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

       All except FILE

EXAMPLE

       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 7.59.0

RETURN VALUE

       Returns CURLE_OK

SEE ALSO

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