22 lines
965 B
D
22 lines
965 B
D
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c: Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
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SPDX-License-Identifier: curl
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Long: happy-eyeballs-timeout-ms
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Arg: <milliseconds>
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Help: Time for IPv6 before trying IPv4
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Added: 7.59.0
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Category: connection
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Example: --happy-eyeballs-timeout-ms 500 $URL
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See-also: max-time connect-timeout
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Multi: single
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---
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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, giving IPv6 a head-start of the specified
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number of milliseconds. If the IPv6 address cannot be connected to within that
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time, then a connection attempt is made to the IPv4 address in parallel. The
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first connection to be established is the one that is used.
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The range of suggested useful values is limited. Happy Eyeballs RFC 6555 says
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"It is RECOMMENDED that connection attempts be paced 150-250 ms apart to
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balance human factors against network load." libcurl currently defaults to
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200 ms. Firefox and Chrome currently default to 300 ms.
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