype>
    <datatype>
      <name name="supports_options_sctp"/>
    </datatype>
    <datatype>
      <name name="supports_options"/>
    </datatype>
  </datatypes>

  <funcs>
    <func>
      <name name="accept" arity="1" since="OTP 22.0"/>
      <name name="accept" arity="2" clause_i="2" since="OTP 22.0"/>
      <fsummary>Accept a connection on a socket.</fsummary>
      <desc>
        <p>Accept a connection on a socket.</p>
        <p>This call is used with connection-based socket types
	(<c>stream</c> or <c>seqpacket</c>). It extracs the first pending
	connection request for the listen socket and returns the (newly)
	connected socket.</p>
      </desc>
    </func>

    <func>
      <name name="accept" arity="2" clause_i="1" anchor="accept_async" since="OTP @OTP-15731@"/>
      <fsummary>Accept a connection on a socket.</fsummary>
      <desc>
        <p>Accept a connection on a socket.</p>

	<p>This call is used with connection-based socket types
	(<c>stream</c> or <c>seqpacket</c>). It extracs the first pending
	connection request for the listen socket and returns the (newly)
	connected socket.</p>

	<p>In the case when there is no connections waiting, the function 
	will return with the <c>SelectInfo</c>. The caller can then await a 
	select message, <c>{'$socket', Socket, select, Info}</c> (where
	<c>Info</c> is the
	<seealso marker="socket#type-select_ref"><c>ref</c></seealso>
	field from the <c>SelectInfo</c>),
	when a client connects (a subsequent call to accept will then return 
	the socket). </p>
      </desc>
    </func>

    <func>
      <name name="bind" arity="2" since="OTP 22.0"/>
      <fsummary>Bind a name to a socket.</fsummary>
      <desc>
        <p>Bind a name to a socket.</p>
        <p>When a socket is created
	(with <seealso marker="#open/2"><c>open</c></seealso>),
	it has no address assigned to it. <c>bind</c> assigns the
	address specified by the <c>Addr</c> argument.</p>
	<p>The rules used for name binding vary between domains.</p>
      </desc>
    </func>

    <func>
      <name name="cancel" arity="2" since="OTP @OTP-15731@"/>
      <fsummary>Cancel an asynchronous request.</fsummary>
      <desc>
	<p>Cancel an asynchronous request.</p>

	<p>Call this function in order to cancel a previous
	asynchronous call to, e.g.
	<seealso marker="#recv/3"><c>recv/3</c></seealso>. </p>
      </desc>
    </func>

    <func>
      <name name="close" arity="1" since="OTP 22.0"/>
      <fsummary>Close a socket.</fsummary>
      <desc>
	<p>Closes the socket.</p>

	<note>
	  <p>Note that for e.g. <c>protocol</c> = <c>tcp</c>, most implementations
	  doing a close does not guarantee that any data sent is delivered to
	  the recipient before the close is detected at the remote side. </p>
	  <p>One way to handle this is to use the
	  <seealso marker="#shutdown/2"><c>shutdown</c></seealso>
	  function
	  (<c>socket:shutdown(Socket, write)</c>) to signal that no more data is
	  to be sent and then wait for the read side of the socket to be closed.</p>
	</note>
      </desc>
    </func>

    <func>
      <name name="connect" arity="2" since="OTP 22.0"/>
      <name name="connect" arity="3" clause_i="2" since="OTP 22.0"/>
      <fsummary>Initiate a connection on a socket.</fsummary>
      <desc>
        <p>This function connects the socket to the address
	specied by the <c>SockAddr</c> argument.</p>
      </desc>
    </func>

    <func>
      <name name="connect" arity="3" clause_i="1" anchor="connect_async" since="OTP @OTP-15731@"/>
      <fsummary>Initiate a connection on a socket.</fsummary>
      <desc>
        <p>This function connects the socket to the address
	specied by the <c>SockAddr</c> argument.</p>

 	<p>In the case when its not possible to immediately establish a
	connection, the function will return with the
	<seealso marker="#type-select_info"><c>SelectInfo</c></seealso>.
	The caller can then await a 
	select message, <c>{'$socket', Socket, select, Info}</c> (where
	<c>Info</c> is the
	<seealso marker="socket#type-select_ref"><c>ref</c></seealso>
	field from the <c>SelectInfo</c>,
	a subsequent call to connect will then 
	establish the connection). </p>
     </desc>
    </func>

    <func>
      <name name="getopt" arity="3" clause_i="1" since="OTP 22.0"/>
      <name name="getopt" arity="3" clause_i="2" since="OTP 22.0"/>
      <name name="getopt" arity="3" clause_i="3" since="OTP 22.0"/>
      <name name="getopt" arity="3" clause_i="4" since="OTP 22.0"/>
      <name name="getopt" arity="3" clause_i="5" since="OTP 22.0"/>
      <name name="getopt" arity="3" clause_i="6" since="OTP 22.0"/>
      <name name="getopt" arity="3" clause_i="7" since="OTP 22.0"/>
      <fsummary>Get an option on a socket.</fsummary>
      <desc>
        <p>Get an option on a socket.</p>
	<p>What properties are valid depend  both on <c>Level</c> and
	on what kind of socket it is (<c>domain</c>, <c>type</c> and
	<c>protocol</c>).</p>

	<p>See the
	<seealso marker="socket_usage#socket_options">socket options</seealso>
	chapter of the users guide for more info. </p>

	<note><p>Not all options are valid on all platforms. That is,
	even if "we" support an option, that does not mean that the
	underlying OS does.</p></note>

      </desc>
    </func>

    <func>
      <name name="getopt" arity="3" clause_i="8" since="OTP 22.0"/>
      <fsummary>Get an option on a socket.</fsummary>
      <desc>
        <p>Get an option on a socket.</p>
	<p>What properties are valid depend  both on <c>Level</c> and
	on what kind of socket it is (<c>domain</c>, <c>type</c> and
	<c>protocol</c>).</p>
	<p>When specifying <c>Level</c> as an integer, and therefor
	using "native mode", it is *currently* up to the caller to
	know how to interpret the result.</p>

	<p>See the
	<seealso marker="socket_usage#socket_options">socket options</seealso>
	chapter of the users guide for more info. </p>

	<note><p>Not all options are valid on all platforms. That is,
	even if "we" support an option, that does not mean that the
	underlying OS does.</p></note>
      </desc>
    </func>

    <func>
      <name name="info" arity="1" since="OTP @OTP-15818@"/>
      <fsummary>Get miscellaneous socket info.</fsummary>
      <desc>
        <p>Get miscellaneous info about the socket.</p>
	<p>The function returns a map with each info item as a key-value
	binding. It reflects the "current" state of the socket. </p>
	<note>
	  <p>In order to ensure data integrity, mutex'es are taken when
	  needed. So, do not call this function often. </p>
	</note>
      </desc>
    </func>

    <func>
      <name name="listen" arity="1" since="OTP 22.0"/>
      <name name="listen" arity="2" since="OTP 22.0"/>
      <fsummary>Listen for connections on a socket.</fsummary>
      <desc>
        <p>Listen for connections on a socket.</p>
      </desc>
    </func>

    <func>
      <name name="open" arity="2" since="OTP 22.0"/>
      <name name="open" arity="3" since="OTP 22.0"/>
      <name name="open" arity="4" since="OTP 22.0"/>
      <fsummary>Create an endpoint for communication.</fsummary>
      <desc>
	<p>Creates an endpoint (socket) for communication.</p>

	<p>For some <c>types</c> there is a default protocol,
	indicated by <c>default</c>, which it <em>may</em> be
	possible to specify.
	And for <c>Domain = local</c>, if a protocol <em>is</em> pecified,
	it <em>must</em> be <c>default</c>. </p>

	<p>The <c>Extra</c> argument is intended for "obscure" options.
	Currently the only supported option is <c>netns</c>, which
	is only supported on the linux platform.</p>

	<note>
	  <p>It may not be possible to specify the default protocol (except
	  when <c>Domain = local</c>). We need to be able to retreive
	  the resulting protocol, which is <em>not</em> possble on all
	  platforms. </p>
	</note>
      </desc>
    </func>

    <func>
      <name name="peername" arity="1" since="OTP 22.0"/>
      <fsummary>Get name of connected socket peer.</fsummary>
      <desc>
        <p>Returns the address of the peer connected to the socket.</p>
      </desc>
    </func>

    <func>
      <name name="recv" arity="1" since="OTP 22.0"/>
      <name name="recv" arity="2" since="OTP 22.0"/>
      <name name="recv" arity="3" clause_i="1" since="OTP 22.0"/>
      <name name="recv" arity="3" clause_i="3" since="OTP 22.0"/>
      <name name="recv" arity="4" clause_i="2" since="OTP 22.0"/>
      <fsummary>Receive a message from a socket.</fsummary>
      <desc>
        <p>Receive a message from a socket.</p>
	<p>There is a special case for the argument <c>Length</c>.
	If it is set to zero (0), it means "give me everything you 
	currently have".</p>
      </desc>
    </func>

    <func>
      <name name="recv" arity="3" clause_i="2" anchor="recv_async" since="OTP @OTP-15731@"/>
      <name name="recv" arity="4" clause_i="1" since="OTP @OTP-15731@"/>
      <fsummary>Receive a message from a socket.</fsummary>
      <desc>
        <p>Receive a message from a socket.</p>

	<p>There is a special case for the argument <c>Length</c>.
	If it is set to zero (0), it means "give me everything you 
	currently have".</p>

	<p>In the case when there is no data waiting, the function 
	will return with the <c>SelectInfo</c>. The caller can then await a 
	select message, <c>{'$socket', Socket, select, Info}</c> (where
	<c>Info</c> is the
	<seealso marker="socket#type-select_ref"><c>ref</c></seealso>
	field from the <c>SelectInfo</c>),
	when data has arrived (a subsequent call to recv will then return 
	the data). </p>
	<p>Note that if a length (<c>> 0</c>) is specified, and only part
	of that amount of data is available, the function will return with
	that data <em>and</em> the <c>SelectInfo</c> (if the caller don't 
	want to wait for the remaining data, it must immediately call
	the <seealso marker="#cancel/2"><c>cancel/2</c></seealso> function.)</p>
      </desc>
    </func>

    <func>
      <name name="recvfrom" arity="1" since="OTP 22.0"/>
      <name name="recvfrom" arity="2" since="OTP 22.0"/>
      <name name="recvfrom" arity="3" clause_i="2" since="OTP 22.0"/>
      <name name="recvfrom" arity="3" clause_i="3" since="OTP 22.0"/>
      <name name="recvfrom" arity="3" clause_i="5" since="OTP 22.0"/>
      <name name="recvfrom" arity="4" clause_i="2" since="OTP 22.0"/>
      <fsummary>Receive a message from a socket.</fsummary>
      <desc>
        <p>Receive a message from a socket.</p>
        <p>This function reads "messages", which means that regardless of
	how much we want to read, it returns when we get a message
	(if the buffer size is to small, the message will be truncated).</p>
        <p>The <c>BufSz</c> argument basically defines the size of the
	receive buffer. By setting the value to zero (0), the configured
	size (setopt with <c>Level</c> = <c>otp</c> and
	<c>Key</c> = <c>rcvbuf</c>) is used.</p>
        <p>It may be impossible to know what (buffer) size is appropriate
	"in advance", and in those cases it may be convenient to use the
	(recv) 'peek' flag. When this flag is provided, the message is *not*
	"consumed" from the underlying buffers, so another recvfrom call
	is needed, possibly with a then adjusted buffer size.</p>
      </desc>
    </func>

    <func>
      <name name="recvfrom" arity="3" clause_i="1" anchor="recvfrom_async" since="OTP @OTP-15731@"/>
      <name name="recvfrom" arity="3" clause_i="4" since="OTP @OTP-15731@"/>
      <name name="recvfrom" arity="4" clause_i="1" since="OTP @OTP-15731@"/>
      <fsummary>Receive a message from a socket.</fsummary>
      <desc>
        <p>Receive a message from a socket.</p>
        <p>This function reads "messages", which means that regardless of
	how much we want to read, it returns when we get a message
	(if the buffer size is to small, the message will be truncated).</p>
        <p>The <c>BufSz</c> argument basically defines the size of the
	receive buffer. By setting the value to zero (0), the configured
	size (setopt with <c>Level</c> = <c>otp</c> and
	<c>Key</c> = <c>rcvbuf</c>) is used.</p>
        <p>It may be impossible to know what (buffer) size is appropriate
	"in advance", and in those cases it may be convenient to use the
	(recv) 'peek' flag. When this flag is provided, the message is *not*
	"consumed" from the underlying buffers, so another recvfrom call
	is needed, possibly with a then adjusted buffer size.</p>

	<p>In the case when there is no data waiting, the function 
	will return with the <c>SelectInfo</c>. The caller can then await a 
	select message, <c>{'$socket', Socket, select, Info}</c> (where
	<c>Info</c> is the
	<seealso marker="socket#type-select_ref"><c>ref</c></seealso>
	field from the <c>SelectInfo</c>),
	when data has arrived (a subsequent call to recvfrom will then return 
	the data). </p>
      </desc>
    </func>

    <func>
      <name name="recvmsg" arity="1" since="OTP 22.0"/>
      <name name="recvmsg" arity="2" clause_i="1" since="OTP 22.0"/>
      <name name="recvmsg" arity="2" clause_i="3" since="OTP 22.0"/>
      <name name="recvmsg" arity="3" clause_i="2" since="OTP 22.0"/>
      <name name="recvmsg" arity="3" clause_i="3" since="OTP 22.0"/>
      <name name="recvmsg" arity="5" clause_i="2" since="OTP 22.0"/>
      <fsummary>Receive a message from a socket.</fsummary>
      <desc>
        <p>Receive a message from a socket.</p>
        <p>This function reads "messages", which means that regardless of
	how much we want to read, it returns when we get a message.</p>
	<p>The message will be delivered in the form of a <c>msghdr()</c>,
	which may contain the source address (if socket not connected),
	a list of <c>cmsghdr_recv()</c> (depends on what socket options have
	been set and what the protocol and platform supports) and
	also a set of flags, providing further info about the read. </p>
	
        <p>The <c>BufSz</c> argument basically defines the size of the
	receive buffer. By setting the value to zero (0), the configured
	size (setopt with <c>Level</c> = <c>otp</c> and
	<c>Key</c> = <c>rcvbuf</c>) is used.</p>

        <p>The <c>CtrlSz</c> argument basically defines the size of the
	receive buffer for the control messages.
	By setting the value to zero (0), the configured size (setopt
	with <c>Level</c> = <c>otp</c>) is used.</p>

	<p>It may be impossible to know what (buffer) size is appropriate
	"in advance", and in those cases it may be convenient to use the
	(recv) 'peek' flag. When this flag is provided, the message is *not*
	"consumed" from the underlying buffers, so another recvmsg call
	is needed, possibly with a then adjusted buffer size.</p>
      </desc>
    </func>

    <func>
      <name name="recvmsg" arity="2" clause_i="2" anchor="recvmsg_async" since="OTP @OTP-15731@"/>
      <name name="recvmsg" arity="3" clause_i="1" since="OTP @OTP-15731@"/>
      <name name="recvmsg" arity="5" clause_i="1" since="OTP @OTP-15731@"/>
      <fsummary>Receive a message from a socket.</fsummary>
      <desc>
        <p>Receive a message from a socket.</p>
        <p>This function reads "messages", which means that regardless of
	how much we want to read, it returns when we get a message.</p>
	<p>The message will be delivered in the form of a <c>msghdr()</c>,
	which may contain the source address (if socket not connected),
	a list of <c>cmsghdr_recv()</c> (depends on what socket options have
	been set and what the protocol and platform supports) and
	also a set of flags, providing further info about the read. </p>
	
        <p>The <c>BufSz</c> argument basically defines the size of the
	receive buffer. By setting the value to zero (0), the configured
	size (setopt with <c>Level</c> = <c>otp</c> and
	<c>Key</c> = <c>rcvbuf</c>) is used.</p>

        <p>The <c>CtrlSz</c> argument basically defines the size of the
	receive buffer for the control messages.
	By setting the value to zero (0), the configured size (setopt
	with <c>Level</c> = <c>otp</c>) is used.</p>

	<p>It may be impossible to know what (buffer) size is appropriate
	"in advance", and in those cases it may be convenient to use the
	(recv) 'peek' flag. When this flag is provided, the message is *not*
	"consumed" from the underlying buffers, so another recvmsg call
	is needed, possibly with a then adjusted buffer size.</p>

	<p>In the case when there is no data waiting, the function 
	will return with the <c>SelectInfo</c>. The caller can then await a 
	select message, <c>{'$socket', Socket, select, Info}</c> (where
	<c>Info</c> is the
	<seealso marker="socket#type-select_ref"><c>ref</c></seealso>
	field from the <c>SelectInfo</c>),
	when data has arrived (a subsequent call to recvmsg will then return 
	the data). </p>
      </desc>
    </func>

    <func>
      <name name="send" arity="2" since="OTP 22.0"/>
      <name name="send" arity="3" clause_i="1" since="OTP 22.0"/>
      <name name="send" arity="3" clause_i="3" since="OTP 22.0"/>
      <name name="send" arity="4" clause_i="2" since="OTP 22.0"/>
      <fsummary>Send a message on a socket.</fsummary>
      <desc>
        <p>Send a message on a connected socket.</p>
      </desc>
    </func>

    <func>
      <name name="send" arity="3" clause_i="2" anchor="send_async" since="OTP @OTP-15731@"/>
      <name name="send" arity="4" clause_i="1" since="OTP @OTP-15731@"/>
      <fsummary>Send a message on a socket.</fsummary>
      <desc>
        <p>Send a message on a connected socket.</p>

	<p>In the case when there is no room in the (system-) buffers,
	the function will return with the <c>SelectInfo</c>. The caller
	can then await a select message,
	<c>{'$socket', Socket, select, Info}</c>
	(where <c>Info</c> is the
	<seealso marker="socket#type-select_ref"><c>ref</c></seealso>
	field from the
	<c>SelectInfo</c>), when there is room for more data (a subsequent
	call to send will then send the data). </p>
	<p>Note that if not all the data was sent, the function will return
	with the remaining data <em>and</em> the <c>SelectInfo</c>
	(if the caller don't 
	want to wait to be able to send the rest, it should immediately call
	the <seealso marker="#cancel/2"><c>cancel/2</c></seealso> function.)</p>
      </desc>
    </func>

    <func>
      <name name="sendmsg" arity="2" since="OTP 22.0"/>
      <name name="sendmsg" arity="3" clause_i="1" since="OTP 22.0"/>
      <name name="sendmsg" arity="3" clause_i="3" since="OTP 22.0"/>
      <name name="sendmsg" arity="4" clause_i="2" since="OTP 22.0"/>
      <fsummary>Send a message on a socket.</fsummary>
      <desc>
	<p>Send a message on a socket. The destination, if needed
	(socket <em>not</em> connected) is provided in the <c>MsgHdr</c>,
	which also contains the message to send,
	The <c>MsgHdr</c> may also contain an list of optional <c>cmsghdr_send()</c>
	(depends on what the protocol and platform supports).</p>

	<p>Unlike the <seealso marker="#send/2"><c>send</c></seealso> function,
	this one sends <em>one message</em>.
	This means that if, for whatever reason, its not possible to send the
	message in one go, the function will instead return with the
	<em>remaining</em> data (<c>{ok, Remaining}</c>). Thereby leaving it
	up to the caller to decide what to do (retry with the remaining data
	of give up). </p>

      </desc>
    </func>

    <func>
      <name name="sendmsg" arity="3" clause_i="2" anchor="sendmsg_async" since="OTP @OTP-15731@"/>
      <name name="sendmsg" arity="4" clause_i="1" since="OTP @OTP-15731@"/>
      <fsummary>Send a message on a socket.</fsummary>
      <desc>
	<p>Send a message on a socket. The destination, if needed
	(socket <em>not</em> connected) is provided in the <c>MsgHdr</c>,
	which also contains the message to send,
	The <c>MsgHdr</c> may also contain an list of optional <c>cmsghdr_send()</c>
	(depends on what the protocol and platform supports).</p>

	<p>Unlike the <seealso marker="#send/2"><c>send</c></seealso> function,
	this one sends <em>one message</em>.
	This means that if, for whatever reason, its not possible to send the
	message in one go, the function will instead return with the
	<em>remaining</em> data (<c>{ok, Remaining}</c>). Thereby leaving it
	up to the caller to decide what to do (retry with the remaining data
	of give up). </p>

	<p>In the case when there is no room in the (system-) buffers,
	the function will return with the <c>SelectInfo</c>. The caller
	can then await a select message,
	<c>{'$socket', Socket, select, Info}</c>
	(where <c>Info</c> is the
	<seealso marker="socket#type-select_ref"><c>ref</c></seealso>
	field from the
	<c>SelectInfo</c>), when there is room for more data (a subsequent
	call to sendmsg will then send the data). </p>
      </desc>
    </func>

    <func>
      <name name="sendto" arity="3" since="OTP 22.0"/>
      <name name="sendto" arity="4" clause_i="1" since="OTP 22.0"/>
      <name name="sendto" arity="4" clause_i="3" since="OTP 22.0"/>
      <name name="sendto" arity="5" clause_i="2" since="OTP 22.0"/>
      <fsummary>Send a message on a socket.</fsummary>
      <desc>
        <p>Send a message on a socket, to the specified destination.</p>
      </desc>
    </func>

    <func>
      <name name="sendto" arity="4" clause_i="2" anchor="sendto_async" since="OTP @OTP-15731@"/>
      <name name="sendto" arity="5" clause_i="1" since="OTP @OTP-15731@"/>
      <fsummary>Send a message on a socket.</fsummary>
      <desc>
        <p>Send a message on a socket, to the specified destination.</p>

	<p>In the case when there is no room in the (system-) buffers,
	the function will return with the <c>SelectInfo</c>. The caller
	can then await a select message,
	<c>{'$socket', Socket, select, Info}</c>
	(where <c>Info</c> is the
	<seealso marker="socket#type-select_ref"><c>ref</c></seealso>
	field from the
	<c>SelectInfo</c>), when there is room for more data (a subsequent
	call to sendto will then send the data). </p>
      </desc>
    </func>

    <func>
      <name name="setopt" arity="4" clause_i="1" since="OTP 22.0"/>
      <name name="setopt" arity="4" clause_i="2" since="OTP 22.0"/>
      <name name="setopt" arity="4" clause_i="3" since="OTP 22.0"/>
      <name name="setopt" arity="4" clause_i="4" since="OTP 22.0"/>
      <name name="setopt" arity="4" clause_i="5" since="OTP 22.0"/>
      <name name="setopt" arity="4" clause_i="6" since="OTP 22.0"/>
      <name name="setopt" arity="4" clause_i="7" since="OTP 22.0"/>
      <fsummary>Set options on a socket.</fsummary>
      <desc>
        <p>Set options on a socket.</p>
	<p>What properties are valid depend both on <c>Level</c> and on
	what kind of socket it is (<c>domain</c>, <c>type</c> and
	<c>protocol</c>).</p>

	<p>See the
	<seealso marker="socket_usage#socket_options">socket options</seealso>
	chapter of the users guide for more info. </p>

	<note><p>Not all options are valid on all platforms. That is,
	even if "we" support an option, that does not mean that the
	underlying OS does.</p></note>

	<note><p>Sockets are set 'non-blocking' when created, so this option
	is *not* available (as it would adversely effect the Erlang VM
	to set a socket 'blocking').</p></note>
      </desc>
    </func>

    <func>
      <name name="setopt" arity="4" clause_i="8" since="OTP 22.0"/>
      <fsummary>Set options on a socket.</fsummary>
      <desc>
        <p>Set options on a socket.</p>
	<p>What properties are valid depend both on <c>Level</c> and on
	what kind of socket it is (<c>domain</c>, <c>type</c> and
	<c>protocol</c>).</p>

	<p>See the
	<seealso marker="socket_usage#socket_options">socket options</seealso>
	chapter of the users guide for more info. </p>

	<note><p>Not all options are valid on all platforms. That is,
	even if "we" support an option, that does not mean that the
	underlying OS does.</p></note>

	<note><p>Sockets are set 'non-blocking' when created, so this option
	is *not* available (as it would adversely effect the Erlang VM
	to set a socket 'blocking').</p></note>
      </desc>
    </func>

    <func>
      <name name="shutdown" arity="2" since="OTP 22.0"/>
      <fsummary>Shut down part of a full-duplex connection.</fsummary>
      <desc>
        <p>Shut down all or part of a full-duplex connection.</p>
      </desc>
    </func>

    <func>
      <name name="sockname" arity="1" since="OTP 22.0"/>
      <fsummary>Get socket name.</fsummary>
      <desc>
        <p>Returns the current address to which the socket is bound.</p>
      </desc>
    </func>

    <func>
      <name name="supports" arity="0" since="OTP 22.0"/>
      <name name="supports" arity="1" clause_i="1" since="OTP 22.0"/>
      <name name="supports" arity="1" clause_i="2" since="OTP 22.0"/>
      <name name="supports" arity="1" clause_i="3" since="OTP 22.0"/>
      <name name="supports" arity="1" clause_i="4" since="OTP 22.0"/>
      <name name="supports" arity="2" clause_i="1" since="OTP 22.0"/>
      <name name="supports" arity="2" clause_i="2" since="OTP 22.0"/>
      <name name="supports" arity="2" clause_i="3" since="OTP 22.0"/>
      <name name="supports" arity="2" clause_i="4" since="OTP 22.0"/>
      <name name="supports" arity="2" clause_i="5" since="OTP 22.0"/>
      <name name="supports" arity="2" clause_i="6" since="OTP 22.0"/>
      <name name="supports" arity="2" clause_i="7" since="OTP 22.0"/>
      <name name="supports" arity="3" clause_i="1" since="OTP 22.0"/>
      <name name="supports" arity="3" clause_i="2" since="OTP 22.0"/>
      <name name="supports" arity="3" clause_i="3" since="OTP 22.0"/>
      <name name="supports" arity="3" clause_i="4" since="OTP 22.0"/>
      <name name="supports" arity="3" clause_i="5" since="OTP 22.0"/>
      <name name="supports" arity="3" clause_i="6" since="OTP 22.0"/>
      <name name="supports" arity="3" clause_i="7" since="OTP 22.0"/>
      <fsummary>Report info about what the platform supports.</fsummary>
      <desc>
	<p>This function intends to retreive information about what the
	platform supports. Such as if SCTP is supported. Or which socket
	options are supported. </p>
      </desc>
    </func>

  </funcs>
  <section>
    <title>Examples</title>
    <marker id="examples"></marker>
    <code type="none">
client(Addr, SAddr, SPort) ->
   {ok, Sock} = socket:open(inet, stream, tcp),
   {ok, _} = socket:bind(Sock, #{family => inet,
                                 addr   => Addr}),
   ok = socket:connect(Sock, #{family => inet,
                               addr   => SAddr,
			       port   => SPort}),
   Msg = list_to_binary("hello"),
   ok = socket:send(Sock, Msg),
   ok = socket:shutdown(Sock, write),
   {ok, Msg} = socket:recv(Sock),
   ok = socket:close(Sock).

server(Addr, Port) ->  
   {ok, LSock} = socket:open(inet, stream, tcp),
   {ok, _} = socket:bind(LSock, #{family => inet,
                                  port   => Port,
		 	          addr   => Addr}),
   ok = socket:listen(LSock),
   {ok, Sock} = socket:accept(LSock),
   {ok, Msg} = socket:recv(Sock),
   ok = socket:send(Sock, Msg),
   ok = socket:shutdown(Sock, write),
   ok = socket:close(Sock),
   ok = socket:close(LSock).
    </code>
  </section>
</erlref>