Support for exporting megolm session data

src/client.js

@@ -461,6 +461,21 @@ MatrixClient.prototype.isRoomEncrypted = function(roomId) {
     return this._crypto.isRoomEncrypted(roomId);
 };
 
+/**
+ * Get a list containing all of the room keys
+ *
+ * This should be encrypted before returning it to the user.
+ *
+ * @return {module:client.Promise} a promise which resolves to a list of
+ *    session export objects
+ */
+MatrixClient.prototype.exportRoomKeys = function() {
+    if (!this._crypto) {
+        return q.reject(new Error("End-to-end encryption disabled"));
+    }
+    return this._crypto.exportRoomKeys();
+};
+
 /**
  * Decrypt a received event according to the algorithm specified in the event.
  *

src/crypto/OlmDevice.js

@@ -739,6 +739,41 @@ OlmDevice.prototype.decryptGroupMessage = function(
     );
 };
 
+/**
+ * Export an inbound group session
+ *
+ * @param {string} senderKey base64-encoded curve25519 key of the sender
+ * @param {string} sessionId session identifier
+ * @return {object} exported session data
+ */
+OlmDevice.prototype.exportInboundGroupSession = function(senderKey, sessionId) {
+    const s = this._sessionStore.getEndToEndInboundGroupSession(
+        senderKey, sessionId
+    );
+
+    if (s === null) {
+        throw new Error("Unknown inbound group session [" + senderKey + "," +
+                        sessionId + "]");
+    }
+    const r = JSON.parse(s);
+
+    const session = new Olm.InboundGroupSession();
+    try {
+        session.unpickle(this._pickleKey, r.session);
+
+        const messageIndex = session.first_known_index();
+
+        return {
+            "sender_key": senderKey,
+            "sender_claimed_keys": r.keysClaimed,
+            "room_id": r.room_id,
+            "session_id": sessionId,
+            "session_key": session.export_session(messageIndex),
+        };
+    } finally {
+        session.free();
+    }
+};
 
 // Utilities
 // =========

src/crypto/index.js

@@ -897,6 +897,28 @@ Crypto.prototype.isRoomEncrypted = function(roomId) {
     return Boolean(this._roomEncryptors[roomId]);
 };
 
+
+/**
+ * Get a list containing all of the room keys
+ *
+ * @return {module:client.Promise} a promise which resolves to a list of
+ *    session export objects
+ */
+Crypto.prototype.exportRoomKeys = function() {
+    return q(
+        this._sessionStore.getAllEndToEndInboundGroupSessionKeys().map(
+            (s) => {
+                const sess = this._olmDevice.exportInboundGroupSession(
+                    s.senderKey, s.sessionId
+                );
+
+                sess.algorithm = olmlib.MEGOLM_ALGORITHM;
+                return sess;
+            }
+        )
+    );
+};
+
 /**
  * Encrypt an event according to the configuration of the room, if necessary.
  *

src/store/session/webstorage.js

@@ -37,7 +37,10 @@ function WebStorageSessionStore(webStore) {
     this.store = webStore;
     if (!utils.isFunction(webStore.getItem) ||
         !utils.isFunction(webStore.setItem) ||
-        !utils.isFunction(webStore.removeItem)) {
+        !utils.isFunction(webStore.removeItem) ||
+        !utils.isFunction(webStore.key) ||
+        typeof(webStore.length) !== 'number'
+       ) {
         throw new Error(
             "Supplied webStore does not meet the WebStorage API interface"
         );
@@ -120,6 +123,32 @@ WebStorageSessionStore.prototype = {
         return getJsonItem(this.store, keyEndToEndSessions(deviceKey));
     },
 
+    /**
+     * Retrieve a list of all known inbound group sessions
+     *
+     * @return {{senderKey: string, sessionId: string}}
+     */
+    getAllEndToEndInboundGroupSessionKeys: function() {
+        const prefix = E2E_PREFIX + 'inboundgroupsessions/';
+        const result = [];
+        for (let i = 0; i < this.store.length; i++) {
+            const key = this.store.key(i);
+            if (!key.startsWith(prefix)) {
+                continue;
+            }
+            // we can't use split, as the components we are trying to split out
+            // might themselves contain '/' characters. We rely on the
+            // senderKey being a (32-byte) curve25519 key, base64-encoded
+            // (hence 43 characters long).
+
+            result.push({
+                senderKey: key.substr(prefix.length, 43),
+                sessionId: key.substr(prefix.length + 44),
+            });
+        }
+        return result;
+    },
+
     getEndToEndInboundGroupSession: function(senderKey, sessionId) {
         let key = keyEndToEndInboundGroupSession(senderKey, sessionId);
         return this.store.getItem(key);