ch15_01.htm

by Randal L. Schwartz and Tom Phoenix ISBN 0-596-00132-0 Third Edition, published July 2001. (See

<p>The <tt class="literal">sockaddr_in</tt> function takes a port number for
its first argument and a 32-bit IP address for the second argument.
The 32-bit address is formed from the <tt class="literal">inet_aton</tt>
function found in the Socket package. This function takes either a
hostname (e.g., www.oreilly.com)
or a dotted-decimal string (e.g., 207.54.2.25) and returns the
corresponding 32-bit structure.
</p>

<p>Continuing with the previous example, a call to
<tt class="literal">connect</tt> could look like this:
</p>

<blockquote><pre class="code">my $dest = sockaddr_in (80, inet_aton('www.oreilly.com'));
connect (SH, $dest) || die $!;</pre></blockquote>

<p>This call attempts to establish a network connection to the specified
server and port. If successful, it returns true. Otherwise, it
returns false and <tt class="literal">die</tt> s with the error in
<tt class="literal">$!</tt>.
</p>

<p>Assuming that the <tt class="literal">connect</tt> call has completed
successfully and a connection has been established, there are a
number of functions we can use to write to and read from the
filehandle. For example, the <tt class="literal">send</tt> function sends
data to a socket:
</p>

<blockquote><pre class="code">$data = "Hello";
send (FH, $data);</pre></blockquote>

<p><a name="INDEX-1923" /></a>The <tt class="literal">print</tt> function
allows a wider variety of expressions for sending data to a
filehandle:
</p>

<blockquote><pre class="code">select (FH);
print "$data";</pre></blockquote>

<p>To read incoming data from a socket, use either the
<tt class="literal">recv</tt> function or the diamond input operator
regularly used on filehandles. For example:
</p>

<blockquote><pre class="code">recv (FH, $buffer);
$input = &lt;FH&gt;;</pre></blockquote>

<p>After the conversation with the server is finished, use
<tt class="literal">close</tt> or <tt class="literal">shutdown</tt> to close the
connection and destroy the socket.
</p>

</div>
<a name="perlnut2-CHP-15-SECT-1.3" /></a><div class="sect2">
<h3 class="sect2">15.1.3. Server Connections</h3>

<p><a name="INDEX-1924" /></a><a name="INDEX-1925" /></a>After creating a socket with the
<tt class="literal">socket</tt> function as you did previously, a server
application must go through the following steps to receive network
connections:
</p>

<ol><li>
<p>Bind a port number and machine address to the
socket<a name="INDEX-1926" /></a>
</p>
</li><li>
<p>Listen for incoming connections from clients on the port</p>
</li><li>
<p>Accept a client request and assign the connection to a specific
filehandle
</p>
</li></ol>
<p>We start out by creating a socket for the server: </p>

<blockquote><pre class="code">my $proto = getprotobyname('tcp');
socket(FH, PF_INET, SOCK_STREAM, $proto) || die $!;</pre></blockquote>

<p>The filehandle <tt class="literal">$FH</tt> is the generic filehandle for
the socket. This filehandle only receives requests from clients; each
specific connection is passed to a different filehandle by
<tt class="literal">accept</tt>, where the rest of the communication
occurs.
</p>

<p>A server-side socket must be bound to a port on the local machine by
passing a port and an address data structure to the
<tt class="literal">bind</tt> <a name="INDEX-1927" /></a>function via
<tt class="literal">sockaddr_in</tt>. The Socket module provides
identifiers for common local addresses, such as localhost and the
broadcast address. Here we use <tt class="literal">INADDR_ANY</tt>, which
allows the system to pick the appropriate address for the machine:
</p>

<blockquote><pre class="code">my $sin = sockaddr_in (80, INADDR_ANY);
bind (FH, $sin) || die $!;</pre></blockquote>

<p><a name="INDEX-1928" /></a>The <tt class="literal">listen</tt> function
tells the operating system that the server is ready to accept
incoming network connections on the port. The first argument is the
socket filehandle. The second argument gives a queue length, in case
multiple clients are connecting to the port at the same time. This
number indicates how many clients can wait for an
<tt class="literal">accept</tt> at one time.
</p>

<blockquote><pre class="code">listen (FH, $length);</pre></blockquote>

<p><a name="INDEX-1929" /></a>The <tt class="literal">accept</tt>
function completes a connection after a client requests and assigns a
new filehandle specific to that connection. The new filehandle is
given as the first argument to <tt class="literal">accept</tt>, and the
generic socket filehandle is given as the second:
</p>

<blockquote><pre class="code">accept (NEW, FH) || die $!;</pre></blockquote>

<p>Now the server can read and write to the filehandle
<tt class="literal">NEW</tt> for its communication with the client.
</p>

</div>
<a name="perlnut2-CHP-15-SECT-1.4" /></a><div class="sect2">
<h3 class="sect2">15.1.4. Socket Module Functions</h3>

<p><a name="INDEX-1930" /></a>The following functions are imported
from the Socket module for use in socket applications.
</p>

<a name="INDEX-1931" /></a><div class="refentry"><table width="515" border="0" cellpadding="5"><tr><td align="left"><font size="+1"><b>inet_aton</b></font></td><td align="right"><i></i></td></tr></table><hr width="515" size="3" true align="left" color="black" /><pre>
inet_aton (<em class="replaceable">hostname</em>)
</pre><p><a name="INDEX-1931" /></a>Translates a hostname such as
<em class="emphasis">www.oreilly.com</em> or 18.181.0.24
into a data structure (a four-byte string) used for socket addresses.
If the hostname cannot be resolved, the function returns the
undefined value.
</p></div>

<a name="INDEX-1932" /></a><div class="refentry"><table width="515" border="0" cellpadding="5"><tr><td align="left"><font size="+1"><b>inet_ntoa</b></font></td><td align="right"><i></i></td></tr></table><hr width="515" size="3" true align="left" color="black" /><pre>
inet_ntoa (<em class="replaceable">addr_string</em>)
</pre><p><a name="INDEX-1932" /></a>Translates a four-byte address string
(as returned by <tt class="literal">inet_aton</tt>) into a string with the
dotted-quad form of IP address.
</p></div>

<a name="INDEX-1933" /></a><div class="refentry"><table width="515" border="0" cellpadding="5"><tr><td align="left"><font size="+1"><b>sockaddr_in</b></font></td><td align="right"><i></i></td></tr></table><hr width="515" size="3" true align="left" color="black" /><table width="515" border="0" cellpadding="5"><tr><td align="left"><pre>
sockaddr_in (<em class="replaceable">port</em>, <em class="replaceable">addr_string</em>)
pack_sockaddr_in (<em class="replaceable">port</em>, <em class="replaceable">addr_string</em>)
</pre></td><td align="right" /></tr></table><p><p><a name="INDEX-1933" /></a>Takes
a port number and a four-byte <em class="replaceable"><tt>addr_string</tt></em>(as returned by <tt class="literal">inet_aton</tt>) and returns the socket
address structure including those arguments packed with the AF_INET
argument. This structure is normally what you need for the arguments
in <tt class="literal">bind</tt>, <tt class="literal">connect</tt>, and
<tt class="literal">send</tt>, and is also returned by
<tt class="literal">getpeername</tt>, <tt class="literal">getsockname</tt>, and
<tt class="literal">recv</tt>.
</p></div>

<a name="INDEX-1934" /></a><div class="refentry"><table width="515" border="0" cellpadding="5"><tr><td align="left"><font size="+1"><b>sockaddr_un</b></font></td><td align="right"><i></i></td></tr></table><hr width="515" size="3" true align="left" color="black" /><table width="515" border="0" cellpadding="5"><tr><td align="left"><pre>
sockaddr_un (<em class="replaceable">pathname</em>)
pack_sockaddr_un (<em class="replaceable">pathname</em>)
</pre></td><td align="right" /></tr></table><p><p><a name="INDEX-1934" /></a>Takes
one argument, a pathname, and returns the Unix domain socket address
structure (the path packed in with AF_UNIX filled in). For Unix
domain sockets, this structure is normally what you need for the
arguments in <tt class="literal">bind</tt>, <tt class="literal">connect</tt>, and
<tt class="literal">send</tt>, and is also returned by
<tt class="literal">getpeername</tt>, <tt class="literal">getsockname</tt>, and
<tt class="literal">recv</tt>.
</p></div>

<a name="INDEX-1935" /></a><div class="refentry"><table width="515" border="0" cellpadding="5"><tr><td align="left"><font size="+1"><b>unpack_sockaddr_in</b></font></td><td align="right"><i></i></td></tr></table><hr width="515" size="3" true align="left" color="black" /><table width="515" border="0" cellpadding="5"><tr><td align="left"><pre>
unpack_sockaddr_in (<em class="replaceable">sockaddr</em>)
sockaddr_in (<em class="replaceable">sockaddr</em>) 
</pre></td><td align="right" /></tr></table><p><p><a name="INDEX-1935" /></a>Takes a socket address structure and
returns an array of two elements (in list context): the port number
and the four-byte IP address.
</p></div>

<a name="INDEX-1936" /></a><a name="INDEX-1937" /></a><a name="INDEX-1938" /></a><a name="INDEX-1939" /></a><a name="INDEX-1940" /></a><div class="refentry"><table width="515" border="0" cellpadding="5"><tr><td align="left"><font size="+1"><b>unpack_sockaddr_un</b></font></td><td align="right"><i></i></td></tr></table><hr width="515" size="3" true align="left" color="black" /><table width="515" border="0" cellpadding="5"><tr><td align="left"><pre>
unpack_sockaddr_un (<em class="replaceable">sockaddr_un</em>)
sockaddr_un (<em class="replaceable">sockaddr_un</em>) 
</pre></td><td align="right" /></tr></table><p><p><a name="INDEX-1936" /></a>Takes a Unix domain socket address
structure (as returned by <tt class="literal">sockaddr_un</tt>) and returns
the pathname.
</p><p>The following constants are defined in the Socket module:</p><dl>
<dt><b><tt class="literal">INADDR_ANY</tt></b></dt>
<dd>
<a name="INDEX-1937" /></a>The
four-byte packed string for the wildcard IP address that specifies
any of the host's addresses (if the host has
multiple addresses). This is equivalent to
<tt class="literal">inet_aton('0.0.0.0')</tt>. 
<p></p>
</dd>


<dt><b><tt class="literal">INADDR_BROADCAST</tt></b></dt>
<dd>
<a name="INDEX-1938" /></a>The four-byte packed string for the
broadcast address. This is equivalent to
<tt class="literal">inet_aton('255.255.255.255')</tt>.
<p></p>
</dd>


<dt><b><tt class="literal">INADDR_LOOPBACK</tt></b></dt>
<dd>
<a name="INDEX-1939" /></a>The four-byte packed string for the
loopback address. This is equivalent to
<tt class="literal">inet_aton('localhost')</tt>.
<p></p>
</dd>


<dt><b><tt class="literal">INADDR_NONE</tt></b></dt>
<dd>
<a name="INDEX-1940" /></a>The
four-byte packed string for the
"invalid" IP address (bitmask).
Equivalent to <tt class="literal">inet_aton('255.255.255.255')</tt>.
<p></p>
</dd>

</dl></div>

</div>
</div>

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