[tor-bugs] #17627 [Tor]: Add missing controller events so we can link every step of the HS dance

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#17627: Add missing controller events so we can link every step of the HS dance
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     Reporter:  robgjansen   |      Owner:
         Type:  enhancement  |     Status:  new
     Priority:  Medium       |  Milestone:
    Component:  Tor          |    Version:
     Severity:  Normal       |   Keywords:
Actual Points:               |  Parent ID:
       Points:               |    Sponsor:  SponsorR
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 For Sponsor R, we'd like to be able to collect async control events on a
 Tor client with `setevents circ stream circ_minor hs_desc`, log the raw
 output to file, and then later reconstruct the HS dance from that file to
 analyze performance/scalability problems. There is some missing
 information in these events that prevents us from fully reconstructing the
 dance.

 1. Cannot link `HS_DESC` events to the stream used to perform the lookup.
 The stream used for the lookup will go to a `$XXX.exit` and will have
 `PURPOSE=DIR_FETCH`.

 This could be solved by adding the stream id to the `HS_DESC` event, which
 would then also allow us to link it up to the circuit used for the
 directory fetch.

 2. Cannot link the HS directory stream/circuit to the rendezvous
 stream/circuit to the introduction circuit.

 We could treat the RP stream as the "parent" stream and link it to the
 directory stream; then we could treat the circuit to which the RP stream
 is attached as the "parent" circuit and link it to the circuit used for
 the directory fetch as well as the circuit used for the introduction.

 We could also add new type of HS event to handle these sorts of issues.

 Humans make mistakes; please let me know if I am wrong about any of this.

 See also Roger's HS walkthrough:
 https://trac.torproject.org/projects/tor/wiki/doc
 /TorControlPortWalkthrough-HS

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/17627>
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