Cache Manifest

Hi Everyone,

 

I have been working with Cache Manifest in order to locally persist the MIMES from my WebApp. However, I have found some quirks that I wanted to share with everyone. The idea is that someone else may, in the future, hit the same issues and be helped by this posting.

 

There are numerous resources on the web on structure of the cache manifest file, so I wont go into that. Here are some of my findings:

 

·         Use of relative, absolute URLs seems to work fine, so don’t be afraid to use them. Just remember that the URLs are relative to the location of the manifest file.

·         If ANY of the URLs are wrong (i.e. return a HTTP 500 or HTTP 404, etc), the whole cache operation will fail. If this happens just switch on the logs on your server and see which request from the browser is failing. Unfortunately Safari (Mobile and/ Desktop) will tell you that the cache download failed but it wont tell you which file. The other option is to simply comment all the files out of the cache manifest file and test. Then add another file back into the cache manifest file and test again. Repeat until you find the offending file.

·         Our app server would do a URL re-write (inject a session ID into each request). This was a NO NO. A 302 redirect (re-write) will make the cache manifest fail.

·         The cache manifest download would fail if any of the URLs was protected by username and password. Even though it did prompt the user for a username and pwd, it still caused the cache manifest download to fail. Luckily for us this was acceptable since the files were not of a sensitive nature so we just made sure they were public. We auth protected the XML files.

·         Based on the above experience (i.e. 302 and Auth request), I would assume that if any of the files don’t return a 200 OK response, the cache manifest will fail

·         You have to REFRESH the page after a download, as the newly downloaded version will not be used until you refresh the page. We handled this by displaying a message to the user to please ‘re-launch the application’. In some ways its like asking the user to reboot their device after installation.

·         Don’t forget to add any of the XML URLs to the NETWORK section of the manifest file, otherwise the browser will not know how to access them.

 

It’s all I can think of for now.

 

Regards,

 

Alon Raskin