README.markdown

Codec.Binary.XDR.Simple

This codec module implements a subset of XDR -- eXternal Data Representation (RFC: 4506)

A thin wrapper around the cereal package, inspired by Python's xdrlib.

A note on string

There are 2 representations of string:

• plain Haskell string, assuming UTF-8-encoded (see examples);
• lazy bytestring, for ASCII texts & so-called opaque data.

Strings in other encodings can always be transformed from/to lazy bytestrings using the proper encode/decode function pair.

Examples

Using this module is quite simple (as the name implies).

Don't forget to enable the ScopedTypeVariables extension.

pack

• String: "abcd测试"
• UInt: 123456
• Hyper: -1234567890
• Boolean: False
• Float: 5.7
• Double: 6.4
• Array of Strings: ["hello", "world"]
• Array of Doubles: [1.9, 2.2, 3.141592653589793238462643383279502884, 0.0]

Output will be written to "test.data".

testPack :: IO ()
testPack = LBS.writeFile "test.data" (xdrPack packs)
    where packs = do
              pack "abcd测试"
              pack (123456 :: UInt)
              pack (-1234567890 :: Hyper)
              pack False
              pack (5.7 :: Float)
              pack (6.4 :: Double)
              pack ["hello", "world"]
              pack ([1.9, 2.2, 3.141592653589793238462643383279502884, 0.0] :: [Double])

unpack

Read a file named "test.data" (...contains data previously generated by testPack).

Print out the result of unpacking.

testUnpack :: IO ()
testUnpack = do
    dat <- LBS.readFile "test.data"
    let (Right result) = xdrUnpack unpacks dat
    putStrLn result
    where unpacks = do
              a :: String   <- unpack
              b :: UInt     <- unpack
              c :: Hyper    <- unpack
              d :: Bool     <- unpack
              e :: Float    <- unpack
              f :: Double   <- unpack
              g :: [String] <- unpack
              h :: [Double] <- unpack
              return $ "got"  ++
                ": string "   ++ a      ++
                ", uint "     ++ show b ++
                ", hyper "    ++ show c ++
                ", boolean "  ++ show d ++
                ", float "    ++ show e ++
                ", double "   ++ show f ++
                ", a list of strings " ++ show g ++
                ", a list of doubles " ++ show h ++ "."

...more?

See examples/GangliaMessage.hs