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| <h4 class="subsection">16.9.1 Making a Connection</h4> |
| |
| <p><a name="index-connecting-a-socket-1791"></a><a name="index-socket_002c-connecting-1792"></a><a name="index-socket_002c-initiating-a-connection-1793"></a><a name="index-socket_002c-client-actions-1794"></a> |
| In making a connection, the client makes a connection while the server |
| waits for and accepts the connection. Here we discuss what the client |
| program must do with the <code>connect</code> function, which is declared in |
| <samp><span class="file">sys/socket.h</span></samp>. |
| |
| <!-- sys/socket.h --> |
| <!-- BSD --> |
| <div class="defun"> |
| — Function: int <b>connect</b> (<var>int socket, struct sockaddr *addr, socklen_t length</var>)<var><a name="index-connect-1795"></a></var><br> |
| <blockquote><p>The <code>connect</code> function initiates a connection from the socket |
| with file descriptor <var>socket</var> to the socket whose address is |
| specified by the <var>addr</var> and <var>length</var> arguments. (This socket |
| is typically on another machine, and it must be already set up as a |
| server.) See <a href="Socket-Addresses.html#Socket-Addresses">Socket Addresses</a>, for information about how these |
| arguments are interpreted. |
| |
| <p>Normally, <code>connect</code> waits until the server responds to the request |
| before it returns. You can set nonblocking mode on the socket |
| <var>socket</var> to make <code>connect</code> return immediately without waiting |
| for the response. See <a href="File-Status-Flags.html#File-Status-Flags">File Status Flags</a>, for information about |
| nonblocking mode. |
| <!-- !!! how do you tell when it has finished connecting? I suspect the --> |
| <!-- way you do it is select for writing. --> |
| |
| <p>The normal return value from <code>connect</code> is <code>0</code>. If an error |
| occurs, <code>connect</code> returns <code>-1</code>. The following <code>errno</code> |
| error conditions are defined for this function: |
| |
| <dl> |
| <dt><code>EBADF</code><dd>The socket <var>socket</var> is not a valid file descriptor. |
| |
| <br><dt><code>ENOTSOCK</code><dd>File descriptor <var>socket</var> is not a socket. |
| |
| <br><dt><code>EADDRNOTAVAIL</code><dd>The specified address is not available on the remote machine. |
| |
| <br><dt><code>EAFNOSUPPORT</code><dd>The namespace of the <var>addr</var> is not supported by this socket. |
| |
| <br><dt><code>EISCONN</code><dd>The socket <var>socket</var> is already connected. |
| |
| <br><dt><code>ETIMEDOUT</code><dd>The attempt to establish the connection timed out. |
| |
| <br><dt><code>ECONNREFUSED</code><dd>The server has actively refused to establish the connection. |
| |
| <br><dt><code>ENETUNREACH</code><dd>The network of the given <var>addr</var> isn't reachable from this host. |
| |
| <br><dt><code>EADDRINUSE</code><dd>The socket address of the given <var>addr</var> is already in use. |
| |
| <br><dt><code>EINPROGRESS</code><dd>The socket <var>socket</var> is non-blocking and the connection could not be |
| established immediately. You can determine when the connection is |
| completely established with <code>select</code>; see <a href="Waiting-for-I_002fO.html#Waiting-for-I_002fO">Waiting for I/O</a>. |
| Another <code>connect</code> call on the same socket, before the connection is |
| completely established, will fail with <code>EALREADY</code>. |
| |
| <br><dt><code>EALREADY</code><dd>The socket <var>socket</var> is non-blocking and already has a pending |
| connection in progress (see <code>EINPROGRESS</code> above). |
| </dl> |
| |
| <p>This function is defined as a cancellation point in multi-threaded |
| programs, so one has to be prepared for this and make sure that |
| allocated resources (like memory, files descriptors, semaphores or |
| whatever) are freed even if the thread is canceled. |
| <!-- @xref{pthread_cleanup_push}, for a method how to do this. --> |
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