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<?xml version="1.0" encoding="iso-8859-1"?>
<!-- $Revision: 1.12 $ -->
<!-- splitted from ./en/functions/sockets.xml, last change in rev 1.27 -->
<refentry id="function.socket-create-pair">
<refnamediv>
<refname>socket_create_pair</refname>
<refpurpose>Creates a pair of indistinguishable sockets and stores them in an array</refpurpose>
</refnamediv>
<refsect1>
<title>Description</title>
<methodsynopsis>
<type>bool</type><methodname>socket_create_pair</methodname>
<methodparam><type>int</type><parameter>domain</parameter></methodparam>
<methodparam><type>int</type><parameter>type</parameter></methodparam>
<methodparam><type>int</type><parameter>protocol</parameter></methodparam>
<methodparam><type>array</type><parameter role="reference">fd</parameter></methodparam>
</methodsynopsis>
<para>
<function>socket_create_pair</function> creates two connected and indistinguishable sockets, and stores
them in <parameter>fd</parameter>. This function is commonly used in IPC (InterProcess Communication).
</para>
<para>
The <parameter>domain</parameter> parameter specifies the protocol
family to be used by the socket.
</para>
<table>
<title>Available address/protocol families</title>
<tgroup cols="2">
<thead>
<row>
<entry>Domain</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry>AF_INET</entry>
<entry>
IPv4 Internet based protocols. TCP and UDP are common protocols of
this protocol family. Supported only in windows.
</entry>
</row>
<row>
<entry>AF_INET6</entry>
<entry>
IPv6 Internet based protocols. TCP and UDP are common protocols of
this protocol family. Support added in PHP 5.0.0.
Supported only in windows.
</entry>
</row>
<row>
<entry>AF_UNIX</entry>
<entry>
Local communication protocol family. High efficiency and low
overhead make it a great form of IPC (Interprocess Communication).
</entry>
</row>
</tbody>
</tgroup>
</table>
<para>
The <parameter>type</parameter> parameter selects the type of communication
to be used by the socket.
</para>
<table>
<title>Available socket types</title>
<tgroup cols="2">
<thead>
<row>
<entry>Type</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry>SOCK_STREAM</entry>
<entry>
Provides sequenced, reliable, full-duplex, connection-based byte streams.
An out-of-band data transmission mechanism may be supported.
The TCP protocol is based on this socket type.
</entry>
</row>
<row>
<entry>SOCK_DGRAM</entry>
<entry>
Supports datagrams (connectionless, unreliable messages of a fixed maximum length).
The UDP protocol is based on this socket type.
</entry>
</row>
<row>
<entry>SOCK_SEQPACKET</entry>
<entry>
Provides a sequenced, reliable, two-way connection-based data transmission path for
datagrams of fixed maximum length; a consumer is required to read an
entire packet with each read call.
</entry>
</row>
<row>
<entry>SOCK_RAW</entry>
<entry>
Provides raw network protocol access. This special type of socket
can be used to manually construct any type of protocol. A common use
for this socket type is to perform ICMP requests (like ping,
traceroute, etc).
</entry>
</row>
<row>
<entry>SOCK_RDM</entry>
<entry>
Provides a reliable datagram layer that does not guarantee ordering.
This is most likely not implemented on your operating system.
</entry>
</row>
</tbody>
</tgroup>
</table>
<para>
The <parameter>protocol</parameter> parameter sets the specific
protocol within the specified <parameter>domain</parameter> to be used
when communicating on the returned socket. The proper value can be retrieved by
name by using <function>getprotobyname</function>. If
the desired protocol is TCP, or UDP the corresponding constants
<constant>SOL_TCP</constant>, and <constant>SOL_UDP</constant>
can also be used.
</para>
<table>
<title>Common protocols</title>
<tgroup cols="2">
<thead>
<row>
<entry>Name</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry>icmp</entry>
<entry>
The Internet Control Message Protocol is used primarily by gateways
and hosts to report errors in datagram communication. The "ping"
command (present in most modern operating systems) is an example
application of ICMP.
</entry>
</row>
<row>
<entry>udp</entry>
<entry>
The User Datagram Protocol is a connectionless, unreliable,
protocol with fixed record lengths. Due to these aspects, UDP
requires a minimum amount of protocol overhead.
</entry>
</row>
<row>
<entry>tcp</entry>
<entry>
The Transmission Control Protocol is a reliable, connection based,
stream oriented, full duplex protocol. TCP guarantees that all data packets
will be received in the order in which they were sent. If any packet is somehow
lost during communication, TCP will automatically retransmit the packet until
the destination host acknowledges that packet. For reliability and performance
reasons, the TCP implementation itself decides the appropriate octet boundaries
of the underlying datagram communication layer. Therefore, TCP applications must
allow for the possibility of partial record transmission.
</entry>
</row>
</tbody>
</tgroup>
</table>
<para>
<example>
<title><function>socket_create_pair</function> example</title>
<programlisting role="php">
<![CDATA[
<?php
$sockets = array();
/* Setup socket pair */
if (!socket_create_pair(AF_UNIX, SOCK_STREAM, 0, $sockets)) {
echo socket_strerror(socket_last_error());
}
/* Send and Recieve Data */
if (!socket_write($sockets[0], "ABCdef123\n", strlen("ABCdef123\n"))) {
echo socket_strerror(socket_last_error());
}
if (!$data = socket_read($sockets[1], strlen("ABCdef123\n"), PHP_BINARY_READ)) {
echo socket_strerror(socket_last_error());
}
var_dump($data);
/* Close sockets */
socket_close($sockets[0]);
socket_close($sockets[1]);
?>
]]>
</programlisting>
</example>
</para>
<para>
<example>
<title><function>socket_create_pair</function> IPC example</title>
<programlisting role="php">
<![CDATA[
<?php
$ary = array();
$strone = 'Message From Parent.';
$strtwo = 'Message From Child.';
if (!socket_create_pair(AF_UNIX, SOCK_STREAM, 0, $ary)) {
echo socket_strerror(socket_last_error());
}
$pid = pcntl_fork();
if ($pid == -1) {
echo 'Could not fork Process.';
} elseif ($pid) {
/*parent*/
socket_close($ary[0]);
if (!socket_write($ary[1], $strone, strlen($strone))) {
echo socket_strerror(socket_last_error());
}
if (socket_read($ary[1], strlen($strtwo), PHP_BINARY_READ) == $strtwo) {
echo "Recieved $strtwo\n";
}
socket_close($ary[1]);
} else {
/*child*/
socket_close($ary[1]);
if (!socket_write($ary[0], $strtwo, strlen($strtwo))) {
echo socket_strerror(socket_last_error());
}
if (socket_read($ary[0], strlen($strone), PHP_BINARY_READ) == $strone) {
echo "Recieved $strone\n";
}
socket_close($ary[0]);
}
?>
]]>
</programlisting>
</example>
</para>
</refsect1>
</refentry>
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