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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%">
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> "<A HREF="../../../ace/SOCK_Stream.h">ace/SOCK_Stream.h</A>"
<font color=blue>#if !defined</font> (<font color=purple>ACE_LACKS_PRAGMA_ONCE</font>)
<font color=blue># pragma</font> <font color=purple>once</font>
<font color=blue>#endif</font> <font color=red>/* ACE_LACKS_PRAGMA_ONCE */</font>
<font color=blue>#include</font> "<A HREF="../../../ace/Stream.h">ace/Stream.h</A>"
<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 the</font>
<font color=red>// reader task just below the stream head so that it can process</font>
<font color=red>// 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</font>
<font color=red>// closed.</font>
int close (void);
<font color=red>// putting data onto the stream will pass it through all protocol</font>
<font color=red>// 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 read</font>
<font color=red>// some data from the peer and pass it upstream. The message block</font>
<font color=red>// is then taken from the stream reader task's 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. The</font>
<font color=red>// data will pass through the protocol tasks and be queued into the</font>
<font color=red>// stream head reader task's message queue. If you've installed a</font>
<font color=red>// _reader in open() then that task's recv() method will see the</font>
<font color=red>// message and may consume it instead of passing it to the stream</font>
<font color=red>// 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>
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