Look at Data.Binary (binary package)
It will marshall and unmarshall data types for you. If you don't like
its binary encoding you can dive in there and use the same principles
Cheers
Neil
On 6 Jun 2009, at 07:13, John Ky wrote:
Hi Haskell Cafe,
I'm trying to send stuff over UDP. To do that, I've written a test
program that sends strings across. That was fine, but I wanted to
send binary data too. So I tried that only to find I am having
difficulty putting together some binary data. For examples take the
fromHex function in the following code.
It is supposed to convert from a Hexadecimal string to a list of
bytes, but I am having trouble coercing the integer types to the
size I want.
Is this the right way to do it?
Cheers,
-John
> import Data.Bits
> import Data.Char
> import Data.Word
> import System.Environment
> import XStream.Tsmr.Client
> data CmdLineOptions = CmdLineOptions
> { optionHelp :: Bool
> , optionVersion :: Bool
> , optionPort :: String
> , optionMessage :: String
> , optionInvalids :: [String]
> }
> deriving (Eq, Show)
> initCmdLineOptions = CmdLineOptions
> { optionHelp = False
> , optionVersion = False
> , optionPort = "1234"
> , optionMessage = ""
> }
> parseArgs :: [String] -> CmdLineOptions
> parseArgs [] = initCmdLineOptions
> parseArgs ("--port":port:xs) = (parseArgs xs) { optionPort = port }
> parseArgs ("--help":xs) = (parseArgs xs) { optionHelp = True }
> parseArgs ("--version":xs) = (parseArgs xs) { optionVersion =
True }
> parseArgs (('-':opt):xs) = let option = (parseArgs xs) in
> option { optionInvalids = ('-':opt):optionInvalids option }
> parseArgs (message:xs) = (parseArgs xs) { optionMessage = message }
> printUsage = do
> putStrLn "Usage: udp-server.lhs [options] <message>"
> putStrLn ""
> putStrLn "Options:"
> putStrLn " --help Get help information."
> putStrLn " --vesion Get version information."
> putStrLn " --port n The port number to listen on."
> putStrLn ""
> putStrLn "Message:"
> putStrLn " The message to send."
> putStrLn ""
> printVersion = do
> putStrLn "Version."
> fromHex :: String -> [Word8]
> fromHex [] = []
> fromHex (u:l:xs) = (hexU .|. hexL):fromHex xs
> where
> hexU = (fromInteger $ hexValue u) :: Word8
> hexL = (fromInteger $ hexValue l) :: Int
> hexValue c
> | '0' <= c && c <= '9' = ord c - ord '0'
> | 'a' <= c && c <= 'z' = ord c - ord 'a' + 10
> run port message = do
> h <- openlog "localhost" port "udp-client.lhs"
> syslog h (fromHex message)
> main = do
> args <- getArgs
> let options = parseArgs args
> let port = optionPort options
> let message = optionMessage options
> if optionHelp options
> then printUsage
> else if optionVersion options
> then printVersion
> else do
> putStrLn ("Starting UDP listener on port: " ++ port)
> run port message
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