A protobuf wire-stream is a byte string that is comprised of zero or more of the above multi-byte wire-stream primitives. Templates are lists of Prolog terms. Each term corresponds to a production rule in the DCG. The purpose of the template is to provide a recipe and value set for encoding and decoding a particular message. Each term in the template has an arity of two. The term's functor is the local "host type". Argument 1 is its tag, which must always be ground, and argument 2 is its associated value, which may or may not be ground.
Note: It is an error to attempt to encode a message using a template that is not ground. Decoding a message into a template that has unbound variables has the effect of unifying the variables with their corresponding values in the wire-stream.
Map a Prolog structure to a Protocol Buffer:
command(add(X,Y), Proto) :-
Proto = protobuf([atom(1, command),
atom(2, add),
integer(3, X),
integer(4, Y)
]).
Later on:
... prepare X, Y for command ... command(add(X,Y), Proto), protobuf_message(Proto, Msg), ... send the message ...
Proto is the protobuf template. Each template describes exactly one
message. Msg is the wire-stream. If you are interworking with other
systems and languages, then the protobuf templates that you supply to
protobuf_message/2 must
be equivalent to those described in the
.proto file that is used on the other side.