162 lines
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HTML
162 lines
11 KiB
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<meta name="DC.Title" content="Use AF_UNIX address family" />
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<meta name="abstract" content="The AF_UNIX address family (sockets using the AF_UNIX or AF_UNIX_CCSID address families) can be connection-oriented (type SOCK_STREAM) or they can be connectionless (type SOCK_DGRAM)." />
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<link rel="stylesheet" type="text/css" href="./ibmdita.css" />
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<link rel="stylesheet" type="text/css" href="./ic.css" />
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<title>Use AF_UNIX address family</title>
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</head>
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<body id="uafunix"><a name="uafunix"><!-- --></a>
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<!-- Java sync-link --><script language="Javascript" src="../rzahg/synch.js" type="text/javascript"></script>
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<h1 class="topictitle1">Use AF_UNIX address family</h1>
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<div><p>The AF_UNIX address family (sockets using the AF_UNIX or AF_UNIX_CCSID
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address families) can be connection-oriented (type SOCK_STREAM) or they can
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be connectionless (type SOCK_DGRAM). </p>
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<div class="section"><p>Both types are reliable because there are no external communication
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functions connecting the two processes. </p>
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</div>
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<div class="section"><p>UNIX<sup>®</sup> domain datagram sockets act differently
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than UDP datagram sockets. With UDP datagram sockets, the client program does
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not need to call the <span class="apiname">bind()</span> function because the system
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assigns an unused port number automatically. The server can then send a datagram
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back to that port number. However, with UNIX domain datagram sockets, the system
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does not automatically assign a path name for the client. Thus, all client
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programs using UNIX domain datagrams must call the <span class="apiname">bind()</span> function.
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The exact path name specified on the client's <span class="apiname">bind()</span> is
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what is passed to the server. Thus, if the client specifies a relative path
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name (that is, a path name that is not fully qualified by starting with /),
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the server cannot send the client a datagram unless it is running with the
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same current directory.</p>
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</div>
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<div class="section"><div class="p">An example path name that an application might use for this address
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family is /tmp/myserver or servers/thatserver. With servers/thatserver, you
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have a path name that is not fully qualified (no / was specified). This means
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that the location of the entry in the file system hierarchy should be determined
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relative to the current working directory. <div class="note"><span class="notetitle">Note:</span> Path names in the file system
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are NLS-enabled. </div>
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</div>
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</div>
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<div class="section"><p>The following figure illustrates the client/server relationship
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of the AF_UNIX address family. </p>
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</div>
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<div class="section"><p><br /><img src="rzab6503.gif" alt="Socket flow of events used in server and client AF_UNIX address family example programs." /><br /></p>
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</div>
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<div class="section"><h4 class="sectiontitle">Socket flow of events: Server application that uses AF_UNIX
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address family</h4><p>The first example uses the following sequence of
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function calls:</p>
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<ol><li>The <span class="apiname">socket()</span> function returns a socket descriptor representing
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an endpoint. The statement also identifies the UNIX address family with the stream transport
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(SOCK_STREAM) being used for this socket. The function returns a socket descriptor
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representing an endpoint. You can also use the <span class="apiname">socketpair()</span> function
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to initialize a UNIX socket. <p>AF_UNIX or AF_UNIX_CCSID are the only
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address families to support the <span class="apiname">socketpair()</span> function.
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The <span class="apiname">socketpair()</span> function returns two socket descriptors
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that are unnamed and connected.</p>
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</li>
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<li>After the socket descriptor is created, the <span class="apiname">bind()</span> function
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gets a unique name for the socket. <p>The name space for UNIX domain sockets
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consists of path names. When a sockets program calls the <span class="apiname">bind()</span> function,
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an entry is created in the file system directory. If the path name already
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exists, the <span class="apiname">bind()</span> fails. Thus, a UNIX domain socket
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program should always call an <span class="apiname">unlink()</span> functions to remove
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the directory entry when it ends. </p>
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</li>
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<li>The <span class="apiname">listen()</span> allows the server to accept incoming
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client connections. In this example, the backlog is set to 10. This means
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that the system queues 10 incoming connection requests before the system starts
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rejecting the incoming requests.</li>
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<li>The <span class="apiname">recv()</span> function receives data
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from the client application. In this example, the client sends 250 bytes of
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data over. Thus SO_RCVLOWAT socket option can be used, specifying that <span class="apiname">recv()</span> is
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not required to wake up until all 250 bytes of data have arrived. </li>
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<li>The <span class="apiname">send()</span> function echoes the data back to the client. </li>
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<li>The <span class="apiname">close()</span> function closes any open socket descriptors.</li>
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<li>The <span class="apiname">unlink()</span> function removes the UNIX path name
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from the file system. </li>
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</ol>
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</div>
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<div class="section"><h4 class="sectiontitle">Socket flow of events: Client application that uses AF_UNIX
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address family</h4><p>The second example uses the following sequence of
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function calls:</p>
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<ol><li>The <span class="apiname">socket()</span> function returns a socket descriptor representing
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an endpoint. The statement also identifies the UNIX address family
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with the stream transport (SOCK_STREAM) being used for this socket. The function
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returns a socket descriptor representing an endpoint. You can also use the <span class="apiname">socketpair()</span> function
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to initialize a UNIX socket. <p>AF_UNIX or AF_UNIX_CCSID are the only
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address families to support the <span class="apiname">socketpair()</span> function.
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The <span class="apiname">socketpair()</span> function returns two socket descriptors
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that are unnamed and connected.</p>
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</li>
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<li>After the socket descriptor is received, the <span class="apiname">connect()</span> function
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is used to establish a connection to the server.</li>
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<li>The <span class="apiname">send()</span> function sends 250 bytes of data that are
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specified in the server application with the SO_RCVLOWAT socket option. </li>
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<li>The <span class="apiname">recv()</span> function loops until all 250 bytes of the
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data have arrived. </li>
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<li>The <span class="apiname">close()</span> function closes any open socket descriptors.</li>
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</ol>
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</div>
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</div>
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<div>
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<ul class="ullinks">
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<li class="ulchildlink"><strong><a href="xafunixsrv.htm">Example: Server application that uses AF_UNIX address family</a></strong><br />
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This example provides a sample program that uses the AF_UNIX address family. The AF_UNIX address family uses many of the same socket calls as other address families, except that it uses the path name structure to identify the server application.</li>
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<li class="ulchildlink"><strong><a href="xafunixcl.htm">Example: Client application that uses AF_UNIX address family</a></strong><br />
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This example provides a sample client application for the AF_UNIX address family. The AF_UNIX address family uses many of the same socket calls as other address families, except that it uses the path name structure to identify the server application.</li>
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</ul>
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<div class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a href="uaddrfam.htm" title="This topic includes sample programs that illustrate each of the socket address families.">Design applications with address families</a></div>
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</div>
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<div class="relref"><strong>Related reference</strong><br />
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<div><a href="cafunix.htm" title="This address family provides interprocess communications on the same system that uses the socket APIs. The address is really a path name to an entry in the file system.">AF_UNIX address family</a></div>
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<div><a href="prerequisites.htm" title="Before writing socket applications, you must first complete these steps.">Prerequisites for socket programming</a></div>
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<div><a href="uafunixccsid.htm" title="AF_UNIX_CCSID address family sockets have the same specifications as AF_UNIX address family sockets. They can be used for connection-oriented or connectionless and provide communications on the same system.">Use AF_UNIX_CCSID address family</a></div>
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</div>
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<div class="relinfo"><strong>Related information</strong><br />
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<div><a href="../apis/close.htm">close()</a></div>
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<div><a href="../apis/socket.htm">socket()</a></div>
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<div><a href="../apis/bind.htm">bind()</a></div>
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<div><a href="../apis/unlink.htm">unlink()</a></div>
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<div><a href="../apis/listen.htm">listen()</a></div>
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<div><a href="../apis/send.htm">send()</a></div>
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<div><a href="../apis/recv.htm">recv()</a></div>
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<div><a href="../apis/socketp.htm">socketpair()</a></div>
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<div><a href="../apis/connec.htm">connect()</a></div>
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</div>
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</div>
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</body>
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</html>
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