Datagram Example - The GNU C Library

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#### 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);
                 }
             }
         }