=head1 NAME

GRID::Machine::Message - Primitives for sending and receiving

=head1 DESCRIPTION


This class is used by both the local and the remote sides of the
C<GRID::Machine>. It implements the low level communication 
layer. It is responsible of marshalling the data.

=head2 The C<read_operation> Method

Syntax:

   my ( $operation, @args ) = $server->read_operation( );

Returns the kind of operation and the data sent by the other
side of the SSH link.

=head2 The C<send_operation> Method

Examples:

  $server->send_operation("RETURNED", GRID::Machine::Result->new( %arg ));

  $server->send_operation("DIED", GRID::Machine::Result->new( 
                                    errmsg  => "$server->{host}: $message")
  );

  $server->send_operation("RETURNED", exists($server->{stored_procedures}{$name}));




=head1 SEE ALSO

=over 2

=item * L<GRID::Machine>

=item * L<GRID::Machine::IOHandle>

=item * L<http://nereida.deioc.ull.es/~pp2/GRID_Machine/Machine.dvi>

=item * L<IPC::PerlSSH>

=item * Man pages of C<ssh>, C<ssh-key-gen>, C<ssh_config>, C<scp>, 
C<ssh-agent>, C<ssh-add>, C<sshd>

=item * L<http://www.openssh.com>

=back




=head1 AUTHOR

Casiano Rodriguez Leon E<lt>casiano@ull.esE<gt>

=head1 ACKNOWLEDGMENTS

This work has been supported by CEE (FEDER) and the Spanish Ministry of
I<Educación y Ciencia> through I<Plan Nacional I+D+I> number TIN2005-08818-C04-04
(ULL::OPLINK project L<http://www.oplink.ull.es/>). 
Support from Gobierno de Canarias was through GC02210601
(I<Grupos Consolidados>).
The University of La Laguna has also supported my work in many ways
and for many years.

I wish to thank Paul Evans for his C<IPC::PerlSSH> module: it was the source
of inspiration for this module. To Dmitri Kargapolov for his contributions.
To the perl monks, and the Perl Community for generously sharing their knowledge.
Finally, thanks to Juana, Coro and  my students at La Laguna.

=head1 LICENCE AND COPYRIGHT
 
Copyright (c) 2007 Casiano Rodriguez-Leon (casiano@ull.es). All rights reserved.

These modules are free software; you can redistribute it and/or
modify it under the same terms as Perl itself. See L<perlartistic>.
 
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. 




