[flutter_tools] optimize fetch requests and remove main.dart.js bypass (#66069)

The main.dart.js bypass is not needed now that we have skipWaiting. Additionally optimize the fetch handler so that resources not in the cache skip the service worker altogether.

Fixes #66068

packages/flutter_tools/lib/src/build_system/targets/web.dart

@@ -334,16 +334,12 @@ class WebReleaseBundle extends Target {
         outputFile.parent.createSync(recursive: true);
       }
       outputResourcesFiles.add(outputFile);
-      // insert a random hash into the requests for main.dart.js and service_worker.js. This is
-      // not a content hash, because it would need to be the hash for the entire bundle and not
-      // just the resource in question.
+      // insert a random hash into the requests for service_worker.js. This is not a content hash,
+      // because it would need to be the hash for the entire bundle and not just the resource
+      // in question.
       if (environment.fileSystem.path.basename(inputFile.path) == 'index.html') {
         final String randomHash = Random().nextInt(4294967296).toString();
         final String resultString = inputFile.readAsStringSync()
-          .replaceFirst(
-            '<script src="main.dart.js" type="application/javascript"></script>',
-            '<script src="main.dart.js?v=$randomHash" type="application/javascript"></script>'
-          )
           .replaceFirst(
             "navigator.serviceWorker.register('flutter_service_worker.js')",
             "navigator.serviceWorker.register('flutter_service_worker.js?v=$randomHash')",
@@ -476,7 +472,7 @@ const CORE = [
   ${coreBundle.map((String file) => '"$file"').join(',\n')}];
 // During install, the TEMP cache is populated with the application shell files.
 self.addEventListener("install", (event) => {
-  skipWaiting();
+  self.skipWaiting();
   return event.waitUntil(
     caches.open(TEMP).then((cache) => {
       return cache.addAll(
@@ -545,6 +541,9 @@ self.addEventListener("activate", function(event) {
 // The fetch handler redirects requests for RESOURCE files to the service
 // worker cache.
 self.addEventListener("fetch", (event) => {
+  if (event.request.method !== 'GET') {
+    return;
+  }
   var origin = self.location.origin;
   var key = event.request.url.substring(origin.length + 1);
   // Redirect URLs to the index.html
@@ -554,9 +553,10 @@ self.addEventListener("fetch", (event) => {
   if (event.request.url == origin || event.request.url.startsWith(origin + '/#') || key == '') {
     key = '/';
   }
-  // If the URL is not the RESOURCE list, skip the cache.
+  // If the URL is not the RESOURCE list then return to signal that the
+  // browser should take over.
   if (!RESOURCES[key]) {
-    return event.respondWith(fetch(event.request));
+    return;
   }
   // If the URL is the index.html, perform an online-first request.
   if (key == '/') {
@@ -580,7 +580,7 @@ self.addEventListener('message', (event) => {
   // SkipWaiting can be used to immediately activate a waiting service worker.
   // This will also require a page refresh triggered by the main worker.
   if (event.data === 'skipWaiting') {
-    skipWaiting();
+    self.skipWaiting();
     return;
   }
   if (event.data === 'downloadOffline') {
@@ -631,11 +631,5 @@ function onlineFirst(event) {
     })
   );
 }
-
-function skipWaiting() {
-  if (self.skipWaiting != undefined) {
-    self.skipWaiting();
-  }
-}
 ''';
 }

packages/flutter_tools/test/general.shard/build_system/targets/web_test.dart

@@ -136,9 +136,9 @@ void main() {
 
     expect(environment.outputDir.childFile('foo.txt')
       .readAsStringSync(), 'B');
-    // Appends number to requests for service worker and main.dart.js
+    // Appends number to requests for service worker only
     expect(environment.outputDir.childFile('index.html').readAsStringSync(), allOf(
-      contains('<script src="main.dart.js?v='),
+      contains('<script src="main.dart.js" type="application/javascript">'),
       contains('flutter_service_worker.js?v='),
     ));
   }));