[tor-bugs] #24047 [Core Tor/Tor]: Add new stats for v2 and v3 onion service traffic

[Tor Bug Tracker & Wiki]

#24047: Add new stats for v2 and v3 onion service traffic
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     Reporter:  teor        |      Owner:  (none)
         Type:  defect      |     Status:  new
     Priority:  Medium      |  Milestone:  Tor: 0.3.3.x-final
    Component:  Core        |    Version:
  Tor/Tor                   |
     Severity:  Normal      |   Keywords:  prop224, tor-hs, privcount-maybe
Actual Points:              |  Parent ID:
       Points:  2           |   Reviewer:
      Sponsor:              |
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 The current onion service traffic statistic includes v2 and v3 services.

 But they are distinguishable at the rend point: v2 services use TAP to
 extend, and v3 use ntor.

 This is how we tag and count circuits for v2 and v3 in experimental
 PrivCount:
 https://github.com/privcount/tor/commit/ab0ee674d72a8b86cf394ecb392c0e829a265cf6
 (Sorry it's not a very clean commit, look for
 `circ->used_legacy_circuit_handshake`.)

 We could add a similar flag to tor, and use that flag to produce two new
 statistics, v2 and v3 data.

 Since there will be a small number of v3 onion sites, we might want to
 implement this using PrivCount in tor, so their rend points do not stand
 out. If we don't use PrivCount in tor, we should fix the stats noise bugs
 in #23061 before we implement this.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/24047>
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