Fix matrix api joinRoom() for remote rooms (#60)

When using self-service mode and trying to link with a remote matrix
room (room not in the same HS as the bridge user), then we need to add
the "via" HSs to join the room with, or else it fails.

We get it from the "m.space.child" in the "children_state" of the space
hierarchy.

Co-authored-by: Cadence Ember <cadence@disroot.org>
Reviewed-on: https://gitdab.com/cadence/out-of-your-element/pulls/60
Co-authored-by: Elliu <elliu@hashi.re>
Co-committed-by: Elliu <elliu@hashi.re>

src/matrix/api.js

@@ -22,7 +22,11 @@ function path(p, mxid, otherParams = {}) {
 	const u = new URL(p, "http://localhost")
 	if (mxid) u.searchParams.set("user_id", mxid)
 	for (const entry of Object.entries(otherParams)) {
-		if (entry[1] != undefined) {
+		if (Array.isArray(entry[1])) {
+			for (const element of entry[1]) {
+				u.searchParams.append(entry[0], element)
+			}
+		} else if (entry[1] != undefined) {
 			u.searchParams.set(entry[0], entry[1])
 		}
 	}
@@ -62,11 +66,14 @@ async function createRoom(content) {
 }
 
 /**
+ * @param {string} roomIDOrAlias
+ * @param {string?} [mxid]
+ * @param {string[]?} [via]
  * @returns {Promise<string>} room ID
  */
-async function joinRoom(roomIDOrAlias, mxid) {
+async function joinRoom(roomIDOrAlias, mxid, via) {
 	/** @type {Ty.R.RoomJoined} */
-	const root = await mreq.mreq("POST", path(`/client/v3/join/${roomIDOrAlias}`, mxid), {})
+	const root = await mreq.mreq("POST", path(`/client/v3/join/${roomIDOrAlias}`, mxid, {via}), {})
 	return root.room_id
 }