问题
I am developing a web app for offline use, thus I need to use the application cache functionality.
Everything works great on Chrome (15.0.874.106) but is doesn't work on Firefox (7.0.1) and Opera (11.52).
This is my cache manifest file cache.manifest.php (I have reduced it to the bare minimum):
<?php
header("Cache-Control: max-age=0, no-cache, no-store, must-revalidate");
header("Pragma: no-cache");
header("Expires: Wed, 11 Jan 1984 05:00:00 GMT");
header('Content-type: text/cache-manifest');
?>CACHE MANIFEST
CACHE:
/app/common/css/reset.css
/favicon.ico
And this is the first 4 lines of the "main" HTML document:
<!DOCTYPE html>
<html manifest="/app/mobile/cache.manifest.php">
<head>
<title>MyApp Mobile</title>
When I try and load the cache manifest (http://www.myapp.com/app/mobile/cache.manifest.php) into the browser the file is displayed correctly but when I try to load the page once offline I get the "Unable to connect" error page. Again, that just happens on Firefox and Opera.
Firebug says "0 items in offline cache" and I didn't find the way to check the application cache on DragonFly.
I am getting mad and I don't know how to debug the problem effectively on Firefox and Opera. Please help.
Thanks, Dan
回答1:
In my experience using the HTML5 AppCache, it is great once you get it working, but extremely brittle. If there's the tiniest thing wrong with it the browser ignores the entire file and, annoyingly, rather than use the browser's ordinary cache, re-loads everything from scratch off the server.
Worse, browsers will not re-load the manifest file unless its text content changes. So you might tweak your server headers or something to fix it, but unless the content of cache.manifest.php changes the browser will blindly ignore it and do exactly what it did last time. So it could have been broken, then you fixed it, but browsers are ignoring the changes because the text content of cache.manifest.php hasn't changed. This even seems to be immune to clearing your browser cache, which is part of what makes it so confusing - app cache is really, really serious about caching.
To get around this, text changes in comments count, so have a comment at the top with a version or timestamp or the date (e.g. # Version 1.2) and change that when you want the browser to "notice".
Then, the browser still won't immediately use it! The way the app cache works is the next time you load the page it will do exactly what it did last time yet again, and start checking for an update in the background. So you probably want the console up, wait for something like "updating..." then "complete", then hit Refresh and the browser will finally start using the new version. At last!
All in all it can be a right pain to get working. However, once it's working it's almost bulletproof: you can pretty much rest assured anything listed in the cache manifest is only every downloaded once, ever, for all time, per user, until you change the text content of the file.
Browser standards compliance is pretty good these days, so my best guess is you actually have it working, but you checked Chrome last and it's the only browser which has cached the manifest file correctly. During development you might have had it broken, but Firefox and Opera are clutching their old manifest files to the death. I bet you also tried clearing the browser cache in Firefox and Opera, which probably did nothing - you need to change the text content of the file and double-refresh before either Firefox and Opera will finally give up their broken versions of the manifest file and start using the one which works which you probably uploaded ages ago.
回答2:
From: http://appcache.offline.technology
In Firefox, any resources served with Cache-control: no-store will not be cached, even if they're explicitly included in the manifest.
My php by default is sending:
Cache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0
It is enough to add:
header("Cache-Control: no-cache, must-revalidate");
To the php file to get it to start caching it.
(This is similar to Mychal Hackman's answer, but a little more specific).
回答3:
To me your cache manifest looks a bit "unusual"... it might help to add a FALLBACK section... another point is that the appcache might interfer with the "normal browser cache" i.e. if the cache manifest is changed it needs to make sure that the browser reloads it, ideally this is achieved by changing the name (for example by having version number, timestamp... as part of the name).
You can interact in your page with the appcache via JS which could help to pinpoint the problem you see.
For in-depth information including JS code and a thorough walk-through see
- http://www.html5rocks.com/en/tutorials/appcache/beginner/
- http://www.w3.org/TR/html5/offline.html
If need be come back with specific questions.
UPDATE
As per comments provided by OP this shows a nice implementation of the JS API for checking/debugging appcache as described in the links above.
回答4:
You can check the current status of the application cache using window.applicationCache.status, which returns a numeric value mapped to the following states:
0 - uncached, 1 - idle, 2 - checking, 3 - downloading, 4 - updateready, 5 - obsolete.
The application cache API has a few things worth noting:
window.applicationCache.update(): This will trigger the application cache download process, which is nearly the same as reloading the page. It simply checks if the manifest has changed, and if so downloads a fresh version of all the content in the cache (respecting any cache headers). Note that even though a new cache is created with this, the page will continue to use the old cache. To make the page use the new cache you have just downloaded, you must use the swapCache() function.
window.applicationCache.swapCache(): This function tells the browser to start using the new cache data if it is available. It is important to note that even if there is a new manifest file, the application will still continue using the old cache (as specified in the old manifest file) untill swapCache() is called. Once swapCache() is called, then the cache will be used as specified from the new manifest file.
from: http://dev.opera.com/articles/view/offline-applications-html5-appcache/
回答5:
Check your cache in about:cache. I am betting you will see "data-size 0 bytes" for your PHP file(s).
Check your caching headers, I found in Firefox the default was "no-cache" on my php files. I just added:
header("Pragma: public");
header("Cache-Control: public, max-age=6000");
to my PHP file and reloaded the offline cache and it is finally working.
HTH
回答6:
Try removing:
header("Cache-Control: max-age=0, no-cache, no-store, must-revalidate");
header("Pragma: no-cache");
header("Expires: Wed, 11 Jan 1984 05:00:00 GMT");
so that you are only sending the Content-type header:
<?php header('Content-type: text/cache-manifest'); ?>
ApplicationCache forces caching (oversimplifying, but not by much). Those first three headers are ways to prevent caching.
Opera appears to prevent caching when those headers are present. Firefox' debugging tools are a bit wonky when it comes to debugging AppCache, but it's probably save to assume this will fix it there as well.
回答7:
For Firefox, try this little trick:
<html manifest="/app/mobile/cache.manifest.php?1">
Its the "?1" that finally get Firefox to check for the latest file. That's what did the trick for me anyway. Hope this helps.
回答8:
From my experience with getting a site working offline on the iPad:
- The name of the file needs to end with
.manifest - The mime type needs to be
text/cache-manifest - Have a version in the comments of your manifest
- Create some javascript functions using
window.applicationCache...to check if the browser sees a change in the manifest and to reload the content, also capture the status events and display them somewhere
See also: http://developer.apple.com/library/safari/#documentation/iPhone/Conceptual/SafariJSDatabaseGuide/OfflineApplicationCache/OfflineApplicationCache.html#//apple_ref/doc/uid/TP40007256-CH7-SW1
回答9:
I had a similar problem. I am very late in answering but this might be helpful for others. Make sure you dont run into problems described by AshleysBrian in his answer. Adding to that
- Make sure the manifest file is served as type "text/cache-manifest"
- Dont try it out in Private Browsing mode in Firefox/IE. It only works in regular browsing mode. But it works in both modes in Chrome
While offline, a simple change in the URL could be a problem
Eg: http://localhost:8080/app doesn't work on Firefox/IE but http://localhost:8080/app/ works in Firefox/IEBoth of them work in Chrome
Use these handy resource viewers to get more detailed perspective
about:cache - Firefox chrome://appcache-internals/ - Chrome Pls fill in if someone knows what is it for IE
回答10:
As I understand, the Offline Web applications section in the W3C HTML5 draft is non-normative; meaning that is it still not part of the formal HTML5 standard as yet.
Since the feature is still not part of the HTML5 standard, different browsers may have different and varying/non-standard implementations, if at all they choose to implement it. Not all browsers may choose to support it. Do not rely on non-normative features until they are part of the standard.
回答11:
I've found something similar, and tracked it down to the Cache-Control: no-store heading on the manifest. Chrome accepts this, but Firefox fails silently with this.
My tests showed that you can keep no-cache headers & expires headers in to ensure frequent refreshes.
回答12:
My only way to make the manifest work everywhere is to do this:
CACHE MANIFEST
# version x.x
# 2015-03-27
# list everything
If I use NETWORK and/or FALLBACK it wont work (in Chrome).
回答13:
I had the same problem also. Everything worked fine in Chrome and IE, but an "Unable to connect" message in FF.
After hours of despair, i found the solution and it was ridiculous simple: In the developer-toolbar the entire cache was deactivated. :/
来源：https://stackoverflow.com/questions/8303785/html5-cache-manifest-working-great-on-chrome-but-not-on-firefox-and-opera