CURLINFO_CONDITION_UNMET man page
CURLINFO_CONDITION_UNMET — get info on unmet time conditional
CURLcode curl_easy_getinfo(CURL *handle, CURLINFO_CONDITION_UNMET, long *unmet);
Pass a pointer to a long to receive the number 1 if the condition provided in the previous request didn't match (see CURLOPT_TIMECONDITION(3)). Alas, if this returns a 1 you know that the reason you didn't get data in return is because it didn't fulfill the condition. The long ths argument points to will get a zero stored if the condition instead was met.
HTTP and some
Added in 7.19.4
Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION if not.