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|
{-# LANGUAGE DeriveDataTypeable, RankNTypes, BangPatterns #-}
-- |
-- Copyright: 2014 Michael Thompson, 2011 Michael Snoyman, 2010-2011 John Millikin
-- License: MIT
--
-- Parts of this code were taken from enumerator and conduits, and adapted for pipes.
module Pipes.Text.Codec
( Decoding(..)
, streamDecodeUtf8
, decodeSomeUtf8
, Codec(..)
, TextException(..)
, utf8
, utf16_le
, utf16_be
, utf32_le
, utf32_be
) where
import Data.Bits ((.&.))
import Data.Char (ord)
import Data.ByteString as B
import Data.ByteString (ByteString)
import Data.ByteString.Internal as B
import Data.ByteString.Char8 as B8
import Data.Text (Text)
import qualified Data.Text as T
import qualified Data.Text.Encoding as TE
import Data.Text.Encoding.Error ()
import GHC.Word (Word8, Word32)
import qualified Data.Text.Array as A
import Data.Word (Word8, Word16)
import System.IO.Unsafe (unsafePerformIO)
import qualified Control.Exception as Exc
import Data.Bits ((.&.), (.|.), shiftL)
import Data.Typeable
import Control.Arrow (first)
import Data.Maybe (catMaybes)
import Pipes.Text.Internal
import Pipes
-- | A specific character encoding.
--
-- Since 0.3.0
data Codec = Codec
{ codecName :: Text
, codecEncode :: Text -> (ByteString, Maybe (TextException, Text))
, codecDecode :: ByteString -> Decoding -- (Text, Either (TextException, ByteString) ByteString)
}
instance Show Codec where
showsPrec d c = showParen (d > 10) $
showString "Codec " . shows (codecName c)
data TextException = DecodeException Codec Word8
| EncodeException Codec Char
| LengthExceeded Int
| TextException Exc.SomeException
deriving (Show, Typeable)
instance Exc.Exception TextException
toDecoding :: (ByteString -> (Text, Either (TextException, ByteString) ByteString))
-> (ByteString -> Decoding)
toDecoding op = loop B.empty where
loop !extra bs0 = case op (B.append extra bs0) of
(txt, Right bs) -> Some txt bs (loop bs)
(txt, Left (_,bs)) -> Other txt bs
-- To do: toDecoding should be inlined in each of the 'Codec' definitions
-- or else Codec changed to the conduit/enumerator definition. We have
-- altered it to use 'streamDecodeUtf8'
splitSlowly :: (ByteString -> Text)
-> ByteString
-> (Text, Either (TextException, ByteString) ByteString)
splitSlowly dec bytes = valid where
valid:_ = catMaybes $ Prelude.map decFirst $ splits (B.length bytes)
splits 0 = [(B.empty, bytes)]
splits n = B.splitAt n bytes : splits (n - 1)
decFirst (a, b) = case tryEvaluate (dec a) of
Left _ -> Nothing
Right text -> let trouble = case tryEvaluate (dec b) of
Left exc -> Left (TextException exc, b)
Right _ -> Right B.empty
in Just (text, trouble) -- this case shouldn't occur,
-- since splitSlowly is only called
-- when parsing failed somewhere
utf8 :: Codec
utf8 = Codec name enc (toDecoding dec) where
name = T.pack "UTF-8"
enc text = (TE.encodeUtf8 text, Nothing)
dec bytes = case decodeSomeUtf8 bytes of (t,b) -> (t, Right b)
-- -- Whether the given byte is a continuation byte.
-- isContinuation byte = byte .&. 0xC0 == 0x80
--
-- -- The number of continuation bytes needed by the given
-- -- non-continuation byte. Returns -1 for an illegal UTF-8
-- -- non-continuation byte and the whole split quickly must fail so
-- -- as the input is passed to TE.decodeUtf8, which will issue a
-- -- suitable error.
-- required x0
-- | x0 .&. 0x80 == 0x00 = 0
-- | x0 .&. 0xE0 == 0xC0 = 1
-- | x0 .&. 0xF0 == 0xE0 = 2
-- | x0 .&. 0xF8 == 0xF0 = 3
-- | otherwise = -1
--
-- splitQuickly bytes
-- | B.null l || req == -1 = Nothing
-- | req == B.length r = Just (TE.decodeUtf8 bytes, B.empty)
-- | otherwise = Just (TE.decodeUtf8 l', r')
-- where
-- (l, r) = B.spanEnd isContinuation bytes
-- req = required (B.last l)
-- l' = B.init l
-- r' = B.cons (B.last l) r
utf16_le :: Codec
utf16_le = Codec name enc (toDecoding dec) where
name = T.pack "UTF-16-LE"
enc text = (TE.encodeUtf16LE text, Nothing)
dec bytes = case splitQuickly bytes of
Just (text, extra) -> (text, Right extra)
Nothing -> splitSlowly TE.decodeUtf16LE bytes
splitQuickly bytes = maybeDecode (loop 0) where
maxN = B.length bytes
loop n | n == maxN = decodeAll
| (n + 1) == maxN = decodeTo n
loop n = let
req = utf16Required
(B.index bytes n)
(B.index bytes (n + 1))
decodeMore = loop $! n + req
in if n + req > maxN
then decodeTo n
else decodeMore
decodeTo n = first TE.decodeUtf16LE (B.splitAt n bytes)
decodeAll = (TE.decodeUtf16LE bytes, B.empty)
utf16_be :: Codec
utf16_be = Codec name enc (toDecoding dec) where
name = T.pack "UTF-16-BE"
enc text = (TE.encodeUtf16BE text, Nothing)
dec bytes = case splitQuickly bytes of
Just (text, extra) -> (text, Right extra)
Nothing -> splitSlowly TE.decodeUtf16BE bytes
splitQuickly bytes = maybeDecode (loop 0) where
maxN = B.length bytes
loop n | n == maxN = decodeAll
| (n + 1) == maxN = decodeTo n
loop n = let
req = utf16Required
(B.index bytes (n + 1))
(B.index bytes n)
decodeMore = loop $! n + req
in if n + req > maxN
then decodeTo n
else decodeMore
decodeTo n = first TE.decodeUtf16BE (B.splitAt n bytes)
decodeAll = (TE.decodeUtf16BE bytes, B.empty)
utf16Required :: Word8 -> Word8 -> Int
utf16Required x0 x1 = if x >= 0xD800 && x <= 0xDBFF then 4 else 2 where
x :: Word16
x = (fromIntegral x1 `shiftL` 8) .|. fromIntegral x0
utf32_le :: Codec
utf32_le = Codec name enc (toDecoding dec) where
name = T.pack "UTF-32-LE"
enc text = (TE.encodeUtf32LE text, Nothing)
dec bs = case utf32SplitBytes TE.decodeUtf32LE bs of
Just (text, extra) -> (text, Right extra)
Nothing -> splitSlowly TE.decodeUtf32LE bs
utf32_be :: Codec
utf32_be = Codec name enc (toDecoding dec) where
name = T.pack "UTF-32-BE"
enc text = (TE.encodeUtf32BE text, Nothing)
dec bs = case utf32SplitBytes TE.decodeUtf32BE bs of
Just (text, extra) -> (text, Right extra)
Nothing -> splitSlowly TE.decodeUtf32BE bs
utf32SplitBytes :: (ByteString -> Text)
-> ByteString
-> Maybe (Text, ByteString)
utf32SplitBytes dec bytes = split where
split = maybeDecode (dec toDecode, extra)
len = B.length bytes
lenExtra = mod len 4
lenToDecode = len - lenExtra
(toDecode, extra) = if lenExtra == 0
then (bytes, B.empty)
else B.splitAt lenToDecode bytes
tryEvaluate :: a -> Either Exc.SomeException a
tryEvaluate = unsafePerformIO . Exc.try . Exc.evaluate
maybeDecode :: (a, b) -> Maybe (a, b)
maybeDecode (a, b) = case tryEvaluate a of
Left _ -> Nothing
Right _ -> Just (a, b)
|
