52 lines
1.3 KiB
Haskell
52 lines
1.3 KiB
Haskell
{- SRV record lookup
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-
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- Copyright 2012 Joey Hess <id@joeyh.name>
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-
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- License: BSD-2-clause
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-}
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module Utility.SRV (
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mkSRVTcp,
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mkSRV,
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lookupSRV,
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HostPort,
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) where
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import Data.Function
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import Data.List
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import Network
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import qualified Network.DNS.Lookup as DNS
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import Network.DNS.Resolver
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import qualified Data.ByteString.UTF8 as B8
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newtype SRV = SRV String
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deriving (Show, Eq)
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type HostPort = (HostName, PortID)
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type PriorityWeight = (Int, Int) -- sort by priority first, then weight
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mkSRV :: String -> String -> HostName -> SRV
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mkSRV transport protocol host = SRV $ concat
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["_", protocol, "._", transport, ".", host]
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mkSRVTcp :: String -> HostName -> SRV
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mkSRVTcp = mkSRV "tcp"
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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 :: SRV -> IO [HostPort]
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lookupSRV (SRV srv) = do
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seed <- makeResolvSeed defaultResolvConf
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r <- withResolver seed $ flip DNS.lookupSRV $ B8.fromString srv
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return $ either (const []) use r
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where
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use = orderHosts . map tohosts
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tohosts (priority, weight, port, hostname) =
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( (fromIntegral priority, fromIntegral weight)
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, (B8.toString hostname, PortNumber $ fromIntegral port)
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)
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orderHosts :: [(PriorityWeight, HostPort)] -> [HostPort]
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orderHosts = map snd . sortBy (compare `on` fst)
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