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happy-eyeballs-timeout-ms.d 965 B

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  1. c: Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
  2. SPDX-License-Identifier: curl
  3. Long: happy-eyeballs-timeout-ms
  4. Arg: <milliseconds>
  5. Help: Time for IPv6 before trying IPv4
  6. Added: 7.59.0
  7. Category: connection
  8. Example: --happy-eyeballs-timeout-ms 500 $URL
  9. See-also: max-time connect-timeout
  10. Multi: single
  11. ---
  12. Happy Eyeballs is an algorithm that attempts to connect to both IPv4 and IPv6
  13. addresses for dual-stack hosts, giving IPv6 a head-start of the specified
  14. number of milliseconds. If the IPv6 address cannot be connected to within that
  15. time, then a connection attempt is made to the IPv4 address in parallel. The
  16. first connection to be established is the one that is used.
  17. The range of suggested useful values is limited. Happy Eyeballs RFC 6555 says
  18. "It is RECOMMENDED that connection attempts be paced 150-250 ms apart to
  19. balance human factors against network load." libcurl currently defaults to
  20. 200 ms. Firefox and Chrome currently default to 300 ms.