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