From e8eef1c31e4aaa282b79717a4f8399b5e9c94f9a Mon Sep 17 00:00:00 2001
From: Tulir Asokan <tulir@maunium.net>
Date: Wed, 22 Jun 2022 12:05:48 +0300
Subject: [PATCH] Add option to not bridge chats with too many members

---
 mautrix_telegram/bot.py                    |  2 ++
 mautrix_telegram/commands/telegram/misc.py |  5 ++++-
 mautrix_telegram/config.py                 |  1 +
 mautrix_telegram/example-config.yaml       |  4 ++++
 mautrix_telegram/portal.py                 | 18 +++++++++++++++++-
 mautrix_telegram/user.py                   |  1 +
 6 files changed, 29 insertions(+), 2 deletions(-)

diff --git a/mautrix_telegram/bot.py b/mautrix_telegram/bot.py
index da763b53..8d2ea36e 100644
--- a/mautrix_telegram/bot.py
+++ b/mautrix_telegram/bot.py
@@ -193,6 +193,8 @@ class Bot(AbstractUser):
                 )
             else:
                 return await reply("Portal is not public. Use `/invite <mxid>` to get an invite.")
+        else:
+            return await reply("Couldn't create portal room")
 
     async def handle_command_invite(
         self, portal: po.Portal, reply: ReplyFunc, mxid_input: UserID
diff --git a/mautrix_telegram/commands/telegram/misc.py b/mautrix_telegram/commands/telegram/misc.py
index f6d9e6f9..f0c141d5 100644
--- a/mautrix_telegram/commands/telegram/misc.py
+++ b/mautrix_telegram/commands/telegram/misc.py
@@ -233,7 +233,10 @@ async def join(evt: CommandEvent) -> EventID | None:
                     updates.stringify(),
                 )
                 raise e
-            return await evt.reply(f"Created room for {portal.title}")
+            if portal.mxid:
+                return await evt.reply(f"Created room for {portal.title}")
+            else:
+                return await evt.reply(f"Couldn't create room for {portal.title}")
     return None
 
 
diff --git a/mautrix_telegram/config.py b/mautrix_telegram/config.py
index 66977545..f22929b6 100644
--- a/mautrix_telegram/config.py
+++ b/mautrix_telegram/config.py
@@ -111,6 +111,7 @@ class Config(BaseBridgeConfig):
         copy("bridge.allow_avatar_remove")
 
         copy("bridge.max_initial_member_sync")
+        copy("bridge.max_member_count")
         copy("bridge.sync_channel_members")
         copy("bridge.skip_deleted_members")
         copy("bridge.startup_sync")
diff --git a/mautrix_telegram/example-config.yaml b/mautrix_telegram/example-config.yaml
index 4e9d747b..7e7915f6 100644
--- a/mautrix_telegram/example-config.yaml
+++ b/mautrix_telegram/example-config.yaml
@@ -148,6 +148,10 @@ bridge:
     # will not send any more members.
     # -1 means no limit (which means it's limited to 10000 by the server)
     max_initial_member_sync: 100
+    # Maximum number of participants in chats to bridge. Only applies when the portal is being created.
+    # If there are more members when trying to create a room, the room creation will be cancelled.
+    # -1 means no limit (which means all chats can be bridged)
+    max_member_count: -1
     # Whether or not to sync the member list in channels.
     # If no channel admins have logged into the bridge, the bridge won't be able to sync the member
     # list regardless of this setting.
diff --git a/mautrix_telegram/portal.py b/mautrix_telegram/portal.py
index 229594ec..8c63c625 100644
--- a/mautrix_telegram/portal.py
+++ b/mautrix_telegram/portal.py
@@ -326,6 +326,7 @@ class Portal(DBPortal, BasePortal):
         self._sponsored_msg_lock = asyncio.Lock()
         self._sponsored_seen = {}
         self._new_messages_after_sponsored = True
+        self._bridging_blocked_at_runtime = False
 
         self._msg_conv = putil.TelegramMessageConverter(self)
 
@@ -385,7 +386,9 @@ class Portal(DBPortal, BasePortal):
 
     @property
     def allow_bridging(self) -> bool:
-        if self.peer_type == "user":
+        if self._bridging_blocked_at_runtime:
+            return False
+        elif self.peer_type == "user":
             return True
         elif self.filter_mode == "whitelist":
             return self.tgid in self.filter_list
@@ -747,6 +750,16 @@ class Portal(DBPortal, BasePortal):
             entity = await self.get_entity(user)
             self.log.trace("Fetched data: %s", entity)
 
+        participants_count = 2
+        if isinstance(entity, Chat):
+            participants_count = entity.participants_count
+        elif isinstance(entity, Channel) and not entity.broadcast:
+            participants_count = entity.participants_count
+        if 0 < self.config["bridge.max_member_count"] < participants_count:
+            self.log.warning(f"Not bridging chat, too many participants (%d)", participants_count)
+            self._bridging_blocked_at_runtime = True
+            return None
+
         self.log.debug("Creating room")
 
         try:
@@ -2636,6 +2649,9 @@ class Portal(DBPortal, BasePortal):
         if not self.mxid:
             self.log.trace("Got telegram message %d, but no room exists, creating...", evt.id)
             await self.create_matrix_room(source, invites=[source.mxid], update_if_exists=False)
+            if not self.mxid:
+                self.log.warning("Room doesn't exist even after creating, dropping %d", evt.id)
+                return
 
         if (
             self.peer_type == "user"
diff --git a/mautrix_telegram/user.py b/mautrix_telegram/user.py
index f98e3fe3..a8c38217 100644
--- a/mautrix_telegram/user.py
+++ b/mautrix_telegram/user.py
@@ -26,6 +26,7 @@ from telethon.tl.functions.contacts import GetContactsRequest, SearchRequest
 from telethon.tl.functions.updates import GetStateRequest
 from telethon.tl.functions.users import GetUsersRequest
 from telethon.tl.types import (
+    Channel,
     Chat,
     ChatForbidden,
     InputUserSelf,