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{- SRV record lookup
-
- Copyright 2012 Joey Hess <id@joeyh.name>
-
- License: BSD-2-clause
-}
{-# LANGUAGE CPP #-}
module Utility.SRV (
mkSRVTcp,
mkSRV,
lookupSRV,
HostPort,
) where
import Data.Function
import Data.List
import Network
import qualified Network.DNS.Lookup as DNS
import Network.DNS.Resolver
import qualified Data.ByteString.UTF8 as B8
newtype SRV = SRV String
deriving (Show, Eq)
type HostPort = (HostName, PortID)
type PriorityWeight = (Int, Int) -- sort by priority first, then weight
mkSRV :: String -> String -> HostName -> SRV
mkSRV transport protocol host = SRV $ concat
["_", protocol, "._", transport, ".", host]
mkSRVTcp :: String -> HostName -> SRV
mkSRVTcp = mkSRV "tcp"
{- Returns an ordered list, with highest priority hosts first.
-
- On error, returns an empty list. -}
lookupSRV :: SRV -> IO [HostPort]
lookupSRV (SRV srv) = do
seed <- makeResolvSeed defaultResolvConf
r <- withResolver seed $ flip DNS.lookupSRV $ B8.fromString srv
return $
#if MIN_VERSION_dns(1,0,0)
either (const []) use r
#else
maybe [] use r
#endif
where
use = orderHosts . map tohosts
tohosts (priority, weight, port, hostname) =
( (priority, weight)
, (B8.toString hostname, PortNumber $ fromIntegral port)
)
orderHosts :: [(PriorityWeight, HostPort)] -> [HostPort]
orderHosts = map snd . sortBy (compare `on` fst)
|
