Chrome doesn't send “If-Modified-Since”

Question

I want browsers to always add (except first time) \"If-Modified-Since\" request header to avoid unnecessary traffic.

Response headers are:

Accept-Ranges:         


        

Answer 1

1. Don't disable cache in Chrome Dev Tools (on "Network" tab).
2. Cache-Control should be Cache-Control: public. Use true as second parameter to header PHP function: header("Cache-Control: public", true);