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fix: adapt chat packet format for MC 1.21.5 (protocol 770)

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1.21.5 changed LastSeenMessages.Update to include a trailing checksum
byte (0 = skip verification). This affects serverbound chat and signed
chat command packets.

Additionally, the clientbound PlayerChat packet now has a globalIndex
VarInt prepended before the sender UUID.

Without these fixes:
- Sending plain chat messages causes DecoderException on the server
- Receiving player chat messages causes Queue empty crash in MCC

Made-with: Cursor
This commit is contained in:
BruceChen 2026-03-21 01:08:08 +08:00
parent 9af6c643e3
commit 26e8a2f2e6
1 changed files with 13 additions and 0 deletions
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13
MinecraftClient/Protocol/Handlers/Protocol18.cs
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@ -1069,6 +1069,11 @@ namespace MinecraftClient.Protocol.Handlers
// 1.19.3+
// Header section
// net.minecraft.network.packet.s2c.play.ChatMessageS2CPacket#write
// 1.21.5+: globalIndex prepended before sender UUID
if (protocolVersion >= MC_1_21_5_Version)
dataTypes.ReadNextVarInt(packetData);
var senderUuid = dataTypes.ReadNextUUID(packetData);
var index = dataTypes.ReadNextVarInt(packetData);
// Signature is fixed size of 256 bytes
@ -3732,6 +3737,10 @@ namespace MinecraftClient.Protocol.Handlers
case >= MC_1_19_3_Version:
fields.AddRange(DataTypes.GetVarInt(messageCount1193));
fields.AddRange(bitset1193);
// Checksum: Byte (1.21.5+, 0 = skip verification)
if (protocolVersion >= MC_1_21_5_Version)
fields.Add(0);
break;
}
@ -3835,6 +3844,10 @@ namespace MinecraftClient.Protocol.Handlers
// Acknowledged: BitSet
fields.AddRange(bitset1193);
// Checksum: Byte (1.21.5+, 0 = skip verification)
if (protocolVersion >= MC_1_21_5_Version)
fields.Add(0);
break;
case MC_1_19_2_Version:
// Message Acknowledgment