Content Caching

CURLOPT_TIMECONDITION must be set to either CURL_TIMECOND_IFMODSINCE or CURL_TIMECOND_IFUNMODSINCE to select whether the If-Modified-Since or If-Unmodified-Since header will be used respectively.

CURLOPT_TIMEVALUE must be set to a UNIX timestamp (a date representation using the number of seconds between the UNIX epoch and the desired date) to indicate the last client access time of the resource. The time function can be used to derive this value.