Add nbtOptionalLengthPrefixed datatype (length-prefixed optional NBT)#1495
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Add nbtOptionalLengthPrefixed datatype (length-prefixed optional NBT)#1495atiweb wants to merge 1 commit into
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A network (anonymous) optional NBT tag preceded by its byte length as a VarInt -- Mojang's ByteBufCodecs.optionalTagCodec(...).apply(ByteBufCodecs.lengthPrefixed(N)), used by ServerboundCustomClickActionPacket and the dialog system added in 1.21.6. An empty tag is a single TAG_END byte, so an absent value encodes as `01 00`. This is the datatype minecraft-data needs to define custom_click_action's payload correctly; it is currently typed as option<anonymousNbt>, which emits a spurious presence boolean and omits the length prefix. See PrismarineJS#1484. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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What
Adds a
nbtOptionalLengthPrefixeddatatype: a network (anonymous) optional NBT tag preceded by its byte length as a VarInt.This is Mojang's
ByteBufCodecs.optionalTagCodec(...).apply(ByteBufCodecs.lengthPrefixed(N)), used byServerboundCustomClickActionPacketand the dialog system introduced in 1.21.6. The empty tag is a singleTAG_END(0x00) byte, so an absent value encodes as01 00(length 1, thenTAG_END).Why
It's the datatype
minecraft-dataneeds to describecustom_click_action's payload correctly. Today that payload is typed asoption<anonymousNbt>, which emits a spurious presence boolean and omits the length prefix, so the bytes sent to the server are wrong. See #1484.Validation
test/nbtOptionalLengthPrefixedTest.jschecks, against bytes captured from a real 1.21.11 dialog submit, that a present compound{ password: "hello world" }encodes as1a(VarInt 26) + the 26-byte anonymous NBT, round-trips, and that an absent tag is01 00.The matching
minecraft-datachange (typingcustom_click_action.payloadasnbtOptionalLengthPrefixed) is a separate PR.