Before I resort to rocket science I figured I would ask the question in hopes that I have overlooked something.  What I am wanting to do is intercept incoming packets from clients before they get handed off to FML/Vanilla packet processing.  Is there a framework in place that allows me to register an interceptor so that my mod can get a crack at the packet before/after processing?

 

The specific thing I am wanting to do is intercept incoming sign text update packets so that I can do some pre/post processing of the event.  What I am hoping for is clean server side entry point to do this without resorting to custom signs/tile entities, ASM, or some other fancy hackery.  The mod I am working on should not be required on a client.

 

(I did look for a Forge event for sign update, but I did not see any.)

There are events such as ClientCustomPacketEvent, ServerCustomPacketEvent, and CustomPacketRegistrationEvent, but I'm not sure how useful these would be to you for intercepting packets.

Yeah.  My understanding, though, that those are for custom packs that my mod generates and send.  Of course, there may be some trick to these guys where I can get vanilla packets.

^ This could be potentially really damn useful.

 

Other question

Goal: Change packet's data before it's being sent from server to client.

Extend NetHandlerPlayerServer and override sendPacket, and then simply check instance of packet and change data.

For every EntityPlayerMP - LoggedIn or JoinedWorld event? - replace handler field with extension.

Happily manipulate packets with e.g world data (e.g: have 2 players in same world but one will receive totally different world data).

 

Can something go wrong?

Excellent! On the surface this is exactly what I am looking for.  Now I have my project for the day.