title: pwa - Service worker does not successfully serve the manifest's start_url
body: <p>I am trying to add PWA functionality to an existing website that is hosted on Azure and uses Cloudflare CDN.</p>
  
  <p>I have run the lighthouse testing tool on the site and it passes everything in the PWA section (e.g. service worker installed, served over https, manifest installed etc.) except: </p>
  
  <p>"Service worker does not successfully serve the manifest's start_url."</p>
  
  <p>My manifest.json has '/' as the start URL and "/" as the scope.</p>
  
  <p>The '/' is actually default.aspx which I have cached as well.</p>
  
  <p>My service worker caches '/', e.g. </p>
  
  <pre><code>var cacheShellFiles = [
    '/',
    '/manifest.json',
    '/index.html',
    '/scripts/app.js',
    '/styles/inline.css'
     ...
  ]
  
  // install - cache the app shell
  self.addEventListener('install', function (event) {
  console.log('From SW install: ', event);
  
  // calling skipWatiing() means the sw will skip the waiting state and immediately 
  // activate even if other tabs open that use the previous sw
  self.skipWaiting();
  
  event.waitUntil(
      caches.open(CACHE_NAME_SHELL)
          .then(function (cache) {
              console.log('Cache opened');
              return cache.addAll(cacheShellFiles);
          })
  );
  });
  </code></pre>
  
  <p>When I view the Cache Storage files in dev tools however, the Content-Length of the / and the .css and .js files is 0:</p>
  
  <p><a href="https://i.stack.imgur.com/VLY2S.png" rel="nofollow noreferrer">Image of Chrome Developer tools showing cache storage with Content-Length=0</a>
  Is the Content-Length = 0 the reason that it is saying it can't serve the manifest's start URL ? </p>