net/resolvers/service.lua

   1 local adns = require "net.adns";
   2 local basic = require "net.resolvers.basic";
   3 local unpack = table.unpack or unpack; -- luacheck: ignore 113
   4
   5 local methods = {};
   6 local resolver_mt = { __index = methods };
   7
   8 -- Find the next target to connect to, and
   9 -- pass it to cb()
  10 function methods:next(cb)
  11         if self.targets then
  12                 if #self.targets == 0 then
  13                         cb(nil);
  14                         return;
  15                 end
  16                 local next_target = table.remove(self.targets, 1);
  17                 self.resolver = basic.new(unpack(next_target, 1, 4));
  18                 self.resolver:next(function (...)
  19                         if ... == nil then
  20                                 self:next(cb);
  21                         else
  22                                 cb(...);
  23                         end
  24                 end);
  25                 return;
  26         end
  27
  28         local targets = {};
  29         local function ready()
  30                 self.targets = targets;
  31                 self:next(cb);
  32         end
  33
  34         -- Resolve DNS to target list
  35         local dns_resolver = adns.resolver();
  36         dns_resolver:lookup(function (answer, err)
  37                 if not answer and not err then
  38                         -- net.adns returns nil if there are zero records or nxdomain
  39                         answer = {};
  40                 end
  41                 if answer then
  42                         if #answer == 0 then
  43                                 if self.extra and self.extra.default_port then
  44                                         table.insert(targets, { self.hostname, self.extra.default_port, self.conn_type, self.extra });
  45                                 end
  46                                 ready();
  47                                 return;
  48                         end
  49
  50                         if #answer == 1 and answer[1].srv.target == "." then -- No service here
  51                                 ready();
  52                                 return;
  53                         end
  54
  55                         table.sort(answer, function (a, b) return a.srv.priority < b.srv.priority end);
  56                         for _, record in ipairs(answer) do
  57                                 table.insert(targets, { record.srv.target, record.srv.port, self.conn_type, self.extra });
  58                         end
  59                 end
  60                 ready();
  61         end, "_" .. self.service .. "._" .. self.conn_type .. "." .. self.hostname, "SRV", "IN");
  62 end
  63
  64 local function new(hostname, service, conn_type, extra)
  65         return setmetatable({
  66                 hostname = hostname;
  67                 service = service;
  68                 conn_type = conn_type or "tcp";
  69                 extra = extra;
  70         }, resolver_mt);
  71 end
  72
  73 return {
  74         new = new;
  75 };