Hello (and sorry for bothering) and thank you for your clarifying.
> The "type" is simply transmitted as a tag on the wire. The wire format
> of extensions is just like the wire format of a regular field - the
> difference is that the containing type (Packet) need not know about
> the extension fields in the .proto definition. Instead, each payload
> type that you might include will have a unique extension number. When
> you include one of the payload messages in your program, it will
> register its extensions of Packet. Then when a packet message is
> parsed, if it sees a tag that is not defined in the .proto but is a
> valid extension, it looks up the extension information and parses it
> appropriately.
The idea is good and clear, but i have problems figuring out the code.
The huge problem is, that the PacketManager should be designed protocol
agnostic, so it
can deal with all protocols designed in the extension way you described.
This said, if i understood it right, i would write it as following:
---File: myProto.proto---
message Packet {
extensions n to m;
}
// Payload messages
// the type field must be the same for all mesages, with differing tag
number
message TestMessage {
extend Packet {
optional TestMessage type = 10;
}
required string msg = 2;
}
-------------------------
---File: PacketHandler.java---
class PacketHandler {
...
// Gets called whenever a new message arrives
// ByteBuffer is passed to this method containing
// the raw data from the net.
public void messageRecieved(ByteBuffer buffer) {
byte[] bytes = buffer.array(); // fetch bytes from buffer
// parse the header data;
// this.header is passed in the constructor of PacketHandler;
// it is an instance of a "Packet" message.
ExtendableMessage header =
this.header.newBuilderForType().mergeFrom(bytes).build();
// lets see what tag number the extension has, this is the type identifier.
// this is done via the extension registry.
ExtensionRegistry extReg = ExtensionRegistry.newInstance();
int type = extReg.findExtensionByName("type").descriptor().getNumber();
// invoke the right handler for that message, it will take care of the
rest:
getHandler(type).handle(header.getExtension(type));
}
...
}
-------------------------
However, as i tried that, it gave me errors i cant solve.
As long as i work with concrete classes and names, all is okay, but that is
not what i want here. What i want is to avoid that hardcoded "switch"
statement on types, so it is easier to add new message types without having
to fiddle around with much code.
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