Bridge some matrix stickers as telegram stickers

With maunium/stickerpicker#49 applied, Element
Desktop users send enough information about telegram-imported stickers
to bridge them as regular telegram stickers.

This commit has a few caveats, most notably it only works with sticker
sets that are currently added to the user’s telegram account, and it
doesn’t cache either the sticker sets or the stickers within these sets.
However I haven’t noticed any performance issues due to this in my own
testing over at chir.rs.

Author: DarkKirb

mautrix_telegram/portal.py

@@ -1626,6 +1626,35 @@ async def _handle_matrix_text(
                 msgtype=content.msgtype,
             )
 
+    async def _find_telegram_sticker(self, client, metadata):
+        sticker_set_id = int(metadata["pack"]["id"])
+        from telethon.tl.functions.messages import GetAllStickersRequest
+
+        sticker_sets = await client(GetAllStickersRequest(0))
+        from telethon.tl.functions.messages import GetStickerSetRequest
+        from telethon.tl.types import InputStickerSetID
+
+        found_sticker_set = None
+        for sticker_set in sticker_sets.sets:
+            if sticker_set.id == sticker_set_id:
+                found_sticker_set = sticker_set
+                break
+        if not found_sticker_set:
+            return None
+
+        stickers = await client(
+            GetStickerSetRequest(
+                hash=0,
+                stickerset=InputStickerSetID(
+                    id=found_sticker_set.id, access_hash=found_sticker_set.access_hash
+                ),
+            )
+        )
+
+        for sticker in stickers.documents:
+            if sticker.id == int(metadata["id"]):
+                return sticker
+
     async def _handle_matrix_file(
         self,
         sender: u.User,
@@ -1646,6 +1675,7 @@ async def _handle_matrix_file(
             w = h = None
         max_image_size = self.config["bridge.image_as_file_size"] * 1000**2
         max_image_pixels = self.config["bridge.image_as_file_pixels"]
+        media = None
 
         if self.config["bridge.parallel_file_transfer"] and content.url:
             file_handle, file_size = await util.parallel_transfer_to_telegram(
@@ -1666,7 +1696,16 @@ async def _handle_matrix_file(
                 file = await self.main_intent.download_media(content.url)
 
             if content.msgtype == MessageType.STICKER:
-                if mime != "image/gif":
+                tg_sticker = None
+
+                if "net.maunium.telegram.sticker" in content.info:
+                    tg_sticker = await self._find_telegram_sticker(
+                        client, content.info["net.maunium.telegram.sticker"]
+                    )
+
+                if tg_sticker is not None:
+                    media = tg_sticker
+                elif mime != "image/gif":
                     mime, file, w, h = util.convert_image(
                         file, source_mime=mime, target_type="webp"
                     )
@@ -1708,7 +1747,9 @@ async def _handle_matrix_file(
         if "fi.mau.telegram.force_document" in content:
             force_document = bool(content["fi.mau.telegram.force_document"])
 
-        if (mime == "image/png" or mime == "image/jpeg") and not force_document:
+        if media is not None:
+            pass
+        elif (mime == "image/png" or mime == "image/jpeg") and not force_document:
             media = InputMediaUploadedPhoto(file_handle)
         else:
             media = InputMediaUploadedDocument(