Emit when count of sessions to backup changes

This will be used in the React SDK to display upload progress when there are
many sessions to upload.

src/client.js

@@ -448,6 +448,7 @@ MatrixClient.prototype.initCrypto = async function() {
 
     this.reEmitter.reEmit(crypto, [
         "crypto.keyBackupFailed",
+        "crypto.keyBackupSessionsRemaining",
         "crypto.roomKeyRequest",
         "crypto.roomKeyRequestCancellation",
         "crypto.warning",

src/crypto/index.js

@@ -1052,6 +1052,9 @@ Crypto.prototype._backupPendingKeys = async function(limit) {
         return 0;
     }
 
+    let remaining = await this._cryptoStore.countSessionsNeedingBackup();
+    this.emit("crypto.keyBackupSessionsRemaining", remaining);
+
     const data = {};
     for (const session of sessions) {
         const roomId = session.sessionData.room_id;
@@ -1088,7 +1091,10 @@ Crypto.prototype._backupPendingKeys = async function(limit) {
         undefined, undefined, this.backupInfo.version,
         {rooms: data},
     );
+
     await this._cryptoStore.unmarkSessionsNeedingBackup(sessions);
+    remaining = await this._cryptoStore.countSessionsNeedingBackup();
+    this.emit("crypto.keyBackupSessionsRemaining", remaining);
 
     return sessions.length;
 };
@@ -1128,6 +1134,9 @@ Crypto.prototype.backupAllGroupSessions = async function(version) {
         },
     );
 
+    const remaining = await this._cryptoStore.countSessionsNeedingBackup();
+    this.emit("crypto.keyBackupSessionsRemaining", remaining);
+
     let numKeysBackedUp;
     do {
         numKeysBackedUp = await this._backupPendingKeys(KEY_BACKUP_KEYS_PER_REQUEST);

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

@@ -563,8 +563,22 @@ export class Backend {
         });
     }
 
-    unmarkSessionsNeedingBackup(sessions) {
-        const txn = this._db.transaction("sessions_needing_backup", "readwrite");
+    countSessionsNeedingBackup(txn) {
+        if (!txn) {
+            txn = this._db.transaction("sessions_needing_backup", "readonly");
+        }
+        const objectStore = txn.objectStore("sessions_needing_backup");
+        return new Promise((resolve, reject) => {
+            const req = objectStore.count();
+            req.onerror = reject;
+            req.onsuccess = () => resolve(req.result);
+        });
+    }
+
+    unmarkSessionsNeedingBackup(sessions, txn) {
+        if (!txn) {
+            txn = this._db.transaction("sessions_needing_backup", "readwrite");
+        }
         const objectStore = txn.objectStore("sessions_needing_backup");
         return Promise.all(sessions.map((session) => {
             return new Promise((resolve, reject) => {

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

@@ -480,14 +480,26 @@ export default class IndexedDBCryptoStore {
         });
     }
 
+    /**
+     * Count the inbound group sessions that need to be backed up.
+     * @param {*} txn An active transaction. See doTxn(). (optional)
+     * @returns {Promise} resolves to the number of sessions
+     */
+    countSessionsNeedingBackup(txn) {
+        return this._connect().then((backend) => {
+            return backend.countSessionsNeedingBackup(txn);
+        });
+    }
+
     /**
      * Unmark sessions as needing to be backed up.
      * @param {Array<object>} sessions The sessions that need to be backed up.
+     * @param {*} txn An active transaction. See doTxn(). (optional)
      * @returns {Promise} resolves when the sessions are unmarked
      */
-    unmarkSessionsNeedingBackup(sessions) {
+    unmarkSessionsNeedingBackup(sessions, txn) {
         return this._connect().then((backend) => {
-            return backend.unmarkSessionsNeedingBackup(sessions);
+            return backend.unmarkSessionsNeedingBackup(sessions, txn);
         });
     }
 

src/crypto/store/localStorage-crypto-store.js

@@ -221,6 +221,12 @@ export default class LocalStorageCryptoStore extends MemoryCryptoStore {
         return Promise.resolve(sessions);
     }
 
+    countSessionsNeedingBackup() {
+        const sessionsNeedingBackup
+              = getJsonItem(this.store, KEY_SESSIONS_NEEDING_BACKUP) || {};
+        return Promise.resolve(Object.keys(sessionsNeedingBackup).length);
+    }
+
     unmarkSessionsNeedingBackup(sessions) {
         const sessionsNeedingBackup
               = getJsonItem(this.store, KEY_SESSIONS_NEEDING_BACKUP) || {};

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

@@ -336,6 +336,10 @@ export default class MemoryCryptoStore {
         return Promise.resolve(sessions);
     }
 
+    countSessionsNeedingBackup() {
+        return Promise.resolve(Object.keys(this._sessionsNeedingBackup).length);
+    }
+
     unmarkSessionsNeedingBackup(sessions) {
         for (const session of sessions) {
             const sessionKey = session.senderKey + '/' + session.sessionId;