Wednesday, February 25, 2009

Using fake query parameters to identify resource versions

When setting the cache expiry headers to somewhere in the far future as to make browsers not hit your server again for a long time (practically forever), you need some way to get the browser to newer versions of your otherwise static files. So far I have used a pattern containing the version of the artifact as part of the path:

http://my.server/js/lib/v123/lib.js

I just noticed the Sonatype repository using a different scheme, which is more like this:

http://my.server/js/lib/lib.js?v123

The version number is stored in a query parameter in this scheme. I assume that this parameter is actually ignored as most webservers would do with static content.

The advantages I see in this approach are:
  • updates can be done in-place (easier deployment, no need to keep multiple copies around)
  • the target doesn't even have to be aware of the scheme
  • the client could even go as far as generating a URL based on its revision, causing a retrieval for each of its upgrades, which would be too much but very safe
Disadvantages I see:
  • any reference will always retrieve the newest version (which could break things subtly if for some reason old references are still around somewhere)
  • (related to the one above) it's just not a proper URI since it identifies a resource with the query parameter (unless you consider the resource as spanning all versions and the versions different representations of it)
  • I don't know if I trust all caches to handle the query part properly (I never even looked into that)
It's an interesting approach and I can see it being a lot easier to manage than having distinct directories for each version. It somehow doesn't feel right, though.

1 comment:

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