Async retry (#1752)

Author: janiversen

API_changes.rst

@@ -14,6 +14,7 @@ Version 3.5.0 (future)
   - :code:`ModbusPlusOperation`
   - :code:`Endian`
   - :code:`ModbusStatus`
+- Async clients now accepts `no_resend_on_retry=True`, to not resend the request when retrying.
 
 -------------
 Version 3.4.2

pymodbus/client/base.py

@@ -32,6 +32,7 @@ class ModbusBaseClient(ModbusClientMixin, ModbusProtocol):
     :param reconnect_delay: (optional) Minimum delay in milliseconds before reconnecting.
     :param reconnect_delay_max: (optional) Maximum delay in milliseconds before reconnecting.
     :param on_reconnect_callback: (optional) Function that will be called just before a reconnection attempt.
+    :param no_resend_on_retry: (optional) Do not resend request when retrying due to missing response.
     :param kwargs: (optional) Experimental parameters.
 
     .. tip::
@@ -75,6 +76,7 @@ def __init__(  # pylint: disable=too-many-arguments
         reconnect_delay: float = 0.1,
         reconnect_delay_max: float = 300,
         on_reconnect_callback: Callable[[], None] | None = None,
+        no_resend_on_retry: bool = False,
         **kwargs: Any,
     ) -> None:
         """Initialize a client instance."""
@@ -114,10 +116,8 @@ def __init__(  # pylint: disable=too-many-arguments
         self.reconnect_delay_max = int(reconnect_delay_max)
         self.on_reconnect_callback = on_reconnect_callback
         self.retry_on_empty: int = 0
-        # -> retry read on nothing
-
+        self.no_resend_on_retry = no_resend_on_retry
         self.slaves: list[int] = []
-        # -> list of acceptable slaves (0 for accept all)
 
         # Common variables.
         self.framer = framer(ClientDecoder(), self)
@@ -189,25 +189,28 @@ async def async_execute(self, request=None):
         """Execute requests asynchronously."""
         request.transaction_id = self.transaction.getNextTID()
         packet = self.framer.buildPacket(request)
-        self.transport_send(packet)
-        if self.params.broadcast_enable and not request.slave_id:
-            resp = b"Broadcast write sent - no response expected"
-        else:
-            count = 0
-            while count <= self.params.retries:
-                try:
-                    req = self._build_response(request.transaction_id)
-                    resp = await asyncio.wait_for(
-                        req, timeout=self.comm_params.timeout_connect
-                    )
-                    break
-                except asyncio.exceptions.TimeoutError:
-                    count += 1
-            if count > self.params.retries:
-                self.close(reconnect=True)
-                raise ModbusIOException(
-                    f"ERROR: No response received after {self.params.retries} retries"
+
+        count = 0
+        while count <= self.params.retries:
+            if not count or not self.no_resend_on_retry:
+                self.transport_send(packet)
+            if self.params.broadcast_enable and not request.slave_id:
+                resp = b"Broadcast write sent - no response expected"
+                break
+            try:
+                req = self._build_response(request.transaction_id)
+                resp = await asyncio.wait_for(
+                    req, timeout=self.comm_params.timeout_connect
                 )
+                break
+            except asyncio.exceptions.TimeoutError:
+                count += 1
+        if count > self.params.retries:
+            self.close(reconnect=True)
+            raise ModbusIOException(
+                f"ERROR: No response received after {self.params.retries} retries"
+            )
+
         return resp
 
     def callback_data(self, data: bytes, addr: tuple = None) -> int:

test/sub_client/test_client.py

@@ -17,7 +17,7 @@
 from pymodbus.client.mixin import ModbusClientMixin
 from pymodbus.datastore import ModbusSlaveContext
 from pymodbus.datastore.store import ModbusSequentialDataBlock
-from pymodbus.exceptions import ConnectionException
+from pymodbus.exceptions import ConnectionException, ModbusIOException
 from pymodbus.framer.ascii_framer import ModbusAsciiFramer
 from pymodbus.framer.rtu_framer import ModbusRtuFramer
 from pymodbus.framer.socket_framer import ModbusSocketFramer
@@ -365,9 +365,10 @@ async def test_client_protocol_handler():
 class MockTransport:
     """Mock transport class which responds with an appropriate encoded packet"""
 
-    def __init__(self, base, req):
+    def __init__(self, base, req, retries=0):
         """Initialize MockTransport"""
         self.base = base
+        self.retries = retries
 
         db = ModbusSequentialDataBlock(0, [0] * 100)
         self.ctx = ModbusSlaveContext(di=db, co=db, hr=db, ir=db)
@@ -382,6 +383,9 @@ async def delayed_resp(self):
 
     def write(self, data, addr=None):
         """Write data to the transport, start a task to send the response"""
+        if self.retries:
+            self.retries -= 1
+            return
         self.delayed_resp_task = asyncio.create_task(self.delayed_resp())
 
     def close(self):
@@ -401,6 +405,35 @@ async def test_client_protocol_execute():
     assert isinstance(response, pdu_bit_read.ReadCoilsResponse)
 
 
+async def test_client_protocol_retry():
+    """Test the client protocol execute method with retries"""
+    base = ModbusBaseClient(host="127.0.0.1", framer=ModbusSocketFramer, timeout=0.1)
+    request = pdu_bit_read.ReadCoilsRequest(1, 1)
+    transport = MockTransport(base, request, retries=2)
+    base.connection_made(transport=transport)
+
+    response = await base.async_execute(request)
+    assert transport.retries == 0
+    assert not response.isError()
+    assert isinstance(response, pdu_bit_read.ReadCoilsResponse)
+
+
+async def test_client_protocol_timeout():
+    """Test the client protocol execute method with timeout"""
+    base = ModbusBaseClient(
+        host="127.0.0.1", framer=ModbusSocketFramer, timeout=0.1, retries=2
+    )
+    # Avoid creating do_reconnect() task
+    base.connection_lost = mock.MagicMock()
+    request = pdu_bit_read.ReadCoilsRequest(1, 1)
+    transport = MockTransport(base, request, retries=4)
+    base.connection_made(transport=transport)
+
+    with pytest.raises(ModbusIOException):
+        await base.async_execute(request)
+    assert transport.retries == 1
+
+
 def test_client_udp_connect():
     """Test the Udp client connection method"""
     with mock.patch.object(socket, "socket") as mock_method: