Add specific error when encoding packet with no encoder

[Moulberry]

Adds a specific error when encoding a packet that doesn't have a registered encoder

To explain a bit more about the issue:
CustomPayload#getCodec returns a dummy decoder using unknownCodecFactory. This is fine when decoding, but not when encoding. When encoding, you'll end up with a confusing exception about casting to DiscardedPayload (or UnknownCustomPayload).

An ideal solution would not use #getCodec for encode, and would instead throw the more helpful exception directly when a codec is missing. Unfortunately I couldn't figure out a good way to do this since map is part of the anonymous class (perhaps someone with more knowledge of mixins could point me in the right direction).

Overwriting the entire #getCodec method is also an option, but I think is generally unfavoured.

For this PR, I just throw the error if the namespace isn't "minecraft", which might be problematic if mods add directly to the map instead of using Fabric's system.

[Patbox]

This does break existing mods such as polymer library (it injects into getCodec method) and carpet (adds to vanilla list). It also requires more specific mixins to work around it.

[modmuss50]

Hi, im just testing out this PR and im not sure its working as expected? Running /networktestcommand sendMissingCodec shows me the following error screen? Putting a breakpoint in the encode doesnt seem to trigger.

[modmuss50]

You might be able to add a unit test for this, see PayloadTypeRegistryTests for an example.

[Moulberry]

Hi, im just testing out this PR and im not sure its working as expected? Running /networktestcommand sendMissingCodec shows me the following error screen? Putting a breakpoint in the encode doesnt seem to trigger.

The current behaviour (which may be possible to change) is that attempting to encode a packet without a codec is still an error, so the client will be disconnected.
The difference is that the logs will show the new RuntimeException ("has no registered codec" etc.), instead of a ClassCastException to DiscardedPayload.

The thrown exception is caught somewhere higher up and the client is disconnected with the "Failed to encode packet" error message, with our RuntimeException being a child.

Below is what appears in the logs (at least on my machine) when running /networktestcommand sendMissingCodec:

[20:16:50] [Netty Server IO #1/ERROR] (Minecraft) Error sending packet clientbound/minecraft:custom_payload
io.netty.handler.codec.EncoderException: Failed to encode packet 'clientbound/minecraft:custom_payload' (fabric-networking-api-v1-testmod:no_codec)
        at net.minecraft.network.handler.PacketCodecDispatcher.handler$zcm000$fabric-networking-api-v1$encode(PacketCodecDispatcher.java:547) ~[minecraft-common-38e832ecca-1.20.5-net.fabricmc.yarn.1_20_5.1.20.5+build.1-v2.jar:?]
        at net.minecraft.network.handler.PacketCodecDispatcher.encode(PacketCodecDispatcher.java:55) ~[minecraft-common-38e832ecca-1.20.5-net.fabricmc.yarn.1_20_5.1.20.5+build.1-v2.jar:?]
        ~~SNIP~~
        at io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74) ~[netty-common-4.1.97.Final.jar:?]
        at java.base/java.lang.Thread.run(Thread.java:1583) [?:?]
Caused by: java.lang.RuntimeException: Custom payload 'fabric-networking-api-v1-testmod:no_codec' has no registered codec
        at net.minecraft.network.packet.UnknownCustomPayload$Anonymous$a4ca0709779d43999db59af12d303b0c.encode(UnknownCustomPayloadMixin.java:41) ~[?:?]
        at net.minecraft.network.packet.UnknownCustomPayload$Anonymous$a4ca0709779d43999db59af12d303b0c.encode(UnknownCustomPayloadMixin.java:33) ~[?:?]
        ~~SNIP~~
        at net.minecraft.network.handler.PacketCodecDispatcher.encode(PacketCodecDispatcher.java:53) ~[minecraft-common-38e832ecca-1.20.5-net.fabricmc.yarn.1_20_5.1.20.5+build.1-v2.jar:?]
        ... 31 more

I can't say for sure why the breakpoint isn't working, but I'd think it has something to do with the mixin+anonymous class?

You might be able to add a unit test for this, see PayloadTypeRegistryTests for an example.

I'll give it a shot!