[tor-bugs] #8956 [Obfsproxy]: obfsproxy should use a SOCKS proxy if Tor wants it to

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#8956: obfsproxy should use a SOCKS proxy if Tor wants it to
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     Reporter:  asn        |      Owner:  asn
         Type:  task       |     Status:  needs_review
     Priority:  normal     |  Milestone:
    Component:  Obfsproxy  |    Version:
   Resolution:             |   Keywords:
Actual Points:             |  Parent ID:  #8402
       Points:             |
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Comment (by yawning):

 I went and cleaned up the error handling slightly per our discussion, see
 commit `      a79b8ae6a147fdebc59e6555ad5e985487c47f94`.

 It turns out that Twisted doesn't have a custom exception type for
 `EHOSTUNREACH` in `twisted.internet.error`, so it generates a failure with
 `ConnectError`.  I put code in to distinguish that case and send the
 proper SOCKS5 error back as an added bonus, yay for a slightly more
 informative Tor log (The case when the proxy just abruptly closes the
 connection, users will still need to look at the obfsproxy log though).

 Unless you want to re-add support for `--proxy` in managed mode (which
 would make this more immediately usable to people), I think that just
 about wraps up all the code for this feature.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/8956#comment:12>
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