allow members to be persisted as part of a larger txn when fetched

src/matrix/room/Room.js

@@ -22,7 +22,7 @@ import {Timeline} from "./timeline/Timeline.js";
 import {FragmentIdComparer} from "./timeline/FragmentIdComparer.js";
 import {SendQueue} from "./sending/SendQueue.js";
 import {WrappedError} from "../error.js"
-import {fetchOrLoadMembers} from "./members/load.js";
+import {loadMembers, fetchMemberSnapshot} from "./members/load.js";
 import {MemberList} from "./members/MemberList.js";
 import {Heroes} from "./members/Heroes.js";
 
@@ -141,20 +141,60 @@ export class Room extends EventEmitter {
         return this._sendQueue.enqueueEvent(eventType, content);
     }
 
+    /**
+     * @package
+     * @return {MemberSnapshot} the member snapshot, be sure to call dispose
+     */
+    async fetchMemberSnapshot() {
+        if (!this.hasFetchedMembers) {
+            if (this._changedMembersDuringSync) {
+                throw new Error("already snapshot being written");
+            }
+            return await fetchMemberSnapshot({
+                summary: this._summary,
+                roomId: this._roomId,
+                hsApi: this._hsApi,
+                // to handle race between /members and /sync
+                setChangedMembersMap: map => this._changedMembersDuringSync = map,
+            });
+        }
+    }
+
+    async _fetchAndWriteMembers() {
+        const snapshot = this.fetchMemberSnapshot();
+        try {  
+            const txn = await this._storage.readWriteTxn([
+                this._storage.storeNames.roomSummary,
+                this._storage.storeNames.roomMembers,
+            ]);
+            let changes;
+            try {
+                changes = snapshot.write(txn);
+            } catch (err) {
+                txn.abort();
+                throw err;
+            }
+            await txn.complete();
+            snapshot.applyWrite(changes);
+            return snapshot.members;
+        } finally {
+            snapshot.dispose();
+        }
+    }
+
     /** @public */
     async loadMemberList() {
         if (this._memberList) {
             this._memberList.retain();
             return this._memberList;
         } else {
-            const members = await fetchOrLoadMembers({
-                summary: this._summary,
-                roomId: this._roomId,
-                hsApi: this._hsApi,
-                storage: this._storage,
-                // to handle race between /members and /sync
-                setChangedMembersMap: map => this._changedMembersDuringSync = map,
-            });
+            let members;
+            if (this.hasFetchedMembers) {
+                const txn = await this._storage.readTxn([this._storage.storeNames.roomMembers]);
+                members = await loadMembers(this._roomId, txn);
+            } else {
+                members = await this._fetchAndWriteMembers();
+            }
             this._memberList = new MemberList({
                 members,
                 closeCallback: () => { this._memberList = null; }
@@ -256,6 +296,10 @@ export class Room extends EventEmitter {
         return !!(tags && tags['m.lowpriority']);
     }
 
+    get hasFetchedMembers() {
+        return this._summary.hasFetchedMembers;
+    }
+
     async _getLastEventId() {
         const lastKey = this._syncWriter.lastMessageKey;
         if (lastKey) {

src/matrix/room/members/load.js

@@ -17,74 +17,80 @@ limitations under the License.
 
 import {RoomMember} from "./RoomMember.js";
 
-async function loadMembers({roomId, storage}) {
-    const txn = await storage.readTxn([
-        storage.storeNames.roomMembers,
-    ]);
+export async function loadMembers(roomId, txn) {
     const memberDatas = await txn.roomMembers.getAll(roomId);
     return memberDatas.map(d => new RoomMember(d));
 }
 
-async function fetchMembers({summary, roomId, hsApi, storage, setChangedMembersMap}) {
+export async function fetchMemberSnapshot({summary, roomId, hsApi, setChangedMembersMap}) {
     // if any members are changed by sync while we're fetching members,
     // they will end up here, so we check not to override them
     const changedMembersDuringSync = new Map();
     setChangedMembersMap(changedMembersDuringSync);
     
-    const memberResponse = await hsApi.members(roomId, {at: summary.lastPaginationToken}).response;
-
-    const txn = await storage.readWriteTxn([
-        storage.storeNames.roomSummary,
-        storage.storeNames.roomMembers,
-    ]);
-
-    let summaryChanges;
-    let members;
-    
-    try {
-        summaryChanges = summary.writeHasFetchedMembers(true, txn);
-        const {roomMembers} = txn;
-        const memberEvents = memberResponse.chunk;
-        if (!Array.isArray(memberEvents)) {
+    const memberResponse = await hsApi.members(roomId, {at: summary.lastPaginationToken}).response();
+    if (!Array.isArray(memberResponse?.chunk)) {
         throw new Error("malformed");
     }
-        members = await Promise.all(memberEvents.map(async memberEvent => {
+    return new MemberSnapshot({memberEvents: memberResponse.chunk,
+        setChangedMembersMap, changedMembersDuringSync, summary, roomId});
+}
+
+/** Container for fetching /members while handling race with /sync. Can be persisted as part of a wider transaction */
+class MemberSnapshot {
+    constructor({memberEvents, setChangedMembersMap, changedMembersDuringSync, summary, roomId}) {
+        this._memberEvents = memberEvents;
+        this._setChangedMembersMap = setChangedMembersMap;
+        this._changedMembersDuringSync = changedMembersDuringSync;
+        this._summary = summary;
+        this._roomId = roomId;
+        this._members = null;
+    }
+
+    write(txn) {
+        let summaryChanges;        
+        // this needs to happen after the txn is opened to prevent a race
+        // between awaiting the opening of the txn and the sync
+        this._members = this._memberEvents.map(memberEvent => {
             const userId = memberEvent?.state_key;
             if (!userId) {
                 throw new Error("malformed");
             }
             // this member was changed during a sync that happened while calling /members
             // and thus is more recent, so don't overwrite
-            const changedMember = changedMembersDuringSync.get(userId);
+            const changedMember = this._changedMembersDuringSync.get(userId);
             if (changedMember) {
                 return changedMember;
             } else {
-                const member = RoomMember.fromMemberEvent(roomId, memberEvent);
+                return RoomMember.fromMemberEvent(this._roomId, memberEvent);
+            }
+        });
+        // store members
+        const {roomMembers} = txn;
+        for (const member of this._members) {
             if (member) {
                 roomMembers.set(member.serialize());
             }
-                return member;
         }
-        }));
-    } catch (err) {
-        // abort txn on any error
-        txn.abort();
-        throw err;
-    } finally {
-        // important this gets cleared
-        // or otherwise Room remains in "fetching-members" mode
-        setChangedMembersMap(null);
-    }
-    await txn.complete();
-    summary.applyChanges(summaryChanges);
-    return members;
+        // store flag
+        summaryChanges = this._summary.writeHasFetchedMembers(true, txn);
+        return summaryChanges;
     }
 
-export async function fetchOrLoadMembers(options) {
-    const {summary} = options;
-    if (!summary.hasFetchedMembers) {
-        return fetchMembers(options);
-    } else {
-        return loadMembers(options);
+    applyWrite(summaryChanges) {
+        this._summary.applyChanges(summaryChanges);
+    }
+
+    get members() {
+        if (!this._members) {
+            throw new Error("call write first");
+        }
+        return this._members;
+    }
+
+    dispose() {
+        // important this gets cleared
+        // or otherwise Room remains in "fetching-members" mode
+        this._setChangedMembersMap(null);
     }
 }