1*6236dae4SAndroid Build Coastguard Worker--- 2*6236dae4SAndroid Build Coastguard Workerc: Copyright (C) Daniel Stenberg, <[email protected]>, et al. 3*6236dae4SAndroid Build Coastguard WorkerSPDX-License-Identifier: curl 4*6236dae4SAndroid Build Coastguard WorkerLong: happy-eyeballs-timeout-ms 5*6236dae4SAndroid Build Coastguard WorkerArg: <ms> 6*6236dae4SAndroid Build Coastguard WorkerHelp: Time for IPv6 before IPv4 7*6236dae4SAndroid Build Coastguard WorkerAdded: 7.59.0 8*6236dae4SAndroid Build Coastguard WorkerCategory: connection timeout 9*6236dae4SAndroid Build Coastguard WorkerMulti: single 10*6236dae4SAndroid Build Coastguard WorkerSee-also: 11*6236dae4SAndroid Build Coastguard Worker - max-time 12*6236dae4SAndroid Build Coastguard Worker - connect-timeout 13*6236dae4SAndroid Build Coastguard WorkerExample: 14*6236dae4SAndroid Build Coastguard Worker - --happy-eyeballs-timeout-ms 500 $URL 15*6236dae4SAndroid Build Coastguard Worker--- 16*6236dae4SAndroid Build Coastguard Worker 17*6236dae4SAndroid Build Coastguard Worker# `--happy-eyeballs-timeout-ms` 18*6236dae4SAndroid Build Coastguard Worker 19*6236dae4SAndroid Build Coastguard WorkerHappy Eyeballs is an algorithm that attempts to connect to both IPv4 and IPv6 20*6236dae4SAndroid Build Coastguard Workeraddresses for dual-stack hosts, giving IPv6 a head-start of the specified 21*6236dae4SAndroid Build Coastguard Workernumber of milliseconds. If the IPv6 address cannot be connected to within that 22*6236dae4SAndroid Build Coastguard Workertime, then a connection attempt is made to the IPv4 address in parallel. The 23*6236dae4SAndroid Build Coastguard Workerfirst connection to be established is the one that is used. 24*6236dae4SAndroid Build Coastguard Worker 25*6236dae4SAndroid Build Coastguard WorkerThe range of suggested useful values is limited. Happy Eyeballs RFC 6555 says 26*6236dae4SAndroid Build Coastguard Worker"It is RECOMMENDED that connection attempts be paced 150-250 ms apart to 27*6236dae4SAndroid Build Coastguard Workerbalance human factors against network load." libcurl currently defaults to 28*6236dae4SAndroid Build Coastguard Worker200 ms. Firefox and Chrome currently default to 300 ms. 29