FrameDecoder for UDP stream

[Jan Van Besien]

Hi

I am looking for ideas on how to implement something in netty.

I am writing a netty client (and test/mock server) for a binary UDP 
protocol. The payload is protobuf and the transport layer is UDP. Each 
protobuf message is splitted over different UDP packets. Each UDP packet 
contains a header and a body. The body is a part of the protobuf 
message, the header contains a conversation number (identifies a single 
request-response conversation), a packet number and a total number of 
packets (total meaning the total to get the whole protobuf payload) and 
a length field describing how long the body is.

Downstream it looks like this (I think this is OK):
- my business logic handler creates protobuf messages
- a protobuf encoder encodes the message in binary format
- a custom OneToOneEncoder creates a ChunkedInput which creates the UDP 
packets as described above
- a chunkedWriteHandler writes the chunks

I currently designed the upstream pipeline like this:

- (1) a lengthfieldbasedframedecoder to cope with potentially fragmented 
UDP packets
- (2) something which assembles multiple "chunked" UDP packets into a 
single protobuf message
- (3) a protobuf decoder
- (4) my business logic

The problem is (2). I think something based on a FrameDecoder is not 
sufficient, because potentially multiple "conversations" are going on at 
the same time. So I should have something which buffers all input per 
ongoing conversation, and sends a message upstream when all packets for 
a certain conversation have arrived. When that happens, it should clear 
the buffer for this conversation, but not the others. Potentially I also 
want to clear incomplete buffers after a certain timeout.

Is there something in netty on which I can build for this kind of 
functionality?

Am I maybe complicating things too much? I am involved in the design of 
the protocol as well, so things can still be changed.

Kind regards
Jan