server tracer example. (#1773)

Author: janiversen

doc/source/examples.rst

@@ -64,6 +64,10 @@ Callback Server example
 ^^^^^^^^^^^^^^^^^^^^^^^
 .. literalinclude:: ../../examples/server_callback.py
 
+Server tracer example
+^^^^^^^^^^^^^^^^^^^^^
+.. literalinclude:: ../../examples/server_hook.py
+
 Custom Message client
 ^^^^^^^^^^^^^^^^^^^^^
 .. literalinclude:: ../../examples/client_custom_msg.py
@@ -107,6 +111,10 @@ Examples contributions
 These examples are supplied by users of pymodbus.
 The pymodbus team thanks for sharing the examples.
 
+Solar
+^^^^^
+.. literalinclude:: ../../examples/contrib/solar.py
+
 Redis datastore
 ^^^^^^^^^^^^^^^
 .. literalinclude:: ../../examples/contrib/redis_datastore.py

examples/server_hook.py

@@ -0,0 +1,87 @@
+#!/usr/bin/env python3
+"""Pymodbus Server With request/response manipulator.
+
+This is an example of using the builtin request/response tracer to
+manipulate the messages to/from the modbus server
+"""
+import asyncio
+import logging
+
+from pymodbus import pymodbus_apply_logging_config
+from pymodbus.datastore import (
+    ModbusSequentialDataBlock,
+    ModbusServerContext,
+    ModbusSlaveContext,
+)
+from pymodbus.server import ModbusTcpServer
+from pymodbus.transaction import ModbusSocketFramer
+
+
+class Manipulator:
+    """A Class to run the server.
+
+    Using a class allows the easy use of global variables, but
+    are not strictly needed
+    """
+
+    message_count: int = 1
+    server: ModbusTcpServer = None
+
+    def server_request_tracer(self, request, *_addr):
+        """Trace requests.
+
+        All server requests passes this filter before being handled.
+        """
+        print(f"---> REQUEST: {request}")
+
+    def server_response_manipulator(self, response):
+        """Manipulate responses.
+
+        All server responses passes this filter before being sent.
+        The filter returns:
+
+        - response, either original or modified
+        - skip_encoding, signals whether or not to encode the response
+        """
+        if not self.message_count:
+            print(f"---> RESPONSE: {response}")
+            self.message_count = 3
+        else:
+            print("---> RESPONSE: NONE")
+            response.should_respond = False
+            self.message_count -= 1
+        return response, False
+
+    async def setup(self):
+        """Prepare server."""
+        pymodbus_apply_logging_config(logging.DEBUG)
+        datablock = ModbusSequentialDataBlock(0x00, [17] * 100)
+        context = ModbusServerContext(
+            slaves=ModbusSlaveContext(
+                di=datablock, co=datablock, hr=datablock, ir=datablock
+            ),
+            single=True,
+        )
+        self.server = ModbusTcpServer(
+            context,
+            ModbusSocketFramer,
+            None,
+            ("127.0.0.1", 5020),
+            request_tracer=self.server_request_tracer,
+            response_manipulator=self.server_response_manipulator,
+        )
+
+    async def run(self):
+        """Attach Run server"""
+        await self.server.serve_forever()
+
+
+async def main():
+    """Run example."""
+    server = Manipulator()
+    await server.setup()
+    await server.run()
+
+
+if __name__ == "__main__":
+    asyncio.run(main(), debug=True)  # pragma: no cover