[tor-bugs] #4483 [Tor]: If k of n authorities are down, k/n bootstrapping clients are delayed for minutes

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#4483: If k of n authorities are down, k/n bootstrapping clients are delayed for
minutes
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 Reporter:  arma                                 |          Owner:  teor
     Type:  defect                               |         Status:
 Priority:  High                                 |  needs_review
Component:  Tor                                  |      Milestone:  Tor:
 Severity:  Normal                               |  0.2.8.x-final
 Keywords:  performance, bootstrap, dirauth-     |        Version:
  dos-resistance, tor-client, large-feature,     |     Resolution:
  prop210, 028-triage, TorCoreTeam201512,        |  Actual Points:
  MikePerry201512R                               |         Points:
Parent ID:  #2664                                |  medium/large
  Sponsor:  SponsorU                             |
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Comment (by teor):

 Replying to [comment:42 nickm]:
 > 86ac0928577c18a9e27c6c4aae24abf9478ffcfa -- still have to review this
 but...
 >    * Is return; really the right thing to do in these
 directory_initiate_command_rend cases?  Why?

 "return" has the effect of cancelling the current connection attempt,
 which is what we want to do if the connection was an excess connection.

 It's what the function already does when the connection fails
 (`connection_connect()` returns -1 or `!linked_conn`), and in all the
 other error cases.

 However, it doesn't make sense to make a connection, then immediately
 close it. So I created connection_dir_avoid_extra_connection_for_purpose()
 and call it at the top of the function. I updated the unit tests
 (including fixing a bug in the unit tests) and updated some comments as
 well.

 See my commit 087ae73 for these fixups.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/4483#comment:44>
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