module Network.HPACK.HeaderBlock.Integer (
encode
, decode
, parseInteger
) where
import Data.Array (Array, listArray, (!))
import Data.Bits ((.&.), shiftR)
import Data.ByteString (ByteString)
import qualified Data.ByteString as BS
import Data.Word (Word8)
powerArray :: Array Int Int
powerArray = listArray (1,8) [1,3,7,15,31,63,127,255]
encode :: Int -> Int -> [Word8]
encode n i
| i < p = fromIntegral i : []
| otherwise = fromIntegral p : encode' (i p)
where
p = powerArray ! n
encode' :: Int -> [Word8]
encode' i
| i < 128 = fromIntegral i : []
| otherwise = fromIntegral (r + 128) : encode' q
where
q = i `shiftR` 7
r = i .&. 0x7f
decode :: Int -> Word8 -> ByteString -> Int
decode n w bs
| i < p = i
| BS.null bs = error $ "decode: n = " ++ show n ++ ", w = " ++ show w ++ ", bs = empty"
| otherwise = decode' bs 0 i
where
p = powerArray ! n
i = fromIntegral w
decode' :: ByteString -> Int -> Int -> Int
decode' "" _ i = i
decode' bs m i = decode' bs' m' i'
where
!b = fromIntegral $ BS.head bs
!bs' = BS.tail bs
!i' = i + (b .&. 127) * 2 ^ m
!m' = m + 7
parseInteger :: Int -> Word8 -> ByteString -> (Int, ByteString)
parseInteger n w bs
| i < p = (i, bs)
| otherwise = (len, rest)
where
p = powerArray ! n
i = fromIntegral w
Just idx = BS.findIndex (< 128) bs
(bs', rest) = BS.splitAt (idx + 1) bs
len = decode n w bs'