[tor-bugs] #20472 [Core Tor/Tor]: circuit_pick_extend_handshake: Non-fatal assertion !(node_prev == NULL) failed

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#20472: circuit_pick_extend_handshake: Non-fatal assertion !(node_prev == NULL)
failed
-------------------------------------------------+-------------------------
 Reporter:  cypherpunks                          |          Owner:
     Type:  defect                               |         Status:
                                                 |  needs_review
 Priority:  Medium                               |      Milestone:  Tor:
                                                 |  0.2.9.x-final
Component:  Core Tor/Tor                         |        Version:  Tor:
                                                 |  0.2.9.3-alpha
 Severity:  Normal                               |     Resolution:
 Keywords:  TorCoreTeam201610, regression,       |  Actual Points:  0.5
  029-backport                                   |
Parent ID:                                       |         Points:  0.3
 Reviewer:                                       |        Sponsor:
-------------------------------------------------+-------------------------
Changes (by teor):

 * status:  needs_revision => needs_review
 * actualpoints:  0.3 => 0.5


Comment:

 Please see my branch bug20472-029-v2 on github.
 It passes `make check-spaces check test-network-all`

 If we can assume every node supports EXTEND2,
 circuit_pick_extend_handshake becomes very simple. (All we need to know is
 whether the next hop has an ntor key.)

 I also refactored circuit_pick_create_handshake so it matched
 circuit_pick_extend_handshake, and renamed
 routerstatus_version_supports_ntor, because it was actually checking
 extend2 support.

 These refactoring commits aren't essential, they can go in 0.3.0 if you
 want.
 (That said, they are trivially correct.)

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/20472#comment:6>
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