React to undecryptable messages

my_project_name/callbacks.py

@@ -1,9 +1,9 @@
 import logging
 
-from nio import JoinError, MatrixRoom, RoomGetEventError, UnknownEvent
+from nio import JoinError, MatrixRoom, MegolmEvent, RoomGetEventError, UnknownEvent
 
 from my_project_name.bot_commands import Command
-from my_project_name.chat_functions import make_pill, send_text_to_room
+from my_project_name.chat_functions import make_pill, react_to_event, send_text_to_room
 from my_project_name.message_responses import Message
 
 logger = logging.getLogger(__name__)
@@ -130,6 +130,28 @@ class Callbacks(object):
             reply_to_event_id=reacted_to_id,
         )
 
+    async def decryption_failure(self, room: MatrixRoom, event: MegolmEvent):
+        """Callback for when an event fails to decrypt. Inform the user"""
+        logger.error(
+            f"Failed to decrypt event '{event.event_id}' in room '{room.room_id}'!"
+            f"\n\n"
+            f"Tip: try using a different device ID in your config file and restart."
+            f"\n\n"
+            f"If all else fails, delete your store directory and let the bot recreate "
+            f"it (your reminders will NOT be deleted, but the bot may respond to existing "
+            f"commands a second time)."
+        )
+
+        red_x_and_lock_emoji = "❌ 🔐"
+
+        # React to the undecryptable event with some emoji
+        await react_to_event(
+            self.client,
+            room.room_id,
+            event.event_id,
+            red_x_and_lock_emoji,
+        )
+
     async def unknown(self, room: MatrixRoom, event: UnknownEvent):
         """Callback for when an event with a type that is unknown to matrix-nio is received.
         Currently this is used for reaction events, which are not specced.

my_project_name/chat_functions.py

@@ -2,7 +2,14 @@ import logging
 from typing import Optional, Union
 
 from markdown import markdown
-from nio import AsyncClient, ErrorResponse, Response, SendRetryError
+from nio import (
+    AsyncClient,
+    ErrorResponse,
+    MatrixRoom,
+    MegolmEvent,
+    Response,
+    SendRetryError,
+)
 
 logger = logging.getLogger(__name__)
 
@@ -116,3 +123,28 @@ async def react_to_event(
         content,
         ignore_unverified_devices=True,
     )
+
+
+async def decryption_failure(self, room: MatrixRoom, event: MegolmEvent):
+    """Callback for when an event fails to decrypt. Inform the user"""
+    logger.error(
+        f"Failed to decrypt event '{event.event_id}' in room '{room.room_id}'!"
+        f"\n\n"
+        f"Tip: try using a different device ID in your config file and restart."
+        f"\n\n"
+        f"If all else fails, delete your store directory and let the bot recreate "
+        f"it (your reminders will NOT be deleted, but the bot may respond to existing "
+        f"commands a second time)."
+    )
+
+    user_msg = (
+        "Unable to decrypt this message. "
+        "Check whether you've chosen to only encrypt to trusted devices."
+    )
+
+    await send_text_to_room(
+        self.client,
+        room.room_id,
+        user_msg,
+        reply_to_event_id=event.event_id,
+    )

my_project_name/main.py

@@ -11,6 +11,7 @@ from nio import (
     InviteMemberEvent,
     LocalProtocolError,
     LoginError,
+    MegolmEvent,
     RoomMessageText,
     UnknownEvent,
 )
@@ -60,6 +61,7 @@ async def main():
     callbacks = Callbacks(client, store, config)
     client.add_event_callback(callbacks.message, (RoomMessageText,))
     client.add_event_callback(callbacks.invite, (InviteMemberEvent,))
+    client.add_event_callback(callbacks.decryption_failure, (MegolmEvent,))
     client.add_event_callback(callbacks.unknown, (UnknownEvent,))
 
     # Keep trying to reconnect on failure (with some time in-between)