[tor-bugs] #7478 [Tor]: Allow routersets to include/exclude nodes by IPv6 address

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#7478: Allow routersets to include/exclude nodes by IPv6 address
-----------------------------------------------+---------------------------
 Reporter:  nickm                              |          Owner:  teor
     Type:  enhancement                        |         Status:
 Priority:  High                               |  needs_revision
Component:  Tor                                |      Milestone:  Tor:
 Severity:  Normal                             |  0.2.9.x-final
 Keywords:  tor-client ipv6 TorCoreTeam201602  |        Version:
Parent ID:                                     |     Resolution:
  Sponsor:                                     |  Actual Points:
                                               |         Points:  small
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Comment (by fergus):

 Replying to [comment:26 teor]:
 > Let's revise this patch so it handles 0.0.0.0 like it used to, and
 handles `::` (IPv6 all zeroes) the same as 0.0.0.0.
 That won't work. If a node doesn't have an IPv6 address, then both
 {{{ipv6_addr}}} and {{{ipv6_orport}}} will be zero, which
 {{{compare_tor_addr_to_addr_policy}}} always rejects (placing it in the
 routerset) and similarly with a hypothetical future node that doesn't have
 an IPv4 address.

 Both {{{routerinfo_t}}} and {{{routerstatus_t}}} contain their addresses
 directly instead of using pointers, so there's no way to distinguish
 between "NULL because this node lacks an address of this type" and "NULL
 because this node's address and port are unknown". I think we just have to
 treat the second case as a bug.

 I've changed the short circuit to only occur when both the IP address and
 port are zero and added a comment to that effect. A rebased branch is
 available as {{{ticket-7478-2}}} at ​https://github.com/fergus-
 dall/tor.git

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/7478#comment:27>
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