[tor-bugs] #23672 [Core Tor/Tor]: hs-v3: With multiple SOCKS connection to the same .onion, don't trigger a descriptor fetch for each connection

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#23672: hs-v3: With multiple SOCKS connection to the same .onion, don't trigger a
descriptor fetch for each connection
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     Reporter:  dgoulet       |      Owner:  dgoulet
         Type:  defect        |     Status:  assigned
     Priority:  Medium        |  Milestone:  Tor: 0.3.2.x-final
    Component:  Core Tor/Tor  |    Version:
     Severity:  Normal        |   Keywords:  tor-hs, tor-client, prop224
Actual Points:                |  Parent ID:
       Points:                |   Reviewer:
      Sponsor:                |
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 This comes out of #23653 for a v3 only fix because a patch for v2 requires
 more refactoring.

 We should only have one descriptor fetch at a time to an HSDir and not
 open one for each SOCKS connection. Because of how the client hsdir
 request cache works, you can't request the same .onion to the same HSDir
 inside a 15 minutes time frame (woa that is big). Thus, if we open 6 SOCKS
 requests and they all trigger a fetch, all HSDir are put in the cache and
 we can't query any of them while they are opened or until an error
 happened or until we can ultimately connect to the service.

 Thus comes a bug where the 7th SOCKS connection (opened rapidly after the
 6) will always fail because no HSDir can be used (#15937)

 What we should do:

 1. At each SOCKS connection, check if we have a pending directory fetch
 for the .onion and if so, wait on it.

 2. On a fetch internal error, not allowed because of
 `FetchHidServDescriptors 0` or no more HSDir are usable, close all pending
 SOCKS connections instead of making them timeout (#23653).

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/23672>
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