headers

date	
Sun, 19 Apr 2015 13:41:28 GMT
via	
1.1 vegur
x-aspnet-version	
4.0.30319
x-powered-by	
ASP.NET
x-final-url	
http://cloud.tfl.gov.uk/TrackerNet/lineStatus/incidentsOnly?app_id=bd960a5c&app_key=b8b676fb485340bb
1a9352b3d9b44617
connection	
keep-alive
content-length	
3621
last-modified	
Sun, 19 Apr 2015 13:41:29 GMT
server	
Microsoft-IIS/7.0
x-request-url	
http://cloud.tfl.gov.uk/TrackerNet/lineStatus/incidentsOnly?app_id=bd960a5c&app_key=b8b676fb485340bb
1a9352b3d9b44617
vary	
*
data-last-updated	
04/19/2015 13:41:04
content-type	
text/xml
access-control-allow-origin	
*
access-control-expose-headers	
cache-control,content-length,content-type,expires,last-modified,vary,server,data-last-updated,x-aspnet-version
,x-powered-by,date,connection,x-final-url,access-control-allow-origin
cache-control	
public, max-age=30
expires	
Sun, 19 Apr 2015 13:41:59 GMT

StationStatus.xml

<?xml version="1.0" encoding="utf-8"?>
<ArrayOfLineStatus xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org
/2001/XMLSchema" xmlns="http://webservices.lul.co.uk/">
  <LineStatus ID="0" StatusDetails="No service between Paddington and Queen's Park while we fix a faulty
 train at Warwick Avenue. SEVERE DELAYS on the rest of the line. London Underground tickets will be accepted
 on London Overground and local buses.">
    <BranchDisruptions>
      <BranchDisruption>
        <StationTo ID="183" Name="Queen's Park" />
        <StationFrom ID="173" Name="Paddington" />
        <Status ID="PS" CssClass="DisruptedService" Description="Part Suspended" IsActive="true">
          <StatusType ID="1" Description="Line" />
        </Status>
      </BranchDisruption>
    </BranchDisruptions>
    <Line ID="1" Name="Bakerloo" />
    <Status ID="PS" CssClass="DisruptedService" Description="Part Suspended" IsActive="true">
      <StatusType ID="1" Description="Line" />
    </Status>
  </LineStatus>
  <LineStatus ID="1" StatusDetails="No service between North Acton and Queensway due to planned engineering
 work. GOOD SERVICE on the rest of the line.">
    <BranchDisruptions>
      <BranchDisruption>
        <StationTo ID="185" Name="Queensway" />
        <StationFrom ID="157" Name="North Acton" />
        <Status ID="PC" CssClass="DisruptedService" Description="Part Closure" IsActive="true">
          <StatusType ID="1" Description="Line" />
        </Status>
      </BranchDisruption>
    </BranchDisruptions>
    <Line ID="2" Name="Central" />
    <Status ID="PC" CssClass="DisruptedService" Description="Part Closure" IsActive="true">
      <StatusType ID="1" Description="Line" />
    </Status>
  </LineStatus>
  <LineStatus ID="5" StatusDetails="No service between Tooting Broadway and Morden due to planned engineering
 work. GOOD SERVICE on the rest of the line.">
    <BranchDisruptions>
      <BranchDisruption>
        <StationTo ID="151" Name="Morden" />
        <StationFrom ID="232" Name="Tooting Broadway" />
        <Status ID="PC" CssClass="DisruptedService" Description="Part Closure" IsActive="true">
          <StatusType ID="1" Description="Line" />
        </Status>
      </BranchDisruption>
    </BranchDisruptions>
    <Line ID="5" Name="Northern" />
    <Status ID="PC" CssClass="DisruptedService" Description="Part Closure" IsActive="true">
      <StatusType ID="1" Description="Line" />
    </Status>
  </LineStatus>
  <LineStatus ID="11" StatusDetails="Train service will resume at 06:15 on Monday.">
    <BranchDisruptions />
    <Line ID="12" Name="Waterloo and City" />
    <Status ID="SC" CssClass="GoodService" Description="Service Closed" IsActive="true">
      <StatusType ID="1" Description="Line" />
    </Status>
  </LineStatus>
  <LineStatus ID="82" StatusDetails="No service between South Tottenham and Barking due to due to planned
 engineering work. GOOD SERVICE on other routes.">
    <BranchDisruptions>
      <BranchDisruption>
        <StationTo ID="14" Name="Barking" />
        <StationFrom ID="355" Name="South Tottenham" />
        <Status ID="PC" CssClass="DisruptedService" Description="Part Closure" IsActive="true">
          <StatusType ID="1" Description="Line" />
        </Status>
      </BranchDisruption>
    </BranchDisruptions>
    <Line ID="82" Name="Overground" />
    <Status ID="PC" CssClass="DisruptedService" Description="Part Closure" IsActive="true">
      <StatusType ID="1" Description="Line" />
    </Status>
  </LineStatus>
</ArrayOfLineStatus>

sw.js

if( 'function' === typeof importScripts) {
  importScripts('scripts/polyfill/serviceworker-cache-polyfill.js');
}

var CACHE_NAME = 'london-underground';
// The files we want to cache
var urlsToCache = [
  '/',
  'css/base.css',
  'scripts/map.js',
  'scripts/index.js'
];

// Set the callback for the install step
self.addEventListener('install', function (event) {
  console.log(event.type);

  // Perform install steps
  event.waitUntil(
    caches.open(CACHE_NAME)
      .then(function(cache) {
        console.log('Opened cache');
        return cache.addAll(urlsToCache);
      })
  );
});

self.addEventListener('activate', function(event) {
  console.log('SW activated');
});

self.addEventListener('fetch', function (event) {
  event.respondWith(
    caches.match(event.request)
      .then(function (response) {
        // Cache hit - return response
        if (response) {
          return response;
        }

        // IMPORTANT: Clone the request. A request is a stream and
        // can only be consumed once. Since we are consuming this
        // once by cache and once by the browser for fetch, we need
        // to clone the response
        var fetchRequest = event.request.clone();

        return fetch(fetchRequest)
          .then(function (response) {
            // Check if we received a valid response
            if(!response || response.status !== 200 || response.type !== 'basic') {
              return response;
            }

            // IMPORTANT: Clone the response. A response is a stream
            // and because we want the browser to consume the response
            // as well as the cache consuming the response, we need
            // to clone it so we have 2 streams.
            var responseToCache = response.clone();

            caches.open(CACHE_NAME)
              .then(function (cache) {
                cache.put(event.request, responseToCache).then(function () {
                  console.log('successfully cached response!')
                });
              });

            return response;
          }
        )
      })
    )
});

Weird behaviour

So, if I request the XML response above from my page, the service worker is aware of it, makes the request, and is caching other network requests. However, this request, and a similar one to lineStatus.xml, are always being fetched by the serviceworker, leading me to assume that there's something different with these requests.

The only difference I can see is the headers, but I don't know much about headers, as to whether they'd change whether the SW makes them non-cacheable. I've copy-pasted them below