[tor-bugs] #27215 [Core Tor/Tor]: hs: Change default HiddenServiceVersion to 3

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#27215: hs: Change default HiddenServiceVersion to 3
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     Reporter:  dgoulet       |      Owner:  (none)
         Type:  enhancement   |     Status:  new
     Priority:  Medium        |  Milestone:  Tor: 0.3.5.x-final
    Component:  Core Tor/Tor  |    Version:
     Severity:  Normal        |   Keywords:  tor-hs, 035-proposed
Actual Points:                |  Parent ID:
       Points:                |   Reviewer:
      Sponsor:                |
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 The next tor release (0.3.5) is an LTS, it would mean that keeping v2 the
 default version forces us to support it until 2020 (minimum).

 Hidden service version 3 have been merged back in 0.3.2 and have been
 extensively tested. Bugs remains but we are confident they can be
 addressed in 0.3.5 and aren't blockers to the mass adoption of v3.

 By making version 3 the default version for new services, we can start
 working on deprecating version 2 in future tor releases.

 Still, for a while, v2 will work on the network so this is *not* about
 removing v2 entirely but simply switching new default services to v3. An
 operator will still be able to specify `HiddenServiceVersion 2` explicitly
 if they do really want a v2.

 NOTE: There is a tricky issue with this. We'll have to make tor "guess"
 the right version when loading the configuration. Right now, we
 _explicitly_ ask the operator to provide `HiddenServiceVersion 3` else we
 consider it a v2.

 Considering that, we can't ask all operators to add `HiddenServiceVersion
 2` to their torrc so we need to make tor smart so it can learn the right
 version if not given.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/27215>
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