[tor-bugs] #28636 [Core Tor/Tor]: Address WTF-PAD comments by Nick (2018-11-27 over IRC)

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#28636: Address WTF-PAD comments by Nick (2018-11-27 over IRC)
-------------------------------------------------+-------------------------
 Reporter:  asn                                  |          Owner:  (none)
     Type:  defect                               |         Status:
                                                 |  needs_review
 Priority:  High                                 |      Milestone:  Tor:
                                                 |  unspecified
Component:  Core Tor/Tor                         |        Version:
 Severity:  Normal                               |     Resolution:
 Keywords:  wtf-pad, tor-relay, tor-cell,        |  Actual Points:
  padding, 041-proposed, network-team-           |
  roadmap-2019-Q1Q2                              |
Parent ID:  #28632                               |         Points:  3
 Reviewer:                                       |        Sponsor:
                                                 |  Sponsor2
-------------------------------------------------+-------------------------
Changes (by asn):

 * status:  new => needs_review


Comment:

 OK I pushed branch `bug28636`: https://github.com/torproject/tor/pull/788

 It does the following:

 - Stops padding when dormant mode is enabled. I'm not sure if this is a
 good idea, but I think it's fairly unlikely that there will be useful
 circuits to pad when dormant mode is enabled since it means that the
 client has been inactive for many many hours. So perhaps this does not
 matter so much, and I erred on the side of network health.
 - Implemented type-safe downcasting functions.
 - Documented the public API of prob distr.
 - Used crypto fast RNG instead of the old RNG.
 - Renamed `circpad_machine_state_t` to `circpad_machine_runtime_t`.

 On the downside, I did not manage to hide the `dist_ops` structure as
 suggested by Nick in comment:15 because the messy `GEOMETRIC()` etc. init
 macros are using it in various places around the codebase and I couldn't
 get it to work. I was thinking of ditching those messy macros and making
 my own init functions (perhaps using a macro) but I couldn't figure out a
 pleasant interface for it that would look real good, so I decided to
 postpone this refactoring task since the above had already taken me the 2
 points that were originally specified for this task, and we still have
 reviews to go.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/28636#comment:17>
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