From f0cd957c7a8a53dea2eb08a45578084b4d8bb5b4 Mon Sep 17 00:00:00 2001
From: Akihiko Odaki <akihiko.odaki.4i@stu.hosei.ac.jp>
Date: Sat, 17 Mar 2018 20:35:13 +0900
Subject: [PATCH] Cache HTML page with Service Worker (#6802)

This is the first step to make Mastodon work offline. It is also required
by Chromium to trigger Web Manifest automated install prompt.
---
 .../mastodon/service_worker/entry.js          | 22 ++++++++++++++++++-
 1 file changed, 21 insertions(+), 1 deletion(-)

diff --git a/app/javascript/mastodon/service_worker/entry.js b/app/javascript/mastodon/service_worker/entry.js
index eea4cfc3c..ad933b95e 100644
--- a/app/javascript/mastodon/service_worker/entry.js
+++ b/app/javascript/mastodon/service_worker/entry.js
@@ -1,10 +1,30 @@
 import './web_push_notifications';
 
+function fetchRoot() {
+  return fetch('/', { credentials: 'include' });
+}
+
 // Cause a new version of a registered Service Worker to replace an existing one
 // that is already installed, and replace the currently active worker on open pages.
 self.addEventListener('install', function(event) {
-  event.waitUntil(self.skipWaiting());
+  const promises = Promise.all([caches.open('mastodon-web'), fetchRoot()]);
+  const asyncAdd = promises.then(([cache, root]) => cache.put('/', root));
+
+  event.waitUntil(asyncAdd);
 });
 self.addEventListener('activate', function(event) {
   event.waitUntil(self.clients.claim());
 });
+self.addEventListener('fetch', function(event) {
+  const url = new URL(event.request.url);
+
+  if (url.pathname.startsWith('/web/')) {
+    event.respondWith(fetchRoot().then(response => {
+      if (response.ok) {
+        return response;
+      }
+
+      throw null;
+    }).catch(() => caches.match('/')));
+  }
+});