    module Network.Wai.Logger.IP (
        NumericAddress, showSockAddr
      ) where

    import Data.Bits (shift, (.&.))
    import Data.Word (Word32)
    import Network.Socket (SockAddr(..))
    import System.ByteOrder (ByteOrder(..), byteOrder)
    import Text.Printf (printf)

    -- |  A type for IP address in numeric string representation.
    type NumericAddress = String

    showIPv4 :: Word32 -> Bool -> NumericAddress
    showIPv4 w32 little
        | little    = show b1 ++ "." ++ show b2 ++ "." ++ show b3 ++ "." ++ show b4
        | otherwise = show b4 ++ "." ++ show b3 ++ "." ++ show b2 ++ "." ++ show b1
      where
        t1 = w32
        t2 = shift t1 (-8)
        t3 = shift t2 (-8)
        t4 = shift t3 (-8)
        b1 = t1 .&. 0x000000ff
        b2 = t2 .&. 0x000000ff
        b3 = t3 .&. 0x000000ff
        b4 = t4 .&. 0x000000ff

    showIPv6 :: (Word32,Word32,Word32,Word32) -> String
    showIPv6 (w1,w2,w3,w4) =
        printf "%x:%x:%x:%x:%x:%x:%x:%x" s1 s2 s3 s4 s5 s6 s7 s8
      where
        (s1,s2) = split16 w1
        (s3,s4) = split16 w2
        (s5,s6) = split16 w3
        (s7,s8) = split16 w4
        split16 w = (h1,h2)
          where
            h1 = shift w (-16) .&. 0x0000ffff
            h2 = w .&. 0x0000ffff
    -- | Convert 'SockAddr' to 'NumericAddress'. If the address is
    --   IPv4-embedded IPv6 address, the IPv4 is extracted.
    showSockAddr :: SockAddr -> NumericAddress
    -- HostAddr is network byte order.
    showSockAddr (SockAddrInet _ addr4)                       = showIPv4 addr4 (byteOrder == LittleEndian)
    -- HostAddr6 is host byte order.
    showSockAddr (SockAddrInet6 _ _ (0,0,0x0000ffff,addr4) _) = showIPv4 addr4 False
    showSockAddr (SockAddrInet6 _ _ (0,0,0,1) _)              = "::1"
    showSockAddr (SockAddrInet6 _ _ addr6 _)                  = showIPv6 addr6
    showSockAddr _                                            = "unknownSocket"