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(libc.info)Example Receiver

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Example of Reading Datagrams
----------------------------

   Here is the client program corresponding to the server above.

   It sends a datagram to the server and then waits for a reply.  Notice
that the socket for the client (as well as for the server) in this
example has to be given a name.  This is so that the server can direct
a message back to the client.  Since the socket has no associated
connection state, the only way the server can do this is by referencing
the name of the client.

     #include <stdio.h>
     #include <errno.h>
     #include <unistd.h>
     #include <stdlib.h>
     #include <sys/socket.h>
     #include <sys/un.h>
     
     #define SERVER  "/tmp/serversocket"
     #define CLIENT  "/tmp/mysocket"
     #define MAXMSG  512
     #define MESSAGE "Yow!!! Are we having fun yet?!?"
     
     int
     main (void)
     {
       extern int make_named_socket (const char *name);
       int sock;
       char message[MAXMSG];
       struct sockaddr_un name;
       size_t size;
       int nbytes;
     
       /* Make the socket. */
       sock = make_named_socket (CLIENT);
     
       /* Initialize the server socket address. */
       name.sun_family = AF_LOCAL;
       strcpy (name.sun_path, SERVER);
       size = strlen (name.sun_path) + sizeof (name.sun_family);
     
       /* Send the datagram. */
       nbytes = sendto (sock, MESSAGE, strlen (MESSAGE) + 1, 0,
                        (struct sockaddr *) & name, size);
       if (nbytes < 0)
         {
           perror ("sendto (client)");
           exit (EXIT_FAILURE);
         }
     
       /* Wait for a reply. */
       nbytes = recvfrom (sock, message, MAXMSG, 0, NULL, 0);
       if (nbytes < 0)
         {
           perror ("recfrom (client)");
           exit (EXIT_FAILURE);
         }
     
       /* Print a diagnostic message. */
       fprintf (stderr, "Client: got message: %s\n", message);
     
       /* Clean up. */
       remove (CLIENT);
       close (sock);
     }

   Keep in mind that datagram socket communications are unreliable.  In
this example, the client program waits indefinitely if the message
never reaches the server or if the server's response never comes back.
It's up to the user running the program to kill and restart it if
desired.  A more automatic solution could be to use `select' (Note:
Waiting for I/O) to establish a timeout period for the reply, and in
case of timeout either re-send the message or shut down the socket and
exit.