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<!-- $Id$ -->
<HTML>
<HEAD>
<META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859-1">
<META NAME="Author" CONTENT="James CE Johnson">
<TITLE>ACE Tutorial 015</TITLE>
</HEAD>
<BODY TEXT="#000000" BGCOLOR="#FFFFFF" LINK="#000FFF" VLINK="#FF0F0F">
<CENTER><B><FONT SIZE=+2>ACE Tutorial 015</FONT></B></CENTER>
<CENTER><B><FONT SIZE=+2>Building a protocol stream</FONT></B></CENTER>
<P>
<HR WIDTH="100%">
The implementation of Xmit isn't too complicated. If we choose to
combine it with the Recv task we simply lift the recv() method from
that object and drop it into this one.
<P>
Note that close() must decide if it's being called when the stream is
shutdown or when it's svc() method exits. Since we tell the baseclass
not to use any threads it's a safe bet that flags will always be
non-zero. Still, it's good practice to plan for the future by
checking the value.
<P>
Note also that when we send the data we prefix it with the data size.
This let's our sibling Recv ensure that an entire block is received
together. This can be very important for compression and encryption
processes which typically work better with blocks of data instead of
streams of data.
<HR>
<PRE>
<font color=red>// $Id$</font>
<font color=blue>#include</font> "<font color=green>Xmit.h</font>"
<font color=blue>#include</font> "<A HREF="../../../ace/SOCK_Stream.h">ace/SOCK_Stream.h</A>"
<font color=red>/* Construct the object with the peer connection and choose not to
activate ourselves into a dedicated thread. You might get some
performance gain by activating but if you really want a
multi-threaded apprroach you should handle that as a separate
issue. Attempting to force threading at this level will likely
cause more trouble than you want to deal with.
*/</font>
<font color=#008888>Xmit::Xmit</font>( ACE_SOCK_Stream & _peer )
: Protocol_Task(), peer_(_peer)
{
}
<font color=#008888>Xmit::~Xmit</font>(void)
{
}
<font color=red>/* Check to see if we're being closed by the stream (flags != 0) or if
we're responding to the exit of our svc() method.
*/</font>
int <font color=#008888>Xmit::close</font>(u_long flags)
{
<font color=red>// Take care of the baseclass closure.</font>
int rval = <font color=#008888>inherited::close</font>(flags);
<font color=red>// Only if we're being called at the stream shutdown do we close</font>
<font color=red>// the peer connection. If, for some reason, we were activated</font>
<font color=red>// into one or more threads we wouldn't want to close the pipe</font>
<font color=red>// before all threads had a chance to flush their data.</font>
if( flags )
{
peer().close();
}
return( rval );
}
<font color=red>/* Our overload of send() will take care of sending the data to the
peer.
*/</font>
int <font color=#008888>Xmit::send</font>(ACE_Message_Block *message, ACE_Time_Value *timeout)
{
int rval;
ACE_DEBUG ((LM_INFO, "<font color=green>(%P|%t) <font color=#008888>Xmit::send</font>() sending (%s)(%d)\n</font>", message->rd_ptr(), message->length() ));
<font color=red>/* Since we're going to be sending data that may have been
compressed and encrypted it's probably important for the
receiver to get an entire "<font color=green>block</font>" instead of having a
partial read.
For that reason, we'll send the length of the message block
(in clear-text) to the peer so that it can then recv_n()
the entire block contents in one read operation.
*/</font>
char msize[32];
sprintf(msize,"<font color=green>%d</font>",message->length());
<font color=red>// Be sure we send the end-of-string NULL so that Recv will</font>
<font color=red>// know when to stop assembling the length.</font>
rval = this->peer().send_n( msize, strlen(msize)+1, 0, timeout );
if( rval == -1 )
{
ACE_ERROR_RETURN ((LM_ERROR, "<font color=green>%p\n</font>", "<font color=green><font color=#008888>Xmit::send</font>() Failed to send message size.</font>"), -1);
}
<font color=red>/* Now we send the actual data. If you're worried about
network efficiency then you may choose to create one buffer
containing msize and the message data and send it all at
once.
*/</font>
rval = this->peer().send_n( message->rd_ptr(), message->length(), 0, timeout );
<font color=red>// Release the message block since we're done with it.</font>
message->release();
return( rval );
}
</PRE>
<P><HR WIDTH="100%">
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