CURLOPT_HAPPY_EYEBALLS_TIMEOUT_MS(3)

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NAME

6       CURLOPT_HAPPY_EYEBALLS_TIMEOUT_MS  - head start for ipv6 for happy eye‐
7       balls
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SYNOPSIS

10       #include <curl/curl.h>
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12       CURLcode  curl_easy_setopt(CURL  *handle,  CURLOPT_HAPPY_EYEBALLS_TIME‐
13       OUT_MS, long timeout);
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DESCRIPTION

16       Happy  eyeballs  is  an algorithm that attempts to connect to both IPv4
17       and IPv6 addresses for dual-stack  hosts,  preferring  IPv6  first  for
18       timeout milliseconds. If the IPv6 address cannot be connected to within
19       that time then a connection attempt is made to the IPv4 address in par‐
20       allel. The first connection to be established is the one that is used.
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22       The range of suggested useful values for timeout is limited. Happy Eye‐
23       balls RFC 6555 says "It is  RECOMMENDED  that  connection  attempts  be
24       paced  150-250 ms apart to balance human factors against network load."
25       libcurl currently defaults to 200 ms. Firefox and Chrome currently  de‐
26       fault to 300 ms.
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DEFAULT

29       CURL_HET_DEFAULT (currently defined as 200L)
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PROTOCOLS

32       All except FILE
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EXAMPLE

35       CURL *curl = curl_easy_init();
36       if(curl) {
37         curl_easy_setopt(curl, CURLOPT_URL, "https://example.com");
38         curl_easy_setopt(curl, CURLOPT_HAPPY_EYEBALLS_TIMEOUT_MS, 300L);
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40         curl_easy_perform(curl);
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42         /* always cleanup */
43         curl_easy_cleanup(curl);
44       }
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AVAILABILITY

47       Added in 7.59.0
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RETURN VALUE

50       Returns CURLE_OK
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