Fix getting difference for channels and for the first time

telethon/client/updates.py

@@ -292,6 +292,9 @@ class UpdateMethods(UserMethods):
 
     async def _dispatch_update(self: 'TelegramClient', update, channel_id, pts_date):
         if not self._entity_cache.ensure_cached(update):
+            # We could add a lock to not fetch the same pts twice if we are
+            # already fetching it. However this does not happen in practice,
+            # which makes sense, because different updates have different pts.
             await self._get_difference(update, channel_id, pts_date)
 
         built = EventBuilderDict(self, update)
@@ -357,6 +360,16 @@ class UpdateMethods(UserMethods):
             try:
                 where = await self.get_input_entity(channel_id)
             except ValueError:
+                # There's a high chance that this fails, since
+                # we are getting the difference to fetch entities.
+                return
+
+            if not pts_date:
+                # First-time, can't get difference. Get pts instead.
+                result = await self(functions.messages.GetPeerDialogsRequest([
+                    utils.get_input_dialog(where)
+                ]))
+                self._state_cache[channel_id] = result.dialogs[0].pts
                 return
 
             result = await self(functions.updates.GetChannelDifferenceRequest(
@@ -367,6 +380,12 @@ class UpdateMethods(UserMethods):
                 force=True
             ))
         else:
+            if not pts_date[0]:
+                # First-time, can't get difference. Get pts instead.
+                result = await self(functions.updates.GetStateRequest())
+                self._state_cache[None] = result.pts, result.date
+                return
+
             result = await self(functions.updates.GetDifferenceRequest(
                 pts=pts_date[0],
                 date=pts_date[1],

telethon/statecache.py

@@ -1,8 +1,32 @@
 import datetime
+import inspect
 
 from .tl import types
 
 
+# Which updates have the following fields?
+_has_channel_id = []
+
+
+# TODO EntityCache does the same. Reuse?
+def _fill():
+    for name in dir(types):
+        update = getattr(types, name)
+        if getattr(update, 'SUBCLASS_OF_ID', None) == 0x9f89304e:
+            cid = update.CONSTRUCTOR_ID
+            sig = inspect.signature(update.__init__)
+            for param in sig.parameters.values():
+                if param.name == 'channel_id' and param.annotation == int:
+                    _has_channel_id.append(cid)
+
+    if not _has_channel_id:
+        raise RuntimeError('FIXME: Did the init signature or updates change?')
+
+
+# We use a function to avoid cluttering the globals (with name/update/cid/doc)
+_fill()
+
+
 class StateCache:
     """
     In-memory update state cache, defaultdict-like behaviour.
@@ -15,11 +39,11 @@ class StateCache:
         if initial:
             self._pts_date = initial.pts, initial.date
         else:
-            self._pts_date = 1, datetime.datetime.now()
+            self._pts_date = None, None
 
     def reset(self):
         self.__dict__.clear()
-        self._pts_date = (1, 1)
+        self._pts_date = None, None
 
     # TODO Call this when receiving responses too...?
     def update(
@@ -90,11 +114,8 @@ class StateCache:
     def get_channel_id(
             self,
             update,
-            has_channel_id=frozenset(x.CONSTRUCTOR_ID for x in (
-                types.UpdateChannelTooLong,
-                types.UpdateDeleteChannelMessages,
-                types.UpdateChannelWebPage
-            )),
+            has_channel_id=frozenset(_has_channel_id),
+            # Hardcoded because only some with message are for channels
             has_message=frozenset(x.CONSTRUCTOR_ID for x in (
                 types.UpdateNewChannelMessage,
                 types.UpdateEditChannelMessage
@@ -122,8 +143,16 @@ class StateCache:
         If `item` is ``None``, returns the default ``(pts, date)``.
 
         If it's an **unmarked** channel ID, returns its ``pts``.
+
+        If no information is known, ``pts`` will be ``None``.
         """
         if item is None:
             return self._pts_date
         else:
-            return self.__dict__.get(item, 1)
+            return self.__dict__.get(item)
+
+    def __setitem__(self, where, value):
+        if where is None:
+            self._pts_date = value
+        else:
+            self.__dict__[where] = value