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|
{- SRV record lookup
-
- Uses either the ADNS Haskell library, or the standalone Haskell DNS
- package, or the host command.
-
- Copyright 2012 Joey Hess <id@joeyh.name>
-
- License: BSD-2-clause
-}
{-# LANGUAGE CPP #-}
module Utility.SRV (
mkSRVTcp,
mkSRV,
lookupSRV,
lookupSRVHost,
HostPort,
) where
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
#else
#ifdef WITH_DNS
import qualified Network.DNS.Lookup as DNS
import Network.DNS.Resolver
import qualified Data.ByteString.UTF8 as B8
#endif
#endif
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]
#ifdef WITH_ADNS
lookupSRV (SRV srv) = initResolver [] $ \resolver -> do
r <- catchDefaultIO (Right []) $
resolveSRV resolver srv
return $ either (\_ -> []) id r
#else
#ifdef WITH_DNS
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)
)
#else
lookupSRV = lookupSRVHost
#endif
#endif
lookupSRVHost :: SRV -> IO [HostPort]
lookupSRVHost (SRV srv) = catchDefaultIO [] $
parseSrvHost <$> readProcessEnv "host" ["-t", "SRV", "--", srv]
-- clear environment, to avoid LANG affecting output
(Just [])
parseSrvHost :: String -> [HostPort]
parseSrvHost = orderHosts . catMaybes . map parse . lines
where
parse l = case words l of
[_, _, _, _, spriority, sweight, sport, hostname] -> do
let v =
( readish sport :: Maybe Int
, readish spriority :: Maybe Int
, readish sweight :: Maybe Int
)
case v of
(Just port, Just priority, Just weight) -> Just
( (priority, weight)
, (hostname, PortNumber $ fromIntegral port)
)
_ -> Nothing
_ -> Nothing
orderHosts :: [(PriorityWeight, HostPort)] -> [HostPort]
orderHosts = map snd . sortBy (compare `on` fst)
|
