1.4.6 Advanced Topics

Precompiled Messages

Performance can be improved using a strategy of precompiling the constant portions of your message. Enumerations for example, are excellent candidates for precompilation. Using protobuf_message/3, the precompiled portion of the message is inserted directly in the wire-stream on encode, and is unified with, and removed from the wire-stream on decode. The following shows how the "send_command" example above, can be converted to precompiled form:

send_precompiled_command(Command, Vector, WireCodes) :-
    basic_vector(Vector, Proto1),
    % precompiled_message/3 is created by term_expansion
    precompiled_message(commands(Command), WireCodes, Tail),
    protobuf_message(protobuf([embedded(3, Proto1)]), Tail).

term_expansion(precompile_commands, Clauses) :-
    findall(precompiled_message(commands(Key), WireCodes, Tail),
            (   protobufs:commands(Key, _),
                Proto = protobuf([atom(1, command),
                                  enum(2, commands(Key))]),
                protobuf_message(Proto, WireCodes, Tail)
            ),
            Clauses).

*
*
*
precompile_commands.  % Trigger the term-expansion precompilation

Supplying Your Own Host Type Message Sequences

You can extend the parser to support your own compound host types. These are treated as first class entities by the parser. That is they can be used either by themselves, or in repeated and embedded clauses just as any other host type would be. You do this by hooking into the parser and adding your own message_sequence productions. Your hook eventually calls back into the parser with your substitution/expansion protobuf, which is then embedded in the wire stream. Recursive structures can be defined this way. A simple example of a recursive XML like structure is shown in the appendix.