HTTP HTTP GET HTTP replaced headers CURLOPT_TIMECONDITION If-Modified-Since # Server-side HTTP/1.1 304 Not Modified Date: Thu, 11 Jul 2019 02:26:59 GMT Server: test-server/swsclose # Client-side http HTTP custom header overrides CURLOPT_TIMECONDITION lib1593 http://%HOSTIP:%HTTPPORT/1593 ^User-Agent:.* # Note here the lack of If-Modified-Since GET /1593 HTTP/1.1 Host: %HOSTIP:%HTTPPORT Accept: */*