16.10.3 Datagram Socket Example

Here is a set of example programs that send messages over a datagram stream in the local namespace. Both the client and server programs use the make_named_socket function that was presented in Local Socket Example, to create and name their sockets.

First, here is the server program. It sits in a loop waiting for messages to arrive, bouncing each message back to the sender. Obviously this isn't a particularly useful program, but it does show the general ideas involved.

     #include <stdio.h>
     #include <errno.h>
     #include <stdlib.h>
     #include <sys/socket.h>
     #include <sys/un.h>
     
     #define SERVER  "/tmp/serversocket"
     #define MAXMSG  512
     
     int
     main (void)
     {
       int sock;
       char message[MAXMSG];
       struct sockaddr_un name;
       size_t size;
       int nbytes;
     
       /* Remove the filename first, it's ok if the call fails */
       unlink (SERVER);
     
       /* Make the socket, then loop endlessly. */
       sock = make_named_socket (SERVER);
       while (1)
         {
           /* Wait for a datagram. */
           size = sizeof (name);
           nbytes = recvfrom (sock, message, MAXMSG, 0,
                              (struct sockaddr *) & name, &size);
           if (nbytes < 0)
             {
               perror ("recfrom (server)");
               exit (EXIT_FAILURE);
             }
     
           /* Give a diagnostic message. */
           fprintf (stderr, "Server: got message: %s\n", message);
     
           /* Bounce the message back to the sender. */
           nbytes = sendto (sock, message, nbytes, 0,
                            (struct sockaddr *) & name, size);
           if (nbytes < 0)
             {
               perror ("sendto (server)");
               exit (EXIT_FAILURE);
             }
         }
     }