CURLOPT_HAPPY_EYEBALLS_TIMEOUT_MS.md (1789B)
1 --- 2 c: Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al. 3 SPDX-License-Identifier: curl 4 Title: CURLOPT_HAPPY_EYEBALLS_TIMEOUT_MS 5 Section: 3 6 Source: libcurl 7 Protocol: 8 - All 9 See-also: 10 - CURLOPT_CONNECTTIMEOUT_MS (3) 11 - CURLOPT_LOW_SPEED_LIMIT (3) 12 - CURLOPT_TIMEOUT (3) 13 Added-in: 7.59.0 14 --- 15 16 # NAME 17 18 CURLOPT_HAPPY_EYEBALLS_TIMEOUT_MS - head start for IPv6 for happy eyeballs 19 20 # SYNOPSIS 21 22 ~~~c 23 #include <curl/curl.h> 24 25 CURLcode curl_easy_setopt(CURL *handle, CURLOPT_HAPPY_EYEBALLS_TIMEOUT_MS, 26 long timeout); 27 ~~~ 28 29 # DESCRIPTION 30 31 Happy eyeballs is an algorithm that attempts to connect to both IPv4 and IPv6 32 addresses for dual-stack hosts, preferring IPv6 first for *timeout* 33 milliseconds. If the IPv6 address cannot be connected to within that time then 34 a connection attempt is made to the IPv4 address in parallel. The first 35 connection to be established is the one that is used. 36 37 The range of suggested useful values for *timeout* is limited. Happy 38 Eyeballs RFC 6555 says "It is RECOMMENDED that connection attempts be paced 39 150-250 ms apart to balance human factors against network load." libcurl 40 currently defaults to 200 ms. Firefox and Chrome currently default to 300 ms. 41 42 # DEFAULT 43 44 CURL_HET_DEFAULT (currently defined as 200L) 45 46 # %PROTOCOLS% 47 48 # EXAMPLE 49 50 ~~~c 51 int main(void) 52 { 53 CURL *curl = curl_easy_init(); 54 if(curl) { 55 curl_easy_setopt(curl, CURLOPT_URL, "https://example.com"); 56 curl_easy_setopt(curl, CURLOPT_HAPPY_EYEBALLS_TIMEOUT_MS, 300L); 57 58 curl_easy_perform(curl); 59 60 /* always cleanup */ 61 curl_easy_cleanup(curl); 62 } 63 } 64 ~~~ 65 66 # %AVAILABILITY% 67 68 # RETURN VALUE 69 70 curl_easy_setopt(3) returns a CURLcode indicating success or error. 71 72 CURLE_OK (0) means everything was OK, non-zero means an error occurred, see 73 libcurl-errors(3).