Implement a mechanism to notify of connection failures (#852)

telethon/client/telegrambaseclient.py

@@ -218,6 +218,14 @@ class TelegramBaseClient(abc.ABC):
     def loop(self):
         return self._loop
 
+    @property
+    def disconnected(self):
+        """
+        Future that resolves when the connection to Telegram
+        ends, either by user action or in the background.
+        """
+        return self._sender.disconnected
+
     # endregion
 
     # region Connecting

telethon/client/updates.py

@@ -14,6 +14,19 @@ class UpdateMethods(UserMethods):
 
     # region Public methods
 
+    def run_until_disconnected(self):
+        """
+        Runs the event loop until `disconnect` is called or if an error
+        while connecting/sending/receiving occurs in the background. In
+        the latter case, said error will ``raise`` so you have a chance
+        to ``except`` it on your own code.
+
+        This method shouldn't be called from ``async def`` as the loop
+        will be running already. Use ``await client.disconnected`` in
+        this situation instead.
+        """
+        self.loop.run_until_complete(self.disconnected)
+
     def on(self, event):
         """
         Decorator helper method around add_event_handler().