Add option to raise last error instead of generic ValueError (#1571)

telethon/client/telegrambaseclient.py

@@ -160,6 +160,12 @@ class TelegramBaseClient(abc.ABC):
             was for 21s, it would ``raise FloodWaitError`` instead. Values
             larger than a day (like ``float('inf')``) will be changed to a day.
 
+        raise_last_call_error (`bool`, optional):
+            When API calls fail in a way that causes Telethon to retry
+            automatically, should the RPC error of the last attempt be raised
+            instead of a generic ValueError. This is mostly useful for
+            detecting when Telegram has internal issues.
+
         device_model (`str`, optional):
             "Device model" to be sent when creating the initial connection.
             Defaults to 'PC (n)bit' derived from ``platform.uname().machine``, or its direct value if unknown.
@@ -216,6 +222,7 @@ class TelegramBaseClient(abc.ABC):
             auto_reconnect: bool = True,
             sequential_updates: bool = False,
             flood_sleep_threshold: int = 60,
+            raise_last_call_error: bool = False,
             device_model: str = None,
             system_version: str = None,
             app_version: str = None,
@@ -306,6 +313,8 @@ class TelegramBaseClient(abc.ABC):
                 )
             )
 
+        self._raise_last_call_error = raise_last_call_error
+
         self._request_retries = request_retries
         self._connection_retries = connection_retries
         self._retry_delay = retry_delay or 0

telethon/client/users.py

@@ -50,8 +50,9 @@ class UserMethods:
                     raise errors.FloodWaitError(request=r, capture=diff)
 
         request_index = 0
+        last_error = None
         self._last_request = time.time()
-        
+
         for attempt in retry_range(self._request_retries):
             try:
                 future = sender.send(request, ordered=ordered)
@@ -82,12 +83,14 @@ class UserMethods:
             except (errors.ServerError, errors.RpcCallFailError,
                     errors.RpcMcgetFailError, errors.InterdcCallErrorError,
                     errors.InterdcCallRichErrorError) as e:
+                last_error = e
                 self._log[__name__].warning(
                     'Telegram is having internal issues %s: %s',
                     e.__class__.__name__, e)
 
                 await asyncio.sleep(2)
             except (errors.FloodWaitError, errors.SlowModeWaitError, errors.FloodTestPhoneWaitError) as e:
+                last_error = e
                 if utils.is_list_like(request):
                     request = request[request_index]
 
@@ -106,6 +109,7 @@ class UserMethods:
                     raise
             except (errors.PhoneMigrateError, errors.NetworkMigrateError,
                     errors.UserMigrateError) as e:
+                last_error = e
                 self._log[__name__].info('Phone migrated to %d', e.new_dc)
                 should_raise = isinstance(e, (
                     errors.PhoneMigrateError, errors.NetworkMigrateError
@@ -114,6 +118,8 @@ class UserMethods:
                     raise
                 await self._switch_dc(e.new_dc)
 
+        if self._raise_last_call_error and last_error is not None:
+            raise last_error
         raise ValueError('Request was unsuccessful {} time(s)'
                          .format(attempt))