[tor-bugs] #23101 [Core Tor/Tor]: Predict and build specific HS purpose circuits (rather than GENERAL)

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#23101: Predict and build specific HS purpose circuits (rather than GENERAL)
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 Reporter:  mikeperry                            |          Owner:
                                                 |  mikeperry
     Type:  enhancement                          |         Status:
                                                 |  needs_revision
 Priority:  Medium                               |      Milestone:  Tor:
                                                 |  0.3.3.x-final
Component:  Core Tor/Tor                         |        Version:
 Severity:  Normal                               |     Resolution:
 Keywords:  tor-hs, tor-guard, guard-discovery-  |  Actual Points:
  prop247-controller, review-group-27            |
Parent ID:  #13837                               |         Points:
 Reviewer:  asn                                  |        Sponsor:
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Comment (by asn):

 OK, thanks for fixups! I reviewed the fixups and did another round of
 review. I still haven't had time to actually test the branch tho.

 In general, this branch was '''hard''' to review IMO mainly due to the
 surrounding code being extremely hairy, the lack of concise high-level
 comments of what we are trying to achieve, and everything being done in a
 single commit (adding circ purpose && handling cannibalization &&
 launching preemptive circs). Also the lack of tests is troubling, and the
 vanguards repo that is supposed to help testing had no README and was very
 hard to understand, but thankfuly mikeperry helped me over IRC. It took me
 3 days of review to get a basic understanding of the subsystem and grasp
 the code changes that were done, and I still haven't actually tested this
 branch. I feel that no strong attempt was done to make the feature
 [https://medium.com/@9len/on-code-review-16ea85f7c585 pleasurable for
 review] and that's why it took me so long.

 I think the next steps here are to squash the `mikeperry/bug23101-rebased`
 branch, then apply my fixes (`bug23101-dev`) on top of it, and then start
 handling the latest review comments. Then we would need a fresh ''merge
 request'' on gitlab because the current one is quite dirty.

 In the next days, I'll try to test the branch on the real network to
 understand more what's going on and provide further review points, or a
 branch.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/23101#comment:17>
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