Which cache-related HTTP request headers are the m

问题:

This is a follow-up to this question on cache-related HTTP headers and the browser behavior they cause. To recap: I have a static file handler (.ashx) in an ASP.NET 2.0 web app that serves images. I've just implemented support for cache-related headers, such as sending cache-control, expires and last-modified, and receiving/processing if-modified-since.

One answer noted that there are several possible request headers to deal with, especially if e-tags are supported:

• If-Match
• If-Modified-Since
• If-None-Match
• If-Range
• If-Unmodified-Since

Besides if-modified-since, are there any that are frequently used? Which other ones will yield the most benefits if supported server-side?