varint128

example.js

@@ -32,18 +32,10 @@ const exampleProtocol = {
         name: 'onGround',
         type: 'bool'
       },
-      {
-        name: 'longId',
-        type: 'varint64'
-      },
-      {
-        name: 'zigzagId',
-        type: 'zigzag32'
-      },
-      {
-        name: 'zigzagBig',
-        type: 'zigzag64'
-      }
+      { name: 'longId', type: 'varint64' },
+      { name: 'longerId', type: 'varint128' },
+      { name: 'zigzagId', type: 'zigzag32' },
+      { name: 'zigzagBig', type: 'zigzag64' }
     ]
   ],
   packet: [
@@ -89,8 +81,9 @@ serializer.write({
     yaw: 1,
     pitch: 1,
     onGround: true,
-    longId: 22n,
-    zigzagId: 66,
+    longId: 13n,
+    longerId: 2n ** 68n, // 9 bytes integer, 10 over wire
+    zigzagId: -3,
     zigzagBig: 4294967296n
   }
 })

src/datatypes/varint.js

@@ -3,6 +3,7 @@ const { PartialReadError } = require('../utils')
 module.exports = {
   varint: [readVarInt, writeVarInt, sizeOfVarInt, require('../../ProtoDef/schemas/utils.json').varint],
   varint64: [readVarLong, writeVarLong, sizeOfVarLong, require('../../ProtoDef/schemas/utils.json').varint],
+  varint128: [readVarLong128, writeVarLong, sizeOfVarLong, require('../../ProtoDef/schemas/utils.json').varint],
   zigzag32: [readSignedVarInt, writeSignedVarInt, sizeOfSignedVarInt, require('../../ProtoDef/schemas/utils.json').varint],
   zigzag64: [readSignedVarLong, writeSignedVarLong, sizeOfSignedVarLong, require('../../ProtoDef/schemas/utils.json').varint]
 }
@@ -67,6 +68,24 @@ function readVarLong (buffer, offset) {
   }
 }
 
+function readVarLong128 (buffer, offset) {
+  let result = 0n
+  let shift = 0n
+  let cursor = offset
+
+  while (true) {
+    if (cursor >= buffer.length) throw new Error('Unexpected buffer end while reading VarLong')
+    const byte = buffer.readUInt8(cursor)
+    result |= (BigInt(byte) & 0x7Fn) << shift // Add the bits, excluding the MSB
+    cursor++
+    if (!(byte & 0x80)) { // If MSB is not set, return result
+      return { value: result, size: cursor - offset }
+    }
+    shift += 7n
+    if (shift > 128n) throw new Error(`varint is too big: ${shift}`)
+  }
+}
+
 function sizeOfVarLong (value) {
   value = BigInt(value)
   let size = 0