Drop the serial port on a transport error, so the client can reconnect

pymodbus/client/serial.py

@@ -265,12 +265,18 @@ def send(self, request: bytes, addr: tuple | None = None) -> int:
         if not self.socket:
             raise ConnectionException(str(self))
         if request:
-            if waitingbytes := self._in_waiting():
-                result = self.socket.read(waitingbytes)
-                Log.warning("Cleanup recv buffer before send: {}", result, ":hex")
-            if (size := self.socket.write(request)) is None:  # pragma: no cover
-                size = 0
-            return size
+            try:
+                if waitingbytes := self._in_waiting():
+                    result = self.socket.read(waitingbytes)
+                    Log.warning("Cleanup recv buffer before send: {}", result, ":hex")
+                if (size := self.socket.write(request)) is None:  # pragma: no cover
+                    size = 0
+                return size
+            except (BlockingIOError, InterruptedError):
+                raise
+            except OSError:
+                self.close()
+                raise ConnectionException(str(self)) from None
         return 0
 
     def _wait_for_data(self) -> int:
@@ -296,12 +302,17 @@ def recv(self, size: int | None) -> bytes:
         """Read data from the underlying descriptor."""
         if not self.socket:
             raise ConnectionException(str(self))
-        if size is None:
-            size = self._wait_for_data()
-        if size > self._in_waiting():
-            self._wait_for_data()
-        result = self.socket.read(size)
-        return result
+        try:
+            if size is None:
+                size = self._wait_for_data()
+            if size > self._in_waiting():
+                self._wait_for_data()
+            return self.socket.read(size)
+        except (BlockingIOError, InterruptedError):
+            raise
+        except OSError:
+            self.close()
+            raise ConnectionException(str(self)) from None
 
     def is_socket_open(self) -> bool:
         """Check if socket is open."""

test/client/test_client_sync.py

@@ -395,6 +395,32 @@ def test_serial_client_cleanup_buffer_before_send(self, mock_serial):
         assert not client.send(b"")
         assert client.send(b"1234") == 4
 
+    def test_serial_client_send_drops_socket_on_os_error(self):
+        """Test that a port the OS tore down is not left in place as connected."""
+        client = ModbusSerialClient("/dev/null")
+        mock_socket = mock.MagicMock()
+        mock_socket.in_waiting = 0
+        mock_socket.write.side_effect = OSError(5, "Input/output error")
+        client.socket = mock_socket
+        with pytest.raises(ConnectionException):
+            client.send(b"1234")
+        assert not client.connected
+        assert client.socket is None
+
+    def test_serial_client_send_keeps_socket_on_transient_error(self):
+        """Test that a transient write error leaves a healthy port in place."""
+        client = ModbusSerialClient("/dev/null")
+        mock_socket = mock.MagicMock()
+        mock_socket.in_waiting = 0
+        mock_socket.write.side_effect = BlockingIOError(
+            11, "Resource temporarily unavailable"
+        )
+        client.socket = mock_socket
+        with pytest.raises(BlockingIOError):
+            client.send(b"1234")
+        assert client.connected
+        assert client.socket is mock_socket
+
     def test_serial_client_recv(self):
         """Test the serial client receive method."""
         client = ModbusSerialClient("/dev/null")
@@ -409,6 +435,32 @@ def test_serial_client_recv(self):
         assert client.recv(None) == b""
         assert client.recv(0) == b""
 
+    def test_serial_client_recv_drops_socket_on_os_error(self):
+        """Test that a read against a torn-down port drops it rather than escaping."""
+        client = ModbusSerialClient("/dev/null")
+        mock_socket = mock.MagicMock()
+        mock_socket.in_waiting = 10
+        mock_socket.read.side_effect = OSError(5, "Input/output error")
+        client.socket = mock_socket
+        with pytest.raises(ConnectionException):
+            client.recv(4)
+        assert not client.connected
+        assert client.socket is None
+
+    def test_serial_client_recv_keeps_socket_on_transient_error(self):
+        """Test that a transient read error leaves a healthy port in place."""
+        client = ModbusSerialClient("/dev/null")
+        mock_socket = mock.MagicMock()
+        mock_socket.in_waiting = 10
+        mock_socket.read.side_effect = BlockingIOError(
+            11, "Resource temporarily unavailable"
+        )
+        client.socket = mock_socket
+        with pytest.raises(BlockingIOError):
+            client.recv(4)
+        assert client.connected
+        assert client.socket is mock_socket
+
     def test_serial_client_recv_split(self):
         """Test the serial client receive method."""
         client = ModbusSerialClient("/dev/null")