Client more robust against faulty response. (#1547)

pymodbus/framer/socket_framer.py

@@ -176,6 +176,7 @@ def _process(self, callback, tid, error=False):
         """Process incoming packets irrespective error condition."""
         data = self.getRawFrame() if error else self.getFrame()
         if (result := self.decoder.decode(data)) is None:
+            self.resetFrame()
             raise ModbusIOException("Unable to decode request")
         if error and result.function_code < 0x80:
             raise InvalidMessageReceivedException(result)

test/test_client_faulty_response.py

@@ -0,0 +1,40 @@
+"""Test server working as slave on a multidrop RS485 line."""
+from unittest import mock
+
+import pytest
+
+from pymodbus.exceptions import ModbusIOException
+from pymodbus.factory import ClientDecoder
+from pymodbus.framer import ModbusSocketFramer
+
+
+class TestFaultyResponses:
+    """Test that server works on a multidrop line."""
+
+    slaves = [0]
+
+    good_frame = b"\x00\x01\x00\x00\x00\x05\x00\x03\x02\x00\x01"
+
+    @pytest.fixture(name="framer")
+    def fixture_framer(self):
+        """Prepare framer."""
+        return ModbusSocketFramer(ClientDecoder())
+
+    @pytest.fixture(name="callback")
+    def fixture_callback(self):
+        """Prepare dummy callback."""
+        return mock.Mock()
+
+    def test_ok_frame(self, framer, callback):
+        """Test ok frame."""
+        framer.processIncomingPacket(self.good_frame, callback, self.slaves)
+        callback.assert_called_once()
+
+    def test_faulty_frame1(self, framer, callback):
+        """Test ok frame."""
+        faulty_frame = b"\x00\x04\x00\x00\x00\x05\x00\x03\x0a\x00\x04"
+        with pytest.raises(ModbusIOException):
+            framer.processIncomingPacket(faulty_frame, callback, self.slaves)
+        callback.assert_not_called()
+        framer.processIncomingPacket(self.good_frame, callback, self.slaves)
+        callback.assert_called_once()