perf: Don't handle expensive requests for rooms we aren't in

Mostly borrowed from dendrite:

https://github.com/element-hq/dendrite/blob/a042861/federationapi/routing/routing.go#L601

src/api/server/backfill.rs

@@ -2,7 +2,7 @@ use std::cmp;
 
 use axum::extract::State;
 use conduwuit::{
-	Event, PduCount, Result,
+	Err, Event, PduCount, Result, debug_warn,
 	result::LogErr,
 	utils::{IterStream, ReadyExt, stream::TryTools},
 };
@@ -34,6 +34,18 @@ pub(crate) async fn get_backfill_route(
 	}
 	.check()
 	.await?;
+	if !services
+		.rooms
+		.state_cache
+		.server_in_room(services.globals.server_name(), &body.room_id)
+		.await
+	{
+		debug_warn!(
+			origin = body.origin().as_str(),
+			"Refusing to serve backfill for room we aren't participating in"
+		);
+		return Err!(Request(NotFound("This server is not participating in that room.")));
+	}
 
 	let limit = body
 		.limit

src/api/server/make_join.rs

@@ -1,7 +1,9 @@
 use std::borrow::ToOwned;
 
 use axum::extract::State;
-use conduwuit::{Err, Error, Result, debug, debug_info, info, matrix::pdu::PduBuilder, warn};
+use conduwuit::{
+	Err, Error, Result, debug, debug_info, debug_warn, info, matrix::pdu::PduBuilder, warn,
+};
 use conduwuit_service::Services;
 use futures::StreamExt;
 use ruma::{
@@ -30,6 +32,18 @@ pub(crate) async fn create_join_event_template_route(
 	if !services.rooms.metadata.exists(&body.room_id).await {
 		return Err!(Request(NotFound("Room is unknown to this server.")));
 	}
+	if !services
+		.rooms
+		.state_cache
+		.server_in_room(services.globals.server_name(), &body.room_id)
+		.await
+	{
+		debug_warn!(
+			origin = body.origin().as_str(),
+			"Refusing to serve make_join for room we aren't participating in"
+		);
+		return Err!(Request(NotFound("This server is not participating in that room.")));
+	}
 
 	if body.user_id.server_name() != body.origin() {
 		return Err!(Request(BadJson("Not allowed to join on behalf of another server/user.")));

src/api/server/make_knock.rs

@@ -20,6 +20,18 @@ pub(crate) async fn create_knock_event_template_route(
 	if !services.rooms.metadata.exists(&body.room_id).await {
 		return Err!(Request(NotFound("Room is unknown to this server.")));
 	}
+	if !services
+		.rooms
+		.state_cache
+		.server_in_room(services.globals.server_name(), &body.room_id)
+		.await
+	{
+		debug_warn!(
+			origin = body.origin().as_str(),
+			"Refusing to serve make_knock for room we aren't participating in"
+		);
+		return Err!(Request(NotFound("This server is not participating in that room.")));
+	}
 
 	if body.user_id.server_name() != body.origin() {
 		return Err!(Request(BadJson("Not allowed to knock on behalf of another server/user.")));

src/api/server/make_leave.rs

@@ -1,5 +1,5 @@
 use axum::extract::State;
-use conduwuit::{Err, Result, matrix::pdu::PduBuilder};
+use conduwuit::{Err, Result, debug_warn, matrix::pdu::PduBuilder};
 use ruma::{
 	api::federation::membership::prepare_leave_event,
 	events::room::member::{MembershipState, RoomMemberEventContent},
@@ -20,6 +20,19 @@ pub(crate) async fn create_leave_event_template_route(
 		return Err!(Request(NotFound("Room is unknown to this server.")));
 	}
 
+	if !services
+		.rooms
+		.state_cache
+		.server_in_room(services.globals.server_name(), &body.room_id)
+		.await
+	{
+		debug_warn!(
+			origin = body.origin().as_str(),
+			"Refusing to serve make_leave for room we aren't participating in"
+		);
+		return Err!(Request(NotFound("This server is not participating in that room.")));
+	}
+
 	if body.user_id.server_name() != body.origin() {
 		return Err!(Request(Forbidden(
 			"Not allowed to leave on behalf of another server/user."

src/api/server/send_join.rs

@@ -4,7 +4,7 @@ use std::{borrow::Borrow, time::Instant, vec};
 
 use axum::extract::State;
 use conduwuit::{
-	Err, Event, Result, at, debug, err, info,
+	Err, Event, Result, at, debug, debug_warn, err, info,
 	matrix::event::gen_event_id_canonical_json,
 	trace,
 	utils::stream::{BroadbandExt, IterStream, TryBroadbandExt},
@@ -36,6 +36,18 @@ async fn create_join_event(
 	if !services.rooms.metadata.exists(room_id).await {
 		return Err!(Request(NotFound("Room is unknown to this server.")));
 	}
+	if !services
+		.rooms
+		.state_cache
+		.server_in_room(services.globals.server_name(), room_id)
+		.await
+	{
+		debug_warn!(
+			origin = origin.as_str(),
+			"Refusing to serve send_join for room we aren't participating in"
+		);
+		return Err!(Request(NotFound("This server is not participating in that room.")));
+	}
 
 	// ACL check origin server
 	services

src/api/server/send_knock.rs

@@ -1,6 +1,6 @@
 use axum::extract::State;
 use conduwuit::{
-	Err, Result, err,
+	Err, Result, debug_warn, err,
 	matrix::{event::gen_event_id_canonical_json, pdu::PduEvent},
 	warn,
 };
@@ -54,6 +54,19 @@ pub(crate) async fn create_knock_event_v1_route(
 		return Err!(Request(NotFound("Room is unknown to this server.")));
 	}
 
+	if !services
+		.rooms
+		.state_cache
+		.server_in_room(services.globals.server_name(), &body.room_id)
+		.await
+	{
+		debug_warn!(
+			origin = body.origin().as_str(),
+			"Refusing to serve send_knock for room we aren't participating in"
+		);
+		return Err!(Request(NotFound("This server is not participating in that room.")));
+	}
+
 	// ACL check origin server
 	services
 		.rooms

src/api/server/send_leave.rs

@@ -1,7 +1,7 @@
 #![allow(deprecated)]
 
 use axum::extract::State;
-use conduwuit::{Err, Result, err, matrix::event::gen_event_id_canonical_json};
+use conduwuit::{Err, Result, debug_warn, err, matrix::event::gen_event_id_canonical_json};
 use conduwuit_service::Services;
 use futures::FutureExt;
 use ruma::{
@@ -50,6 +50,19 @@ async fn create_leave_event(
 		return Err!(Request(NotFound("Room is unknown to this server.")));
 	}
 
+	if !services
+		.rooms
+		.state_cache
+		.server_in_room(services.globals.server_name(), room_id)
+		.await
+	{
+		debug_warn!(
+			origin = origin.as_str(),
+			"Refusing to serve backfill for room we aren't participating in"
+		);
+		return Err!(Request(NotFound("This server is not participating in that room.")));
+	}
+
 	// ACL check origin
 	services
 		.rooms

src/api/server/state.rs

@@ -1,7 +1,7 @@
 use std::{borrow::Borrow, iter::once};
 
 use axum::extract::State;
-use conduwuit::{Result, at, err, utils::IterStream};
+use conduwuit::{Err, Result, at, debug_warn, err, utils::IterStream};
 use futures::{FutureExt, StreamExt, TryStreamExt};
 use ruma::{OwnedEventId, api::federation::event::get_room_state};
 
@@ -24,6 +24,19 @@ pub(crate) async fn get_room_state_route(
 	.check()
 	.await?;
 
+	if !services
+		.rooms
+		.state_cache
+		.server_in_room(services.globals.server_name(), &body.room_id)
+		.await
+	{
+		debug_warn!(
+			origin = body.origin().as_str(),
+			"Refusing to serve state for room we aren't participating in"
+		);
+		return Err!(Request(NotFound("This server is not participating in that room.")));
+	}
+
 	let shortstatehash = services
 		.rooms
 		.state_accessor