feat: Allow room moderators to view redacted event content (MSC2815)

changelog.d/+msc2815-unredacted-content.feature.md

@@ -0,0 +1 @@
+Added [MSC2815](https://github.com/matrix-org/matrix-spec-proposals/pull/2815), letting room moderators fetch the content of redacted events, behind the `allow_moderators_to_view_redacted_content` config option. Contributed by @eleboucher.

conduwuit-example.toml

@@ -1664,6 +1664,15 @@
 # env: CONTINUWUITY_ALLOW_STICKY_EVENTS
 #allow_sticky_events = false
 
+# Allow room moderators to view redacted event content ([MSC2815]).
+#
+# Redacted content is kept in the database indefinitely, and readable by
+# users at or above the room's `redact` power level, and server admins.
+#
+# MSC2815: https://github.com/matrix-org/matrix-spec-proposals/pull/2815
+#
+#allow_moderators_to_view_redacted_content = false
+
 # Maximum time federation user can indicate typing.
 #
 # env: CONTINUWUITY_TYPING_FEDERATION_TIMEOUT_S

src/api/client/room/event.rs

@@ -1,14 +1,28 @@
-use axum::extract::State;
-use conduwuit::{Err, Event, Result, debug_warn, err};
-use ruma::api::client::room::get_room_event;
+use axum::extract::{Query, State};
+use conduwuit::{Err, Error, Event, PduEvent, Result, debug_warn, err};
+use futures::{FutureExt, TryFutureExt, future::try_join};
+use http::StatusCode;
+use ruma::{
+	UserId,
+	api::{client::room::get_room_event, error::ErrorKind},
+};
+use serde::Deserialize;
+use serde_json::json;
 
 use crate::{Ruma, client::is_ignored_pdu};
 
+#[derive(Deserialize)]
+pub(crate) struct Msc2815Params {
+	#[serde(rename = "fi.mau.msc2815.include_unredacted_content", default)]
+	include_unredacted_content: Option<String>,
+}
+
 /// # `GET /_matrix/client/r0/rooms/{roomId}/event/{eventId}`
 ///
 /// Gets a single event.
 pub(crate) async fn get_room_event_route(
 	State(ref services): State<crate::State>,
+	Query(params): Query<Msc2815Params>,
 	ref body: Ruma<get_room_event::v3::Request>,
 ) -> Result<get_room_event::v3::Response> {
 	let sender_user = body.identity.expect_sender_user()?;
@@ -54,6 +68,13 @@ pub(crate) async fn get_room_event_route(
 		return Err!(Request(Forbidden("You don't have permission to view this event.")));
 	}
 
+	if services.config.allow_moderators_to_view_redacted_content
+		&& params.include_unredacted_content.as_deref() == Some("true")
+		&& event.is_redacted()
+	{
+		unredact(services, sender_user, &mut event).await?;
+	}
+
 	if let Err(e) = services
 		.rooms
 		.pdu_metadata
@@ -72,3 +93,49 @@ pub(crate) async fn get_room_event_route(
 
 	Ok(get_room_event::v3::Response::new(event.into_format()))
 }
+
+async fn unredact(services: &crate::State, sender_user: &UserId, event: &mut PduEvent) -> Result {
+	let power_levels = services
+		.rooms
+		.state_accessor
+		.get_room_power_levels(&event.room_id_or_hash())
+		.await;
+
+	if power_levels.for_user(sender_user) < power_levels.redact
+		&& !services.users.is_admin(sender_user).await
+	{
+		return Err!(Request(Forbidden(
+			"You don't have permission to view redacted content in this room."
+		)));
+	}
+
+	let Ok(pdu_id) = services.rooms.timeline.get_pdu_id(event.event_id()).await else {
+		return Err(content_unavailable());
+	};
+
+	let Ok(content) = services
+		.rooms
+		.timeline
+		.get_unredacted_content(&pdu_id)
+		.await
+	else {
+		return Err(content_unavailable());
+	};
+
+	event.content = content;
+
+	Ok(())
+}
+
+fn content_unavailable() -> Error {
+	let kind = serde_json::from_value::<ErrorKind>(
+		json!({ "errcode": "FI.MAU.MSC2815_UNREDACTED_CONTENT_DELETED" }),
+	)
+	.expect("errcode is a valid custom error kind");
+
+	Error::Request(
+		kind,
+		"The unredacted content of this event is not available.".into(),
+		StatusCode::NOT_FOUND,
+	)
+}

src/api/client/unversioned.rs

@@ -34,6 +34,11 @@ pub(crate) async fn get_supported_versions_route(
 		unstable_features.insert("org.matrix.msc4354".to_owned(), true);
 	}
 
+	if services.config.allow_moderators_to_view_redacted_content {
+		// moderators can view redacted content (https://github.com/matrix-org/matrix-spec-proposals/pull/2815)
+		unstable_features.insert("fi.mau.msc2815".to_owned(), true);
+	}
+
 	Ok(assign!(get_supported_versions::Response::new(versions()), {
 		unstable_features
 	}))

src/core/config/mod.rs

@@ -1776,6 +1776,17 @@ pub struct Config {
 	#[serde(default)]
 	pub allow_sticky_events: bool,
 
+	/// Allow room moderators to view redacted event content ([MSC2815]).
+	///
+	/// Redacted content is kept in the database indefinitely, and readable by
+	/// users at or above the room's `redact` power level, and server admins.
+	///
+	/// MSC2815: https://github.com/matrix-org/matrix-spec-proposals/pull/2815
+	///
+	/// default: false
+	#[serde(default)]
+	pub allow_moderators_to_view_redacted_content: bool,
+
 	/// Maximum time federation user can indicate typing.
 	///
 	/// default: 30

src/database/maps.rs

@@ -153,6 +153,11 @@ pub(super) static MAPS: &[Descriptor] = &[
 		index_size: 512,
 		..descriptor::SEQUENTIAL
 	},
+	Descriptor {
+		name: "pduid_unredactedcontent",
+		key_size_hint: Some(16),
+		..descriptor::SEQUENTIAL
+	},
 	Descriptor {
 		name: "publicroomids",
 		..descriptor::RANDOM_SMALL

src/service/rooms/timeline/data.rs

@@ -8,6 +8,7 @@ use conduwuit::{
 use database::{Database, Deserialized, Json, KeyVal, Map};
 use futures::{FutureExt, Stream, TryFutureExt, TryStreamExt, future::select_ok, pin_mut};
 use ruma::{CanonicalJsonObject, EventId, OwnedUserId, RoomId, api::Direction};
+use serde_json::value::RawValue as RawJsonValue;
 
 use super::{PduId, RawPduId};
 use crate::{Dep, rooms, rooms::short::ShortRoomId};
@@ -16,6 +17,7 @@ pub(super) struct Data {
 	eventid_outlierpdu: Arc<Map>,
 	eventid_pduid: Arc<Map>,
 	pduid_pdu: Arc<Map>,
+	pduid_unredactedcontent: Arc<Map>,
 	roomid_lasttimelinecount: Arc<Map>,
 	userroomid_highlightcount: Arc<Map>,
 	userroomid_notificationcount: Arc<Map>,
@@ -36,6 +38,7 @@ impl Data {
 			eventid_outlierpdu: db["eventid_outlierpdu"].clone(),
 			eventid_pduid: db["eventid_pduid"].clone(),
 			pduid_pdu: db["pduid_pdu"].clone(),
+			pduid_unredactedcontent: db["pduid_unredactedcontent"].clone(),
 			roomid_lasttimelinecount: db["roomid_lasttimelinecount"].clone(),
 			userroomid_highlightcount: db["userroomid_highlightcount"].clone(),
 			userroomid_notificationcount: db["userroomid_notificationcount"].clone(),
@@ -234,6 +237,20 @@ impl Data {
 		Ok(())
 	}
 
+	pub(super) fn save_unredacted_content(&self, pdu_id: &RawPduId, content: &RawJsonValue) {
+		self.pduid_unredactedcontent.raw_put(pdu_id, Json(content));
+	}
+
+	pub(super) async fn get_unredacted_content(
+		&self,
+		pdu_id: &RawPduId,
+	) -> Result<Box<RawJsonValue>> {
+		self.pduid_unredactedcontent
+			.get(pdu_id)
+			.await
+			.deserialized()
+	}
+
 	/// Returns an iterator over all events and their tokens in a room that
 	/// happened before the event with id `until` in reverse-chronological
 	/// order.

src/service/rooms/timeline/mod.rs

@@ -25,6 +25,7 @@ use ruma::{
 	events::room::encrypted::Relation,
 };
 use serde::Deserialize;
+use serde_json::value::RawValue as RawJsonValue;
 
 use self::data::Data;
 pub use self::{create::pdu_fits, data::PdusIterItem};
@@ -242,6 +243,11 @@ impl Service {
 		self.db.replace_pdu(pdu_id, pdu_json).await
 	}
 
+	#[inline]
+	pub async fn get_unredacted_content(&self, pdu_id: &RawPduId) -> Result<Box<RawJsonValue>> {
+		self.db.get_unredacted_content(pdu_id).await
+	}
+
 	/// Returns an iterator over all PDUs in a room. Unknown rooms produce no
 	/// items.
 	#[inline]

src/service/rooms/timeline/redact.rs

@@ -52,6 +52,15 @@ impl super::Service {
 			.get_room_version(&pdu.room_id_or_hash())
 			.await?;
 
+		if !pdu.is_redacted()
+			&& self
+				.services
+				.config
+				.allow_moderators_to_view_redacted_content
+		{
+			self.db.save_unredacted_content(&pdu_id, &pdu.content);
+		}
+
 		pdu.redact(&room_version_id, Some(reason.event_id()))?;
 
 		let obj = utils::to_canonical_object(&pdu).map_err(|e| {