Element-R: Avoid errors in VerificationRequest.generateQRCode when …

…QR code is unavailable (#3779)

* Avoid `VerificationRequest.generateQRCode` to crash when QRCode is unavailable

* Add tests `can try to generate a QR code when QR code is not supported`

spec/integ/crypto/verification.spec.ts

@@ -498,6 +498,29 @@ describe.each(Object.entries(CRYPTO_BACKENDS))("verification (%s)", (backend: st
             expect(request.phase).toEqual(VerificationPhase.Done);
         });
 
+        it("can try to generate a QR code when QR code is not supported", async () => {
+            aliceClient = await startTestClient();
+            // we need cross-signing keys for a QR code verification
+            e2eKeyResponder.addCrossSigningData(SIGNED_CROSS_SIGNING_KEYS_DATA);
+            await waitForDeviceList();
+
+            // Alice sends a m.key.verification.request
+            const [, request] = await Promise.all([
+                expectSendToDeviceMessage("m.key.verification.request"),
+                aliceClient.getCrypto()!.requestDeviceVerification(TEST_USER_ID, TEST_DEVICE_ID),
+            ]);
+            const transactionId = request.transactionId!;
+
+            // The dummy device replies with an m.key.verification.ready, indicating it can only use SaS
+            returnToDeviceMessageFromSync(buildReadyMessage(transactionId, ["m.sas.v1"]));
+            await waitForVerificationRequestChanged(request);
+            expect(request.phase).toEqual(VerificationPhase.Ready);
+
+            // Alice tries to generate a QR Code but it's unavailable
+            const qrCodeBuffer = await request.generateQRCode();
+            expect(qrCodeBuffer).toBeUndefined();
+        });
+
         newBackendOnly("can verify another by scanning their QR code", async () => {
             aliceClient = await startTestClient();
             // we need cross-signing keys for a QR code verification

src/rust-crypto/verification.ts

@@ -392,7 +392,10 @@ export class RustVerificationRequest
      * Implementation of {@link Crypto.VerificationRequest#generateQRCode}.
      */
     public async generateQRCode(): Promise<Buffer | undefined> {
-        const innerVerifier: RustSdkCryptoJs.Qr = await this.inner.generateQrCode();
+        const innerVerifier: RustSdkCryptoJs.Qr | undefined = await this.inner.generateQrCode();
+        // If we are unable to generate a QRCode, we return undefined
+        if (!innerVerifier) return;
+
         return Buffer.from(innerVerifier.toBytes());
     }