Author: James CE Johnson

ACE Tutorial 015
Building a protocol stream

The Recv implementation is nearly as simple as Xmit. There's opportunity for error when we get the message size and we have to manage the lifetime of the tickler but other than that it's pretty basic stuff.

    // page17.html,v 1.12 1999/04/03 21:56:31 jcej Exp

    #include "Recv.h"
    #include "ace/SOCK_Stream.h"

    /* Construct the object with the peer reference and other appropriate
       initializations.
    */
    Recv::Recv( ACE_SOCK_Stream & _peer )
            : Protocol_Task(), peer_(_peer), error_(0)
    {
         // Create the tickler that get() will use to trigger recv()
         // through the baseclass.  Since we're single-threaded this is
         // probably overkill but it makes multi-threading easier if we
         // choose to do that.
        tickler_ = new ACE_Message_Block(1);
    }

    /* Be sure we manage the lifetime of the tickler to prevent a memory
       leak.
    */
    Recv::~Recv(void)
    {
        tickler_->release();
    }

    /* By putting the tickler to ourselves we cause things to happen in
       the baseclass that will invoke recv().  If we know we're single
       threaded we could directly call recv() and be done with it but then
       we'd have to do something else if we're multi-threaded.  Just let
       the baseclass worry about those things!
    */
    int Recv::get(void)
    {
        return this->put( tickler_, 0 );
    }

    int Recv::recv(ACE_Message_Block * message, ACE_Time_Value *timeout)
    {
        int rval;

            /* Xmit will send us the message length in clear-text.  I
               assume that will be less than 32-bytes!
            */
        char msize[32];
        int b = 0;

            /* Read from the socket one byte at a time until we see then
               end-of-string NULL character.  Since the OS layers (at least
               in Unix) will provide some buffering this isn't as bad as
               it may seem at first.

               The byte-at-a-time recv breaks horribly on Win32 where the
               WFMO_Reactor is used.  This is because the socket has been
               placed into non-blocking mode and only the recv() of the
               first byte will block.  The solution is to use
               ACE_Select_Reactor which doesn't change the socket
               characteristics.  We did that back in main(), so we should
               be in good shape now.
            */
        do
        {
            rval = this->peer().recv( &msize[b], 1, timeout );
            if( rval == -1 )
            {
                error_ = 1;
                ACE_ERROR_RETURN ((LM_ERROR, "%p\n", "Recv::recv() Failed to get message size."), -1);
            }
        }
        while( msize[b++] != 0 );

        int size = ACE_OS::atoi(msize);

            // Make a block big enough to contain the data we'll read
        message = new ACE_Message_Block( size );

            // Read the actual message data into our new message block
        rval = this->peer().recv_n( message->wr_ptr(), size, 0, timeout );

            // If we got the data correctly then send it on upstream.
        if( rval > 0 )
        {
            message->wr_ptr( rval );
            return( this->put_next( message ) );
        }

            // Something bad happend on the recv_n().  Set an error flag
            // and return error.
        error_ = 1;

        return( -1 );
    }

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