prototype how we could store ll members

src/client.js

@@ -757,6 +757,20 @@ MatrixClient.prototype.getRoom = function(roomId) {
     return this.store.getRoom(roomId);
 };
 
+MatrixClient.prototype._loadMembers = async function(room) {
+    const roomId = room.roomId;
+    let rawMembersEvents = await this.store.getOutOfBandMembers(roomId);
+    if (rawMembersEvents.length == 0) {
+        const lastEventId = room.getLastEventId();
+        const response = await this.members(roomId, "join", "leave", lastEventId);
+        rawMembersEvents = response.chunk;
+        // TODO don't block on writing
+        await this.store.setOutOfBandMembers(roomId, rawMembersEvents);
+    }
+    const memberEvents = rawMembersEvents.map(this.getEventMapper());
+    return memberEvents;
+};
+
 /**
  * Preloads the member list for the given room id,
  * in case lazy loading of memberships is in use.
@@ -767,13 +781,8 @@ MatrixClient.prototype.loadRoomMembersIfNeeded = async function(roomId) {
     if (!room || !room.needsOutOfBandMembers()) {
         return;
     }
-
-    const lastEventId = room.getLastEventId();
-    const responsePromise = this.members(roomId, "join", "leave", lastEventId);
-    const eventsPromise = responsePromise.then((response) => {
-        return response.chunk.map(this.getEventMapper());
-    });
-    await room.loadOutOfBandMembers(eventsPromise);
+    const membersPromise = this._loadMembers(room);
+    await room.loadOutOfBandMembers(membersPromise);
 };
 
 /**

src/store/indexeddb-local-backend.js

@@ -19,7 +19,7 @@ import Promise from 'bluebird';
 import SyncAccumulator from "../sync-accumulator";
 import utils from "../utils";
 
-const VERSION = 1;
+const VERSION = 2;
 
 function createDatabase(db) {
     // Make user store, clobber based on user ID. (userId property of User objects)
@@ -33,6 +33,11 @@ function createDatabase(db) {
     db.createObjectStore("sync", { keyPath: ["clobber"] });
 }
 
+function upgradeSchemaV2(db) {
+    const llMembersStore = db.createObjectStore("lazy_loaded_members", { keyPath: ["roomId", "userId"]});
+    llMembersStore.createIndex("room", "roomId");
+}
+
 /**
  * Helper method to collect results from a Cursor and promiseify it.
  * @param {ObjectStore|Index} store The store to perform openCursor on.
@@ -136,6 +141,9 @@ LocalIndexedDBStoreBackend.prototype = {
             if (oldVersion < 1) { // The database did not previously exist.
                 createDatabase(db);
             }
+            if (oldVersion < 2) {
+                upgradeSchemaV2(db);
+            }
             // Expand as needed.
         };
 
@@ -187,6 +195,56 @@ LocalIndexedDBStoreBackend.prototype = {
         });
     },
 
+    getOutOfBandMembers: function(roomId) {
+        return new Promise((resolve, reject) =>{
+            const tx = this.db.transaction(["lazy_loaded_members"], "readonly");
+            const store = tx.objectStore("lazy_loaded_members");
+            const roomIndex = store.index("room");
+            const range = IDBKeyRange.only(roomId);
+            const request = roomIndex.openCursor(range);
+
+            const members = [];
+            request.onsuccess = (event) => {
+                const cursor = event.target.result;
+                if (!cursor) {
+                    return resolve(members);
+                }
+                const record = cursor.value;
+                members.push({
+                    userId: record.userId,
+                    displayName: record.displayName,
+                    membership: record.membership,
+                    avatarUrl: record.avatarUrl,
+                });
+                cursor.continue();
+            };
+            request.onerror = (err) => {
+                reject(err);
+            };
+        });
+    },
+
+    setOutOfBandMembers: function(roomId, members) {
+        function ignoreResult() {};
+        // run everything in a promise so anything that throws will reject
+        return new Promise((resolve) =>{
+            const tx = this.db.transaction(["lazy_loaded_members"], "readwrite");
+            const store = tx.objectStore("lazy_loaded_members");
+            const puts = members.map((m) => {
+                const record = {
+                    roomId: roomId,
+                    userId: m.userId,
+                    displayName: m.displayName,
+                    avatarUrl: m.avatarUrl,
+                    membership: m.membership
+                };
+                let putPromise = promiseifyRequest(store.put(record));
+                return putPromise.then(ignoreResult);
+            });
+            resolve(Promise.all(puts).then(ignoreResult));
+        });
+    },
+
     /**
      * Clear the entire database. This should be used when logging out of a client
      * to prevent mixing data between accounts.

src/store/indexeddb-remote-backend.js

@@ -87,6 +87,13 @@ RemoteIndexedDBStoreBackend.prototype = {
         return this._doCmd('syncToDatabase', [users]);
     },
 
+    getOutOfBandMembers: function(roomId) {
+        return this._doCmd('getOutOfBandMembers', [roomId]);
+    },
+
+    setOutOfBandMembers: function(roomId, members) {
+        return this._doCmd('setOutOfBandMembers', [roomId, members]);
+    },
 
     /**
      * Load all user presence events from the database. This is not cached.

src/store/indexeddb-store-worker.js

@@ -92,6 +92,12 @@ class IndexedDBStoreWorker {
             case 'getNextBatchToken':
                 prom = this.backend.getNextBatchToken();
                 break;
+            case 'getOutOfBandMembers':
+                prom = this.backend.getOutOfBandMembers(msg.args[0]);
+                break;
+            case 'setOutOfBandMembers':
+                prom = this.backend.setOutOfBandMembers(msg.args[0], msg.args[1]);
+                break;
         }
 
         if (prom === undefined) {

src/store/indexeddb.js

@@ -219,4 +219,12 @@ IndexedDBStore.prototype.setSyncData = function(syncData) {
     return this.backend.setSyncData(syncData);
 };
 
+IndexedDBStore.prototype.getOutOfBandMembers = function(roomId) {
+    return this.backend.getOutOfBandMembers(roomId);
+};
+
+IndexedDBStore.prototype.setOutOfBandMembers = function(roomId, members) {
+    return this.backend.setOutOfBandMembers(roomId, members);
+};
+
 module.exports.IndexedDBStore = IndexedDBStore;