Resubmit: Don't close/reopen tcp connection on single modbus message timeout

doc/source/client.rst

@@ -166,6 +166,14 @@ The line :mod:`result = await client.read_coils(2, 3, slave=1)` is an example of
 
 The last line :mod:`client.close()` closes the connection and render the object inactive.
 
+Retry logic for async clients
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+If no response is received to a request (call), it is retried (parameter retries) times, if not successful
+an exception response is returned, BUT the connection is not touched.
+
+If 3 consequitve requests (calls) do not receive a response, the connection is terminated.
+
 Development notes
 ^^^^^^^^^^^^^^^^^
 

pymodbus/client/base.py

@@ -11,7 +11,7 @@
 from pymodbus.exceptions import ConnectionException, ModbusIOException
 from pymodbus.framer import FRAMER_NAME_TO_CLASS, FramerBase, FramerType
 from pymodbus.logging import Log
-from pymodbus.pdu import DecodePDU, ModbusPDU
+from pymodbus.pdu import DecodePDU, ExceptionResponse, ModbusPDU
 from pymodbus.transaction import SyncModbusTransactionManager
 from pymodbus.transport import CommParams
 from pymodbus.utilities import ModbusTransactionState
@@ -50,6 +50,8 @@ def __init__(
         self.last_frame_end: float | None = 0
         self.silent_interval: float = 0
         self._lock = asyncio.Lock()
+        self.accept_no_response_limit = 3
+        self.count_no_responses = 0
 
     @property
     def connected(self) -> bool:
@@ -115,11 +117,16 @@ async def async_execute(self, request) -> ModbusPDU:
                 except asyncio.exceptions.TimeoutError:
                     count += 1
         if count > self.retries:
-            self.ctx.connection_lost(asyncio.TimeoutError("Server not responding"))
-            raise ModbusIOException(
-                f"ERROR: No response received after {self.retries} retries"
-            )
-
+            if self.count_no_responses >= self.accept_no_response_limit:
+                self.ctx.connection_lost(asyncio.TimeoutError("Server not responding"))
+                raise ModbusIOException(
+                    f"ERROR: No response received of the last {self.accept_no_response_limit} request, CLOSING CONNECTION."
+                )
+            self.count_no_responses += 1
+            Log.error(f"No response received after {self.retries} retries, continue with next request")
+            return ExceptionResponse(request.function_code)
+
+        self.count_no_responses = 0
         return resp
 
     def build_response(self, request: ModbusPDU):

pymodbus/pdu/__init__.py

@@ -2,13 +2,10 @@
 __all__ = [
     "DecodePDU",
     "ExceptionResponse",
+    "ExceptionResponse",
     "ModbusExceptions",
     "ModbusPDU",
 ]
 
 from pymodbus.pdu.decoders import DecodePDU
-from pymodbus.pdu.pdu import (
-    ExceptionResponse,
-    ModbusExceptions,
-    ModbusPDU,
-)
+from pymodbus.pdu.pdu import ExceptionResponse, ModbusExceptions, ModbusPDU

test/sub_client/test_client.py

@@ -20,8 +20,8 @@
 from pymodbus.client.mixin import ModbusClientMixin
 from pymodbus.datastore import ModbusSlaveContext
 from pymodbus.datastore.store import ModbusSequentialDataBlock
-from pymodbus.exceptions import ConnectionException, ModbusException, ModbusIOException
-from pymodbus.pdu import ModbusPDU
+from pymodbus.exceptions import ConnectionException, ModbusException
+from pymodbus.pdu import ExceptionResponse, ModbusPDU
 from pymodbus.transport import CommParams, CommType
 
 
@@ -436,8 +436,9 @@ async def test_client_execute_broadcast():
     transport = MockTransport(base, request)
     base.ctx.connection_made(transport=transport)
 
-    with pytest.raises(ModbusIOException):
-        assert not await base.async_execute(request)
+    # with pytest.raises(ModbusIOException):
+    #    assert not await base.async_execute(request)
+    assert await base.async_execute(request)
 
 async def test_client_protocol_retry():
     """Test the client protocol execute method with retries."""
@@ -477,8 +478,8 @@ async def test_client_protocol_timeout():
     transport = MockTransport(base, request, retries=4)
     base.ctx.connection_made(transport=transport)
 
-    with pytest.raises(ModbusIOException):
-        await base.async_execute(request)
+    pdu = await base.async_execute(request)
+    assert isinstance(pdu, ExceptionResponse)
     assert transport.retries == 1