[tor-bugs] #18873 [Core Tor/Tor]: Refactor circuit_predict_and_launch_new()

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#18873: Refactor circuit_predict_and_launch_new()
--------------------------+------------------------------------
 Reporter:  asn           |          Owner:
     Type:  defect        |         Status:  needs_revision
 Priority:  Low           |      Milestone:  Tor: 0.3.0.x-final
Component:  Core Tor/Tor  |        Version:
 Severity:  Normal        |     Resolution:
 Keywords:  refactoring   |  Actual Points:
Parent ID:                |         Points:
 Reviewer:  dgoulet       |        Sponsor:
--------------------------+------------------------------------

Comment (by chelseakomlo):

 Replying to [comment:17 dgoulet]:
 > Replying to [comment:15 chelseakomlo]:
 [snip]
 > > Hey! Ok, here is my understanding:
 > >
 > > A circuit with purpose CIRCUIT_PURPOSE_C_GENERAL will always be an
 origin circuit, because:
 > >
 > > in or.h
 > > {{{
 > > #define CIRCUIT_IS_ORIGIN(c) (CIRCUIT_PURPOSE_IS_ORIGIN((c)->purpose))
 > > #define CIRCUIT_PURPOSE_IS_ORIGIN(p) ((p)>CIRCUIT_PURPOSE_OR_MAX_)
 > > #define CIRCUIT_PURPOSE_OR_MAX_ 4
 > > #define CIRCUIT_PURPOSE_C_GENERAL 5
 > > }}}
 > >
 >
 > I see that `CIRCUIT_IS_ORIGIN(c)` translates to `if c >
 CIRCUIT_PURPOSE_OR_MAX_ then circ is origin`. We have lots of purposes
 that are above `CIRCUIT_PURPOSE_C_GENERAL = 5` in values like a client
 doing an HS introduction to a relay `CIRCUIT_PURPOSE_C_INTRODUCING = 6`.
 Am I missing something here?
 >
 > Origin circuits means that we (tor) initiated them and just with the HS,
 there are lots of purposes.


 In circuit_is_available_for_use, we exclude all circuits that don't have
 purpose `CIRCUIT_PURPOSE_C_GENERAL,` which is an origin circuit. See line
 1023.

 I can add a comment in the code explaining this if it isn't clear in the
 code.


 >
 > I think you missed this syntax fix as well:
 >
 > {{{
 > #define CBT_MAX_UNUSED_OPEN_CIRCUITS (MAX_UNUSED_OPEN_CIRCUITS- \
 >     CBT_MIN_REMAINING_PREEMPTIVE_CIRCUITS)
 > }}}


 That change is in commit `extract magic numbers in circuituse.c`

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/18873#comment:18>
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