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<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%">
And so finally we come to the Protocol_Stream. That, after all, is
the focus of the entire tutorial but it took us half of the day to get
here!
<P>
The Protocol_Stream uses an ACE_Stream to move an ACE_Message_Block
through a series of tasks. Each task in the stream is responsible for
performing some operation on the data in the message block. That is
the nature of a protocol stream (or "stack" if you prefer). In this
stream, the data is compressed and encrypted* on its way between
peers. We also allow users of the stream to install a reader task to
handle data that percolates up from the peer. As you saw a page or
two ago, this is most useful for a server.
<P>
<font size=-1>*Again, I just pretend to do these things. It would
take another day or two to go through any sort of reasonable
encryption or compression!</font>
<P>
Before we get into the code, here's a picture that's shows what's
going on here.
<P><center><img src="stream.gif"></center></p>
<HR>
<PRE>
<font color=red>// $Id$</font>
<font color=blue>#ifndef</font> <font color=purple>PROTOCOL_STREAM_H</font>
<font color=blue>#define</font> <font color=purple>PROTOCOL_STREAM_H</font>
<font color=blue>#include</font> "<font color=green>ace/SOCK_Stream.h</font>"
<font color=blue>#if !defined</font> (<font color=purple>ACE_LACKS_PRAGMA_ONCE</font>)
# pragma once
<font color=blue>#endif</font> <font color=red>/* ACE_LACKS_PRAGMA_ONCE */</font>
<font color=blue>#include</font> "<font color=green>ace/Stream.h</font>"
<font color=red>// Shorthand for the stream.</font>
typedef ACE_Stream<ACE_MT_SYNCH> Stream;
<font color=red>// Forward references to cut down on the number of <font color=blue>#include</font>s</font>
class ACE_Message_Block;
class Recv;
class Protocol_Task;
<font color=red>/* The Protocol_Stream provides a tidy interface to an ACE_Stream
setup to process a data block through a series of protocol stages.
*/</font>
class Protocol_Stream
{
public:
Protocol_Stream(void);
~Protocol_Stream(void);
<font color=red>// Provide the stream with an ACE_SOCK_Stream on which it can</font>
<font color=red>// communicate. If _reader is non-null, it will be added as</font>
<font color=red>// the reader task just below the stream head so that it can</font>
<font color=red>// process data read from the peer.</font>
int open( ACE_SOCK_Stream & _peer, Protocol_Task * _reader = 0 );
<font color=red>// Close the stream. All of the tasks & modules will also be closed.</font>
int close(void);
<font color=red>// putting data onto the stream will pass it through all</font>
<font color=red>// protocol levels and send it to the peer.</font>
int put( ACE_Message_Block * & _message, ACE_Time_Value *
_timeout = 0 );
<font color=red>// get will cause the Recv task (at the tail of the stream) to</font>
<font color=red>// read some data from the peer and pass it upstream. The</font>
<font color=red>// message block is then taken from the stream reader task's</font>
<font color=red>// message queue.</font>
int get( ACE_Message_Block * & _response, ACE_Time_Value *
_timeout = 0 );
<font color=red>// Tell the Recv task to read some data and send it upstream.</font>
<font color=red>// The data will pass through the protocol tasks and be queued</font>
<font color=red>// into the stream head reader task's message queue. If</font>
<font color=red>// you've installed a _reader in open() then that task's</font>
<font color=red>// recv() method will see the message and may consume it</font>
<font color=red>// instead of passing it to the stream head for queueing.</font>
int get(void);
ACE_SOCK_Stream & peer(void)
{
return this->peer_;
}
private:
<font color=red>// Our peer connection</font>
ACE_SOCK_Stream peer_;
<font color=red>// The stream managing the various protocol tasks</font>
Stream stream_;
<font color=red>// A task which is capable of receiving data on a socket.</font>
<font color=red>// Note that this is only useful by client-side applications.</font>
Recv * recv_;
Stream & stream(void)
{
return this->stream_;
}
<font color=red>// Install the protocol tasks into the stream.</font>
int open(void);
};
<font color=blue>#endif</font> <font color=red>// PROTOCOL_STREAM_H</font>
</PRE>
<P><HR WIDTH="100%">
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