Add basic storage consistency check

This adds a storage consistency check just before creating a client on login.
Each data store we used is checked for data and any problems are logged to the
console.

Fixes element-hq/element-web#9271

src/Lifecycle.js

@@ -31,7 +31,8 @@ import Modal from './Modal';
 import sdk from './index';
 import ActiveWidgetStore from './stores/ActiveWidgetStore';
 import PlatformPeg from "./PlatformPeg";
-import {sendLoginRequest} from "./Login";
+import { sendLoginRequest } from "./Login";
+import * as StorageManager from './utils/StorageManager';
 
 /**
  * Called at startup, to attempt to build a logged-in Matrix session. It tries
@@ -353,6 +354,8 @@ async function _doSetLoggedIn(credentials, clearStorage) {
         await _clearStorage();
     }
 
+    await StorageManager.checkConsistency();
+
     Analytics.setLoggedIn(credentials.guest, credentials.homeserverUrl, credentials.identityServerUrl);
 
     if (localStorage) {

src/utils/StorageManager.js

@@ -0,0 +1,87 @@
+/*
+Copyright 2019 New Vector Ltd
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import Matrix from 'matrix-js-sdk';
+
+const localStorage = window.localStorage;
+
+// just *accessing* indexedDB throws an exception in firefox with
+// indexeddb disabled.
+let indexedDB;
+try {
+    indexedDB = window.indexedDB;
+} catch (e) {}
+
+// The JS SDK will add a prefix of "matrix-js-sdk:" to the sync store name.
+const SYNC_STORE_NAME = "riot-web-sync";
+const CRYPTO_STORE_NAME = "matrix-js-sdk:crypto";
+
+function log(msg) {
+    console.log(`StorageManager: ${msg}`);
+}
+
+function error(msg) {
+    console.error(`StorageManager: ${msg}`);
+}
+
+export async function checkConsistency() {
+    log("Checking storage consistency");
+    log(`Local storage supported? ${!!localStorage}`);
+    log(`IndexedDB supported? ${!!indexedDB}`);
+
+    let dataInLocalStorage = false;
+    let dataInCryptoStore = false;
+    let healthy = true;
+
+    if (localStorage) {
+        dataInLocalStorage = localStorage.length > 0;
+        log(`Local storage contains data? ${dataInLocalStorage}`);
+    }
+
+    if (indexedDB && localStorage) {
+        const dataInSyncStore = await Matrix.IndexedDBStore.exists(
+            indexedDB, SYNC_STORE_NAME,
+        );
+        log(`Sync store contains data? ${dataInSyncStore}`);
+    } else {
+        healthy = false;
+        error("Sync store cannot be used on this browser");
+    }
+
+    if (indexedDB) {
+        dataInCryptoStore = await Matrix.IndexedDBCryptoStore.exists(
+            indexedDB, CRYPTO_STORE_NAME,
+        );
+        log(`Crypto store contains data? ${dataInCryptoStore}`);
+    } else {
+        healthy = false;
+        error("Crypto store cannot be used on this browser");
+    }
+
+    if (dataInLocalStorage && !dataInCryptoStore) {
+        healthy = false;
+        error(
+            "Data exists in local storage but not in crypto store. " +
+            "IndexedDB storage has likely been evicted by the browser!",
+        );
+    }
+
+    if (healthy) {
+        log("Storage consistency checks passed");
+    } else {
+        error("Storage consistency checks failed");
+    }
+}