[tor-bugs] #31228 [Core Tor/Tor]: Support spawning multiple transport instances

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#31228: Support spawning multiple transport instances
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     Reporter:  phw           |      Owner:  (none)
         Type:  enhancement   |     Status:  new
     Priority:  Medium        |  Milestone:
    Component:  Core Tor/Tor  |    Version:
     Severity:  Normal        |   Keywords:
Actual Points:                |  Parent ID:
       Points:  10            |   Reviewer:
      Sponsor:                |
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 One Tor instance can only handle one transport instance, i.e., one cannot
 run two obfs4 instances in one tor. Adding support for this use case will
 require changes in our PT spec, in PT spec implementations, and in tor.

 As pointed out
 [https://trac.torproject.org/projects/tor/ticket/29285#comment:5 in this
 comment], tor would need the config options `ServerTransportPlugin`,
 `ServerTransportListenAddr`, and `ServerTransportOptions` to support
 multiple instances of a single transport. One way to accomplish this would
 be to append a numeric, incrementing suffix to a transport's name, e.g.:

 {{{
 ServerTransportPlugin obfs4-0 exec /usr/bin/obfs4proxy
 ServerTransportPlugin obfs4-1 exec /usr/bin/obfs4proxy

 ServerTransportListenAddr obfs4-0 0.0.0.0:10000
 ServerTransportListenAddr obfs4-1 0.0.0.0:20000
 }}}

 #11211 is vaguely related in that it aims to add dual stack support for
 bridges so that, say, an obfs4 instance can listen on both an IPv4 and
 IPv6 address. #29285 is also related because it tracks our PT spec
 improvement process and supporting multiple instances of a transport is
 one potential improvement.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/31228>
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