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23 .TH CURLOPT_HAPPY_EYEBALLS_TIMEOUT_MS 3 "February 21, 2018" "libcurl 7.59.0" "curl_easy_setopt options"
26 CURLOPT_HAPPY_EYEBALLS_TIMEOUT_MS \- head start for ipv6 for happy eyeballs
28 #include <curl/curl.h>
30 CURLcode curl_easy_setopt(CURL *handle, CURLOPT_HAPPY_EYEBALLS_TIMEOUT_MS, long timeout);
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.
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.
43 CURL_HET_DEFAULT (currently defined as 200L)
46 CURL *curl = curl_easy_init();
48 curl_easy_setopt(curl, CURLOPT_URL, "https://example.com");
49 curl_easy_setopt(curl, CURLOPT_HAPPY_EYEBALLS_TIMEOUT_MS, 300L);
51 curl_easy_perform(curl);
54 curl_easy_cleanup(curl);