[tor-bugs] #32165 [Core Tor/Tor]: On first boot, Tor mistakenly tells me "The current consensus has no exit nodes"

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#32165: On first boot, Tor mistakenly tells me "The current consensus has no exit
nodes"
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 Reporter:  arma          |          Owner:  (none)
     Type:  defect        |         Status:  needs_revision
 Priority:  Medium        |      Milestone:  Tor: 0.4.2.x-final
Component:  Core Tor/Tor  |        Version:
 Severity:  Normal        |     Resolution:
 Keywords:  bootstrap     |  Actual Points:
Parent ID:                |         Points:
 Reviewer:  ahf           |        Sponsor:
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Comment (by arma):

 Replying to [comment:9 teor]:
 > We've switched this check a few times, and it breaks different things
 each time.
 > So we need to be very careful about this change.
 > I'm not sure if it is correct.
 > Please check the history of changes to this line.

 Ok, there have been three changes to this line:

 The original commit, 9b2d106e4, which documented np and nu clearly (yay)
 but got their meanings reversed (oops).

 Nick's fix in #14918, which went in as commit 8eb3d81e6: it clarified the
 function comment in count_usable_descriptors (yay), fixed np to nu as it
 should, but left the (still wrong) comments explaining np and nu in place
 (oops).

 teor's update for #27236, which went in as commit 3ebbc1c84, which
 reintroduced the np vs nu bug.

 I just checked num_present vs num_usable again, and I am confident that
 the fix in 94cb4f8 (which was the same fix as 8eb3d81e6) is right:
 num_usable is how many are in the consensus that we would use, and
 num_present is how many of those we actually have descriptors for right
 now. So on first boot, when we have no descriptors present, we must check
 nu, not np, or we will wrongly conclude that we have a consensus with no
 exits.

 Now, #27236 speaks of internal-only onion service networks and chutney.
 But I don't see how commit 3ebbc1c8 does anything about those -- it
 essentially just reverts Nick's fix. I'm guessing it has something to do
 with the nearby commit 588c7767. It looks like that commit is trying to
 make sure that at least one relay in the consensus can exit to at least
 one port. Makes sense -- but it appears to accidentally also be checking
 that *we have a local descriptor* for such a relay. Can you help me
 understand what exactly we need to check for, in the "internal-only onion
 service networks and chutney" case? We shouldn't merge this new patch
 until we understand the chutney requirements better.

 > We also need to change variable names, log messages, and documentation,
 see:
 > https://trac.torproject.org/projects/tor/ticket/27448#comment:3

 Yes, I agree. I'll give this a go if you like my proposed name changes
 above: "present" -> "ready" and "usable" -> "listed". (I figure going
 through and doing it for the wrong names isn't a good use of anybody's
 time.)

 Thanks!

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/32165#comment:10>
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