Author: James CE Johnson

ACE Tutorial 015
Building a protocol stream

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

    // page21.html,v 1.11 1999/04/03 21:56:31 jcej Exp

    #include "Crypt.h"
    #include "ace/SOCK_Stream.h"

    /* The expected constructor...
     */
    Crypt::Crypt( void )
            : Protocol_Task()
    {
    }

    Crypt::~Crypt(void)
    {
    }

    /* To send the data we'll apply a signature and encryption.
     */
    int Crypt::send(ACE_Message_Block *message, ACE_Time_Value *timeout)
    {
        ACE_DEBUG ((LM_INFO, "(%P|%t) Crypt::send() encrypting (%s)\n", message->rd_ptr() ));

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

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

            // Send the encrypted data down the stream to the next module
        this->put_next( encrypted );

            // We're done here.
        message->release();

        return( 0 );
    }

    /* The upstream movement requires that we decrypt what the peer has
       given us.
    */
    int Crypt::recv(ACE_Message_Block *message, ACE_Time_Value *timeout)
    {
        ACE_DEBUG ((LM_INFO, "(%P|%t) Crypt::recv() decrypting (%s)\n", message->rd_ptr() ));

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

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

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

            // Perform a bogus decryption algorithm
        ACE_OS::sprintf( decrypted->wr_ptr(), "%s", message->rd_ptr() );
        decrypted->wr_ptr( strlen(decrypted->wr_ptr())+1 );

            // Send the decrypted data down the stream to the next module
        this->put_next( decrypted );

            // We're done here.
        message->release();

        return( 0 );
    }

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