Fix custom_click_action payload (length-prefixed optional NBT) for 1.21.6+

[atiweb]

Problem

ServerboundCustomClickActionPacket (the packet a client sends when a dialog button is clicked; dialogs were added in 1.21.6) has:

UNTRUSTED_TAG_CODEC = ByteBufCodecs.optionalTagCodec(() -> new NbtAccounter(32768L, 16))
                          .apply(ByteBufCodecs.lengthPrefixed(65536));
STREAM_CODEC = StreamCodec.composite(Identifier.STREAM_CODEC, ::id, UNTRUSTED_TAG_CODEC, ::payload, ::new);

So the payload is a VarInt byte-length followed by an anonymous optional NBT tag (an empty tag is a single TAG_END byte).

It was typed as nbt?: anonymousNbt (i.e. option<anonymousNbt>), which emits a spurious presence boolean and omits the length prefix. The server then reads that boolean (0x01) as a TAG_Byte and rejects the packet with an "invalid value" error (PrismarineJS/node-minecraft-protocol#1484).

Fix

Type the payload as the new nbtOptionalLengthPrefixed datatype (added in PrismarineJS/node-minecraft-protocol#1495), and rename the field nbt → payload to match the packet record.

Validation

End-to-end with the new datatype, a real form submit — id = "nlogin:login/yes", payload = { password: "hello world" } — serializes to:

10 6e6c6f67696e3a6c6f67696e2f796573   # id string
1a 0a 08 0008 password 000b "hello world" 00   # VarInt(26) + anonymous NBT

which matches the buffer reported as correct in #1484, and round-trips.

Depends on PrismarineJS/node-minecraft-protocol#1495.

[MayorLeon20]

You modified the custom click action packet only for 1.21.11.
This packet is not unique to this version

[atiweb]

Good catch, thanks — you're right. I've extended the fix to every version that has the packet: 1.21.6, 1.21.8 and 1.21.9 (1.21.7 inherits 1.21.6 and 1.21.10 inherits 1.21.9 via dataPaths.json; 1.21.11 was already in this PR).

I verified each one against its official Mojang server jar — all encode the payload identically:

ByteBufCodecs.optionalTagCodec(() -> new NbtAccounter(32768L, 16)).apply(ByteBufCodecs.lengthPrefixed(65536))

So the packet has been length-prefixed since it was introduced in 1.21.6; minecraft-data just defined it as option<anonymousNbt> uniformly. Same change applied to each: register nbtOptionalLengthPrefixed as native and switch the packet payload to it.

[MayorLeon20]

Good catch, thanks — you're right. I've extended the fix to every version that has the packet: 1.21.6, 1.21.8 and 1.21.9 (1.21.7 inherits 1.21.6 and 1.21.10 inherits 1.21.9 via dataPaths.json; 1.21.11 was already in this PR).

I verified each one against its official Mojang server jar — all encode the payload identically:

ByteBufCodecs.optionalTagCodec(() -> new NbtAccounter(32768L, 16)).apply(ByteBufCodecs.lengthPrefixed(65536))

So the packet has been length-prefixed since it was introduced in 1.21.6; minecraft-data just defined it as option<anonymousNbt> uniformly. Same change applied to each: register nbtOptionalLengthPrefixed as native and switch the packet payload to it.

what about 1.21.7 and 1.21.10?

[atiweb]

Good question — and it made me re-check my earlier note, which had a mistake.

1.21.10: it's a supported version, but its dataPaths.json entry points everything (including protocol) to pc/1.21.9, so it shares 1.21.9's protocol.json — the fix already covers it (both are protocol 773).

1.21.7: minecraft-data has no 1.21.7 entry at all (not in versions.json / dataPaths.json, no data dir). 1.21.7 and 1.21.8 share protocol 772, and 1.21.8 is the dataset that carries it — which this PR fixes. So protocol 772 is covered by the 1.21.8 change. (My earlier "inherits 1.21.6" was wrong — 1.21.6 is protocol 771. Sorry for the mix-up.)

For reference: 1.21.6=771, 1.21.7/1.21.8=772, 1.21.9/1.21.10=773, 1.21.11=774 — so every protocol carrying custom_click_action (771–774) is covered by the four datasets changed here (1.21.6, 1.21.8, 1.21.9, 1.21.11).