On Tuesday 12 October 2010 18:38:31, David McBride wrote:
I'm writing a pcap sniffer, and I have IP addresses from two different libraries that are equivalent, but typed differently.
Data.IP.IPv4 Data.ByteString.Internal.ByteString
and
Network.Info.IPv4 = Network.Info.IPv4 !GHC.Word.Word32
Both are probably identical, but I cannot for the life of me figure out how to get from one to the other. Bytestring has the ability to take arrays of Word8, how do I split Word32 into Word8's?
If you have the binary package and know the endianness of the IP addresses, the simplest way to convert between those is conv1 :: Network.Info.IPv4 -> Data.IP.IPv4 conv1 (Network.Info.IPv4 w32) = Data.IP.IPv4 (runPut $ putWord32be w32) -- or putWord32le conv2 :: Data.IP.IPv4 -> Network.Info.IPv4 conv2 (Data.IP.IPv4 bs) = Network.Ifo.IPv4 (runGet $ getWord32be) -- or getWord32le Alternatively, you can convert a Word32 to [Word8] per import Data.Word import Data.Bits octets :: Word32 -> [Word8] octets w = [ fromIntegral (w `shiftR` 24) , fromIntegral (w `shiftR` 16) , fromIntegral (w `shiftR` 8) , fromIntegral w ] for big-endian conversion (for little-endian, reverse the list ;) And a list of Word8 to a Word32 per fromOctets :: [Word8] -> Word32 fromOctets = foldl' accum 0 where accum a o = (a `shiftL` 8) .|. fromIntegral o (reverse or use foldr for little-endian conversion).
I have also had this problem in the past with Word8's, Octets and Chars. Beyond this specific problem, what is a good strategy for figuring out how to do these conversions in the future? Sometimes I find a function somewhere, but I have never found a general way to deal with it.