[tor-bugs] #31241 [Core Tor/Tor]: Refactor config validation

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#31241: Refactor config validation
-----------------------------------------+---------------------------------
 Reporter:  nickm                        |          Owner:  nickm
     Type:  task                         |         Status:  needs_review
 Priority:  Medium                       |      Milestone:  Tor:
                                         |  0.4.2.x-final
Component:  Core Tor/Tor                 |        Version:
 Severity:  Normal                       |     Resolution:
 Keywords:  network-team-roadmap-august  |  Actual Points:
Parent ID:  #29211                       |         Points:  1.5
 Reviewer:                               |        Sponsor:  Sponsor31-can
-----------------------------------------+---------------------------------

Comment (by nickm):

 Summary of design.

 Previously, there were "validate" functions for config objects, most
 notably options_validate().  There was no generic way to call the
 "validate" function for a given config object -- you would just call it
 directly.

 These functions had a horrible signature, since they were allowed to
 modify the configuration object, compare it to an old object, learn
 whether it came from setconf (!), and compare it to its defaults (!).

 So the old process was:
   * Call options_verify.
   * Call options_transition_allowed.

 Now the configuration verification process follows a more strict multi-
 stage process:
   * Call config_validate()
      * For each config_format_t, call config_validate_single():
        * Callback to modifications to the configuration object (early,
 pre-validation)
        * Callback to validation function (only sees current object, may
 not change it).
        * legacy validation callback (whatever we have not moved out of
 options_validate)
        * callback to check transition (can see current and previous
 object, may not change them)
        * modifications to the configuration object (final, late-
 validation)

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/31241#comment:4>
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