Tribblix: manual page: CURLOPT_HAPPY_EYEBALLS_TIMEOUT

CURLOPT_HAPPY_EYEBALLS_TIMEOUT_MS(3) Introduction to Library Functions

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

curl_easy_setopt(3) returns a CURLcode indicating success or error.

CURLE_OK (0) means everything was OK, non-zero means an error
occurred, see libcurl-errors(3).