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CURLOPT_H...TIMEOUT_MS(3)  Library Functions Manual  CURLOPT_H...TIMEOUT_MS(3)

NAME
       CURLOPT_HAPPY_EYEBALLS_TIMEOUT_MS  - head start for IPv6	for happy eye-
       balls

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 par-
       allel. The first	connection to be established is	the one	that is	used.

       The range of suggested useful values for	timeout	is limited. Happy Eye-
       balls 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  de-
       fault 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).

SEE ALSO
       CURLOPT_CONNECTTIMEOUT_MS(3), CURLOPT_LOW_SPEED_LIMIT(3), CURLOPT_TIME-
       OUT(3)

libcurl				  2025-06-03	     CURLOPT_H...TIMEOUT_MS(3)

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