ACE Tutorial 005
On the road to a multithreaded server

Now we're finally at client_handler.cpp where we have to write some code. This file has more code than the rest of the application all together.

    // page05.html,v 1.13 2000/03/19 20:09:22 jcej Exp

    /* In client_handler.h I alluded to the fact that we'll mess around
       with a Client_Acceptor pointer.  To do so, we need the
       Client_Acceptor object declaration.

       We know that including client_handler.h is redundant because
       client_acceptor.h includes it.  Still, the sentry prevents
       double-inclusion from causing problems and it's sometimes good to
       be explicit about what we're using.

       On the other hand, we don't directly include any ACE header files
       here.  */
    #include "client_acceptor.h"
    #include "client_handler.h"

    /* Our constructor doesn't do anything.  That's generally a good idea.
       Unless you want to start throwing exceptions, there isn't a really
       good way to indicate that a constructor has failed.  If I had my
       way, I'd have a boolean return code from it that would cause new to
       return 0 if I failed.  Oh well...  */
    Client_Handler::Client_Handler (void)
    {
    }

    /* Our destructor doesn't do anything either.  That is also by design.
       Remember, we really want folks to use destroy() to get rid of us.
       If that's so, then there's nothing left to do when the destructor
       gets invoked.  */
    Client_Handler::~Client_Handler (void)
    {
      // Make sure that our peer closes when we're deleted.  This
      // will probably happened when the peer is deleted but it
      // doesn't hurt to be explicit.
      this->peer ().close ();
    }

    /* The much talked about destroy() method!  The reason I keep going on
       about this is because it's just a Bad Idea (TM) to do real work
       inside of a destructor.  Although this method is void, it really
       should return int so that it can tell the caller there was a
       problem.  Even as void you could at least throw an exception which
       you would never want to do in a destructor.  */
    void
    Client_Handler::destroy (void)
    {
      /* Tell the reactor to forget all about us.  Notice that we use the
        same args here that we use in the open() method to register
        ourselves.  In addition, we use the DONT_CALL flag to prevent
        handle_close() being called.  Since we likely got here due to
        handle_close(), that could cause a bit of nasty recursion!  */
      this->reactor ()->remove_handler (this,
                                        ACE_Event_Handler:: READ_MASK | ACE_Event_Handler::DONT_CALL);

      /* This is how we're able to tell folks not to use delete.  By
        deleting our own instance, we take care of memory leaks after
        ensuring that the object is shut down correctly.  */
      delete this;
    }

    /* As mentioned before, the open() method is called by the
       Client_Acceptor when a new client connection has been accepted.
       The Client_Acceptor instance pointer is cast to a void* and given
       to us here.  We'll use that to avoid some global data...  */
    int
    Client_Handler::open (void *_acceptor)
    {
      /* Convert the void* to a Client_Acceptor*.  You should probably use
         those fancy ACE_*_cast macros but I can never remember how/when
         to do so.  Since you can cast just about anything around a void*
         without compiler warnings be very sure of what you're doing when
         you do this kind of thing.  That's where the new-style cast
         operators can save you.  */
      Client_Acceptor *acceptor = (Client_Acceptor *) _acceptor;

      /* Our reactor reference will be set when we register ourselves but
         I decided to go ahead and set it here.  No good reason really...  */
      this->reactor (acceptor->reactor ());

      /* We need this to store the address of the client that we are now
         connected to.  We'll use it later to display a debug message.  */
      ACE_INET_Addr addr;

      /* Our ACE_Svc_Handler baseclass gives us the peer() method as a way
         to access our underlying ACE_SOCK_Stream.  On that object, we can
         invoke the get_remote_addr() method to get an ACE_INET_Addr
         having our client's address information. As with most ACE
         methods, we'll get back (and return) a -1 if there was any kind
         of error.  Once we have the ACE_INET_Addr, we can query it to
         find out the clien's host name, TCP/IP address, TCP/IP port value
         and so forth.  One word of warning: the get_host_name() method of
         ACE_INET_Addr may return you an empty string if your name server
         can't resolve it.  On the other hand, get_host_addr() will always
         give you the dotted-decimal string representing the TCP/IP
         address.  */
      if (this->peer ().get_remote_addr (addr) == -1)
        return -1;

      /* If we managed to get the client's address then we're connected to
         a real and valid client.  I suppose that in some cases, the
         client may connect and disconnect so quickly that it is invalid
         by the time we get here. In any case, the test above should
         always be done to ensure that the connection is worth keeping.

         Now, register ourselves with a reactor and tell that reactor that
         we want to be notified when there is something to read.
         Remember, we took our reactor value from the acceptor which
         created us in the first place.  Since we're exploring a
         single-threaded implementation, this is the correct thing to do.  */
      if (this->reactor ()->register_handler (this,
                                              ACE_Event_Handler::READ_MASK) == -1)
        ACE_ERROR_RETURN ((LM_ERROR,
                           "(%P|%t) can't register with reactor\n"),
                          -1);

      /* Here, we use the ACE_INET_Addr object to print a message with the
         name of the client we're connected to.  Again, it is possible
         that you'll get an empty string for the host name if your DNS
         isn't configured correctly or if there is some other reason that
         a TCP/IP addreess cannot be converted into a host name.  */
      ACE_DEBUG ((LM_DEBUG,
                  "(%P|%t) connected with %s\n",
                  addr.get_host_name ()));

      /* Always return zero on success.  */
      return 0;
    }

    /* In the open() method, we registered with the reactor and requested
       to be notified when there is data to be read.  When the reactor
       sees that activity it will invoke this handle_input() method on us.
       As I mentioned, the _handle parameter isn't useful to us but it
       narrows the list of methods the reactor has to worry about and the
       list of possible virtual functions we would have to override.  */
    int
    Client_Handler::handle_input (ACE_HANDLE handle)
    {
      /* Some compilers don't like it when you fail to use a parameter.
         This macro will keep 'em quiet for you.  */
      ACE_UNUSED_ARG (handle);

      /* Now, we create and initialize a buffer for receiving the data.
         Since this is just a simple test app, we'll use a small buffer
         size.  */
      char buf[BUFSIZ];

      /* Invoke the process() method with a pointer to our data area.
         We'll let that method worry about interfacing with the data.  You
         might choose to go ahead and read the data and then pass the
         result to process().  However, application logic may require that
         you read a few bytes to determine what else to read...  It's best
         if we push that all into the application-logic level.  */
      return this->process (buf, sizeof (buf));
    }

    /* If we return -1 out of handle_input() or if the reactor sees other
       problems with us then handle_close() will be called.  The reactor
       framework will take care of removing us (due to the -1), so we
       don't need to use the destroy() method.  Instead, we just delete
       ourselves directly.  */
    int
    Client_Handler::handle_close (ACE_HANDLE handle,
                                  ACE_Reactor_Mask mask)
    {
      ACE_UNUSED_ARG (handle);
      ACE_UNUSED_ARG (mask);

      delete this;
      return 0;
    }

    /* And, at last, we get to the application-logic level.  Out of
       everything we've done so far, this is the only thing that really
       has anything to do with what your application will do.  In this
       method we will read and process the client's data.  In a real
       appliation, you will probably have a bit more in main() to deal
       with command line options but after that point, all of the action
       takes place here.  */
    int
    Client_Handler::process (char *rdbuf,
                             int rdbuf_len)
    {
        ssize_t bytes_read = -1;

      /* Using the buffer provided for us, we read the data from the
         client. If there is a read error (eg -- recv() returns -1) then
         it's a pretty good bet that the connection is gone.  Likewise, if
         we read zero bytes then something wrong has happened.  The
         reactor wouldn't have called us if there wasn't some kind of read
         activity but there wouldn't be activity if there were no bytes to
         read...

         On the other hand, if we got some data then we can display it in
         a debug message for everyone to see.  */
        switch ( (bytes_read = this->peer ().recv (rdbuf, rdbuf_len)) )
        {
        case -1: // Complain and leave
          ACE_ERROR_RETURN ((LM_ERROR,
                             "(%P|%t) %p bad read\n",
                             "client"),
                            -1);
        case 0: // Complain and leave
          ACE_ERROR_RETURN ((LM_ERROR,
                             "(%P|%t) closing daemon (fd = %d)\n",
                             this->get_handle ()),
                            -1);
        default: // Show the data
            // NULL-terminate the string before printing it.
          rdbuf[bytes_read] = 0;
          ACE_DEBUG ((LM_DEBUG,
                      "(%P|%t) from client: %s",
                      rdbuf));
        }

       /* It's also worth mentioning that recv() has a cousin: recv_n().
         recv_n() will receive exactly the number of bytes you provide it.
         This is very good when you know exactly how much you expect to
         receive.  For the application here, unfortunately, we don't have
         any idea how much the client will be sending.  recv() will read
         up-to-but-not-more-than the number of bytes we specify (e.g. --
         _rdbuf_len).  That works well when we don't know how much the
         client will provide.  */

      return 0;
    }

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