[tor-bugs] #32605 [Metrics]: Remove external dependencies to implementation classes

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#32605: Remove external dependencies to implementation classes
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     Reporter:  karsten      |      Owner:  karsten
         Type:  enhancement  |     Status:  assigned
     Priority:  Medium       |  Milestone:
    Component:  Metrics      |    Version:
     Severity:  Normal       |   Keywords:
Actual Points:               |  Parent ID:
       Points:               |   Reviewer:
      Sponsor:               |
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 Last week I started working on #24028. But after making a few local
 commits I realized that there's one major issue that makes this task
 harder than it should be: external dependencies to metrics-lib's
 implementation classes.

 Some background: The idea behind metrics-lib was to provide a library for
 parsing descriptors. It contains one package with interfaces and another
 package with implementations of those interfaces. External applications,
 including our own, shall only depend on the first package, so that we can
 make changes to the second package at any time.

 After a while we started sharing code (not interfaces) from metrics-lib in
 other applications, including code to parse `index.json` files or code to
 sanitize web server logs. And even though sharing code is a good idea in
 many cases, it sometimes comes at the cost of creating unwanted
 dependencies. I'd rather want to turn metrics-lib into just the
 descriptor-parsing library as it was before and share more generic code
 between all code bases in another way than stuffing it into metrics-lib.

 Here's my suggestion: We remove external dependencies to metrics-lib's
 `impl`, `index`, `internal`, and `log` packages, put out a set of
 releases, refactor those packages including renaming them as planned in
 #24028, and finally come up with a better plan for sharing code between
 modules.

 I'm going to post two branches for review here in a minute.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/32605>
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