CURLOPT_TIMECONDITION (3) Linux Manual Page
CURLOPT_TIMECONDITION – select condition for a time request
Synopsis
#include <curl/curl.h> CURLcode curl_easy_setopt(CURL *handle, CURLOPT_TIMECONDITION, long cond);
Description
Pass a long as parameter. This defines how the CURLOPT_TIMEVALUE(3) time value is treated. You can set this parameter to CURL_TIMECOND_IFMODSINCE or CURL_TIMECOND_IFUNMODSINCE. The last modification time of a file is not always known and in such instances this feature will have no effect even if the given time condition would not have been met. curl_easy_getinfo(3) with the CURLINFO_CONDITION_UNMET option can be used after a transfer to learn if a zero-byte successful "transfer" was due to this condition not matching.