Add CryptoApi.getBackupInfo (#4512)

* Add `CryptoApi.getBackupInfo`

* improve doc

spec/unit/crypto/backup.spec.ts

@@ -780,4 +780,12 @@ describe("MegolmBackup", function () {
             client.stopClient();
         });
     });
+
+    describe("getKeyBackupInfo", () => {
+        it("should return throw an `Not implemented`", async () => {
+            const client = makeTestClient(cryptoStore);
+            await client.initCrypto();
+            await expect(client.getCrypto()?.getKeyBackupInfo()).rejects.toThrow("Not implemented");
+        });
+    });
 });

spec/unit/rust-crypto/rust-crypto.spec.ts

@@ -1526,6 +1526,20 @@ describe("RustCrypto", () => {
                 failures: 1,
             });
         });
+
+        describe("getKeyBackupInfo", () => {
+            it("should return the current key backup info", async () => {
+                fetchMock.get("path:/_matrix/client/v3/room_keys/version", testData.SIGNED_BACKUP_DATA);
+
+                const rustCrypto = await makeTestRustCrypto(makeMatrixHttpApi());
+                await expect(rustCrypto.getKeyBackupInfo()).resolves.toStrictEqual(testData.SIGNED_BACKUP_DATA);
+            });
+
+            it("should return null if not available", async () => {
+                const rustCrypto = await makeTestRustCrypto(makeMatrixHttpApi());
+                await expect(rustCrypto.getKeyBackupInfo()).resolves.toBeNull();
+            });
+        });
     });
 
     describe("device dehydration", () => {

src/client.ts

@@ -3359,7 +3359,7 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
      *
      * @returns Information object from API, or null if no backup is present on the server.
      *
-     * @deprecated Prefer {@link CryptoApi.getActiveSessionBackupVersion}.
+     * @deprecated Prefer {@link CryptoApi.getKeyBackupInfo}.
      */
     public async getKeyBackupVersion(): Promise<IKeyBackupInfo | null> {
         let res: IKeyBackupInfo;

src/crypto-api/index.ts

@@ -534,6 +534,18 @@ export interface CryptoApi {
      */
     isKeyBackupTrusted(info: KeyBackupInfo): Promise<BackupTrustInfo>;
 
+    /**
+     * Return the details of the latest backup on the server, when we last checked.
+     *
+     * This normally returns a cached value, but if we haven't yet made a request to the server, it will fire one off.
+     * It will always return the details of the active backup if key backup is enabled.
+     *
+     * Return null if there is no backup.
+     *
+     * @returns the key backup information
+     */
+    getKeyBackupInfo(): Promise<KeyBackupInfo | null>;
+
     /**
      * Force a re-check of the key backup and enable/disable it as appropriate.
      *

src/crypto/index.ts

@@ -1327,6 +1327,13 @@ export class Crypto extends TypedEventEmitter<CryptoEvent, CryptoEventHandlerMap
         return null;
     }
 
+    /**
+     * Implementation of {@link Crypto.CryptoApi#getKeyBackupInfo}.
+     */
+    public async getKeyBackupInfo(): Promise<KeyBackupInfo | null> {
+        throw new Error("Not implemented");
+    }
+
     /**
      * Determine if a key backup can be trusted.
      *

src/rust-crypto/rust-crypto.ts

@@ -1233,6 +1233,13 @@ export class RustCrypto extends TypedEventEmitter<RustCryptoEvents, CryptoEventH
         return await this.backupManager.getActiveBackupVersion();
     }
 
+    /**
+     * Implementation of {@link CryptoApi#getKeyBackupInfo}.
+     */
+    public async getKeyBackupInfo(): Promise<KeyBackupInfo | null> {
+        return (await this.backupManager.getServerBackupInfo()) || null;
+    }
+
     /**
      * Determine if a key backup can be trusted.
      *