Raise StreamNotFound for 404 errors in YouTube RSS feed (#4746)

* Raise `StreamNotFound` for 404 errors in YouTube RSS feed

* Catch `StreamNotFound` exception in bg task and remove such streams

redbot/cogs/streams/streams.py

@@ -724,6 +724,7 @@ class Streams(commands.Cog):
         stream._messages_cache.append(m)
 
     async def check_streams(self):
+        to_remove = []
         for stream in self.streams:
             try:
                 try:
@@ -738,6 +739,10 @@ class Streams(commands.Cog):
 
                     else:
                         embed = await stream.is_online()
+                except StreamNotFound:
+                    log.info("Stream with name %s no longer exists. Removing...", stream.name)
+                    to_remove.append(stream)
+                    continue
                 except OfflineStream:
                     if not stream._messages_cache:
                         continue
@@ -818,6 +823,11 @@ class Streams(commands.Cog):
             except Exception as e:
                 log.error("An error has occured with Streams. Please report it.", exc_info=e)
 
+        if to_remove:
+            for stream in to_remove:
+                self.streams.remove(stream)
+            await self.save_streams()
+
     async def _get_mention_str(
         self, guild: discord.Guild, channel: discord.TextChannel
     ) -> Tuple[str, List[discord.Role]]:

redbot/cogs/streams/streamtypes.py

@@ -106,6 +106,8 @@ class YoutubeStream(Stream):
 
         async with aiohttp.ClientSession() as session:
             async with session.get(YOUTUBE_CHANNEL_RSS.format(channel_id=self.id)) as r:
+                if r.status == 404:
+                    raise StreamNotFound()
                 rssdata = await r.text()
 
         if self.not_livestreams: