add jsdoc and implementation for memory crypto store

src/crypto/store/indexeddb-crypto-store.js

@@ -582,14 +582,25 @@ export class IndexedDBCryptoStore {
         return this._backend.markSessionsNeedingBackup(sessions, txn);
     }
 
-    /* FIXME: jsdoc
+    /**
+     * Add a shared-history group session for a room.
+     * @param {string} roomId The room that the key belongs to
+     * @param {string} senderKey The sender's curve 25519 key
+     * @param {string} sessionId The ID of the session
+     * @param {*} txn An active transaction. See doTxn(). (optional)
      */
     addSharedHistoryInboundGroupSession(roomId, senderKey, sessionId, txn) {
-        return this._backend.addSharedHistoryInboundGroupSession(
+        this._backend.addSharedHistoryInboundGroupSession(
             roomId, senderKey, sessionId, txn,
         );
     }
 
+    /**
+     * Get the shared-history group session for a room.
+     * @param {string} roomId The room that the key belongs to
+     * @param {*} txn An active transaction. See doTxn(). (optional)
+     * @returns {Promise} Resolves to an array of [senderKey, sessionId]
+     */
     getSharedHistoryInboundGroupSessions(roomId, txn) {
         return this._backend.getSharedHistoryInboundGroupSessions(roomId, txn);
     }

src/crypto/store/memory-crypto-store.js

@@ -51,6 +51,8 @@ export class MemoryCryptoStore {
         this._rooms = {};
         // Set of {senderCurve25519Key+'/'+sessionId}
         this._sessionsNeedingBackup = {};
+        // roomId -> array of [senderKey, sessionId]
+        this._sharedHistoryInboundGroupSessions = {};
     }
 
     /**
@@ -467,6 +469,16 @@ export class MemoryCryptoStore {
         return Promise.resolve();
     }
 
+    addSharedHistoryInboundGroupSession(roomId, senderKey, sessionId) {
+        const sessions = this._sharedHistoryInboundGroupSessions[roomId] || [];
+        sessions.push([senderKey, sessionId]);
+        this._sharedHistoryInboundGroupSessions[roomId] = sessions;
+    }
+
+    getSharedHistoryInboundGroupSessions(roomId) {
+        return Promise.resolve(this._sharedHistoryInboundGroupSessions[roomId] || []);
+    }
+
     // Session key backups
 
     doTxn(mode, stores, func) {