[tor-bugs] #21902 [Core Tor/Tor]: evdns adds default DNS servers, but chutney wants a consistent environment

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#21902: evdns adds default DNS servers, but chutney wants a consistent environment
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     Reporter:  teor          |      Owner:
         Type:  defect        |     Status:  new
     Priority:  Medium        |  Milestone:  Tor: unspecified
    Component:  Core Tor/Tor  |    Version:
     Severity:  Normal        |   Keywords:  chutney-wants, ipv6
Actual Points:                |  Parent ID:
       Points:  1             |   Reviewer:
      Sponsor:                |
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 When we test tor exits using chutney, we want a consistent network
 environment, so that tests pass or fail reliably.

 This means that we want to be able to configure exits with no DNS servers,
 and have them only connect to IP addresses.

 But evdns adds default name server(s) in some circumstances (for example,
 127.0.0.1:53.)

 This default could also be an issue on an IPv6-only system, where we'd
 want [::1]:53. (Yes, some IPv6-only systems don't even have an IPv4
 localhost!)

 This is also broken because of the empty/missing resolv.conf behaviour in
 #21900.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/21902>
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