I see.
Another option is to send some kind of identifier preceding the
message (just like the total size of the message), right?
-- Chris
On Dec 3, 5:23 pm, Adam Vartanian <flo...@google.com> wrote:
> > I just started looking into protobuf for a project of mine.
> > From the Java Api page I could not really find how to parse a
> > generated (compiled .proto is present) but "unknown" message.
>
> > So for example: I have messages types MessageA and MessageB. The
> > client component receives some bytes representing a message of type A
> > OR B. Do I have to add information of the type of message that's been
> > send, or is there an easy way of automatically parsing the message
> > like:
>
> > byte[] b; //hols byte representation of message
> > Message message = foo(b); //parse message
> > if(message instanceof MessageA)
> > System.out.println("was type A");
> > else
> > System.out.println("was type B");
>
> No, there's no way to do this, because the wire format doesn't include
> information about the type of message. It's even possible that the
> same set of bytes could be a valid message of both types.
>
> The usual way to handle this is to create a wrapper message that can
> hold either, like so:
>
> // Only one field may be filled out
> message AorB {
> optional MessageA message_a;
> optional MessageB message_b;
>
> }
>
> And then you can parse it via:
>
> AorB result = AorB.parseFrom(data);
> if (result.hasMessageA()) {
> System.out.println("Was type A");} else if (result.hasMessageB()) {
>
> System.out.println("Was type B");
>
> }
>
> - Adam
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