fix(gateway): make WriteEngine + converter raise-safe against malformed write commands

ingestor/converters.py

@@ -25,6 +25,8 @@ def to_typed_value(raw, data_type: str):
     data_type: 'boolean' | 'int' | 'float' | 'double' | 'string'.
     Raises ConversionError on any invalid input (never a bare TypeError).
     """
+    if not isinstance(data_type, str):
+        raise ConversionError(f'data_type must be a string, got {type(data_type).__name__}')
     dtype = data_type.strip().lower()
     try:
         if dtype in ('bool', 'boolean'):

ingestor/engines/write.py

@@ -88,6 +88,10 @@ class WriteEngine(SientiaMonitoring):
     async def write(self, cmd: dict) -> WriteResult:
         await self._rate_limit()
 
+        missing = [k for k in ('value', 'data_type', 'server_id', 'addr') if k not in cmd]
+        if missing:
+            return await self._emit_error(cmd, 'bad_command', f'missing fields: {missing}', 'error')
+
         try:
             typed = to_typed_value(cmd['value'], cmd['data_type'])
         except ConversionError as e:
@@ -156,7 +160,7 @@ class WriteEngine(SientiaMonitoring):
         return result
 
     async def _emit_success(self, cmd: dict, start: float):
-        tags = {'pod_id': self.pod_id, 'server_name': cmd['server_id']}
+        tags = {'pod_id': self.pod_id, 'server_name': cmd.get('server_id', 'unknown')}
         await self.emit_metric(
             metric_object=metrics.OPC_WRITE_TOTAL,
             tags={**tags, 'model_id': cmd.get('model_id', 'unknown'), 'result': 'success'},

tests/unit/engines/test_write.py

@@ -161,6 +161,46 @@ async def test_write_bad_type_returns_error_without_raising():
     )
 
 
+@pytest.mark.asyncio
+async def test_write_none_data_type_returns_error_without_raising():
+    eng = make_engine()
+
+    result = await eng.write(base_cmd(data_type=None))
+
+    assert result.ok is False
+    assert result.status == 'error'
+    eng.sink.update_write_status.assert_awaited_once()
+    eng.pool.get.assert_not_awaited()
+
+
+@pytest.mark.asyncio
+async def test_write_missing_value_key_returns_error_without_raising():
+    eng = make_engine()
+    cmd = base_cmd()
+    del cmd['value']
+
+    result = await eng.write(cmd)
+
+    assert result.ok is False
+    assert result.status == 'error'
+    eng.sink.update_write_status.assert_awaited_once()
+    eng.pool.get.assert_not_awaited()
+
+
+@pytest.mark.asyncio
+async def test_write_missing_data_type_key_returns_error_without_raising():
+    eng = make_engine()
+    cmd = base_cmd()
+    del cmd['data_type']
+
+    result = await eng.write(cmd)
+
+    assert result.ok is False
+    assert result.status == 'error'
+    eng.sink.update_write_status.assert_awaited_once()
+    eng.pool.get.assert_not_awaited()
+
+
 @pytest.mark.asyncio
 async def test_write_value_raises_maps_to_error_result_not_raised():
     eng = make_engine()

tests/unit/test_converters.py

@@ -22,3 +22,10 @@ def test_float_and_int():
 def test_invalid_raises_conversion_error(raw, dtype):
     with pytest.raises(ConversionError):
         to_typed_value(raw, dtype)
+
+
+@pytest.mark.parametrize('dtype', [None, 123])
+def test_non_string_data_type_raises_conversion_error(dtype):
+    # contract: never a bare AttributeError/TypeError, always ConversionError
+    with pytest.raises(ConversionError):
+        to_typed_value('5', dtype)