Author: James CE Johnson
Description: A first step towards using ACE productively

ACE Tutorial 003
Creating a Simple Client

Now that we've seen how to create servers, let's spend just a moment making a client. Since this is so easy, I'm going to do all of it in this one page.

Kirthika says, "Here's an one paragraph abstract for a one page client app:"

The server is an Stream object of ACE_SOCK_Stream type. The ACE_Sock_Connector does the job of actively making a connection with the listening server. It does so using the server_host_address and port number which are stored in the ACE_INET_Addr object.Once the connection has been established, the client begins its interaction with the server and bombards it with messages. Note: send_n() call is used since this call sees to the issues of network buffering and reliably gets the data across to the server. Also, a timeout value is set to provide fault tolerance if the server ever dies before the transaction is completed. The server calls a close() method once it reads in zero bytes during the Event_Handler::handle_input() call. This proves that the client has severed its connection. The server then shuts down.

    // page01.html,v 1.9 1999/04/03 21:56:23 jcej Exp

    /* To establish a socket connection to a server, we'll need an
      ACE_SOCK_Connector.  */
    #include "ace/SOCK_Connector.h"

    /* Unlike the previous two tutorials, we're going to allow the user to
      provide command line options this time.  Still, we need defaults in
      case that isn't done.  */
    static u_short SERVER_PORT = ACE_DEFAULT_SERVER_PORT;
    static const char *const SERVER_HOST = ACE_DEFAULT_SERVER_HOST;
    static const int MAX_ITERATIONS = 4;

    int
    main (int argc, char *argv[])
    {
      /* Accept the users's choice of hosts or use the default.  Then do
        the same for the TCP/IP port at which the server is listening as
        well as the number of iterations to perform.  */
      const char *server_host = argc > 1 ? argv[1] : SERVER_HOST;
      u_short server_port = argc > 2 ? ACE_OS::atoi (argv[2]) : SERVER_PORT;
      int max_iterations = argc > 3 ? ACE_OS::atoi (argv[3]) : MAX_ITERATIONS;

      /* Build ourselves a Stream socket. This is a connected socket that
        provides reliable end-to-end communications. We will use the
        server object to send data to the server we connect to.  */
      ACE_SOCK_Stream server;

      /* And we need a connector object to establish that connection. The
        ACE_SOCK_Connector object provides all of the tools we need to
        establish a connection once we know the server's network
        address...  */
      ACE_SOCK_Connector connector;

      /* Which we create with an ACE_INET_Addr object. This object is
        given the TCP/IP port and hostname of the server we want to
        connect to.  */
      ACE_INET_Addr addr (server_port,
                          server_host);

      /* So, we feed the Addr object and the Stream object to the
        connector's connect() member function. Given this information, it
        will establish the network connection to the server and attach
        that connection to the server object.  */
      if (connector.connect (server, addr) == -1)
        ACE_ERROR_RETURN ((LM_ERROR,
                           "%p\n",
                           "open"),
                          -1);

      /* Just for grins, we'll send the server several messages.  */
      for (int i = 0; i < max_iterations; i++)
        {
          char buf[BUFSIZ];

          /* Create our message with the message number */
          ACE_OS::sprintf (buf,
                           "message = %d\n",
                           i + 1);
          /* Send the message to the server.  We use the server object's
            send_n() function to send all of the data at once. There is
            also a send() function but it may not send all of the
            data. That is due to network buffer availability and such. If
            the send() doesn't send all of the data, it is up to you to
            program things such that it will keep trying until all of the
            data is sent or simply give up. The send_n() function already
            does the "keep trying" option for us, so we use it.

            Like the send() method used in the servers we've seen, there
            are two additional parameters you can use on the send() and
            send_n() method calls.  The timeout parameter limits the
            amount of time the system will attempt to send the data to the
            peer.  The flags parameter is passed directly to the OS send()
            system call.  See send(2) for the valid flags values.  */
          if (server.send_n (buf,
                             ACE_OS::strlen (buf)) == -1)
            ACE_ERROR_RETURN ((LM_ERROR,
                               "%p\n",
                               "send"),
                              -1);
          else
            /* Pause for a second.  */
            ACE_OS::sleep (1);
        }

      /* Close the connection to the server.  The servers we've created so
        far all are based on the ACE_Reactor.  When we close(), the
        server's reactor will see activity for the registered event
        handler and invoke handle_input().  That, in turn, will try to
        read from the socket but get back zero bytes.  At that point, the
        server will know that we've closed from our side.  */
      if (server.close () == -1)
        ACE_ERROR_RETURN ((LM_ERROR,
                           "%p\n",
                           "close"),
                          -1);
      return 0;
    }

Ok, so that was pretty easy. What would be even easier would be to wrap all of the connection mess up in an object and overload a couple of basic operators to make things less network-centric. Perhaps we'll see that in another tutorial.

If you want to compile it yourself, here's the source, the Makefile, and Environment settings.

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