[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)
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     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:12 arma]:
 > Replying to [comment:10 atagar]:
 > > {{{
 > > If one or more Server are given, they are used instead.
 > > }}}
 > >
 > > What happens when you specify multiple? Does it pick among them
 randomly?
 >
 > I kind of thought that it would cause Tor to initiate multiple fetches,
 one from each.
 >
 > But, good question. I wonder if that feature is valuable enough for the
 complexity, compared to just making the controller send you one HSFETCH
 per fetch you want it to launch.
 >
 > Or maybe David did indeed mean to choose just one.

 "They are used instead", I meant by that if there are more than one Server
 specified, they are all used and a fetch is triggered on *all* of them

 >
 > > {{{
 > > The HS_DESC event should be used to get
 > > the results of the fetches.
 > > }}}
 > >
 > > How long does it take to retrieve a hidden service descriptor in
 practice? This is a lot clunkier for controllers. How about a 'BLOCKING=n'
 call for "I'm willing to wait up to n ms to get this descriptor"?
 >
 > That's exactly what we've been heading away from with the async
 approach. That said, David, it would indeed be nice to give the controller
 writers some guess about how long they might need to wait until they see
 their HSDESC received or failed. I think the answer is "it's like fetching
 a thing over the Tor network -- typically pretty fast, but sometimes 5 to
 even 60 seconds."

 Yup, "few seconds" up to a dir request timeout of <insert seconds>? (I
 don't know the value here). Should be added to the spec!

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/14847#comment:15>
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