Protobuf Annotations

[Michael Muller]

[I've decided to start posting general information to blog, mailing list and
G+ because not everyone subscribes to all of these. This is annoying for me,
but hopefully it won't be for you :-)]

We've had a module to deal with protobuf wire protocols for a while now
(crack.protobuf), but you've always had to code your message serialization by
hand. Not any more!

I've just checked in crack.protobuf.ann, which is an annotation that allows
you to define protobuf message definitions inline and generates the
appropriate code. So, for example, this:

@protobuf {
# Uncomment "debug" to emit the generated code to standard output with
# line numbers.
#debug

message Bar {
repeated string name = 1;
}
}

Generates this:

class Bar @impl Message {
Array[String] name = {};
oper init() {}
void serialize(ProtoWriter dst) {
for (item :in this.name)
dst.write(1, item);

}
void addField(Field field) {
if (field.id == 1) {
this.name.append(field.getString());

}

}
int cmp(Bar other) {
int rc;
((rc = cmp(this.name, other.name))
);
return rc;
}
int cmp(Object other) {
if (o := Bar.cast(other))
return cmp(o);
else
return Object.cmp(other);
}
uint makeHashVal() {
return makeHashVal(this.name);
}
@static Bar makeFromField(Field field) {
Bar inst = {};
field.readMessage(inst);
return inst;
}


}

As protobuf generation goes, this isn't all that great. For one thing, it
would be much better if we could just generate crack code from the proto
compiler like everything else and then we could use the same .proto files as
everything else. The implementation is also very incomplete. It only
supports the int32, int64, string and bytes types (and int64 is currently
broken) and it doesn't support any protobuf syntax that is even slightly
advanced. That said, it still beats coding the serialization by hand.

=============================================================================
michaelMuller = mmu...@enduden.com | http://www.mindhog.net/~mmuller
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