Implementing ETag in Squid

In order to implement ETag in Squid changes will be needed at a number of locations.

• client side needs to be extended with If-None-Match, If-Match and If-Range support.
• store needs to be redesigned (again) to support ETag indexing of a varying object
• cache validation needs to extended to send If-None-Match with the ETag value of the object being validated.
• Cache misses on varying objects needs to be extended to send the known ETag values in If-None-Match.