feat: Give send_knock the invite treatment

src/api/server/utils.rs

@@ -1,7 +1,10 @@
-use conduwuit::{Err, Result, is_false};
+use conduwuit::{Err, Result, err, is_false};
 use conduwuit_service::Services;
 use futures::{FutureExt, future::OptionFuture, join};
-use ruma::{EventId, RoomId, ServerName};
+use ruma::{
+	CanonicalJsonObject, EventId, OwnedEventId, OwnedRoomId, OwnedUserId, RoomId, ServerName,
+	UserId, events::room::member::MembershipState, room_version_rules::RoomVersionRules,
+};
 
 pub(super) struct AccessCheck<'a> {
 	pub(super) services: &'a Services,
@@ -63,3 +66,101 @@ pub(super) async fn assert(&self) -> Result {
 		Ok(())
 	}
 }
+
+/// Performs validation on a membership event that should be run on any event a
+/// remote is trying to send via us.
+///
+/// ## Checks performed
+///
+/// 1. PDU room ID matches request path room ID
+/// 2. PDU event ID matches request path event ID
+/// 3. Signature check
+/// 4. Event type check
+/// 5. `sender` field presence (and parsing)
+/// 6. `state_key` field presence (and parsing)
+/// 7. PDU room format check (PDU check 1)
+///
+/// ## Returns
+///
+/// A resulting tuple of (PDU JSON, target membership state, sender, recipient).
+pub(crate) async fn validate_any_membership_event(
+	services: &crate::State,
+	body: &serde_json::value::RawValue,
+	room_version_rules: &RoomVersionRules,
+	create_event_id: OwnedEventId,
+	expected_room_id: OwnedRoomId,
+	expected_event_id: OwnedEventId,
+) -> Result<(CanonicalJsonObject, MembershipState, OwnedUserId, OwnedUserId)> {
+	let (template_room_id, template_event_id, pdu) = services
+		.rooms
+		.event_handler
+		.parse_incoming_pdu(body)
+		.await
+		.map_err(|e| err!(Request(BadJson("Invalid membership PDU: {e}"))))?;
+
+	if template_room_id != expected_room_id {
+		return Err!(Request(InvalidParam("Membership event does not belong to requested room")));
+	}
+	if template_event_id != expected_event_id {
+		return Err!(Request(InvalidParam(
+			"Membership event ID does not match provided event ID"
+		)));
+	}
+
+	services
+		.server_keys
+		.verify_event(&pdu, room_version_rules)
+		.await
+		.map_err(|e| {
+			err!(Request(InvalidParam("Signature verification failed on membership event: {e}")))
+		})?;
+
+	// Ensure this is a membership event
+	if pdu
+		.get("type")
+		.expect("event must have a type")
+		.as_str()
+		.expect("type must be a string")
+		!= "m.room.member"
+	{
+		return Err!(Request(BadJson(
+			"Not allowed to send non-membership event to this endpoint"
+		)));
+	}
+	let membership = pdu
+		.get("content")
+		.ok_or_else(|| err!(Request(BadJson("Event missing content property"))))?
+		.as_object()
+		.ok_or_else(|| err!(Request(BadJson("Event content is not an object"))))?
+		.get("membership")
+		.ok_or_else(|| err!(Request(BadJson("Event missing membership property"))))?
+		.as_str()
+		.ok_or_else(|| err!(Request(BadJson("Event is not a string"))))?
+		.to_owned();
+
+	let sender_user = pdu
+		.get("sender")
+		.and_then(|v| v.as_str())
+		.map(UserId::parse)
+		.and_then(Result::ok)
+		.ok_or_else(|| err!(Request(InvalidParam("Invalid sender property"))))?;
+	let recipient_user = pdu
+		.get("state_key")
+		.and_then(|v| v.as_str())
+		.map(UserId::parse)
+		.and_then(Result::ok)
+		.ok_or_else(|| err!(Request(InvalidParam("Invalid state_key property"))))?;
+
+	// Do a quick format check. The spec doesn't suggest this, but it's probably
+	// a good idea nonetheless.
+	service::rooms::event_handler::Service::pdu_format_check_1(
+		&pdu,
+		room_version_rules,
+		&create_event_id,
+	)
+	.map_err(|e| {
+		err!(Request(InvalidParam("Membership event violates the room event format: {e}")))
+	})?;
+
+	Ok((pdu, membership.into(), sender_user, recipient_user))
+}