It seems that if the cache manifest on the server changes it will re-download everything in file? Is there any way to only make it re-download some of the files? If I only make code fixes to a script and then update the manifest (say just put a timestamp comment in it) to force local copies to see a change has been made, I might not want images re-downloaded that haven't changed but still need to be in the manifest. Is there a way to get more precision around this or is it an all or nothing thing?
From what i've expreienced, updating the cache manifest doesn't explicitly download all the content again, but rather checks if they've been modified. So if there are 10 items in your cache manifest and you were to update a single file (and also the manifest file), then each file would be checked for modification, and depending on how they are being served (CDN?) they should be returning a 304 Not Modified, and thus not be downloaded again.
Related
I changed my cache.manifest file to the following:
CACHE MANIFEST
NETWORK:
*
CACHE:
FALLBACK:
This triggered an update to my site.
I tried adding a "#" to the manifest file and then removed the manifest="cache.manifest"from my page.
This triggered the cache to be updated again, even though the reference to the manifest was gone. The console indicated it was still being loaded from cache.
I even tried renaming my cache.manifest file and it still was being loaded from cache.
How in the world can I safely stop using cache manifest? I have a completely new version of my site I want to roll out, but if cache manifest is still trying to cache the new site, that will be a disaster for all my visitors who do not know they need to clear their browser cache.
I believe I found the trick.
It seems I need to keep the old cache.manifest but change (not remove) the reference to a non-existent manifest file.
Presumably, I'll need to keep the broken reference there for several years in case I have visitors who only visit periodically.
I have an issue with offline cache manifests that I don't quite know how to troubleshoot.
1) A .json file which is part of the manifest is stored together with the manifest.
2) I change that file, and verify that it is indeed changed on the server.
3) I re-generate the manifest (it has a timestamp for uniqueness)
4) The chrome://appcache-internals show that the manifest is indeed updated at the expected time
5) The .json file is still in the old verison, ie. different from the version I have on server, even though the manifest itself is verified to have been updated minutes later.
I don't understand while one file of the manifest is still in the old version.
Update:
It seems to primarily be a problem on localhost, on my DEV environment
My issue was that I had two different sites on the same domain serving different cache manifests. They seem to block one another out. By clearing the manifest from site one, site two works like expected and vice versa.
I guess the offline cache specs is only intended for one manifest per domain.
I have noticed that a touch, or another modification of the manifest file's metadata will not trigger an update (at least when testing with Google Chrome). The browser will fire the noupdate event unless I change something more meaningful in the file, such as adding a line of whitespace.
How does the browser compare the old manifest against the new? Does it download the new manifest and compare it? Is it determined somehow from the file header?
http://diveintohtml5.info/offline.html includes a good explanation of the process that the browser follows when loading the manifest.
Briefly:
the server attempts to get a new copy of the manifest
if you have an old version, it will compare the content of the manifest file to the old manifest - so if your index page has changed, but you have no new files, it'll fire noupdate. Any change to the manifest contents, as trivial as adding whitespace (as you saw), will cause your listed assets to be redownloaded.
a common way to deal with this is to add a SHA or something as a comment to your manifest, generated in such a way that it'll change when any of the assets themselves change.
I am trying to build a web app for iphone, and I don't understand
how to cache all the files under the "images" directory ?
and I modify one file on the server like "brandDB.txt", how to make the cache manifest update this file, and this file only to avoid downloading everything again ?
Thanks
CACHE MANIFEST
# 20131104-1430
index.html
brandDB.txt
icon.png
splashiphone.png
touch-icon-iphone.png
css/style.css
images/shareicon.png
images/bourez.png
images/john.png
...
NETWORK:
*
FALLBACK:
I did a program to easily generate the cache manifest file with the complete list directly from the Windows explorer, if you need it : http://matthieu.com/cmfg/
how to cache all the files under the "images" directory ?
List them all in the manifest file (easiest to use a script to generate the list if it's a lot of files).
how to make the cache manifest update this file, and this file only to avoid downloading everything again
Ensure your HTTP headers are set correctly for the frequency of updates you expect
Update the manifest file
The browser will populate the app cache from its own cache if you've set the headers on each file to allow caching. If you want to version control the files without using HTTP headers, add a query string to the end of the file, eg. brandDB.txt?v=1 - be sure to update the reference in the application if you do that, however.
Well, What I'm going to say, unfortunately is as Jake Archibald Said:
"Application cache is a douchebag !" (Good Article on how it works (not actually a douchebag))
http://alistapart.com/article/application-cache-is-a-douchebag
Basically, you could create a script to list all your files in your image directory
and paste it inside a generated AppCache File.
Application cache will only update when its file's content is changed , you'll also need ensure that the file itself is not cached.
I think you'll be needing your clients to reload the page twice for them to actually see the updates. (You could however using javascript tell the user that the page has updated and they'll need to refresh)
I know how to tell the browser to download cached fuiles again by simply changing a character in the appcache manifest, but when I do that, how can I make sure the browser downloads the new file without doing things like changing filenames?
I am aware of file expiration headers I can send, but I have no experience with them. Would they even work with HTML5 caching? Which ones do I send?
I'm under the impression that browsers aren't smart enough to detect when a file is modified, and will continue using the cached file until you force it by refreshing the page or changing the filename. I don't want to do that since it also means updating the manifest and is just extra work.
My optimal solution is to change the manifest slightly, then the browser goes and fetches any changed files without me forcing it to.
What I do is add the timestamp as a comment in the manifest
# 20130623 025200
And just update it each time I want to force a refresh.
EDIT: As I noted in the comments, The browser will re-download all files explicitly enumerated in the manifest. For files that are not in the manifest (for example, CSS or images referenced in an HTML file but not in the manifest), the default expiry take precedence.
The algorithm is described in the standard: http://www.w3.org/html/wg/drafts/html/master/browsers.html#downloading-or-updating-an-application-cache