Distinguish room state and timeline events in embedded clients

This change enables room widget clients to take advantage of the more reliable method of communicating room state over the widget API provided by a recent update to MSC2762.

spec/unit/embedded.spec.ts

@@ -28,7 +28,6 @@ import {
     WidgetApiToWidgetAction,
     MatrixCapabilities,
     ITurnServer,
-    IRoomEvent,
     IOpenIDCredentials,
     ISendEventFromWidgetResponseData,
     WidgetApiResponseError,
@@ -635,12 +634,20 @@ describe("RoomWidgetClient", () => {
         });
 
         it("receives", async () => {
-            await makeClient({ receiveState: [{ eventType: "org.example.foo", stateKey: "bar" }] });
+            const init = makeClient({ receiveState: [{ eventType: "org.example.foo", stateKey: "bar" }] });
             expect(widgetApi.requestCapabilityForRoomTimeline).toHaveBeenCalledWith("!1:example.org");
             expect(widgetApi.requestCapabilityToReceiveState).toHaveBeenCalledWith("org.example.foo", "bar");
+            // Client needs to be told that the room state is loaded
+            widgetApi.emit(
+                `action:${WidgetApiToWidgetAction.UpdateState}`,
+                new CustomEvent(`action:${WidgetApiToWidgetAction.UpdateState}`, { detail: { data: { state: [] } } }),
+            );
+            await init;
 
             const emittedEvent = new Promise<MatrixEvent>((resolve) => client.once(ClientEvent.Event, resolve));
             const emittedSync = new Promise<SyncState>((resolve) => client.once(ClientEvent.Sync, resolve));
+            // Let's assume that a state event comes in but it doesn't actually
+            // update the state of the room just yet (maybe it's unauthorized)
             widgetApi.emit(
                 `action:${WidgetApiToWidgetAction.SendEvent}`,
                 new CustomEvent(`action:${WidgetApiToWidgetAction.SendEvent}`, { detail: { data: event } }),
@@ -649,26 +656,43 @@ describe("RoomWidgetClient", () => {
             // The client should've emitted about the received event
             expect((await emittedEvent).getEffectiveEvent()).toEqual(event);
             expect(await emittedSync).toEqual(SyncState.Syncing);
-            // It should've also inserted the event into the room object
+            // However it should not have changed the room state
             const room = client.getRoom("!1:example.org");
-            expect(room).not.toBeNull();
+            expect(room!.currentState.getStateEvents("org.example.foo", "bar")).toBe(null);
+
+            // Now assume that the state event becomes favored by state
+            // resolution for whatever reason and enters into the current state
+            // of the room
+            widgetApi.emit(
+                `action:${WidgetApiToWidgetAction.UpdateState}`,
+                new CustomEvent(`action:${WidgetApiToWidgetAction.UpdateState}`, {
+                    detail: { data: { state: [event] } },
+                }),
+            );
+            // It should now have changed the room state
             expect(room!.currentState.getStateEvents("org.example.foo", "bar")?.getEffectiveEvent()).toEqual(event);
         });
 
-        it("backfills", async () => {
-            widgetApi.readStateEvents.mockImplementation(async (eventType, limit, stateKey) =>
-                eventType === "org.example.foo" && (limit ?? Infinity) > 0 && stateKey === "bar"
-                    ? [event as IRoomEvent]
-                    : [],
+        it("ignores state updates for other rooms", async () => {
+            const init = makeClient({ receiveState: [{ eventType: "org.example.foo", stateKey: "bar" }] });
+            // Client needs to be told that the room state is loaded
+            widgetApi.emit(
+                `action:${WidgetApiToWidgetAction.UpdateState}`,
+                new CustomEvent(`action:${WidgetApiToWidgetAction.UpdateState}`, { detail: { data: { state: [] } } }),
             );
+            await init;
 
-            await makeClient({ receiveState: [{ eventType: "org.example.foo", stateKey: "bar" }] });
-            expect(widgetApi.requestCapabilityForRoomTimeline).toHaveBeenCalledWith("!1:example.org");
-            expect(widgetApi.requestCapabilityToReceiveState).toHaveBeenCalledWith("org.example.foo", "bar");
-
-            const room = client.getRoom("!1:example.org");
-            expect(room).not.toBeNull();
-            expect(room!.currentState.getStateEvents("org.example.foo", "bar")?.getEffectiveEvent()).toEqual(event);
+            // Now a room we're not interested in receives a state update
+            widgetApi.emit(
+                `action:${WidgetApiToWidgetAction.UpdateState}`,
+                new CustomEvent(`action:${WidgetApiToWidgetAction.UpdateState}`, {
+                    detail: { data: { state: [{ ...event, room_id: "!other-room:example.org" }] } },
+                }),
+            );
+            // No change to the room state
+            for (const room of client.getRooms()) {
+                expect(room.currentState.getStateEvents("org.example.foo", "bar")).toBe(null);
+            }
         });
     });
 

src/embedded.ts

@@ -28,6 +28,7 @@ import {
     WidgetApiAction,
     IWidgetApiResponse,
     IWidgetApiResponseData,
+    IUpdateStateToWidgetActionRequest,
 } from "matrix-widget-api";
 
 import { MatrixEvent, IEvent, IContent, EventStatus } from "./models/event.ts";
@@ -136,6 +137,7 @@ export type EventHandlerMap = { [RoomWidgetClientEvent.PendingEventsChanged]: ()
 export class RoomWidgetClient extends MatrixClient {
     private room?: Room;
     private readonly widgetApiReady: Promise<void>;
+    private readonly roomStateSynced: Promise<void>;
     private lifecycle?: AbortController;
     private syncState: SyncState | null = null;
 
@@ -189,6 +191,11 @@ export class RoomWidgetClient extends MatrixClient {
         };
 
         this.widgetApiReady = new Promise<void>((resolve) => this.widgetApi.once("ready", resolve));
+        this.roomStateSynced = capabilities.receiveState?.length
+            ? new Promise<void>((resolve) =>
+                  this.widgetApi.once(`action:${WidgetApiToWidgetAction.UpdateState}`, resolve),
+              )
+            : Promise.resolve();
 
         // Request capabilities for the functionality this client needs to support
         if (
@@ -241,6 +248,7 @@ export class RoomWidgetClient extends MatrixClient {
 
         widgetApi.on(`action:${WidgetApiToWidgetAction.SendEvent}`, this.onEvent);
         widgetApi.on(`action:${WidgetApiToWidgetAction.SendToDevice}`, this.onToDevice);
+        widgetApi.on(`action:${WidgetApiToWidgetAction.UpdateState}`, this.onStateUpdate);
 
         // Open communication with the host
         widgetApi.start();
@@ -276,37 +284,16 @@ export class RoomWidgetClient extends MatrixClient {
 
         await this.widgetApiReady;
 
-        // Backfill the requested events
-        // We only get the most recent event for every type + state key combo,
-        // so it doesn't really matter what order we inject them in
-        await Promise.all(
-            this.capabilities.receiveState?.map(async ({ eventType, stateKey }) => {
-                const rawEvents = await this.widgetApi.readStateEvents(eventType, undefined, stateKey, [this.roomId]);
-                const events = rawEvents.map((rawEvent) => new MatrixEvent(rawEvent as Partial<IEvent>));
-
-                if (this.syncApi instanceof SyncApi) {
-                    // Passing undefined for `stateAfterEventList` allows will make `injectRoomEvents` run in legacy mode
-                    // -> state events in `timelineEventList` will update the state.
-                    await this.syncApi.injectRoomEvents(this.room!, undefined, events);
-                } else {
-                    await this.syncApi!.injectRoomEvents(this.room!, events); // Sliding Sync
-                }
-                events.forEach((event) => {
-                    this.emit(ClientEvent.Event, event);
-                    logger.info(`Backfilled event ${event.getId()} ${event.getType()} ${event.getStateKey()}`);
-                });
-            }) ?? [],
-        );
-
         if (opts.clientWellKnownPollPeriod !== undefined) {
             this.clientWellKnownIntervalID = setInterval(() => {
                 this.fetchClientWellKnown();
             }, 1000 * opts.clientWellKnownPollPeriod);
             this.fetchClientWellKnown();
         }
 
+        await this.roomStateSynced;
         this.setSyncState(SyncState.Syncing);
-        logger.info("Finished backfilling events");
+        logger.info("Finished initial sync");
 
         this.matrixRTC.start();
 
@@ -317,6 +304,7 @@ export class RoomWidgetClient extends MatrixClient {
     public stopClient(): void {
         this.widgetApi.off(`action:${WidgetApiToWidgetAction.SendEvent}`, this.onEvent);
         this.widgetApi.off(`action:${WidgetApiToWidgetAction.SendToDevice}`, this.onToDevice);
+        this.widgetApi.off(`action:${WidgetApiToWidgetAction.UpdateState}`, this.onStateUpdate);
 
         super.stopClient();
         this.lifecycle!.abort(); // Signal to other async tasks that the client has stopped
@@ -574,36 +562,15 @@ export class RoomWidgetClient extends MatrixClient {
             // Only inject once we have update the txId
             await this.updateTxId(event);
 
-            // The widget API does not tell us whether a state event came from `state_after` or not so we assume legacy behaviour for now.
             if (this.syncApi instanceof SyncApi) {
-                // The code will want to be something like:
-                // ```
-                // if (!params.addToTimeline && !params.addToState) {
-                // // Passing undefined for `stateAfterEventList` makes `injectRoomEvents` run in "legacy mode"
-                // // -> state events part of the `timelineEventList` parameter will update the state.
-                //     this.injectRoomEvents(this.room!, [], undefined, [event]);
-                // } else {
-                //     this.injectRoomEvents(this.room!, undefined, params.addToState ? [event] : [], params.addToTimeline ? [event] : []);
-                // }
-                // ```
-
-                // Passing undefined for `stateAfterEventList` allows will make `injectRoomEvents` run in legacy mode
-                // -> state events in `timelineEventList` will update the state.
-                await this.syncApi.injectRoomEvents(this.room!, [], undefined, [event]);
+                this.syncApi.injectRoomEvents(this.room!, undefined, [], [event]);
             } else {
-                // The code will want to be something like:
-                // ```
-                // if (!params.addToTimeline && !params.addToState) {
-                //     this.injectRoomEvents(this.room!, [], [event]);
-                // } else {
-                //     this.injectRoomEvents(this.room!, params.addToState ? [event] : [], params.addToTimeline ? [event] : []);
-                // }
-                // ```
-                await this.syncApi!.injectRoomEvents(this.room!, [], [event]); // Sliding Sync
+                // Sliding Sync
+                this.syncApi!.injectRoomEvents(this.room!, [], [event]);
             }
             this.emit(ClientEvent.Event, event);
             this.setSyncState(SyncState.Syncing);
-            logger.info(`Received event ${event.getId()} ${event.getType()} ${event.getStateKey()}`);
+            logger.info(`Received event ${event.getId()} ${event.getType()}`);
         } else {
             const { event_id: eventId, room_id: roomId } = ev.detail.data;
             logger.info(`Received event ${eventId} for a different room ${roomId}; discarding`);
@@ -628,6 +595,32 @@ export class RoomWidgetClient extends MatrixClient {
         await this.ack(ev);
     };
 
+    private onStateUpdate = async (ev: CustomEvent<IUpdateStateToWidgetActionRequest>): Promise<void> => {
+        ev.preventDefault();
+
+        for (const rawEvent of ev.detail.data.state) {
+            // Verify the room ID matches, since it's possible for the client to
+            // send us state updates from other rooms if this widget is always
+            // on screen
+            if (rawEvent.room_id === this.roomId) {
+                const event = new MatrixEvent(rawEvent as Partial<IEvent>);
+
+                if (this.syncApi instanceof SyncApi) {
+                    this.syncApi.injectRoomEvents(this.room!, undefined, [event]);
+                } else {
+                    // Sliding Sync
+                    this.syncApi!.injectRoomEvents(this.room!, [event]);
+                }
+                logger.info(`Updated state entry ${event.getType()} ${event.getStateKey()} to ${event.getId()}`);
+            } else {
+                const { event_id: eventId, room_id: roomId } = ev.detail.data;
+                logger.info(`Received state entry ${eventId} for a different room ${roomId}; discarding`);
+            }
+        }
+
+        await this.ack(ev);
+    };
+
     private async watchTurnServers(): Promise<void> {
         const servers = this.widgetApi.getTurnServers();
         const onClientStopped = (): void => {