-- | Helpers to perform DNS queries.
module DNS (
  Domain,
  PTRResult,
  lookup_ptrs )
where

import Control.Concurrent.ParallelIO.Global ( parallel )
import Network.DNS (
  Domain,
  DNSError,
  ResolvConf(..),
  defaultResolvConf,
  lookupRDNS,
  makeResolvSeed,
  withResolver )


-- The return type of lookupRDNS.
type PTRResult = Either DNSError [Domain]


-- | Take the default ResolvConf and increase the timeout to 15
--   seconds.
our_resolv_conf :: ResolvConf
our_resolv_conf =
  defaultResolvConf { resolvTimeout = 15*1000*1000 } -- 15s


-- | Takes a list of IP addresses (as ByteStrings) and performs
--   reverse (PTR) lookups on each of them.
lookup_ptrs :: [Domain] -> IO [PTRResult]
lookup_ptrs ips = do
  rs <- makeResolvSeed our_resolv_conf
  let lookup' addr = withResolver rs $ \resolver ->
                       lookupRDNS resolver addr

  parallel $ map lookup' ips