computeChatChecksum returns unsigned byte but schema is i8 → RangeError on MC 1.21.11

[mio-rei]

Versions

• node-minecraft-protocol: 1.66.0
• mineflayer: 4.37.0
• Minecraft server: 1.21.11 (vanilla single-player, opened to LAN)
• Node: 22

What happens

When the bot attempts to send any slash command whose packet goes through chat_command_signed (e.g. /say hello, /tell target msg), it crashes with:

RangeError [ERR_OUT_OF_RANGE]: Write error for undefined :
  The value of "value" is out of range. It must be >= -128 and <= 127. Received 143
    at writeU_Int8 (node:internal/buffer:740:11)
    at Buffer.writeInt8 (node:internal/buffer:871:10)
    at Object.writer [as i8] (.../protodef/src/datatypes/numeric.js:97:25)
    at Object.packet_chat_command_signed ...
  code: 'ERR_OUT_OF_RANGE',
  field: 'play.toServer'

The value received varies (143, 212, ...) — it's the chat checksum.

Root cause

In src/datatypes/checksums.js:

function computeChatChecksum (lastSeenMessages) {
  // ...
  const result = checksum & 0xff        // <-- returns 0..255 (unsigned)
  return result === 0 ? 1 : result
}

The function returns an unsigned byte (& 0xff → 0..255).

The schema for packet_chat_command_signed (and packet_chat_message) in 1.21.5+ defines this field as a signed i8 (-128..127):

{ "name": "checksum", "type": "i8" }

Whenever the hash happens to have its top bit set (~50% of the time), the resulting unsigned byte is ≥ 128, and writeInt8 throws.

Suggested fix

const unsigned = checksum & 0xff
const signed = unsigned > 127 ? unsigned - 256 : unsigned
return signed === 0 ? 1 : signed

or equivalently new Int8Array([checksum & 0xff])[0].

Applied this as a local monkey-patch against node_modules/minecraft-protocol/src/datatypes/checksums.js and the bot can now reliably send slash commands to 1.21.11 without the ERR_OUT_OF_RANGE crash.

Happy to open a PR if that would help.