Daniel Stenberg e694c8284a

docs/libcurl/opts: clarify the return values

Expand a little.

- mention the type name of the return code
- avoid stating which exact return codes that might be returned, as that
  varies over time, builds and conditions
- avoid stating some always return OK
- refer to the manpage documenting all the return codes

Closes #15900

2025-01-02 17:13:33 +01:00

1.7 KiB

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SPDX-License-Identifier

Title

Section

Source

Protocol

See-also

Added-in

curl

CURLOPT_HAPPY_EYEBALLS_TIMEOUT_MS

libcurl

All

CURLOPT_CONNECTTIMEOUT_MS (3)

CURLOPT_LOW_SPEED_LIMIT (3)

CURLOPT_TIMEOUT (3)

7.59.0

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%

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%

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).

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