Fix max recv length to 1.024bytes.

pymodbus/transport/transport.py

@@ -305,9 +305,10 @@ def datagram_received(self, data: bytes, addr: tuple | None) -> None:
             if not data:
                 return
         Log.transport_dump(Log.RECV_DATA, data, self.recv_buffer)
+        self.recv_buffer += data
         if len(self.recv_buffer) > 1024:
             self.recv_buffer = b""
-        self.recv_buffer += data
+            return
         cut = self.callback_data(self.recv_buffer, addr=addr)
         self.recv_buffer = self.recv_buffer[cut:]
         if self.recv_buffer:

test/transport/test_comm.py

@@ -182,7 +182,7 @@ async def test_serial_poll(self, client, server, use_port):
         await asyncio.sleep(0.5)
         assert len(server.active_connections) == 1
         server_connected = list(server.active_connections.values())[0]
-        test_data = b"abcd" * 1000
+        test_data = b"abcd" * 10
         client.send(test_data)
         await asyncio.sleep(0.5)
         assert server_connected.recv_buffer == test_data

test/transport/test_protocol.py

@@ -142,7 +142,7 @@ async def test_datagram_buffer_overrun(self, client):
         client.callback_data = mock.MagicMock(return_value=0)
         client.recv_buffer = bytearray([0x01] * 2000)
         client.datagram_received(b"abc", "127.0.0.1")
-        assert client.recv_buffer == b"abc"
+        assert client.recv_buffer == b""
 
     async def test_callback_connected(self, use_clc, dummy_protocol):
         """Test callbacks."""