Read the HTTP specification. Specifically, section 14.25, 'If-Modified-Since'.

You return the 'Last-Modified' timestamp from when you cached the file (or the date you got it, but then you have to deal with generating the date format), and if the file hasn't been modified, and the webserver supports this header, it should return a '304' status message, rather than the full content all over again.

In reply to Re^3: How to get web creation date from webserver? by jhourcle
in thread How to get web creation date from webserver? by gube

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