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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 encryption implementation isn't any smarter than that of the
compressor.  Still, the hooks are there for you to insert your
favorite library.
<HR>
<PRE>

<font color=red>// $Id$</font>

<font color=blue>#include</font> "<font color=green>Crypt.h</font>"
<font color=blue>#include</font> "<A HREF="../../../ace/SOCK_Stream.h">ace/SOCK_Stream.h</A>"

<font color=red>/* The expected constructor...
 */</font>
<font color=#008888>Crypt::Crypt</font>( void )
        : Protocol_Task()
{
}

<font color=#008888>Crypt::~Crypt</font>(void)
{
}

<font color=red>/* To send the data we'll apply a signature and encryption.
 */</font>
int <font color=#008888>Crypt::send</font>(ACE_Message_Block *message, ACE_Time_Value *timeout)
{
    ACE_UNUSED_ARG(timeout);

    ACE_DEBUG ((LM_INFO, "<font color=green>(%P|%t) <font color=#008888>Crypt::send</font>() encrypting (%s)\n</font>", message->rd_ptr() ));

        <font color=red>// I suspect that some encryptors might change the data size.</font>
        <font color=red>// It probably isn't safe to create a same-size destination buffer.</font>
    ACE_Message_Block * encrypted = new ACE_Message_Block(
        message->size() +16 );

        <font color=red>// Perform a bogus encryption algorithm and add our safety</font>
        <font color=red>// signature.  Adding the original data size is also probably</font>
        <font color=red>// a good idea that I haven't encorporated here.</font>
    <font color=#008888>ACE_OS::sprintf</font>( encrypted->wr_ptr(), "<font color=green>ED:%s</font>", message->rd_ptr() );
    encrypted->wr_ptr( strlen(encrypted->wr_ptr())+1 );

        <font color=red>// Send the encrypted data down the stream to the next module</font>
    this->put_next( encrypted );

        <font color=red>// We're done here.</font>
    message->release();

    return( 0 );
}

<font color=red>/* The upstream movement requires that we decrypt what the peer has
   given us.
*/</font>
int <font color=#008888>Crypt::recv</font>(ACE_Message_Block *message, ACE_Time_Value *timeout)
{
    ACE_UNUSED_ARG(timeout);

    ACE_DEBUG ((LM_INFO, "<font color=green>(%P|%t) <font color=#008888>Crypt::recv</font>() decrypting (%s)\n</font>", message->rd_ptr() ));

        <font color=red>// Create a destination for the decrypted data.  The same</font>
        <font color=red>// block size caveat exists of course.</font>
    ACE_Message_Block * decrypted = new ACE_Message_Block(
        message->size() +16 );

        <font color=red>// Check the signature as expected.</font>
    if( <font color=#008888>ACE_OS::strncmp</font>( message->rd_ptr(), "<font color=green>ED:</font>", 3  ) )
    {
        ACE_DEBUG ((LM_INFO, "<font color=green>(%P|%t) Improperly encrypted data.\n</font>" ));
        message->release();
        return(-1);
    }

        <font color=red>// Don't forget to skip past the signature before decrypting</font>
        <font color=red>// or things will be quite exciting!</font>
    message->rd_ptr( 3 );

        <font color=red>// Perform a bogus decryption algorithm</font>
    <font color=#008888>ACE_OS::sprintf</font>( decrypted->wr_ptr(), "<font color=green>%s</font>", message->rd_ptr() );
    decrypted->wr_ptr( strlen(decrypted->wr_ptr())+1 );

        <font color=red>// Send the decrypted data down the stream to the next module</font>
    this->put_next( decrypted );

        <font color=red>// We're done here.</font>
    message->release();

    return( 0 );
}
</PRE>
<P><HR WIDTH="100%">
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