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                     23: .TH CURLOPT_HAPPY_EYEBALLS_TIMEOUT_MS 3 "March 23, 2020" "libcurl 7.70.0" "curl_easy_setopt options"
                     24: 
                     25: .SH NAME
                     26: CURLOPT_HAPPY_EYEBALLS_TIMEOUT_MS \- head start for ipv6 for happy eyeballs
                     27: .SH SYNOPSIS
                     28: #include <curl/curl.h>
                     29: 
                     30: CURLcode curl_easy_setopt(CURL *handle, CURLOPT_HAPPY_EYEBALLS_TIMEOUT_MS, long timeout);
                     31: .SH DESCRIPTION
                     32: Happy eyeballs is an algorithm that attempts to connect to both IPv4 and IPv6
                     33: addresses for dual-stack hosts, preferring IPv6 first for \fItimeout\fP
                     34: milliseconds. If the IPv6 address cannot be connected to within that time then
                     35: a connection attempt is made to the IPv4 address in parallel. The first
                     36: connection to be established is the one that is used.
                     37: 
                     38: The range of suggested useful values for \fItimeout\fP is limited. Happy
                     39: Eyeballs RFC 6555 says "It is RECOMMENDED that connection attempts be paced
                     40: 150-250 ms apart to balance human factors against network load." libcurl
                     41: currently defaults to 200 ms. Firefox and Chrome currently default to 300 ms.
                     42: .SH DEFAULT
                     43: CURL_HET_DEFAULT (currently defined as 200L)
                     44: .SH EXAMPLE
                     45: .nf
                     46: CURL *curl = curl_easy_init();
                     47: if(curl) {
                     48:   curl_easy_setopt(curl, CURLOPT_URL, "https://example.com");
                     49:   curl_easy_setopt(curl, CURLOPT_HAPPY_EYEBALLS_TIMEOUT_MS, 300L);
                     50: 
                     51:   curl_easy_perform(curl);
                     52: 
                     53:   /* always cleanup */
                     54:   curl_easy_cleanup(curl);
                     55: }
                     56: .fi
                     57: .SH AVAILABILITY
                     58: Added in 7.59.0
                     59: .SH RETURN VALUE
                     60: Returns CURLE_OK