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<h4 class="subsection">16.9.7 Byte Stream Connection Server Example</h4>

<p>The server end is much more complicated.  Since we want to allow
multiple clients to be connected to the server at the same time, it
would be incorrect to wait for input from a single client by simply
calling <code>read</code> or <code>recv</code>.  Instead, the right thing to do is
to use <code>select</code> (see <a href="Waiting-for-I_002fO.html#Waiting-for-I_002fO">Waiting for I/O</a>) to wait for input on
all of the open sockets.  This also allows the server to deal with
additional connection requests.

   <p>This particular server doesn't do anything interesting once it has
gotten a message from a client.  It does close the socket for that
client when it detects an end-of-file condition (resulting from the
client shutting down its end of the connection).

   <p>This program uses <code>make_socket</code> to set up the socket address; see
<a href="Inet-Example.html#Inet-Example">Inet Example</a>.

<pre class="smallexample">     #include &lt;stdio.h&gt;
     #include &lt;errno.h&gt;
     #include &lt;stdlib.h&gt;
     #include &lt;unistd.h&gt;
     #include &lt;sys/types.h&gt;
     #include &lt;sys/socket.h&gt;
     #include &lt;netinet/in.h&gt;
     #include &lt;netdb.h&gt;
     
     #define PORT    5555
     #define MAXMSG  512
     
     int
     read_from_client (int filedes)
     {
       char buffer[MAXMSG];
       int nbytes;
     
       nbytes = read (filedes, buffer, MAXMSG);
       if (nbytes &lt; 0)
         {
           /* <span class="roman">Read error.</span> */
           perror ("read");
           exit (EXIT_FAILURE);
         }
       else if (nbytes == 0)
         /* <span class="roman">End-of-file.</span> */
         return -1;
       else
         {
           /* <span class="roman">Data read.</span> */
           fprintf (stderr, "Server: got message: `%s'\n", buffer);
           return 0;
         }
     }
     
     int
     main (void)
     {
       extern int make_socket (uint16_t port);
       int sock;
       fd_set active_fd_set, read_fd_set;
       int i;
       struct sockaddr_in clientname;
       size_t size;
     
       /* <span class="roman">Create the socket and set it up to accept connections.</span> */
       sock = make_socket (PORT);
       if (listen (sock, 1) &lt; 0)
         {
           perror ("listen");
           exit (EXIT_FAILURE);
         }
     
       /* <span class="roman">Initialize the set of active sockets.</span> */
       FD_ZERO (&amp;active_fd_set);
       FD_SET (sock, &amp;active_fd_set);
     
       while (1)
         {
           /* <span class="roman">Block until input arrives on one or more active sockets.</span> */
           read_fd_set = active_fd_set;
           if (select (FD_SETSIZE, &amp;read_fd_set, NULL, NULL, NULL) &lt; 0)
             {
               perror ("select");
               exit (EXIT_FAILURE);
             }
     
           /* <span class="roman">Service all the sockets with input pending.</span> */
           for (i = 0; i &lt; FD_SETSIZE; ++i)
             if (FD_ISSET (i, &amp;read_fd_set))
               {
                 if (i == sock)
                   {
                     /* <span class="roman">Connection request on original socket.</span> */
                     int new;
                     size = sizeof (clientname);
                     new = accept (sock,
                                   (struct sockaddr *) &amp;clientname,
                                   &amp;size);
                     if (new &lt; 0)
                       {
                         perror ("accept");
                         exit (EXIT_FAILURE);
                       }
                     fprintf (stderr,
                              "Server: connect from host %s, port %hd.\n",
                              inet_ntoa (clientname.sin_addr),
                              ntohs (clientname.sin_port));
                     FD_SET (new, &amp;active_fd_set);
                   }
                 else
                   {
                     /* <span class="roman">Data arriving on an already-connected socket.</span> */
                     if (read_from_client (i) &lt; 0)
                       {
                         close (i);
                         FD_CLR (i, &amp;active_fd_set);
                       }
                   }
               }
         }
     }
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