Datagram Example (The GNU C Library)

#### 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 Example of Local-Namespace Sockets, 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>
    #include <unistd.h>

    #define SERVER  "/tmp/serversocket"
    #define MAXMSG  512

    int
    main (void)
    {
      int sock;
      char message[MAXMSG];
      struct sockaddr_un name;
      socklen_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);
            }
        }
    }