patch flutter web to load faster

build_tools/patch_web.sh

@@ -0,0 +1,6 @@
+#!/usr/bin/env sh
+
+set -e
+
+patch build/web/flutter.js < build_tools/web/flutter.js.patch
+patch build/web/flutter_service_worker.js < build_tools/web/flutter_service_worker.js.patch

build_tools/web/flutter.js.patch

@@ -0,0 +1,20 @@
+--- build/web/flutter.js.orig	2023-03-01 15:40:58.588065610 +0800
++++ build/web/flutter.js	2023-03-01 15:43:48.879605009 +0800
+@@ -375,7 +375,16 @@
+       // Install the `didCreateEngineInitializer` listener where Flutter web expects it to be.
+       this.didCreateEngineInitializer =
+         entrypointLoader.didCreateEngineInitializer.bind(entrypointLoader);
+-      return entrypointLoader.loadEntrypoint(entrypoint);
++      const main = entrypointLoader.loadEntrypoint(entrypoint);
++
++      fetch("canvaskit/canvaskit.js");
++      fetch("canvaskit/canvaskit.wasm");
++      fetch("assets/FontManifest.json");
++      fetch("assets/fonts/MaterialIcons-Regular.otf");
++      fetch("assets/packages/cupertino_icons/assets/CupertinoIcons.ttf");
++      fetch("/");
++
++      return main;
+     }
+   }
+

build_tools/web/flutter_service_worker.js.patch

@@ -0,0 +1,62 @@
+--- build/web/flutter_service_worker.js.orig	2023-02-14 05:46:14.641558233 +0800
++++ build/web/flutter_service_worker.js	2023-02-14 05:48:16.339943489 +0800
+@@ -29,21 +29,6 @@
+ "/": "edf4d01f5266c63075af78507efdc906"};
+ // The application shell files that are downloaded before a service worker can
+ // start.
+-const CORE = ["main.dart.js",
+-"index.html",
+-"assets/AssetManifest.json",
+-"assets/FontManifest.json"];
+-
+-// During install, the TEMP cache is populated with the application shell files.
+-self.addEventListener("install", (event) => {
+-  self.skipWaiting();
+-  return event.waitUntil(
+-    caches.open(TEMP).then((cache) => {
+-      return cache.addAll(
+-        CORE.map((value) => new Request(value, {'cache': 'reload'})));
+-    })
+-  );
+-});
+ // During activate, the cache is populated with the temp files downloaded in
+ // install. If this service worker is upgrading from one with a saved
+ // MANIFEST, then use this to retain unchanged resource files.
+@@ -104,6 +89,7 @@
+     }
+   }());
+ });
++var IN_PROCESSING_REQUESTS = {};
+ // The fetch handler redirects requests for RESOURCE files to the service
+ // worker cache.
+ self.addEventListener("fetch", (event) => {
+@@ -133,12 +119,27 @@
+       return cache.match(event.request).then((response) => {
+         // Either respond with the cached resource, or perform a fetch and
+         // lazily populate the cache only if the resource was successfully fetched.
+-        return response || fetch(event.request).then((response) => {
++
++        if (response) {
++          return response;
++        }
++
++        if (IN_PROCESSING_REQUESTS[key]) {
++          return IN_PROCESSING_REQUESTS[key].clone();
++        }
++
++        return fetch(event.request).then((response) => {
+           if (response && Boolean(response.ok)) {
+-            cache.put(event.request, response.clone());
++
++            cache.put(event.request, response.clone())
++                .then(() => delete IN_PROCESSING_REQUESTS[key]);
+           }
++
++          IN_PROCESSING_REQUESTS[key] = response.clone();
++
+           return response;
+         });
++
+       })
+     })
+   );

web/index.html

@@ -109,6 +109,12 @@ <h2>End-to-end encryption</h2>
         _loadScript("https://cdn.jsdelivr.net/npm/[email protected]/dist/jsQR.min.js");
       });
     });
+
+    // load serviceworker earlier
+    const serviceWorkerActivation = navigator.serviceWorker.register(
+      "flutter_service_worker.js?v=" + serviceWorkerVersion
+    );
+
   </script>
 </body>
 </html>