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| <h4 class="subsection">16.9.2 Listening for Connections</h4> |
| |
| <p><a name="index-listening-_0028sockets_0029-1796"></a><a name="index-sockets_002c-server-actions-1797"></a><a name="index-sockets_002c-listening-1798"></a> |
| Now let us consider what the server process must do to accept |
| connections on a socket. First it must use the <code>listen</code> function |
| to enable connection requests on the socket, and then accept each |
| incoming connection with a call to <code>accept</code> (see <a href="Accepting-Connections.html#Accepting-Connections">Accepting Connections</a>). Once connection requests are enabled on a server socket, |
| the <code>select</code> function reports when the socket has a connection |
| ready to be accepted (see <a href="Waiting-for-I_002fO.html#Waiting-for-I_002fO">Waiting for I/O</a>). |
| |
| <p>The <code>listen</code> function is not allowed for sockets using |
| connectionless communication styles. |
| |
| <p>You can write a network server that does not even start running until a |
| connection to it is requested. See <a href="Inetd-Servers.html#Inetd-Servers">Inetd Servers</a>. |
| |
| <p>In the Internet namespace, there are no special protection mechanisms |
| for controlling access to a port; any process on any machine |
| can make a connection to your server. If you want to restrict access to |
| your server, make it examine the addresses associated with connection |
| requests or implement some other handshaking or identification |
| protocol. |
| |
| <p>In the local namespace, the ordinary file protection bits control who has |
| access to connect to the socket. |
| |
| <!-- sys/socket.h --> |
| <!-- BSD --> |
| <div class="defun"> |
| — Function: int <b>listen</b> (<var>int socket, int n</var>)<var><a name="index-listen-1799"></a></var><br> |
| <blockquote><p>The <code>listen</code> function enables the socket <var>socket</var> to accept |
| connections, thus making it a server socket. |
| |
| <p>The argument <var>n</var> specifies the length of the queue for pending |
| connections. When the queue fills, new clients attempting to connect |
| fail with <code>ECONNREFUSED</code> until the server calls <code>accept</code> to |
| accept a connection from the queue. |
| |
| <p>The <code>listen</code> function returns <code>0</code> on success and <code>-1</code> |
| on failure. The following <code>errno</code> error conditions are defined |
| for this function: |
| |
| <dl> |
| <dt><code>EBADF</code><dd>The argument <var>socket</var> is not a valid file descriptor. |
| |
| <br><dt><code>ENOTSOCK</code><dd>The argument <var>socket</var> is not a socket. |
| |
| <br><dt><code>EOPNOTSUPP</code><dd>The socket <var>socket</var> does not support this operation. |
| </dl> |
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