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I am working on a caching server that will cache only documents (PDF, MS Word, Powerpoint, Excel) that will be fetched over HTTP.

I am aware of the various HTTP headers available for cache invalidation, but am wondering if I can do something smart in case the required headers are missing. Note: in my case I know the type of document being fetched.

Is it possible that I can do some selective byte range requests and based on the result decide if my cache should be invalidated or not. For e.g. for PDFs, if for a given file, the content length matches, the first 'n'K bytes and last 'm' K bytes match, the PDF file has most likely not changed because of how the PDF writers work.

Is something like this possible for MS Office documents? If yes, is there any project already doing this? If not, some general guidelines on how can I go about doing it?

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closed as not a real question by Ƭᴇcʜιᴇ007, Simon Sheehan, HackToHell, Hennes, Diogo Dec 17 '12 at 13:15

It's difficult to tell what is being asked here. This question is ambiguous, vague, incomplete, overly broad, or rhetorical and cannot be reasonably answered in its current form. For help clarifying this question so that it can be reopened, visit the help center.If this question can be reworded to fit the rules in the help center, please edit the question.

Will definitely appreciate some pointers on what part is vague. I provided an example for Pdf, and would like to know if something similar exists for MS Office docs. I assume that part wasn't clear? – Sunil Agrawal Dec 17 '12 at 18:40

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