[tor-bugs] #21206 [Core Tor/Tor]: Measure client up/down bandwidth for directory requests, split by type

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#21206: Measure client up/down bandwidth for directory requests, split by type
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 Reporter:  nickm         |          Owner:  ahf
     Type:  defect        |         Status:  needs_review
 Priority:  Medium        |      Milestone:  Tor: 0.3.1.x-final
Component:  Core Tor/Tor  |        Version:
 Severity:  Normal        |     Resolution:
 Keywords:  sponsor4      |  Actual Points:
Parent ID:  #21205        |         Points:  3
 Reviewer:                |        Sponsor:
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Changes (by ahf):

 * status:  needs_revision => needs_review


Comment:

 I've updated my branch to support keeping information on the number of
 sent and received `RELAY_DATA` cells. This should allow us to calculate
 the following overheads as mentioned above:

 - The number of bytes sent/received in the payloads.
 - The number of cells containing data that have been passed over the
 directory connection.

 We should therefore be able to estimate:
 - Relay cell headers.
 - Padding bytes.

 I'm unsure how we should measure/estimate the TLS record sizes and the
 circuit headers/cells needed to setup the directory connection. I'll have
 to dig into that to be sure.

 I've left the two additional `unsigned data_cells_received` and `unsigned
 data_cells_sent` members on `dir_connection_t` as unguarded, since their
 lifetime is relatively short. If we do not want to have them around unless
 for very specific builds I'll wrap them in a guard.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/21206#comment:7>
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