From 143e046cf523a6d342e1804d821345411fdbdf9f Mon Sep 17 00:00:00 2001
From: Lonami Exo <totufals@hotmail.com>
Date: Mon, 18 Sep 2017 10:59:54 +0200
Subject: [PATCH] Attempt at passing errors to the main thread through .updates

---
 telethon/telegram_client.py |  7 +++++++
 telethon/update_state.py    | 20 +++++++++++++++++++-
 2 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/telethon/telegram_client.py b/telethon/telegram_client.py
index 38cf4303..bf915b04 100644
--- a/telethon/telegram_client.py
+++ b/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
diff --git a/telethon/update_state.py b/telethon/update_state.py
index f9303258..a6cf324b 100644
--- a/telethon/update_state.py
+++ b/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.