Handle FloodWaitError in client.download_media

Fixes #1426. Not entirely happy with the new indirection layer,
but the original __call__ method is already a mess anyway and
the additional cost of an extra call should be neglible compared
to the actual IO.

telethon/client/downloads.py

@@ -68,7 +68,7 @@ class _DirectDownloadIter(RequestIter):
 
     async def _request(self):
         try:
-            result = await self._sender.send(self.request)
+            result = await self.client._call(self._sender, self.request)
             if isinstance(result, types.upload.FileCdnRedirect):
                 raise NotImplementedError  # TODO Implement
             else:

telethon/client/messages.py

@@ -1039,7 +1039,7 @@ class MessageMethods:
             if exported:
                 try:
                     sender = await self._borrow_exported_sender(entity.dc_id)
-                    return await sender.send(request)
+                    return await self._call(sender, request)
                 finally:
                     await self._return_exported_sender(sender)
             else:

telethon/client/users.py

@@ -27,6 +27,9 @@ def _fmt_flood(delay, request, *, early=False, td=datetime.timedelta):
 
 class UserMethods:
     async def __call__(self: 'TelegramClient', request, ordered=False):
+        return await self._call(self._sender, request, ordered=ordered)
+
+    async def _call(self: 'TelegramClient', sender, request, ordered=False):
         requests = (request if utils.is_list_like(request) else (request,))
         for r in requests:
             if not isinstance(r, TLRequest):
@@ -50,7 +53,7 @@ class UserMethods:
         self._last_request = time.time()
         for attempt in retry_range(self._request_retries):
             try:
-                future = self._sender.send(request, ordered=ordered)
+                future = sender.send(request, ordered=ordered)
                 if isinstance(future, list):
                     results = []
                     exceptions = []