add high-level export/import methods

not sure how to test these high-level methods though

src/client.js

@@ -97,6 +97,11 @@ function keyFromRecoverySession(session, decryptionKey) {
  * @param {string} opts.accessToken The access_token for this user.
  *
  * @param {string} opts.userId The user ID for this user.
+ * 
+ * @param {Object} opts.deviceToImport Device data exported with
+ *     (TODO link to export method) that must be imported to recreate this device.
+ *     Should only be useful for deviced with end-to-end crypto enabled.
+ *     If provided, opts.userId should **not** be provided.
  *
  * @param {IdentityServerProvider} [opts.identityServer]
  * Optional. A provider object with one function `getAccessToken`, which is a
@@ -243,6 +248,18 @@ export function MatrixClient(opts) {
 
     this.deviceId = opts.deviceId || null;
 
+    if (opts.deviceToImport) {
+        if (this.deviceId) {
+            logger.warn('not importing device because device ID is provided to constructor independently of exported data');
+        } else if (!(opts.deviceToImport.deviceId)){
+            logger.warn('not importing device because no device ID in exported data');
+        } else {
+            this.deviceId = opts.deviceToImport.deviceId;
+            // will be used during async initialization of the crypto
+            this._exportedOlmDeviceToImport = opts.deviceToImport.olmDevice;
+        }
+    }
+
     const userId = (opts.userId || null);
     this.credentials = {
         userId: userId,
@@ -391,6 +408,17 @@ export function MatrixClient(opts) {
 utils.inherits(MatrixClient, EventEmitter);
 utils.extend(MatrixClient.prototype, MatrixBaseApis.prototype);
 
+MatrixClient.prototype.exportDevice = async function() {
+    if (!(this._crypto)) {
+        logger.warn('not exporting device if crypto is not enabled');
+        return;
+    }
+    return {
+        deviceId: this.deviceId,
+        olmDevice: await this._crypto._olmDevice.export(),
+    };
+};
+
 /**
  * Clear any data out of the persistent stores used by the client.
  *
@@ -684,7 +712,10 @@ MatrixClient.prototype.initCrypto = async function() {
     ]);
 
     logger.log("Crypto: initialising crypto object...");
-    await crypto.init();
+    await crypto.init({
+        exportedOlmDevice: this._exportedOlmDeviceToImport,
+    });
+    delete this._exportedOlmDeviceToImport;
 
     this.olmVersion = Crypto.getOlmVersion();
 

src/crypto/OlmDevice.js

@@ -225,7 +225,7 @@ OlmDevice.prototype._storeAccount = function(txn, account) {
  * Export data for re-creating the Olm device later.
  * TODO export data other than just account and (P2P) sessions.
  * 
- * @return {Promise<object>} The export data (see specs for structure)
+ * @return {Promise<object>} The exported data
 */
 OlmDevice.prototype.export = async function() {
     const result = {

src/crypto/index.js

@@ -228,12 +228,24 @@ utils.inherits(Crypto, EventEmitter);
  * Initialise the crypto module so that it is ready for use
  *
  * Returns a promise which resolves once the crypto module is ready for use.
+ * 
+ * @param {Object} kwargs keyword arguments.
+ * @param {string} kwargs.exportedOlmDevice (Optional) data from exported device
+ *     that must be re-created.
  */
-Crypto.prototype.init = async function() {
+Crypto.prototype.init = async function(kwargs) {
+    const {
+        exportedOlmDevice,
+    } = kwargs;
+
     logger.log("Crypto: initialising Olm...");
     await global.Olm.init();
-    logger.log("Crypto: initialising Olm device...");
+    logger.log(
-    await this._olmDevice.init();
+        exportedOlmDevice
+            ? "Crypto: initialising Olm device from exported device..."
+            : "Crypto: initialising Olm device..."
+    );
+    await this._olmDevice.init(exportedOlmDevice);
     logger.log("Crypto: loading device list...");
     await this._deviceList.load();