72 lines
1.6 KiB
Markdown
72 lines
1.6 KiB
Markdown
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---
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c: Copyright (C) Daniel Stenberg, <daniel.se>, et al.
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SPDX-License-Identifier: curl
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Title: CURLOPT_HAPPY_EYEBALLS_TIMEOUT_MS
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Section: 3
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Source: libcurl
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See-also:
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- CURLOPT_CONNECTTIMEOUT_MS (3)
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- CURLOPT_LOW_SPEED_LIMIT (3)
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- CURLOPT_TIMEOUT (3)
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---
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# NAME
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CURLOPT_HAPPY_EYEBALLS_TIMEOUT_MS - head start for IPv6 for happy eyeballs
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# SYNOPSIS
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~~~c
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#include <curl/curl.h>
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CURLcode curl_easy_setopt(CURL *handle, CURLOPT_HAPPY_EYEBALLS_TIMEOUT_MS,
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long timeout);
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~~~
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# DESCRIPTION
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Happy eyeballs is an algorithm that attempts to connect to both IPv4 and IPv6
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addresses for dual-stack hosts, preferring IPv6 first for *timeout*
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milliseconds. If the IPv6 address cannot be connected to within that time then
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a connection attempt is made to the IPv4 address in parallel. The first
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connection to be established is the one that is used.
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The range of suggested useful values for *timeout* is limited. Happy
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Eyeballs RFC 6555 says "It is RECOMMENDED that connection attempts be paced
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150-250 ms apart to balance human factors against network load." libcurl
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currently defaults to 200 ms. Firefox and Chrome currently default to 300 ms.
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# DEFAULT
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CURL_HET_DEFAULT (currently defined as 200L)
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# PROTOCOLS
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All except FILE
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# EXAMPLE
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~~~c
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int main(void)
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{
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CURL *curl = curl_easy_init();
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if(curl) {
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curl_easy_setopt(curl, CURLOPT_URL, "https://example.com");
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curl_easy_setopt(curl, CURLOPT_HAPPY_EYEBALLS_TIMEOUT_MS, 300L);
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curl_easy_perform(curl);
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/* always cleanup */
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curl_easy_cleanup(curl);
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}
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}
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~~~
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# AVAILABILITY
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Added in 7.59.0
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# RETURN VALUE
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Returns CURLE_OK
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