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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 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.
<HR>
<PRE>
<font color=red>// $Id$</font>
<font color=blue>#include</font> "<font color=green>Recv.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 reference and other appropriate
initializations.
*/</font>
<font color=#008888>Recv::Recv</font>( ACE_SOCK_Stream & _peer )
: Protocol_Task(), peer_(_peer), error_(0)
{
<font color=red>// Create the tickler that get() will use to trigger recv()</font>
<font color=red>// through the baseclass. Since we're single-threaded this is</font>
<font color=red>// probably overkill but it makes multi-threading easier if we</font>
<font color=red>// choose to do that.</font>
tickler_ = new ACE_Message_Block(1);
}
<font color=red>/* Be sure we manage the lifetime of the tickler to prevent a memory
leak.
*/</font>
<font color=#008888>Recv::~Recv</font>(void)
{
tickler_->release();
}
<font color=red>/* 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!
*/</font>
int <font color=#008888>Recv::get</font>(void)
{
return this->put( tickler_, 0 );
}
int <font color=#008888>Recv::recv</font>(ACE_Message_Block * message, ACE_Time_Value *timeout)
{
int rval;
<font color=red>/* Xmit will send us the message length in clear-text. I
assume that will be less than 32-bytes!
*/</font>
char msize[32];
int b = 0;
<font color=red>/* 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.
*/</font>
do
{
rval = this->peer().recv( &msize[b], 1, timeout );
if( rval == -1 )
{
error_ = 1;
ACE_ERROR_RETURN ((LM_ERROR, "<font color=green>%p\n</font>", "<font color=green><font color=#008888>Recv::recv</font>() Failed to get message size.</font>"), -1);
}
}
while( msize[b++] != 0 );
int size = <font color=#008888>ACE_OS::atoi</font>(msize);
<font color=red>// Make a block big enough to contain the data we'll read</font>
message = new ACE_Message_Block( size );
<font color=red>// Read the actual message data into our new message block</font>
rval = this->peer().recv_n( message->wr_ptr(), size, 0, timeout );
<font color=red>// If we got the data correctly then send it on upstream.</font>
if( rval > 0 )
{
message->wr_ptr( rval );
return( this->put_next( message ) );
}
<font color=red>// Something bad happend on the recv_n(). Set an error flag</font>
<font color=red>// and return error.</font>
error_ = 1;
return( -1 );
}
</PRE>
<P><HR WIDTH="100%">
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