Author: James CE Johnson

ACE Tutorial 009
Sending and receiving datagrams again

Our new directed_client.cpp is very much like our previous one. The primary difference is the addition of a timeout to the recv() call so that we can exit somewhat gracefully if the server doesn't like what we have to say.

    // page03.html,v 1.8 1999/04/03 21:56:26 jcej Exp

    #include "ace/SOCK_Dgram.h"
    #include "ace/INET_Addr.h"

    static const u_short PORT = ACE_DEFAULT_SERVER_PORT;

    int
    main (int argc, char *argv[])
    {
      ACE_INET_Addr local ((u_short) 0);
      ACE_INET_Addr remote (PORT,
                            argc > 1 ? argv[1] : "localhost");
      ACE_SOCK_Dgram dgram;

      if (dgram.open (local) == -1)
        ACE_ERROR_RETURN ((LM_ERROR,
                           "%p\n",
                           "open"),
                          -1);

      char buf[BUFSIZ];

      /* In order to conform to the "protocol" required by the server, we
        allow the user to specify a signature.  A default matching the
        server's default is also available.  */
      sprintf (buf,
               argc > 2 ? argv[2] : "Hello World!");

      if (dgram.send (buf,
                      ACE_OS::strlen (buf) + 1,
                      remote) == -1)
        ACE_ERROR_RETURN ((LM_ERROR,
                           "%p\n",
                           "send"),
                          -1);

      /* Because we may have sent a signature that the server doesn't
        honor, we have to have some way to get out of the recv().  Most
        ACE objects that have potential for infinite blocking give you the
        option of providing a timeout.  recv() is no exception.  Here, we
        construct an ACE_Time_Value representing two seconds and no
        micro-seconds.  If recv() fails to get a response within the two
        seconds, it will return -1.  */
      ACE_Time_Value timeout (2, 0);
      if (dgram.recv (buf,
                      sizeof (buf),
                      remote,
                      0,
                      &timeout) == -1)
        ACE_ERROR_RETURN ((LM_ERROR,
                           "%p\n",
                           "recv"),
                          -1);

      /* Note: The fourth parameter to recv() is for flags.  These flags
        are passed directly to the underlying recv() or recvfrom() system
        call.  For Linux, resonable values are: MSG_OOB process
        out-of-band data MSG_PEEK peek at incoming message (but leave it
        in the OS buffers) MSG_WAITALL wait for full request or error See
        your system documentation for the gory details.  */

      ACE_DEBUG ((LM_DEBUG,
                  "(%P|%t) The server said (%s)\n",
                  buf));

      return 0;
    }

On the next page, we see that the directed_client gets similar upgrades.

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