[tor-bugs] #23114 [Core Tor/Tor]: Circuit Build Timeout should apply at circuit completion

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#23114: Circuit Build Timeout should apply at circuit completion
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     Reporter:  mikeperry     |      Owner:  mikeperry
         Type:  enhancement   |     Status:  new
     Priority:  Medium        |  Milestone:
    Component:  Core Tor/Tor  |    Version:
     Severity:  Normal        |   Keywords:
Actual Points:                |  Parent ID:
       Points:                |   Reviewer:
      Sponsor:                |
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 Back when the CBT code was first written, circuit build times were around
 10 seconds. This meant it was fine to check if the timeout had passed in
 circuit_expire_building(), which was called once per second.

 However, now that the typical timeout is more like 2 seconds or less, we
 actually let a significantly larger fraction of circuits through by
 waiting for this once-per-second callback.

 The fix is to switch the purpose of circuits as they are being built
 and/or opened to MEASUREMENT circuits as soon as they pass the timeout,
 but before use. This will cause us to actually discard the proper fraction
 of slow paths.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/23114>
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