Validate LeaderRequest body length and reserved value on decode

``LeaderRequest.encode_body`` writes a single uint64 reserved word of
0. The decoder was accepting any payload and ignoring the field
entirely, so truncated / extended bodies and non-zero reserved values
silently produced a valid ``LeaderRequest()``. Assert the length is 8
bytes and the reserved word is 0, raising ``DecodeError`` otherwise —
same strict-decode pattern as the Header.reserved and zero-column row
marker checks.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: antoineleclair

src/dqlitewire/messages/requests.py

@@ -46,6 +46,15 @@ def encode_body(self) -> bytes:
 
     @classmethod
     def decode_body(cls, data: bytes, schema: int = 0) -> "LeaderRequest":
+        # Strict decode symmetric with ``encode_body``: the body is
+        # exactly one uint64 reserved word, defined as 0 by upstream.
+        # Reject truncated/extended bodies and non-zero reserved values
+        # rather than silently accepting them.
+        if len(data) != 8:
+            raise DecodeError(f"LeaderRequest body must be 8 bytes, got {len(data)}")
+        reserved = decode_uint64(data)
+        if reserved != 0:
+            raise DecodeError(f"LeaderRequest reserved field must be 0, got {reserved}")
         return cls()
 
 

tests/test_messages_requests.py

@@ -71,6 +71,33 @@ def test_roundtrip(self) -> None:
         decoded = LeaderRequest.decode_body(encoded[HEADER_SIZE:])
         assert isinstance(decoded, LeaderRequest)
 
+    def test_decode_rejects_short_body(self) -> None:
+        import pytest
+
+        from dqlitewire.exceptions import DecodeError
+
+        with pytest.raises(DecodeError, match="must be 8 bytes"):
+            LeaderRequest.decode_body(b"")
+        with pytest.raises(DecodeError, match="must be 8 bytes"):
+            LeaderRequest.decode_body(b"\x00" * 7)
+
+    def test_decode_rejects_extended_body(self) -> None:
+        import pytest
+
+        from dqlitewire.exceptions import DecodeError
+
+        with pytest.raises(DecodeError, match="must be 8 bytes"):
+            LeaderRequest.decode_body(b"\x00" * 16)
+
+    def test_decode_rejects_nonzero_reserved(self) -> None:
+        import pytest
+
+        from dqlitewire.exceptions import DecodeError
+        from dqlitewire.types import encode_uint64
+
+        with pytest.raises(DecodeError, match="reserved field must be 0"):
+            LeaderRequest.decode_body(encode_uint64(1))
+
 
 class TestClientRequest:
     def test_encode(self) -> None: