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|
{- SRV record lookup
-
- Uses either the ADNS Haskell library, or if it's not installed,
- the host command.
-
- Copyright 2012 Joey Hess <joey@kitenet.net>
-
- Licensed under the GNU GPL version 3 or higher.
-}
{-# LANGUAGE CPP #-}
module Utility.SRV (
lookupSRV,
) where
import qualified Build.SysConfig
import Utility.Process
import Utility.Exception
import Utility.PartialPrelude
import Network
import Data.Function
import Data.List
import Control.Applicative
import Data.Maybe
#ifdef WITH_ADNS
import ADNS.Resolver
import Data.Either
#endif
type HostPort = (HostName, PortID)
{- Returns an ordered list, with highest priority hosts first.
-
- On error, returns an empty list. -}
lookupSRV :: String -> IO [HostPort]
#ifdef WITH_ADNS
lookupSRV srv = initResolver [] $ \resolver -> do
r <- catchDefaultIO (Right []) $
resolveSRV resolver srv
return $ either (\_ -> []) id r
#else
lookupSRV = lookupSRVHost
#endif
lookupSRVHost :: String -> IO [HostPort]
lookupSRVHost srv
| Build.SysConfig.host = catchDefaultIO [] $
parseSrvHost <$> readProcessEnv "host" ["-t", "SRV", "--", srv]
-- clear environment, to avoid LANG affecting output
(Just [])
| otherwise = return []
parseSrvHost :: String -> [HostPort]
parseSrvHost = map snd . reverse . sortBy priority . catMaybes . map parse . lines
where
priority = compare `on` fst
parse l = case words l of
[_, _, _, _, priority, weight, sport, hostname] ->
case PortNumber . fromIntegral <$> readish sport of
Nothing -> Nothing
Just port -> Just
( (priority, weight)
, (hostname, port)
)
_ -> Nothing
|
