Fix infinite loop when restoring cached read receipts (#2963)

Author: Germain

src/models/room.ts

@@ -2079,8 +2079,13 @@ export class Room extends ReadReceipt<RoomEmittedEvents, RoomEventHandlerMap> {
             room: this,
             client: this.client,
             pendingEventOrdering: this.opts.pendingEventOrdering,
+            receipts: this.cachedThreadReadReceipts.get(threadId) ?? [],
         });
 
+        // All read receipts should now come down from sync, we do not need to keep
+        // a reference to the cached receipts anymore.
+        this.cachedThreadReadReceipts.delete(threadId);
+
         // This is necessary to be able to jump to events in threads:
         // If we jump to an event in a thread where neither the event, nor the root,
         // nor any thread event are loaded yet, we'll load the event as well as the thread root, create the thread,
@@ -2110,17 +2115,6 @@ export class Room extends ReadReceipt<RoomEmittedEvents, RoomEventHandlerMap> {
         if (this.threadsReady) {
             this.updateThreadRootEvents(thread, toStartOfTimeline, false);
         }
-
-        // Pulling all the cached thread read receipts we've discovered when we
-        // did an initial sync, and applying them to the thread now that it exists
-        // on the client side
-        if (this.cachedThreadReadReceipts.has(threadId)) {
-            for (const { event, synthetic } of this.cachedThreadReadReceipts.get(threadId)!) {
-                this.addReceipt(event, synthetic);
-            }
-            this.cachedThreadReadReceipts.delete(threadId);
-        }
-
         this.emit(ThreadEvent.New, thread, toStartOfTimeline);
 
         return thread;

src/models/thread.ts

@@ -27,7 +27,7 @@ import { RoomState } from "./room-state";
 import { ServerControlledNamespacedValue } from "../NamespacedValue";
 import { logger } from "../logger";
 import { ReadReceipt } from "./read-receipt";
-import { ReceiptType } from "../@types/read_receipts";
+import { Receipt, ReceiptContent, ReceiptType } from "../@types/read_receipts";
 
 export enum ThreadEvent {
     New = "Thread.new",
@@ -50,6 +50,7 @@ interface IThreadOpts {
     room: Room;
     client: MatrixClient;
     pendingEventOrdering?: PendingEventOrdering;
+    receipts?: { event: MatrixEvent; synthetic: boolean }[];
 }
 
 export enum FeatureSupport {
@@ -127,6 +128,8 @@ export class Thread extends ReadReceipt<EmittedEvents, EventHandlerMap> {
         this.room.on(RoomEvent.LocalEchoUpdated, this.onEcho);
         this.timelineSet.on(RoomEvent.Timeline, this.onTimelineEvent);
 
+        this.processReceipts(opts.receipts);
+
         // even if this thread is thought to be originating from this client, we initialise it as we may be in a
         // gappy sync and a thread around this event may already exist.
         this.updateThreadMetadata();
@@ -284,6 +287,26 @@ export class Thread extends ReadReceipt<EmittedEvents, EventHandlerMap> {
         this.timeline = this.events;
     }
 
+    /**
+     * Processes the receipts that were caught during initial sync
+     * When clients become aware of a thread, they try to retrieve those read receipts
+     * and apply them to the current thread
+     * @param receipts - A collection of the receipts cached from initial sync
+     */
+    private processReceipts(receipts: { event: MatrixEvent; synthetic: boolean }[] = []): void {
+        for (const { event, synthetic } of receipts) {
+            const content = event.getContent<ReceiptContent>();
+            Object.keys(content).forEach((eventId: string) => {
+                Object.keys(content[eventId]).forEach((receiptType: ReceiptType | string) => {
+                    Object.keys(content[eventId][receiptType]).forEach((userId: string) => {
+                        const receipt = content[eventId][receiptType][userId] as Receipt;
+                        this.addReceiptToStructure(eventId, receiptType as ReceiptType, userId, receipt, synthetic);
+                    });
+                });
+            });
+        }
+    }
+
     private getRootEventBundledRelationship(rootEvent = this.rootEvent): IThreadBundledRelationship | undefined {
         return rootEvent?.getServerAggregatedRelation<IThreadBundledRelationship>(THREAD_RELATION_TYPE.name);
     }