[tor-bugs] #14135 [Pluggable transport]: Incorrect SocksListener temporary error check

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#14135: Incorrect SocksListener temporary error check
-------------------------------------+--------------------------
     Reporter:  adam-p               |      Owner:  dcf
         Type:  defect               |     Status:  needs_review
     Priority:  minor                |  Milestone:
    Component:  Pluggable transport  |    Version:
   Resolution:                       |   Keywords:  goptlib
Actual Points:                       |  Parent ID:
       Points:                       |
-------------------------------------+--------------------------
Changes (by yawning):

 * keywords:   => goptlib
 * status:  new => needs_review
 * component:  meek => Pluggable transport


Comment:

 Since I was looking over the SOCKS code again in relation to #12535, I
 went and wrote something that also implements "second thing".

 Similar approach taken to adam-p's branch, all errors in
 `SocksListener.AcceptSocks()` past the `ln.Listener.Accept()` call are
 returned as a `net.Error` that has a `Temporary()` that always returns
 `true`.

 Either version of the check will continue to work, since
 `ln.Listener.Accept()`'s errors are returned untouched, and if non-
 temporary, will cause the loop to terminate, as they should.  All other
 net.Errors will be re-wrapped since they are net.Errors generated from the
 new client connection, and have absolutely nothing to do with the
 listener.

 A defer in `SocksListener.AcceptSocks()` used since it's cleaner to do it
 that way, saving the need to splatter the wrapper all over the rest of the
 socks code.

 https://github.com/Yawning/goptlib/commit/e43b7d4ae09aaf10f0d544cf86da62bf1de3d74b

 Note: My change depends on my #12535 branch, since modifying the SOCKS4a
 code is for people that are living in the past.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/14135#comment:4>
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