Not really. Wanna write one?
It's quite easy, actually - compile, run (with 2 parameters - incoming port number and outgoing port number) and then connect to the incoming port with the client. ProtoProxy will connect to localhost:outgoing port, which should be a vanilla server, and it logs the entire communication to a logfile.
I regularly use ProtoProxy even with MCServer, so that I can see what our server sends to the client - did we do something wrong to the protocol etc. If the client crashes, I can point a finger at the most likely packets to have caused the crash, since the client disconnects right after that; usually it's the packet right before, sometimes a few packets before that, since it takes time for them to be delivered.
It's quite easy, actually - compile, run (with 2 parameters - incoming port number and outgoing port number) and then connect to the incoming port with the client. ProtoProxy will connect to localhost:outgoing port, which should be a vanilla server, and it logs the entire communication to a logfile.
I regularly use ProtoProxy even with MCServer, so that I can see what our server sends to the client - did we do something wrong to the protocol etc. If the client crashes, I can point a finger at the most likely packets to have caused the crash, since the client disconnects right after that; usually it's the packet right before, sometimes a few packets before that, since it takes time for them to be delivered.