Signal key backup in cache (#3928)

* Signal key backup in cache

* code review

* quick doc

* code review

spec/integ/crypto/verification.spec.ts

@@ -1259,14 +1259,11 @@ describe.each(Object.entries(CRYPTO_BACKENDS))("verification (%s)", (backend: st
 
             const requestId = await requestPromises.get("m.megolm_backup.v1");
 
+            const keyBackupIsCached = emitPromise(aliceClient, CryptoEvent.KeyBackupDecryptionKeyCached);
+
             await sendBackupGossipAndExpectVersion(requestId!, BACKUP_DECRYPTION_KEY_BASE64, matchingBackupInfo);
 
-            // We are lacking a way to signal that the secret has been received, so we wait a bit..
-            jest.useRealTimers();
-            await new Promise((resolve) => {
-                setTimeout(resolve, 500);
-            });
-            jest.useFakeTimers();
+            await keyBackupIsCached;
 
             // the backup secret should be cached
             const cachedKey = await aliceClient.getCrypto()!.getSessionBackupPrivateKey();

src/client.ts

@@ -951,6 +951,7 @@ type CryptoEvents =
     | CryptoEvent.KeyBackupStatus
     | CryptoEvent.KeyBackupFailed
     | CryptoEvent.KeyBackupSessionsRemaining
+    | CryptoEvent.KeyBackupDecryptionKeyCached
     | CryptoEvent.RoomKeyRequest
     | CryptoEvent.RoomKeyRequestCancellation
     | CryptoEvent.VerificationRequest
@@ -2359,6 +2360,7 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
             CryptoEvent.KeyBackupStatus,
             CryptoEvent.KeyBackupSessionsRemaining,
             CryptoEvent.KeyBackupFailed,
+            CryptoEvent.KeyBackupDecryptionKeyCached,
         ]);
     }
 

src/crypto/index.ts

@@ -232,6 +232,18 @@ export enum CryptoEvent {
     KeyBackupStatus = "crypto.keyBackupStatus",
     KeyBackupFailed = "crypto.keyBackupFailed",
     KeyBackupSessionsRemaining = "crypto.keyBackupSessionsRemaining",
+
+    /**
+     * Fires when a new valid backup decryption key is in cache.
+     * This will happen when a secret is received from another session, from secret storage,
+     * or when a new backup is created from this session.
+     *
+     * The payload is the version of the backup for which we have the key for.
+     *
+     * This event is only fired by the rust crypto backend.
+     */
+    KeyBackupDecryptionKeyCached = "crypto.keyBackupDecryptionKeyCached",
+
     KeySignatureUploadFailure = "crypto.keySignatureUploadFailure",
     /** @deprecated Use `VerificationRequestReceived`. */
     VerificationRequest = "crypto.verification.request",
@@ -297,6 +309,13 @@ export type CryptoEventHandlerMap = {
     [CryptoEvent.KeyBackupStatus]: (enabled: boolean) => void;
     [CryptoEvent.KeyBackupFailed]: (errcode: string) => void;
     [CryptoEvent.KeyBackupSessionsRemaining]: (remaining: number) => void;
+
+    /**
+     * Fires when the backup decryption key is received and cached.
+     *
+     * @param version - The version of the backup for which we have the key for.
+     */
+    [CryptoEvent.KeyBackupDecryptionKeyCached]: (version: string) => void;
     [CryptoEvent.KeySignatureUploadFailure]: (
         failures: IUploadKeySignaturesResponse["failures"],
         source: "checkOwnCrossSigningTrust" | "afterCrossSigningLocalKeyChange" | "setDeviceVerification",

src/rust-crypto/backup.ts

@@ -154,8 +154,7 @@ export class RustBackupManager extends TypedEventEmitter<RustBackupCryptoEvents,
             logger.info(
                 `handleBackupSecretReceived: A valid backup decryption key has been received and stored in cache.`,
             );
-
-            await this.olmMachine.saveBackupDecryptionKey(backupDecryptionKey, backupCheck.backupInfo.version);
+            await this.saveBackupDecryptionKey(backupDecryptionKey, backupCheck.backupInfo.version);
             return true;
         } catch (e) {
             logger.warn("handleBackupSecretReceived: Invalid backup decryption key", e);
@@ -164,6 +163,16 @@ export class RustBackupManager extends TypedEventEmitter<RustBackupCryptoEvents,
         return false;
     }
 
+    public async saveBackupDecryptionKey(
+        backupDecryptionKey: RustSdkCryptoJs.BackupDecryptionKey,
+        version: string,
+    ): Promise<void> {
+        await this.olmMachine.saveBackupDecryptionKey(backupDecryptionKey, version);
+        // Emit an event that we have a new backup decryption key, so that the sdk can start
+        // importing keys from backup if needed.
+        this.emit(CryptoEvent.KeyBackupDecryptionKeyCached, version);
+    }
+
     private keyBackupCheckInProgress: Promise<KeyBackupCheck | null> | null = null;
 
     /** Helper for `checkKeyBackup` */
@@ -393,7 +402,7 @@ export class RustBackupManager extends TypedEventEmitter<RustBackupCryptoEvents,
             },
         );
 
-        this.olmMachine.saveBackupDecryptionKey(randomKey, res.version);
+        await this.saveBackupDecryptionKey(randomKey, res.version);
 
         return {
             version: res.version,
@@ -503,10 +512,12 @@ export class RustBackupDecryptor implements BackupDecryptor {
 export type RustBackupCryptoEvents =
     | CryptoEvent.KeyBackupStatus
     | CryptoEvent.KeyBackupSessionsRemaining
-    | CryptoEvent.KeyBackupFailed;
+    | CryptoEvent.KeyBackupFailed
+    | CryptoEvent.KeyBackupDecryptionKeyCached;
 
 export type RustBackupCryptoEventMap = {
     [CryptoEvent.KeyBackupStatus]: (enabled: boolean) => void;
     [CryptoEvent.KeyBackupSessionsRemaining]: (remaining: number) => void;
     [CryptoEvent.KeyBackupFailed]: (errCode: string) => void;
+    [CryptoEvent.KeyBackupDecryptionKeyCached]: (version: string) => void;
 };

src/rust-crypto/rust-crypto.ts

@@ -150,6 +150,7 @@ export class RustCrypto extends TypedEventEmitter<RustCryptoEvents, RustCryptoEv
             CryptoEvent.KeyBackupStatus,
             CryptoEvent.KeyBackupSessionsRemaining,
             CryptoEvent.KeyBackupFailed,
+            CryptoEvent.KeyBackupDecryptionKeyCached,
         ]);
 
         this.crossSigningIdentity = new CrossSigningIdentity(olmMachine, this.outgoingRequestProcessor, secretStorage);
@@ -1148,7 +1149,7 @@ export class RustCrypto extends TypedEventEmitter<RustCryptoEvents, RustCryptoEv
             throw new Error("storeSessionBackupPrivateKey: version is required");
         }
 
-        await this.olmMachine.saveBackupDecryptionKey(
+        await this.backupManager.saveBackupDecryptionKey(
             RustSdkCryptoJs.BackupDecryptionKey.fromBase64(base64Key),
             version,
         );
@@ -1867,4 +1868,6 @@ type RustCryptoEventMap = {
      * Fires when the trust status of a user changes.
      */
     [CryptoEvent.UserTrustStatusChanged]: (userId: string, userTrustLevel: UserVerificationStatus) => void;
+
+    [CryptoEvent.KeyBackupDecryptionKeyCached]: (version: string) => void;
 } & RustBackupCryptoEventMap;