[tor-bugs] #18929 [Core Tor/Tor]: Fix selection of directories with non-preferred address families

[Tor Bug Tracker & Wiki]

#18929: Fix selection of directories with non-preferred address families
-------------------------+-------------------------------------------------
     Reporter:  teor     |      Owner:
         Type:  defect   |     Status:  new
     Priority:  Medium   |  Milestone:  Tor: 0.2.8.x-final
    Component:  Core     |    Version:  Tor: 0.2.8.1-alpha
  Tor/Tor                |   Keywords:  must-fix-before-028-rc,
     Severity:  Normal   |  CoreTorTeam201605
Actual Points:  2 hours  |  Parent ID:  #18483
       Points:  small    |   Reviewer:
      Sponsor:           |
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 In #17840 in 0.2.8.1-alpha, we sometimes fail to fall back to directories
 with addresses in non-preferred IP families:
 * we didn't identify relays that we could fall back to correctly;
 * we incorrectly assumed that every node would have an IPv4 address - this
 doesn't apply to bridges;
 * we counted relays when we had already fallen back to non-preferred
 addresses.

 This likely affected bridge clients with IPv4 bridges, and clients in
 small networks.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/18929>
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