Add webhook filter

This adds a way to add custom coroutines to the context, to execute when the filtering result is actioned.

5 files changed, 76 insertions, 5 deletions

diff --git a/bot/exts/filtering/_filter_context.py b/bot/exts/filtering/_filter_context.py
index 5e2f5b45b..da7ba0c77 100644
--- a/bot/exts/filtering/_filter_context.py
+++ b/bot/exts/filtering/_filter_context.py
@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+from collections.abc import Coroutine
 from dataclasses import dataclass, field, replace
 from enum import Enum, auto
 from typing import Optional, Union
@@ -34,6 +35,7 @@ class FilterContext:
     action_descriptions: list = field(default_factory=list)  # What actions were taken
     matches: list = field(default_factory=list)  # What exactly was found
     notification_domain: str = field(default_factory=str)  # A domain to send the user for context
+    additional_actions: list[Coroutine] = field(default_factory=list)  # Additional actions to perform
 
     def replace(self, **changes) -> FilterContext:
         """Return a new context object assigning new values to the specified fields."""
diff --git a/bot/exts/filtering/_filters/unique/webhook.py b/bot/exts/filtering/_filters/unique/webhook.py
new file mode 100644
index 000000000..10f27a922
--- /dev/null
+++ b/bot/exts/filtering/_filters/unique/webhook.py
@@ -0,0 +1,58 @@
+import re
+
+from botcore.utils.logging import get_logger
+
+import bot
+from bot import constants
+from bot.exts.filtering._filter_context import Event, FilterContext
+from bot.exts.filtering._filters.filter import UniqueFilter
+from bot.exts.moderation.modlog import ModLog
+
+log = get_logger(__name__)
+
+
+WEBHOOK_URL_RE = re.compile(
+    r"((?:https?://)?(?:ptb\.|canary\.)?discord(?:app)?\.com/api/webhooks/\d+/)\S+/?",
+    re.IGNORECASE
+)
+
+
+class WebhookFilter(UniqueFilter):
+    """Scan messages to detect Discord webhooks links."""
+
+    name = "webhook"
+    events = (Event.MESSAGE, Event.MESSAGE_EDIT)
+
+    @property
+    def mod_log(self) -> ModLog | None:
+        """Get current instance of `ModLog`."""
+        return bot.instance.get_cog("ModLog")
+
+    def triggered_on(self, ctx: FilterContext) -> bool:
+        """Search for a webhook in the given content. If found, attempt to delete it."""
+        matches = set(WEBHOOK_URL_RE.finditer(ctx.content))
+        if not matches:
+            return False
+
+        # Don't log this.
+        if mod_log := self.mod_log:
+            mod_log.ignore(constants.Event.message_delete, ctx.message.id)
+
+        for i, match in enumerate(matches, start=1):
+            extra = "" if len(matches) == 1 else f" ({i})"
+            # Queue the webhook for deletion.
+            ctx.additional_actions.append(self._delete_webhook(ctx, match[0], extra))
+            # Don't show the full webhook in places such as the mod alert.
+            ctx.content = ctx.content.replace(match[0], match[1] + "xxx")
+
+        return True
+
+    @staticmethod
+    async def _delete_webhook(ctx: FilterContext, webhook_url: str, extra_message: str) -> None:
+        """Delete the given webhook and update the filter context."""
+        async with bot.instance.http_session.delete(webhook_url) as resp:
+            # The Discord API Returns a 204 NO CONTENT response on success.
+            if resp.status == 204:
+                ctx.action_descriptions.append("webhook deleted" + extra_message)
+            else:
+                ctx.action_descriptions.append("failed to delete webhook" + extra_message)
diff --git a/bot/exts/filtering/_settings.py b/bot/exts/filtering/_settings.py
index 066c7a369..d53334c1c 100644
--- a/bot/exts/filtering/_settings.py
+++ b/bot/exts/filtering/_settings.py
@@ -193,10 +193,19 @@ class ActionSettings(Settings[ActionEntry]):
         return result
 
     async def action(self, ctx: FilterContext) -> None:
-        """Execute the action of every action entry stored."""
+        """Execute the action of every action entry stored, as well as any additional actions in the context."""
         for entry in self.values():
             await entry.action(ctx)
 
+        _i = len(ctx.additional_actions)
+        try:
+            for _i, action in enumerate(ctx.additional_actions):
+                await action
+        except Exception:
+            for action in ctx.additional_actions[_i+1:]:
+                action.close()
+            raise
+
     def fallback_to(self, fallback: ActionSettings) -> ActionSettings:
         """Fill in missing entries from `fallback`."""
         new_actions = self.copy()
diff --git a/bot/exts/filtering/_settings_types/actions/delete_messages.py b/bot/exts/filtering/_settings_types/actions/delete_messages.py
index d1ddf8241..1770c29ec 100644
--- a/bot/exts/filtering/_settings_types/actions/delete_messages.py
+++ b/bot/exts/filtering/_settings_types/actions/delete_messages.py
@@ -1,4 +1,3 @@
-from contextlib import suppress
 from typing import ClassVar
 
 from discord.errors import NotFound
@@ -25,9 +24,12 @@ class DeleteMessages(ActionEntry):
         if not ctx.message.guild:
             return
 
-        with suppress(NotFound):
+        try:
             await ctx.message.delete()
-        ctx.action_descriptions.append("deleted")
+        except NotFound:
+            ctx.action_descriptions.append("failed to delete")
+        else:
+            ctx.action_descriptions.append("deleted")
 
     def __or__(self, other: ActionEntry):
         """Combines two actions of the same type. Each type of action is executed once per filter."""
diff --git a/bot/exts/filtering/_settings_types/actions/infraction_and_notification.py b/bot/exts/filtering/_settings_types/actions/infraction_and_notification.py
index 7835a7d0b..922101d6d 100644
--- a/bot/exts/filtering/_settings_types/actions/infraction_and_notification.py
+++ b/bot/exts/filtering/_settings_types/actions/infraction_and_notification.py
@@ -149,7 +149,7 @@ class InfractionAndNotification(ActionEntry):
                 await ctx.author.send(dm_content, embed=dm_embed)
                 ctx.action_descriptions.append("notified")
             except Forbidden:
-                ctx.action_descriptions.append("notified (failed)")
+                ctx.action_descriptions.append("failed to notify")
 
         if self.infraction_type is not None:
             await self.infraction_type.invoke(