Attempt at passing errors to the main thread through .updates

telethon/telegram_client.py

@@ -230,6 +230,8 @@ class TelegramClient(TelegramBareClient):
                 threading.get_ident() == self._recv_thread.ident:
             raise AssertionError('Cannot invoke requests from the ReadThread')
 
+        self.updates.check_error()
+
         try:
             # Users may call this method from within some update handler.
             # If this is the case, then the thread invoking the request
@@ -1025,5 +1027,10 @@ class TelegramClient(TelegramBareClient):
                     self._recv_thread = None  # Not running anymore
                     self.reconnect()
                     return
+            except Exception as e:
+                # Unknown exception, pass it to the main thread
+                self.updates.set_error(e)
+                self._recv_thread = None
+                return
 
     # endregion

telethon/update_state.py

@@ -34,7 +34,10 @@ class UpdateState:
             if not self._updates:
                 self._updates_available.clear()
 
-            return update
+        if isinstance(update, Exception):
+            raise update  # Some error was set through .set_error()
+
+        return update
 
     def get_polling(self):
         return self._polling
@@ -47,6 +50,21 @@ class UpdateState:
 
     polling = property(fget=get_polling, fset=set_polling)
 
+    def set_error(self, error):
+        """Sets an error, so that the next call to .poll() will raise it.
+           Can be (and is) used to pass exceptions between threads.
+        """
+        with self._updates_lock:
+            # Insert at the beginning so the very next poll causes an error
+            # TODO Should this reset the pts and such?
+            self._updates.insert(0, error)
+            self._updates_available.set()
+
+    def check_error(self):
+        with self._updates_lock:
+            if self._updates and isinstance(self._updates[0], Exception):
+                raise self._updates.pop()
+
     def process(self, update):
         """Processes an update object. This method is normally called by
            the library itself.