Improve EventHandler response sending pattern

lib/tfw/event_handlers/event_handler_base.py

@@ -5,8 +5,6 @@ import logging
 from inspect import currentframe
 from typing import Iterable
 
-from tfw.networking import Scope
-
 LOG = logging.getLogger(__name__)
 
 
@@ -17,7 +15,7 @@ class EventHandlerBase:
 
     Derived classes must implement the handle_event() method
     """
-    def __init__(self, key, server_connector, scope=Scope.ZMQ):
+    def __init__(self, key, server_connector, scope):
         self.server_connector = server_connector
         self.scope = scope
         self.keys = []
@@ -29,12 +27,18 @@ class EventHandlerBase:
         self.subscribe(*self.keys)
         self.server_connector.register_callback(self.event_handler_callback)
 
-    @property
-    def key(self):
+    def subscribe(self, *keys):
         """
-        Returns the oldest key this EventHandler was subscribed to.
+        Subscribe this EventHandler to receive events for given keys.
+        Note that you can subscribe to the same key several times in which
+        case you will need to unsubscribe multiple times in order to stop
+        receiving events.
+
+        :param keys: list of keys to subscribe to
         """
-        return self.keys[0]
+        for key in keys:
+            self.server_connector.subscribe(key)
+            self.keys.append(key)
 
     def event_handler_callback(self, message):
         """
@@ -43,15 +47,8 @@ class EventHandlerBase:
         a response back in case the handler returned something.
         This is subscribed in __init__().
         """
-        if not self.check_key(message):
-            return
-
-        response = self.dispatch_handling(message)
-        if response:
-            self.send_message(response)
-
-    def send_message(self, message):
-        self.server_connector.send_message(message, self.scope)
+        if self.check_key(message):
+            self.dispatch_handling(message)
 
     def check_key(self, message):
         """
@@ -74,7 +71,7 @@ class EventHandlerBase:
         :param message: the message received
         :returns: the message to send back
         """
-        return self.handle_event(message)
+        self.handle_event(message)
 
     def handle_event(self, message):
         """
@@ -85,18 +82,8 @@ class EventHandlerBase:
         """
         raise NotImplementedError
 
-    def subscribe(self, *keys):
-        """
-        Subscribe this EventHandler to receive events for given keys.
-        Note that you can subscribe to the same key several times in which
-        case you will need to unsubscribe multiple times in order to stop
-        receiving events.
-
-        :param keys: list of keys to subscribe to
-        """
-        for key in keys:
-            self.server_connector.subscribe(key)
-            self.keys.append(key)
+    def send_message(self, message):
+        self.server_connector.send_message(message, self.scope)
 
     def unsubscribe(self, *keys):
         """