[tor-bugs] #25784 [Core Tor/Tor]: Misleading error message when asking for IPv6 in a network with no IPv6-capable exits

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#25784: Misleading error message when asking for IPv6 in a network with no
IPv6-capable exits
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     Reporter:  pastly        |      Owner:  (none)
         Type:  defect        |     Status:  new
     Priority:  Medium        |  Milestone:  Tor: 0.3.5.x-final
    Component:  Core Tor/Tor  |    Version:  Tor: 0.3.2.10
     Severity:  Minor         |   Keywords:  easy, ipv6
Actual Points:                |  Parent ID:
       Points:                |   Reviewer:
      Sponsor:                |
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 I created a small test Tor network. 3 authorities, 7 relays, 3 exits.
 Great.

 I didn't set `IPv6Exit 1` on any of the exits.

 I had a client try to request `::1` over this Tor network on a hand
 crafted circuit (it makes sense to ask an exit to connect to localhost
 when this is all local ... trust me). I got the following confusing error
 message on the client.

 > [warn] I'm about to ask a node for a connection that I am telling it to
 fulfil with neither IPv4 nor IPv6. That's not going to work. Did you
 perhaps ask for an IPv6 address on an IPv4Only port, or vice versa?

 I think it's important to point out (again) that I was hand crafting these
 circuits and was not considering IPv6 support. That said, I don't know
 what Tor would do if I let it make the circuit for me and it couldn't find
 an IPv6-supporting exit.

 As you can see, I'm talking myself out of this being a bug and it just
 being me screwing things up for myself. I was encouraged to make a ticket
 though, so here we are.

 If rewriting the error message is the solution, maybe after fixing the
 "fulfil" typo, we should add "It's also possible we couldn't find any
 exits supporting the IP version you want to use"

 I'm picking 0.3.5.x-final just because I've been told you have to pick a
 milestone or else your tickets generally fall through the cracks. :)

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/25784>
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