Added way to surface exceptions in a controlled manner.

Author: jmattsson

src/powersensor_local/async_event_emitter.py

@@ -21,8 +21,13 @@ def unsubscribe(self, evstr, cb):
     async def emit(self, evstr, *args):
         """Emits an event to all registered listeners for that event type.
         Additional arguments may be supplied with event as appropriate. Each
-        event handler is awaited before delivering the event to the next."""
+        event handler is awaited before delivering the event to the next.
+        If an event handler raises an exception, this is funneled through
+        to an 'exception' event being emitted. This can chain."""
         if self._listeners.get(evstr) is None:
             return
         for cb in self._listeners[evstr]:
-            await cb(evstr, *args)
+            try:
+                await cb(evstr, *args)
+            except BaseException as e:
+                await self.emit('exception', e)

src/powersensor_local/plug_api.py

@@ -27,6 +27,7 @@ def __init__(self, mac, ip, port=49476):
         self._mac = mac
         self._listener = PlugListener(ip, port)
         self._listener.subscribe('message', self._on_message)
+        self._listener.subscribe('exception', self._on_exception)
         self._seen = set()
 
     def connect(self):
@@ -43,6 +44,10 @@ async def disconnect(self):
         await self._listener.disconnect()
 
     async def _on_message(self, _, message):
+        """Translates the raw message and emits the resulting messages, if any.
+
+        Also synthesises 'now_relaying_for' messages as needed.
+        """
         evs = None
         try:
             evs = translate_raw_message(message, self._mac)
@@ -64,5 +69,6 @@ async def _on_message(self, _, message):
         for name, ev in evs.items():
             await self.emit(name, ev)
 
-# FIXME - we'll want to use mac:role for the unique ID in HA, so a reassigned
-# sensor shows up differently
+    async def _on_exception(self, _, e):
+        """Propagates exceptions from the plug listener."""
+        await self.emit('exception', e)

src/powersensor_local/plugevents.py

@@ -23,9 +23,6 @@ async def do_exit():
 async def on_evt_msg(evt, msg):
     print(evt, msg)
 
-async def on_evt(evt):
-    print(evt)
-
 async def main():
     if len(sys.argv) < 3:
         print(f"Syntax: {sys.argv[0]} <id> <ip> [port]")
@@ -41,6 +38,7 @@ def handle_sigint(signum, frame):
     global plug
     plug = PlugApi(sys.argv[1], sys.argv[2], *sys.argv[3:3])
     known_evs = [
+        'exception',
         'average_flow',
         'average_power',
         'average_power_components',

src/powersensor_local/rawplug.py

@@ -40,6 +40,7 @@ def handle_sigint(signum, frame):
 
     global plug
     plug = PlugListener(sys.argv[1], *sys.argv[2:2])
+    plug.subscribe('exception', on_evt_msg)
     plug.subscribe('message', on_evt_msg)
     plug.subscribe('connecting', on_evt)
     plug.subscribe('connecting', on_evt)