Cache room alias to room ID mapping in memory

This adds very basic cache (literally just a `Map` for now) to store room alias
to room ID mappings. The improves the perceived performance of Riot when
switching rooms via browser navigation (back / forward), as we no longer try to
resolve the room alias every time.

The cache is only in memory, so reloading manually or as part of the clear cache
process will start afresh.

Fixes https://github.com/vector-im/riot-web/issues/10020

src/stores/RoomViewStore.js

@@ -20,6 +20,7 @@ import MatrixClientPeg from '../MatrixClientPeg';
 import sdk from '../index';
 import Modal from '../Modal';
 import { _t } from '../languageHandler';
+import { getCachedRoomIDForAlias, storeRoomAliasInCache } from '../RoomAliasCache';
 
 const INITIAL_STATE = {
     // Whether we're joining the currently viewed room (see isJoining())
@@ -137,7 +138,7 @@ class RoomViewStore extends Store {
         }
     }
 
-    _viewRoom(payload) {
+    async _viewRoom(payload) {
         if (payload.room_id) {
             const newState = {
                 roomId: payload.room_id,
@@ -176,6 +177,22 @@ class RoomViewStore extends Store {
                 this._joinRoom(payload);
             }
         } else if (payload.room_alias) {
+            // Try the room alias to room ID navigation cache first to avoid
+            // blocking room navigation on the homeserver.
+            const roomId = getCachedRoomIDForAlias(payload.room_alias);
+            if (roomId) {
+                dis.dispatch({
+                    action: 'view_room',
+                    room_id: roomId,
+                    event_id: payload.event_id,
+                    highlighted: payload.highlighted,
+                    room_alias: payload.room_alias,
+                    auto_join: payload.auto_join,
+                    oob_data: payload.oob_data,
+                });
+                return;
+            }
+            // Room alias cache miss, so let's ask the homeserver.
             // Resolve the alias and then do a second dispatch with the room ID acquired
             this._setState({
                 roomId: null,
@@ -186,8 +203,9 @@ class RoomViewStore extends Store {
                 roomLoading: true,
                 roomLoadError: null,
             });
-            MatrixClientPeg.get().getRoomIdForAlias(payload.room_alias).done(
-            (result) => {
+            try {
+                const result = await MatrixClientPeg.get().getRoomIdForAlias(payload.room_alias);
+                storeRoomAliasInCache(payload.room_alias, result.room_id);
                 dis.dispatch({
                     action: 'view_room',
                     room_id: result.room_id,
@@ -197,14 +215,14 @@ class RoomViewStore extends Store {
                     auto_join: payload.auto_join,
                     oob_data: payload.oob_data,
                 });
-            }, (err) => {
+            } catch (err) {
                 dis.dispatch({
                     action: 'view_room_error',
                     room_id: null,
                     room_alias: payload.room_alias,
-                    err: err,
+                    err,
                 });
-            });
+            }
         }
     }