Haskell Language Attoparsec Bitmap - Parsing Binary Data
Example
Attoparsec makes parsing binary data trivial. Assuming these definitions:
import Data.Attoparsec.ByteString (Parser, eitherResult, parse, take)
import Data.Binary.Get (getWord32le, runGet)
import Data.ByteString (ByteString, readFile)
import Data.ByteString.Char8 (unpack)
import Data.ByteString.Lazy (fromStrict)
import Prelude hiding (readFile, take)
-- The DIB section from a bitmap header
data DIB = BM | BA | CI | CP | IC | PT
deriving (Show, Read)
type Reserved = ByteString
-- The entire bitmap header
data Header = Header DIB Int Reserved Reserved Int
deriving (Show)
We can parse the header from a bitmap file easily. Here, we have 4 parser functions that represent the header section from a bitmap file:
Firstly, the DIB section can be read by taking the first 2 bytes
dibP :: Parser DIB
dibP = read . unpack <$> take 2
Similarly, the size of the bitmap, the reserved sections and the pixel offset can be read easily too:
sizeP :: Parser Int sizeP = fromIntegral . runGet getWord32le . fromStrict <$> take 4 reservedP :: Parser Reserved reservedP = take 2 addressP :: Parser Int addressP = fromIntegral . runGet getWord32le . fromStrict <$> take 4
which can then be combined into a larger parser function for the entire header:
bitmapHeader :: Parser Header
bitmapHeader = do
dib <- dibP
sz <- sizeP
reservedP
reservedP
offset <- addressP
return $ Header dib sz "" "" offset
