Catch errors in debug token exchange logic

.changeset/tough-kiwis-smile.md

@@ -0,0 +1,5 @@
+---
+'@firebase/app-check': patch
+---
+
+Fixed a bug that caused an error to be thrown when the debug exchange failed.

packages/app-check/src/internal-api.test.ts

@@ -176,6 +176,29 @@ describe('internal api', () => {
       errorStub.restore();
     });
 
+    it('resolves with a dummy token and an error if failed to get a token in debug mode', async () => {
+      const errorStub = stub(console, 'error');
+      window.FIREBASE_APPCHECK_DEBUG_TOKEN = true;
+      const appCheck = initializeAppCheck(app, {
+        provider: new ReCaptchaV3Provider(FAKE_SITE_KEY)
+      });
+
+      const error = new Error('oops, something went wrong');
+      stub(client, 'exchangeToken').returns(Promise.reject(error));
+
+      const token = await getToken(appCheck as AppCheckService);
+
+      expect(token).to.deep.equal({
+        token: formatDummyToken(defaultTokenErrorData),
+        error
+      });
+      expect(errorStub.args[0][1].message).to.include(
+        'oops, something went wrong'
+      );
+      delete window.FIREBASE_APPCHECK_DEBUG_TOKEN;
+      errorStub.restore();
+    });
+
     it('resolves with a dummy token and an error if recaptcha failed', async () => {
       const errorStub = stub(console, 'error');
       const appCheck = initializeAppCheck(app, {

packages/app-check/src/internal-api.ts

@@ -116,24 +116,36 @@ export async function getToken(
    * Check token using the debug token, and return it directly.
    */
   if (isDebugMode()) {
-    // Avoid making another call to the exchange endpoint if one is in flight.
-    if (!state.exchangeTokenPromise) {
-      state.exchangeTokenPromise = exchangeToken(
-        getExchangeDebugTokenRequest(app, await getDebugToken()),
-        appCheck.heartbeatServiceProvider
-      ).finally(() => {
-        // Clear promise when settled - either resolved or rejected.
-        state.exchangeTokenPromise = undefined;
-      });
-      shouldCallListeners = true;
+    try {
+      // Avoid making another call to the exchange endpoint if one is in flight.
+      if (!state.exchangeTokenPromise) {
+        state.exchangeTokenPromise = exchangeToken(
+          getExchangeDebugTokenRequest(app, await getDebugToken()),
+          appCheck.heartbeatServiceProvider
+        ).finally(() => {
+          // Clear promise when settled - either resolved or rejected.
+          state.exchangeTokenPromise = undefined;
+        });
+        shouldCallListeners = true;
+      }
+      const tokenFromDebugExchange: AppCheckTokenInternal =
+        await state.exchangeTokenPromise;
+      // Write debug token to indexedDB.
+      await writeTokenToStorage(app, tokenFromDebugExchange);
+      // Write debug token to state.
+      state.token = tokenFromDebugExchange;
+      return { token: tokenFromDebugExchange.token };
+    } catch (e) {
+      if ((e as FirebaseError).code === `appCheck/${AppCheckError.THROTTLED}`) {
+        // Warn if throttled, but do not treat it as an error.
+        logger.warn((e as FirebaseError).message);
+      } else {
+        // `getToken()` should never throw, but logging error text to console will aid debugging.
+        logger.error(e);
+      }
+      // Return dummy token and error
+      return makeDummyTokenResult(e as FirebaseError);
     }
-    const tokenFromDebugExchange: AppCheckTokenInternal =
-      await state.exchangeTokenPromise;
-    // Write debug token to indexedDB.
-    await writeTokenToStorage(app, tokenFromDebugExchange);
-    // Write debug token to state.
-    state.token = tokenFromDebugExchange;
-    return { token: tokenFromDebugExchange.token };
   }
 
   /**