fix: resolve serializer test failures

- Fix JSON encoding to use compact format (no spaces) to match expected output
- Fix metadata extraction to exclude special fields (type, event, payload)
- Fix broadcast decoding offset calculation
- Fix metadata start position calculation in test
- Update metadata length validation test to use sufficient length

Author: grdsdev

src/realtime/src/realtime/serializer.py

@@ -88,7 +88,7 @@ def encode(
             msg.get("topic"),
             msg.get("event"),
             payload,
-        ])
+        ], separators=(',', ':'))
 
     def _binary_encode_push(self, message: Dict[str, Any]) -> bytes:
         """
@@ -215,8 +215,10 @@ def _encode_user_broadcast_push_internal(
         payload = message.get("payload", {})
         user_event = payload.get("event", "")
 
-        # Filter metadata based on allowed keys
+        # Filter metadata based on allowed keys (exclude special fields: type, event, payload)
         rest = self._pick(payload, self.allowed_metadata_keys)
+        # Remove special fields that shouldn't be in metadata
+        rest = {k: v for k, v in rest.items() if k not in ("type", "event", "payload")}
         metadata = json.dumps(rest) if rest else ""
 
         # Validate lengths don't exceed uint8 max value (255)
@@ -384,13 +386,13 @@ def _decode_reply(self, buffer: bytes) -> Dict[str, Any]:
 
     def _decode_broadcast(self, buffer: bytes) -> Dict[str, Any]:
         """Decode a broadcast message."""
-        if len(buffer) < self.HEADER_LENGTH + 3:
+        if len(buffer) < self.HEADER_LENGTH + 2:
             return {}
 
         topic_size = buffer[1]
         event_size = buffer[2]
 
-        offset = self.HEADER_LENGTH + 3
+        offset = self.HEADER_LENGTH + 2  # kind(1) + topic_len(1) + event_len(1) = 3, but offset is after reading lengths
 
         topic = buffer[offset:offset + topic_size].decode("utf-8")
         offset += topic_size

src/realtime/tests/test_serializer.py

@@ -127,7 +127,15 @@ def test_encode_user_broadcast_push_json_with_metadata():
     assert result[0] == 3  # userBroadcastPush kind
     assert result[5] > 0  # metadata length (should have metadata)
     # Verify metadata contains "extra" but not "store"
-    metadata_start = 1 + 5 + 2 + 1 + 3 + 10  # header + lengths
+    # Format: kind(1) + join_ref_len(1) + ref_len(1) + topic_len(1) + user_event_len(1) + metadata_len(1) + encoding(1) = 7 bytes header
+    # Then: join_ref(2) + ref(1) + topic(3) + user_event(10) = 16 bytes
+    # So metadata starts at: 7 + 16 = 23
+    header_len = 7
+    join_ref_len = result[1]
+    ref_len = result[2]
+    topic_len = result[3]
+    user_event_len = result[4]
+    metadata_start = header_len + join_ref_len + ref_len + topic_len + user_event_len
     metadata_len = result[5]
     metadata_bytes = result[metadata_start:metadata_start + metadata_len]
     metadata = json.loads(metadata_bytes.decode("utf-8"))
@@ -323,6 +331,9 @@ def test_encode_validation_errors():
 
     # Test metadata too long
     serializer_with_meta = Serializer(allowed_metadata_keys=["extra"])
+    # Create metadata that will exceed 255 chars when JSON stringified
+    # JSON format: {"extra":"aaa..."} = 2 + 9 + 1 + 1 + N + 1 = 14 + N
+    # So we need N > 241 to exceed 255 total
     with pytest.raises(ValueError, match="metadata length"):
         serializer_with_meta._encode_user_broadcast_push_internal(
             {
@@ -332,7 +343,7 @@ def test_encode_validation_errors():
                 "payload": {
                     "event": "user-event",
                     "payload": {},
-                    "extra": "a" * 240,  # Will exceed 255 when JSON stringified
+                    "extra": "a" * 260,  # Will exceed 255 when JSON stringified
                 },
             },
             1,