util/rfc6724.lua

   1 -- Prosody IM
   2 -- Copyright (C) 2011-2013 Florian Zeitz
   3 --
   4 -- This project is MIT/X11 licensed. Please see the
   5 -- COPYING file in the source package for more information.
   6 --
   7
   8 -- This is used to sort destination addresses by preference
   9 -- during S2S connections.
  10 -- We can't hand this off to getaddrinfo, since it blocks
  11
  12 local ip_commonPrefixLength = require"util.ip".commonPrefixLength
  13
  14 local function commonPrefixLength(ipA, ipB)
  15         local len = ip_commonPrefixLength(ipA, ipB);
  16         return len < 64 and len or 64;
  17 end
  18
  19 local function t_sort(t, comp)
  20         for i = 1, (#t - 1) do
  21                 for j = (i + 1), #t do
  22                         local a, b = t[i], t[j];
  23                         if not comp(a,b) then
  24                                 t[i], t[j] = b, a;
  25                         end
  26                 end
  27         end
  28 end
  29
  30 local function source(dest, candidates)
  31         local function comp(ipA, ipB)
  32                 -- Rule 1: Prefer same address
  33                 if dest == ipA then
  34                         return true;
  35                 elseif dest == ipB then
  36                         return false;
  37                 end
  38
  39                 -- Rule 2: Prefer appropriate scope
  40                 if ipA.scope < ipB.scope then
  41                         if ipA.scope < dest.scope then
  42                                 return false;
  43                         else
  44                                 return true;
  45                         end
  46                 elseif ipA.scope > ipB.scope then
  47                         if ipB.scope < dest.scope then
  48                                 return true;
  49                         else
  50                                 return false;
  51                         end
  52                 end
  53
  54                 -- Rule 3: Avoid deprecated addresses
  55                 -- XXX: No way to determine this
  56                 -- Rule 4: Prefer home addresses
  57                 -- XXX: Mobility Address related, no way to determine this
  58                 -- Rule 5: Prefer outgoing interface
  59                 -- XXX: Interface to address relation. No way to determine this
  60                 -- Rule 6: Prefer matching label
  61                 if ipA.label == dest.label and ipB.label ~= dest.label then
  62                         return true;
  63                 elseif ipB.label == dest.label and ipA.label ~= dest.label then
  64                         return false;
  65                 end
  66
  67                 -- Rule 7: Prefer temporary addresses (over public ones)
  68                 -- XXX: No way to determine this
  69                 -- Rule 8: Use longest matching prefix
  70                 if commonPrefixLength(ipA, dest) > commonPrefixLength(ipB, dest) then
  71                         return true;
  72                 else
  73                         return false;
  74                 end
  75         end
  76
  77         t_sort(candidates, comp);
  78         return candidates[1];
  79 end
  80
  81 local function destination(candidates, sources)
  82         local sourceAddrs = {};
  83         local function comp(ipA, ipB)
  84                 local ipAsource = sourceAddrs[ipA];
  85                 local ipBsource = sourceAddrs[ipB];
  86                 -- Rule 1: Avoid unusable destinations
  87                 -- XXX: No such information
  88                 -- Rule 2: Prefer matching scope
  89                 if ipA.scope == ipAsource.scope and ipB.scope ~= ipBsource.scope then
  90                         return true;
  91                 elseif ipA.scope ~= ipAsource.scope and ipB.scope == ipBsource.scope then
  92                         return false;
  93                 end
  94
  95                 -- Rule 3: Avoid deprecated addresses
  96                 -- XXX: No way to determine this
  97                 -- Rule 4: Prefer home addresses
  98                 -- XXX: Mobility Address related, no way to determine this
  99                 -- Rule 5: Prefer matching label
 100                 if ipAsource.label == ipA.label and ipBsource.label ~= ipB.label then
 101                         return true;
 102                 elseif ipBsource.label == ipB.label and ipAsource.label ~= ipA.label then
 103                         return false;
 104                 end
 105
 106                 -- Rule 6: Prefer higher precedence
 107                 if ipA.precedence > ipB.precedence then
 108                         return true;
 109                 elseif ipA.precedence < ipB.precedence then
 110                         return false;
 111                 end
 112
 113                 -- Rule 7: Prefer native transport
 114                 -- XXX: No way to determine this
 115                 -- Rule 8: Prefer smaller scope
 116                 if ipA.scope < ipB.scope then
 117                         return true;
 118                 elseif ipA.scope > ipB.scope then
 119                         return false;
 120                 end
 121
 122                 -- Rule 9: Use longest matching prefix
 123                 if commonPrefixLength(ipA, ipAsource) > commonPrefixLength(ipB, ipBsource) then
 124                         return true;
 125                 elseif commonPrefixLength(ipA, ipAsource) < commonPrefixLength(ipB, ipBsource) then
 126                         return false;
 127                 end
 128
 129                 -- Rule 10: Otherwise, leave order unchanged
 130                 return true;
 131         end
 132         for _, ip in ipairs(candidates) do
 133                 sourceAddrs[ip] = source(ip, sources);
 134         end
 135
 136         t_sort(candidates, comp);
 137         return candidates;
 138 end
 139
 140 return {source = source,
 141         destination = destination};