Add ban appeal server kicks and thread notices (#3561)

Author: ChrisLovering

bot/constants.py

@@ -128,12 +128,16 @@ class _Channels(EnvConfig, env_prefix="channels_"):
 
     rules: int = 693837295685730335
 
+    ban_appeal_logs: int = 891680793351553068
+
 
 Channels = _Channels()
 
 
 class _Roles(EnvConfig, env_prefix="roles_"):
 
+    ban_appeal_server_staff: int = 890273013671526481
+
     # Self-assignable roles, see the Subscribe cog
     advent_of_code: int = 518565788744024082
     announcements: int = 463658397560995840
@@ -198,6 +202,7 @@ class _Guild(EnvConfig, env_prefix="guild_"):
 
     id: int = 267624335836053506
     invite: str = "https://discord.gg/python"
+    ban_appeal_id: int = 890261951979061298
 
     moderation_categories: tuple[int, ...] = (
         Categories.moderators,
@@ -452,6 +457,9 @@ class _BaseURLs(EnvConfig, env_prefix="urls_"):
     site_api: str = "http://site.web.svc.cluster.local/api"
     paste_url: str = "https://paste.pythondiscord.com"
 
+    # Polonium (modmail)
+    polonium_api: str = "http://polonium-api.modmail.svc.cluster.local/api"
+
 
 BaseURLs = _BaseURLs()
 

bot/exts/moderation/ban_appeal_server.py

@@ -0,0 +1,179 @@
+import asyncio
+import weakref
+from pathlib import Path
+
+import aiohttp
+import discord
+from discord.ext import commands
+from pydis_core.utils import members, scheduling
+from pydis_core.utils.channel import get_or_fetch_channel
+
+from bot.bot import Bot
+from bot.constants import Channels, Colours, Guild, Roles, URLs
+from bot.log import get_logger
+
+log = get_logger(__name__)
+
+
+PYDIS_NO_KICK_ROLE_IDS = (Roles.admins, Roles.devops)
+# A Kubernetes service account token for the Polonium API, mounted by the bot's deployment.
+POLONIUM_TOKEN_FILE = Path("/var/run/secrets/polonium-api/token")
+
+
+class BanAppeals(commands.Cog):
+    """Keep the ban appeal server to banned users only, and post their joins and leaves in their modmail thread."""
+
+    def __init__(self, bot: Bot):
+        self.bot = bot
+        self.user_locks: weakref.WeakValueDictionary[int, asyncio.Lock] = weakref.WeakValueDictionary()
+        # Users we kicked ourselves, so the leave that follows isn't also posted as them leaving.
+        self.ignore_next_remove_event: set[int] = set()
+
+    async def cog_load(self) -> None:
+        """Look up the guilds and log channel, then kick anyone who shouldn't be in the appeals server."""
+        self.appeals_guild = self.bot.get_guild(Guild.ban_appeal_id)
+        self.pydis_guild = self.bot.get_guild(Guild.id)
+        self.logs_channel = self.bot.get_channel(Channels.ban_appeal_logs)
+        scheduling.create_task(self._sync_kicks())
+
+    async def _sync_kicks(self) -> None:
+        """Kick every member of the appeals server who shouldn't be there."""
+        await self.bot.wait_until_ready()
+        log.info("Starting kick job for ban appeals server")
+        for member in self.appeals_guild.members:
+            await self._maybe_kick_user(member)
+        log.info("Kick job for ban appeals server completed")
+
+    async def _is_banned_pydis(self, member: discord.Member) -> bool:
+        """See if the given member is banned in PyDis."""
+        try:
+            await self.pydis_guild.fetch_ban(member)
+        except discord.NotFound:
+            return False
+        return True
+
+    async def _can_bypass_kick(self, member: discord.Member) -> bool:
+        """See if the given appeals server member is staff who may stay without being banned."""
+        pydis_member = await members.get_or_fetch_member(self.pydis_guild, member.id)
+        if not pydis_member:
+            return False
+        return (
+            any(role.id in PYDIS_NO_KICK_ROLE_IDS for role in pydis_member.roles)
+            or any(role.id == Roles.ban_appeal_server_staff for role in member.roles)
+        )
+
+    async def _get_thread(self, user: discord.abc.Snowflake) -> discord.Thread | None:
+        """Return the user's currently open modmail thread, if they have one."""
+        try:
+            # Read on every call, as Kubernetes rotates this token every few minutes.
+            token = POLONIUM_TOKEN_FILE.read_text().strip()
+            async with self.bot.http_session.get(
+                f"{URLs.polonium_api}/users/{user.id}/current-post",
+                headers={"Authorization": f"Bearer {token}"},
+            ) as resp:
+                if resp.status == 404:
+                    return None
+                resp.raise_for_status()
+                post = await resp.json()
+                if post["guild_id"] != Guild.id:
+                    return None
+                return await get_or_fetch_channel(self.bot, post["post_id"])
+        except (OSError, aiohttp.ClientError, discord.HTTPException):
+            # Thread notices are best-effort, they shouldn't stop the kicks.
+            log.exception("Failed to get the modmail thread for %d.", user.id)
+            return None
+
+    async def _notify_thread(self, user: discord.abc.Snowflake, description: str, colour: int) -> bool:
+        """Post a notice in the user's modmail thread. Return whether they had a thread to post in."""
+        thread = await self._get_thread(user)
+        if not thread:
+            return False
+        await thread.send(embed=discord.Embed(description=description, colour=colour))
+        return True
+
+    async def _maybe_kick_user(self, member: discord.Member) -> bool:
+        """
+        Kick the member from the appeals server unless they are banned in PyDis or are staff.
+
+        Return whether the member was kicked.
+        """
+        if member.bot or await self._is_banned_pydis(member):
+            return False
+
+        if await self._can_bypass_kick(member):
+            log.info("Not kicking %s (%d) as they have a bypass role", member, member.id)
+            return False
+
+        try:
+            await member.kick(reason="Not banned in main server")
+        except discord.Forbidden:
+            log.error("Failed to kick %s (%d) due to insufficient permissions.", member, member.id)
+            return False
+
+        await self.logs_channel.send(f"Kicked {member} ({member.id}) on join as they're not banned in main server.")
+        log.info("Kicked %s (%d).", member, member.id)
+
+        if await self._notify_thread(
+            member,
+            "The recipient joined the appeals server and has been automatically kicked.",
+            Colours.soft_red,
+        ):
+            self.ignore_next_remove_event.add(member.id)
+        return True
+
+    async def _handle_pydis_join(self, member: discord.Member) -> None:
+        """Kick the member from the appeals server now that they're back in PyDis."""
+        appeals_member = await members.get_or_fetch_member(self.appeals_guild, member.id)
+        if not appeals_member:
+            return
+
+        await appeals_member.kick(reason="Rejoined PyDis")
+        await self.logs_channel.send(f"Kicked {member} ({member.id}) as they rejoined PyDis.")
+        log.info("Kicked %s (%d) as they rejoined PyDis.", member, member.id)
+
+        if await self._notify_thread(
+            member,
+            "The recipient has been kicked from the appeals server.",
+            Colours.soft_red,
+        ):
+            self.ignore_next_remove_event.add(member.id)
+
+    async def _handle_appeals_join(self, member: discord.Member) -> None:
+        """Kick the member if they shouldn't be in the appeals server, otherwise post that they joined."""
+        if not await self._maybe_kick_user(member):
+            await self._notify_thread(member, "The recipient has joined the appeals server.", Colours.soft_green)
+
+    async def _handle_remove(self, member: discord.Member) -> None:
+        """Post that the member left the appeals server, unless we were the ones who kicked them."""
+        if member.guild != self.appeals_guild:
+            return
+
+        if member.id in self.ignore_next_remove_event:
+            self.ignore_next_remove_event.discard(member.id)
+            return
+
+        await self._notify_thread(member, "The recipient has left the appeals server.", Colours.soft_red)
+
+    def _user_lock(self, user_id: int) -> asyncio.Lock:
+        """Return the user's lock, so their join and leave events are handled one at a time, in order."""
+        return self.user_locks.setdefault(user_id, asyncio.Lock())
+
+    @commands.Cog.listener()
+    async def on_member_join(self, member: discord.Member) -> None:
+        """Handle a member joining either PyDis or the appeals server."""
+        async with self._user_lock(member.id):
+            if member.guild == self.pydis_guild:
+                await self._handle_pydis_join(member)
+            elif member.guild == self.appeals_guild:
+                await self._handle_appeals_join(member)
+
+    @commands.Cog.listener()
+    async def on_member_remove(self, member: discord.Member) -> None:
+        """Handle a member leaving the appeals server."""
+        async with self._user_lock(member.id):
+            await self._handle_remove(member)
+
+
+async def setup(bot: Bot) -> None:
+    """Load the BanAppeals cog."""
+    await bot.add_cog(BanAppeals(bot))