Add ServiceWorker caching for static assets (#5524)

app/views/home/index.html.haml

@@ -3,8 +3,6 @@
   %link{ href: asset_pack_path('features/compose.js'), crossorigin: 'anonymous', rel: 'preload', as: 'script' }/
   %link{ href: asset_pack_path('features/home_timeline.js'), crossorigin: 'anonymous', rel: 'preload', as: 'script' }/
   %link{ href: asset_pack_path('features/notifications.js'), crossorigin: 'anonymous', rel: 'preload', as: 'script' }/
-  %link{ href: asset_pack_path('features/community_timeline.js'), crossorigin: 'anonymous', rel: 'preload', as: 'script' }/
-  %link{ href: asset_pack_path('features/public_timeline.js'), crossorigin: 'anonymous', rel: 'preload', as: 'script' }/
   %meta{name: 'applicationServerKey', content: Rails.configuration.x.vapid_public_key}
   %script#initial-state{ type: 'application/json' }!= json_escape(@initial_state_json)
 

config/webpack/production.js

@@ -48,7 +48,37 @@ module.exports = merge(sharedConfig, {
     }),
     new OfflinePlugin({
       publicPath: publicPath, // sw.js must be served from the root to avoid scope issues
-      caches: { }, // do not cache things, we only use it for push notifications for now
+      caches: {
+        main: [':rest:'],
+        additional: [':externals:'],
+        optional: [
+          '**/locale_*.js', // don't fetch every locale; the user only needs one
+          '**/*_polyfills-*.js', // the user may not need polyfills
+          '**/*.woff2', // the user may have system-fonts enabled
+          // images/audio can be cached on-demand
+          '**/*.png',
+          '**/*.jpg',
+          '**/*.jpeg',
+          '**/*.svg',
+          '**/*.mp3',
+          '**/*.ogg',
+        ],
+      },
+      externals: [
+        '/emoji/1f602.svg', // used for emoji picker dropdown
+        '/emoji/sheet.png', // used in emoji-mart
+      ],
+      excludes: [
+        '**/*.gz',
+        '**/*.map',
+        'stats.json',
+        'report.html',
+        // any browser that supports ServiceWorker will support woff2
+        '**/*.eot',
+        '**/*.ttf',
+        '**/*-webfont-*.svg',
+        '**/*.woff',
+      ],
       ServiceWorker: {
         entry: path.join(__dirname, '../../app/javascript/mastodon/service_worker/entry.js'),
         cacheName: 'mastodon',