[tor-bugs] #21136 [Obfuscation/Obfsproxy]: obfs4proxy doesn't listen on both 0.0.0.0 and [::]

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#21136: obfs4proxy doesn't listen on both 0.0.0.0 and [::]
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     Reporter:  kaie                   |      Owner:  asn
         Type:  defect                 |     Status:  new
     Priority:  Medium                 |  Milestone:
    Component:  Obfuscation/Obfsproxy  |    Version:
     Severity:  Normal                 |   Keywords:
Actual Points:                         |  Parent ID:
       Points:                         |   Reviewer:
      Sponsor:                         |
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 I'm using a system that has native IPv6 support and also IPv4

 If obfs4proxy is started with the following configuration:
   TOR_PT_SERVER_BINDADDR="obfs4-0.0.0.0:1234,obfs4-[::]:1234"
 then obfs4proxy fails to bind to both ipv4 and ipv6.

 Instead, the first call to Net.Listen will cause it to listen on [::], and
 the second call will fail with "bind: port 1234 is already in use".

 I found some discussions around the behavior of the Net, and it seems that
 it tries to some automatic decisions which aren't perfect. I've seen a
 recommendation that it's best to specifically request which tcp family is
 requested.

 I've implemented a patch that will request either tcp4 or tcp6, which
 makes it work correctly for me, with the patch obfs4proxy will listen on
 both 0.0.0.0 and [::]

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/21136>
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