How to properly invalidate an HTML5 Cache Manifest for online/offline web apps?

Question

I\'m currently using a Cache Manifest (as described here). This effectively makes the necessary resources to run the application available when the user is offline.

Answer 1

I think I've got this figured out: if there's an error in one's cache-manifest (say, a referenced file does not exist), then Firefox completely will stop processing anything applicationCache related. Meaning, it won't update anything in your cache, including your cached cache-manifest.

To uncover that this was the issue, I borrowed some code from Mozilla and dropped this into a new (non-cached) HTML file in my application. The final message logged stated that there might be a problem in my cache-manifest, and sure enough there was (a missing file).

// Convenience array of status values
var cacheStatusValues = [];
 cacheStatusValues[0] = 'uncached';
 cacheStatusValues[1] = 'idle';
 cacheStatusValues[2] = 'checking';
 cacheStatusValues[3] = 'downloading';
 cacheStatusValues[4] = 'updateready';
 cacheStatusValues[5] = 'obsolete';

 // Listeners for all possible events
 var cache = window.applicationCache;
 cache.addEventListener('cached', logEvent, false);
 cache.addEventListener('checking', logEvent, false);
 cache.addEventListener('downloading', logEvent, false);
 cache.addEventListener('error', logEvent, false);
 cache.addEventListener('noupdate', logEvent, false);
 cache.addEventListener('obsolete', logEvent, false);
 cache.addEventListener('progress', logEvent, false);
 cache.addEventListener('updateready', logEvent, false);

 // Log every event to the console
 function logEvent(e) {
     var online, status, type, message;
     online = (isOnline()) ? 'yes' : 'no';
     status = cacheStatusValues[cache.status];
     type = e.type;
     message = 'online: ' + online;
     message+= ', event: ' + type;
     message+= ', status: ' + status;
     if (type == 'error' && navigator.onLine) {
         message+= ' There was an unknown error, check your Cache Manifest.';
     }
     log('
'+message);
 }

 function log(s) {
    alert(s);
 }

 function isOnline() {
     return navigator.onLine;
 }

 if (!$('html').attr('manifest')) {
    log('No Cache Manifest listed on the  tag.')
 }

 // Swap in newly download files when update is ready
 cache.addEventListener('updateready', function(e){
         // Don't perform "swap" if this is the first cache
         if (cacheStatusValues[cache.status] != 'idle') {
             cache.swapCache();
             log('Swapped/updated the Cache Manifest.');
         }
     }
 , false);

 // These two functions check for updates to the manifest file
 function checkForUpdates(){
     cache.update();
 }
 function autoCheckForUpdates(){
     setInterval(function(){cache.update()}, 10000);
 }

 return {
     isOnline: isOnline,
     checkForUpdates: checkForUpdates,
     autoCheckForUpdates: autoCheckForUpdates
 }

This was certainly helpful, but I should definitely request a feature from Mozilla that prints out malformed cache-manifests at least to the Error Console. It shouldn't require custom code to attach to these events to diagnose an issue as trivial as a renamed file.