Fix: MultiBlockChangePacket.ChunkSectionPos reads/writes incorrectly

minecraft/networking/packets/clientbound/play/block_change_packet.py

@@ -1,7 +1,7 @@
 from minecraft.networking.packets import Packet
 from minecraft.networking.types import (
-    Type, VarInt, VarLong, Long, Integer, UnsignedByte, Position, Vector,
-    MutableRecord, PrefixedArray, Boolean, attribute_alias,
+    Type, VarInt, VarLong, UnsignedLong, Integer, UnsignedByte, Position,
+    Vector, MutableRecord, PrefixedArray, Boolean, attribute_alias,
     multi_attribute_alias,
 )
 
@@ -63,17 +63,19 @@ class MultiBlockChangePacket(Packet):
     class ChunkSectionPos(Vector, Type):
         @classmethod
         def read(cls, file_object):
-            value = Long.read(file_object)
-            x = value >> 42
-            z = (value >> 20) & 0x3FFFFF
-            y = value & 0xFFFFF
+            value = UnsignedLong.read(file_object)
+            y = value | ~0xFFFFF if value & 0x80000 else value & 0xFFFFF
+            value >>= 20
+            z = value | ~0x3FFFFF if value & 0x200000 else value & 0x3FFFFF
+            value >>= 22
+            x = value | ~0x3FFFFF if value & 0x200000 else value
             return cls(x, y, z)
 
         @classmethod
         def send(cls, pos, socket):
             x, y, z = pos
             value = (x & 0x3FFFFF) << 42 | (z & 0x3FFFFF) << 20 | y & 0xFFFFF
-            Long.send(value, socket)
+            UnsignedLong.send(value, socket)
 
     class Record(MutableRecord, Type):
         __slots__ = 'x', 'y', 'z', 'block_state_id'

tests/test_serialization.py

@@ -7,6 +7,9 @@ from minecraft.networking.types import (
     ShortPrefixedByteArray, VarIntPrefixedByteArray, UUID,
     String as StringType, Position, TrailingByteArray, UnsignedLong,
 )
+from minecraft.networking.packets.clientbound.play import (
+    MultiBlockChangePacket
+)
 from minecraft.networking.packets import PacketBuffer
 from minecraft.networking.connection import ConnectionContext
 from minecraft import SUPPORTED_PROTOCOL_VERSIONS, RELEASE_PROTOCOL_VERSIONS
@@ -36,6 +39,12 @@ TEST_DATA = {
     UUID: ["12345678-1234-5678-1234-567812345678"],
     StringType: ["hello world"],
     Position: [(758, 0, 691), (-500, -12, -684)],
+    MultiBlockChangePacket.ChunkSectionPos: [
+        (x, y, z)
+        for x in [-0x200000, -123, -1, 0, 123, 0x1FFFFF]
+        for z in [-0x200000, -456, -1, 0, 456, 0x1FFFFF]
+        for y in [-0x80000, -789, -1, 0, 789, 0x7FFFF]
+    ]
 }