On tis, 2007-10-16 at 11:33 +0100, Nick Kew wrote: > For example, Henrik Nordstrom suggests ";gzip". If we expand that to, > say, ";CE=gzip", then we can start to apply semantics to decoding the > Etag, and determine equivalence. So in that case, we could determine > that the (uncompressed) file does indeed match the ETag. Not sure if > there's anything we might do with other negotiated headers, but maybe > we could leave that open, providing a hook that something like > mod_negotiation might someday use.
It's not immediately relevant to mod_negotiation, mainly to filters doing negotiated transformation of responses where the original response has an ETag. mod_deflate is the most apparent and most frequently used such filter, but I can think of many other such as dynamic image conversion (png->jpg for user-agents not handling png, lowres for small devices etc.) etc. Having some structure on the tokens is helpful, but not strictly needed as long as each step in the filter chain can recognise it's token and add/remove it as needed. Add token to ETag when the response goes out, reflecting the negotiation process done by the filter. As discussed earlier a token may need to be always added to avoid conflicts with other ETag sources possibly generating ETag values with the same token format. remove from If-* when processing requests and conditions still match for the step in question. If conditions no longer match the token then the condition needs to be rejected. Having a clear structure may allow you to make efficient shortcuts in the processing, but probably only when the resource has changed making the original resource ETag different. Hmm.. looking at mod_negotiate again it may be relevant there as well when using the body typemap feature. Today mod_negotiate do not return an ETag under such conditions, but using tokens it could, allowing for proper cache validation of body typemap negotiated resources. Using tokens is in fact not very different from what mod_negotiate does today chaining the etags of the typemap and the selected variant. The token idea is however not relevant to mod_negotiate multiviews as the selected variant already has an unique ETag and is sufficient identification of the selected variant. No need to complicate that quite common case. Regards Henrik
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