NAME

       CURLOPT_HAPPY_EYEBALLS_TIMEOUT_MS - head start for IPv6 for happy eyeballs

SYNOPSIS

       #include <curl/curl.h>

       CURLcode curl_easy_setopt(CURL *handle, CURLOPT_HAPPY_EYEBALLS_TIMEOUT_MS,
                                 long timeout);

DESCRIPTION

       Happy  eyeballs  is  an algorithm that attempts to connect to both IPv4 and IPv6 addresses
       for dual-stack hosts, preferring IPv6 first for timeout milliseconds. If the IPv6  address
       cannot  be  connected  to  within  that time then a connection attempt is made to the IPv4
       address in parallel. The first connection to be established is the one that is used.

       The range of suggested useful values for timeout is limited. Happy Eyeballs RFC 6555  says
       "It  is  RECOMMENDED  that  connection attempts be paced 150-250 ms apart to balance human
       factors against network load." libcurl currently defaults to 200 ms.  Firefox  and  Chrome
       currently default to 300 ms.

DEFAULT

       CURL_HET_DEFAULT (currently defined as 200L)

PROTOCOLS

       This functionality affects all supported protocols

EXAMPLE

       int main(void)
       {
         CURL *curl = curl_easy_init();
         if(curl) {
           curl_easy_setopt(curl, CURLOPT_URL, "https://example.com");
           curl_easy_setopt(curl, CURLOPT_HAPPY_EYEBALLS_TIMEOUT_MS, 300L);

           curl_easy_perform(curl);

           /* always cleanup */
           curl_easy_cleanup(curl);
         }
       }

AVAILABILITY

       Added in curl 7.59.0

RETURN VALUE

       Returns CURLE_OK

SEE ALSO

       CURLOPT_CONNECTTIMEOUT_MS(3), CURLOPT_LOW_SPEED_LIMIT(3), CURLOPT_TIMEOUT(3)