fix(service-worker): ensure initialization in handleMessage()

- community members with this issue have tested this fix
  - @hsta verified that users have not seen the issue with this fix
    through all of August
- resolves "Invariant violated (initialize): latest hash null has no known manifest"

Fixes #25611

packages/service-worker/worker/src/driver.ts

@@ -295,7 +295,32 @@ export class Driver implements Debuggable, UpdateSource {
     event.waitUntil(this.handleClick(event.notification, event.action));
   }
 
+  private async ensureInitialized(): Promise<void> {
+    // Since the SW may have just been started, it may or may not have been initialized already.
+    // this.initialized will be null if initialization has not yet been attempted, or will be a
+    // Promise which will resolve (successfully or unsuccessfully) if it has.
+    if (this.initialized === null) {
+      // Initialization has not yet been attempted, so attempt it. This should only ever happen once
+      // per SW instantiation.
+      this.initialized = this.initialize();
+    }
+
+    // If initialization fails, the SW needs to enter a safe state, where it declines to respond to
+    // network requests.
+    try {
+      // Wait for initialization.
+      await this.initialized;
+    } catch (error) {
+      // Initialization failed. Enter a safe state.
+      this.state = DriverReadyState.SAFE_MODE;
+      this.stateMessage = `Initialization failed due to error: ${errorToString(error)}`;
+      throw error;
+    }
+  }
+
   private async handleMessage(msg: MsgAny&{action: string}, from: Client): Promise<void> {
+    await this.ensureInitialized();
+
     if (isMsgCheckForUpdates(msg)) {
       const action = (async() => { await this.checkForUpdate(); })();
       await this.reportStatus(from, action, msg.statusNonce);
@@ -383,32 +408,7 @@ export class Driver implements Debuggable, UpdateSource {
   }
 
   private async handleFetch(event: FetchEvent): Promise<Response> {
-    // Since the SW may have just been started, it may or may not have been initialized already.
-    // this.initialized will be `null` if initialization has not yet been attempted, or will be a
-    // Promise which will resolve (successfully or unsuccessfully) if it has.
-    if (this.initialized === null) {
-      // Initialization has not yet been attempted, so attempt it. This should only ever happen once
-      // per SW instantiation.
-      this.initialized = this.initialize();
-    }
-
-    // If initialization fails, the SW needs to enter a safe state, where it declines to respond to
-    // network requests.
-    try {
-      // Wait for initialization.
-      await this.initialized;
-    } catch (e) {
-      // Initialization failed. Enter a safe state.
-      this.state = DriverReadyState.SAFE_MODE;
-      this.stateMessage = `Initialization failed due to error: ${errorToString(e)}`;
-
-      // Even though the driver entered safe mode, background tasks still need to happen.
-      event.waitUntil(this.idle.trigger());
-
-      // Since the SW is already committed to responding to the currently active request,
-      // respond with a network fetch.
-      return this.safeFetch(event.request);
-    }
+    await this.ensureInitialized();
 
     // On navigation requests, check for new updates.
     if (event.request.mode === 'navigate' && !this.scheduledNavUpdateCheck) {

packages/service-worker/worker/test/happy_spec.ts

@@ -366,6 +366,15 @@ import {SwTestHarness, SwTestHarnessBuilder} from '../testing/scope';
       server.assertNoOtherRequests();
     });
 
+    it('initializes the service worker on fetch if it has not yet been initialized', async() => {
+      expect(await makeRequest(scope, '/foo.txt')).toEqual('this is foo');
+      server.assertSawRequestFor('ngsw.json');
+      server.assertSawRequestFor('/foo.txt');
+      server.assertSawRequestFor('/bar.txt');
+      server.assertSawRequestFor('/redirected.txt');
+      server.assertNoOtherRequests();
+    });
+
     it('handles non-relative URLs', async() => {
       expect(await makeRequest(scope, '/foo.txt')).toEqual('this is foo');
       await driver.initialized;