[tor-bugs] #14847 [Tor]: Controller: add a command to fetch HS descriptor from HSdir(s)

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#14847: Controller: add a command to fetch HS descriptor from HSdir(s)
-----------------------------+----------------------------------------
     Reporter:  dgoulet      |      Owner:  dgoulet
         Type:  enhancement  |     Status:  needs_review
     Priority:  normal       |  Milestone:  Tor: 0.2.7.x-final
    Component:  Tor          |    Version:
   Resolution:               |   Keywords:  SponsorR tor-hs controller
Actual Points:               |  Parent ID:  #3521
       Points:               |
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Comment (by dgoulet):

 Replying to [comment:19 atagar]:
 > {{{
 > DescId = 32*Base32Character
 > }}}
 >
 > Out of curiosity where do hidden service descriptor ids reside? That is
 to say, what are the use cases where someone will have one of these ids
 and want to look it up?

 One use case we have for this is to create a tool that will help us
 measure the impact of relay churn on HS reachability. With a descriptor
 id, we can use it to fetch HSdir from a couple consensus back in time and
 track movement of it. It's not entirely clear if it will help but our
 first assessment is yes. See #13209 for a bit more info.

 >
 > -----
 >
 > {{{
 > TimePeriod = Specified in rend-spec.txt section 1.3.
 > }}}
 >
 > Please say what this actually is. I'm sure it's discussed in there, but
 it's actually not a well defined field in the rend-spec...

 Yeah, it's "time-period" field in the rend-spec so I will add that to the
 description. The only thing I want to avoid here is to copy-paste text
 between spec document because if one changes, chances are we forgot the
 other one.

 >
 > {{{
 > + It is also possible to specify a TimePeriod and/or a Replica value for
 an
 > + HSAddress. They can't be used with a DescId because they are part of a
 > + descriptor id for an HSAddress. A 552 error is returned in that case.
 > }}}
 >
 > Admittedly I'm not overly familiar with hidden services, but I'm not
 sure what this paragraph means or what the fields do.

 TimePeriod, Replica and HSAddress are all used to compute a descriptor ID.
 Thus if you provide a descriptor ID, they are useless. From your native
 english speaker perspective, how can I phrase that better? :)

 >
 > ----
 >
 > {{{
 > + Examples are:
 > + C: HSFETCH v2-gezdgnbvgy3tqolbmjrwizlgm5ugs2tl
 > + S: 250 OK
 > }}}
 >
 > Oh, I appreciate the examples - thanks for including that!

 Yeah I figured, the definition of this command went from VERY simple to
 omgbbqwtf-medium-rare.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/14847#comment:20>
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