Best practice for determining the type of a protocol buffers message

Question

I need to serialize and deserialize a sequence of protocol buffers messages to and from a byte stream. There are a handful of predetermined message types. What is the recommended way of encoding the type information so that my application can know which type it should be reading?

Answer 1

The most common way to do this is to use a union message.

For example:

message AnyMessage {
    optional Message1 msg1 = 1;
    optional Message2 msg2 = 2;
    ...
}

Then all messages are encoded/decoded inside an AnyMessage container. Starting with protobuf 2.6, you can also use the oneof specifier which will ensure that only one of the submessages is set.