[tor-bugs] #2576 [Tor Relay]: Can we try to extend from the bridge to a website and learn if the website is reachable?

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#2576: Can we try to extend from the bridge to a website and learn if the website
is reachable?
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 Reporter:  arma       |          Owner:     
     Type:  task       |         Status:  new
 Priority:  normal     |      Milestone:     
Component:  Tor Relay  |        Version:     
 Keywords:             |         Parent:     
   Points:             |   Actualpoints:     
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 Ticket #1851 suggests reprogramming bridges to connect to baidu
 periodically, and then report the reachability results in their extrainfo
 descriptors. We'd have to specify how that reporting works, how often the
 tests happen, whether we should generalize to write "baidu.com" in the
 consensus, etc.

 A much simpler approach would be to build a circuit to the bridge, extend
 that circuit to baidu.com:80, and then look at the failure error code and
 discern whether it was reachable and just didn't TLS right or whether it
 was unreachable.

 Can we manipulate Tor's protocol to learn this? Or is the error code too
 opaque? If it works, we should whip up a Torflow like thing that checks
 reachability of baidu from every bridge.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/2576>
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