implement local room preview

Signed-off-by: Jason Volk <jason@zemos.net>

src/api/client/room/initial_sync.rs

@@ -0,0 +1,72 @@
+use axum::extract::State;
+use conduit::{at, utils::BoolExt, Err, Result};
+use futures::StreamExt;
+use ruma::api::client::room::initial_sync::v3::{PaginationChunk, Request, Response};
+
+use crate::Ruma;
+
+const LIMIT_MAX: usize = 100;
+
+pub(crate) async fn room_initial_sync_route(
+	State(services): State<crate::State>, body: Ruma<Request>,
+) -> Result<Response> {
+	let room_id = &body.room_id;
+
+	if !services
+		.rooms
+		.state_accessor
+		.user_can_see_state_events(body.sender_user(), room_id)
+		.await
+	{
+		return Err!(Request(Forbidden("No room preview available.")));
+	}
+
+	let limit = LIMIT_MAX;
+	let events: Vec<_> = services
+		.rooms
+		.timeline
+		.pdus_rev(None, room_id, None)
+		.await?
+		.take(limit)
+		.collect()
+		.await;
+
+	let state: Vec<_> = services
+		.rooms
+		.state_accessor
+		.room_state_full_pdus(room_id)
+		.await?
+		.into_iter()
+		.map(|pdu| pdu.to_state_event())
+		.collect();
+
+	let messages = PaginationChunk {
+		start: events.last().map(at!(0)).as_ref().map(ToString::to_string),
+
+		end: events
+			.first()
+			.map(at!(0))
+			.as_ref()
+			.map(ToString::to_string)
+			.unwrap_or_default(),
+
+		chunk: events
+			.into_iter()
+			.map(at!(1))
+			.map(|pdu| pdu.to_room_event())
+			.collect(),
+	};
+
+	Ok(Response {
+		room_id: room_id.to_owned(),
+		account_data: None,
+		state: state.into(),
+		messages: messages.chunk.is_empty().or_some(messages),
+		visibility: services.rooms.directory.visibility(room_id).await.into(),
+		membership: services
+			.rooms
+			.state_cache
+			.user_membership(body.sender_user(), room_id)
+			.await,
+	})
+}

src/api/client/room/mod.rs

@@ -1,9 +1,10 @@
 mod aliases;
 mod create;
 mod event;
+mod initial_sync;
 mod upgrade;
 
 pub(crate) use self::{
 	aliases::get_room_aliases_route, create::create_room_route, event::get_room_event_route,
-	upgrade::upgrade_room_route,
+	initial_sync::room_initial_sync_route, upgrade::upgrade_room_route,
 };