Improve comments and explainer for new decryption approach

src/components/structures/MatrixChat.tsx

@@ -906,6 +906,10 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
             let presentedId = roomInfo.room_alias || roomInfo.room_id;
             const room = MatrixClientPeg.get().getRoom(roomInfo.room_id);
             if (room) {
+                // Not all timeline events are decrypted ahead of time anymore
+                // Only the critical ones for a typical UI are
+                // This will start the decryption process for all events when a
+                // user views a room
                 room.decryptAllEvents();
                 const theAlias = Rooms.getDisplayAliasForRoom(room);
                 if (theAlias) {

src/indexing/EventIndex.js

@@ -188,6 +188,7 @@ export default class EventIndex extends EventEmitter {
         }
 
         if (ev.isBeingDecrypted()) {
+            // XXX: Private member access
             await ev._decryptionPromise;
         }
 
@@ -523,6 +524,11 @@ export default class EventIndex extends EventEmitter {
                             emit: false,
                         });
                     } else {
+                        // TODO the decryption promise is a private property, this
+                        // should either be made public or we should convert the
+                        // event that gets fired when decryption is done into a
+                        // promise using the once event emitter method:
+                        // https://nodejs.org/api/events.html#events_events_once_emitter_name
                         return event._decryptionPromise;
                     }
                 });

src/stores/BreadcrumbsStore.ts

@@ -16,13 +16,14 @@ limitations under the License.
 
 import SettingsStore from "../settings/SettingsStore";
 import { Room } from "matrix-js-sdk/src/models/room";
+import { EventType } from "matrix-js-sdk/src/@types/event";
 import { ActionPayload } from "../dispatcher/payloads";
 import { AsyncStoreWithClient } from "./AsyncStoreWithClient";
 import defaultDispatcher from "../dispatcher/dispatcher";
 import { arrayHasDiff } from "../utils/arrays";
 import { isNullOrUndefined } from "matrix-js-sdk/src/utils";
 import { SettingLevel } from "../settings/SettingLevel";
-import {MatrixClientPeg} from '../MatrixClientPeg';
+import { MatrixClientPeg } from '../MatrixClientPeg';
 
 const MAX_ROOMS = 20; // arbitrary
 const AUTOJOIN_WAIT_THRESHOLD_MS = 90000; // 90s, the time we wait for an autojoined room to show up
@@ -64,21 +65,18 @@ export class BreadcrumbsStore extends AsyncStoreWithClient<IState> {
         const prevRoomCount = (prevState.rooms?.length || 0);
         const currentRoomCount = (this.state.rooms?.length || 0)
 
-        /**
+        // Only decrypting the breadcrumb rooms events on app initialisation
-         * Only decrypting the breadcrumb rooms events on app initialisation
+        // when room count transitions from 0 to the number of rooms it contains
-         * when room count transitions from 0 to the number of rooms it contains
-         */
         if (prevRoomCount === 0 && currentRoomCount > prevRoomCount) {
             const client = MatrixClientPeg.get();
-            /**
+            // Rooms in the breadcrumb have a good chance to be interacted with
-             * Rooms in the breadcrumb have a good chance to be interacted with
+            // again by a user. Decrypting the messages ahead of time will help
-             * again by a user. Decrypting the messages ahead of time will help
+            // reduce content shift on first render
-             * reduce content shift on first render
-             */
             this.state.rooms?.forEach(async room => {
-                const [cryptoEvent] = room.currentState.getStateEvents("m.room.encryption");
+                const [cryptoEvent] = room.currentState.getStateEvents(EventType.RoomEncryption);
                 if (cryptoEvent) {
                     if (!client.isRoomEncrypted(room.roomId)) {
+                        // XXX: Private member access
                         await client._crypto.onCryptoEvent(cryptoEvent);
                     }
                     room?.decryptAllEvents();