rn: evaluate config.js in a sandboxed environment

We are downloading code off the Internet and executing it on the user's device,
so run it sandboxed to avoid potential bad actors.

Since it's impossible to eval() safely in JS and React Native doesn't offer
something akin to Node's vm module, here we are rolling our own.

On Android it uses the Duktape JavaScript engine and on iOS the builtin
JavaScriptCore engine. The extra JS engine is *only* used for evaluating the
downloaded code and returning a JSON string which is then passed back to RN.

react/features/base/lib-jitsi-meet/functions.any.js

@@ -1,12 +1,7 @@
 // @flow
 
 import { toState } from '../redux';
-import { loadScript } from '../util';
-
 import JitsiMeetJS from './_';
-import logger from './logger';
-
-declare var APP: Object;
 
 const JitsiConferenceErrors = JitsiMeetJS.errors.conference;
 const JitsiConnectionErrors = JitsiMeetJS.errors.connection;
@@ -97,42 +92,3 @@ export function isFatalJitsiConnectionError(error: Object | string) {
             || error === JitsiConnectionErrors.OTHER_ERROR
             || error === JitsiConnectionErrors.SERVER_ERROR);
 }
-
-/**
- * Loads config.js from a specific remote server.
- *
- * @param {string} url - The URL to load.
- * @returns {Promise<Object>}
- */
-export function loadConfig(url: string): Promise<Object> {
-    let promise;
-
-    if (typeof APP === 'undefined') {
-        promise
-            = loadScript(url, 2.5 * 1000 /* Timeout in ms */)
-                .then(() => {
-                    const { config } = window;
-
-                    // We don't want to pollute the global scope.
-                    window.config = undefined;
-
-                    if (typeof config !== 'object') {
-                        throw new Error('window.config is not an object');
-                    }
-
-                    return config;
-                })
-                .catch(err => {
-                    logger.error(`Failed to load config from ${url}`, err);
-
-                    throw err;
-                });
-    } else {
-        // Return "the config.js file" from the global scope - that is how the
-        // Web app on both the client and the server was implemented before the
-        // React Native app was even conceived.
-        promise = Promise.resolve(window.config);
-    }
-
-    return promise;
-}

react/features/base/lib-jitsi-meet/functions.native.js

@@ -0,0 +1,36 @@
+// @flow
+
+import { NativeModules } from 'react-native';
+
+import { loadScript } from '../util';
+import logger from './logger';
+
+export * from './functions.any';
+
+const { JavaScriptSandbox } = NativeModules;
+
+/**
+ * Loads config.js from a specific remote server.
+ *
+ * @param {string} url - The URL to load.
+ * @returns {Promise<Object>}
+ */
+export async function loadConfig(url: string): Promise<Object> {
+    try {
+        const configTxt = await loadScript(url, 2.5 * 1000 /* Timeout in ms */, true /* skipeval */);
+        const configJson = await JavaScriptSandbox.evaluate(`${configTxt}\nJSON.stringify(config);`);
+        const config = JSON.parse(configJson);
+
+        if (typeof config !== 'object') {
+            throw new Error('config is not an object');
+        }
+
+        logger.info(`Config loaded from ${url}`);
+
+        return config;
+    } catch (err) {
+        logger.error(`Failed to load config from ${url}`, err);
+
+        throw err;
+    }
+}

react/features/base/lib-jitsi-meet/functions.web.js

@@ -0,0 +1,16 @@
+// @flow
+
+export * from './functions.any';
+
+/**
+ * Loads config.js from a specific remote server.
+ *
+ * @param {string} url - The URL to load.
+ * @returns {Promise<Object>}
+ */
+export async function loadConfig(url: string): Promise<Object> { // eslint-disable-line no-unused-vars
+    // Return "the config.js file" from the global scope - that is how the
+    // Web app on both the client and the server was implemented before the
+    // React Native app was even conceived.
+    return window.config;
+}