[tor-bugs] #20593 [Core Tor/Tor]: Avoid resetting download status on 503

[Tor Bug Tracker & Wiki]

#20593: Avoid resetting download status on 503
------------------------------+--------------------------------
     Reporter:  nickm         |      Owner:
         Type:  defect        |     Status:  new
     Priority:  Medium        |  Milestone:  Tor: 0.2.9.x-final
    Component:  Core Tor/Tor  |    Version:
     Severity:  Normal        |   Keywords:
Actual Points:                |  Parent ID:  #20499
       Points:                |   Reviewer:
      Sponsor:                |
------------------------------+--------------------------------
 On comment:31:ticket:20499 , Teor notes:
 >
 > If we really do want every failure to result in a schedule increment, we
 have to remove the following code:
 >
 > download_status_increment_failure:
 > {{{
 >   /* only count the failure if it's permanent, or we're a server */
 >   if (status_code != 503 || server) {
 >     if (dls->n_download_failures < IMPOSSIBLE_TO_DOWNLOAD-1)
 >       ++dls->n_download_failures;
 >   }
 > }}}
 >
 > Because combined with this code in download_status_schedule_get_delay,
 it causes a reset on every 503:
 > {{{
 >     /* Check if we missed a reset somehow */
 >     if (dls->last_backoff_position > dls_schedule_position) {
 >       dls->last_backoff_position = 0;
 >       dls->last_delay_used = 0;
 >     }
 > }}}
 >
 > Which is exactly what we don't want when relays are busy - imagine
 clients doing an automatic reset every time they DoS a relay...

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/20593>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
The Tor Project: anonymity online