{-# LANGUAGE RankNTypes, BangPatterns #-} -- | This module uses the stream decoding functions from -- <http://hackage.haskell.org/package/streaming-commons streaming-commons> -- package to define decoding functions and lenses. The exported names -- conflict with names in @Data.Text.Encoding@ but not with the @Prelude@ module Pipes.Text.Encoding ( -- * Decoding ByteStrings and Encoding Texts -- ** Simple usage -- $usage -- ** Lens usage -- $lenses -- * Basic lens operations Codec , decode , eof -- * Decoding lenses , utf8 , utf8Pure , utf16LE , utf16BE , utf32LE , utf32BE -- * Non-lens decoding functions -- $decoders , decodeUtf8 , decodeUtf8Pure , decodeUtf16LE , decodeUtf16BE , decodeUtf32LE , decodeUtf32BE -- * Re-encoding functions -- $encoders , encodeUtf8 , encodeUtf16LE , encodeUtf16BE , encodeUtf32LE , encodeUtf32BE -- * Functions for latin and ascii text -- $ascii , encodeAscii , decodeAscii , encodeIso8859_1 , decodeIso8859_1 ) where import Data.Functor.Constant (Constant(..)) import Data.Char (ord) import Data.ByteString 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 qualified Data.Streaming.Text as Stream import Data.Streaming.Text (DecodeResult(..)) import Control.Monad (join, liftM) import Pipes {- $usage Encoding is of course simple. Given > text :: Producer Text IO () we can encode it with @Data.Text.Encoding.encodeUtf8@ > TE.encodeUtf8 :: Text -> ByteString and ordinary pipe operations: > text >-> P.map TE.encodeUtf8 :: Producer.ByteString IO () or, equivalently > for text (yield . TE.encodeUtf8) But, using this module, we might use > encodeUtf8 :: Text -> Producer ByteString m () to write > for text encodeUtf8 :: Producer.ByteString IO () All of the above come to the same. Given > bytes :: Producer ByteString IO () we can apply a decoding function from this module: > decodeUtf8 bytes :: Producer Text IO (Producer ByteString IO ()) The Text producer ends wherever decoding first fails. The un-decoded material is returned. If we are confident it is of no interest, we can write: > void $ decodeUtf8 bytes :: Producer Text IO () Thus we can re-encode as uft8 as much of our byte stream as is decodeUtf16BE decodable, with, e.g. > for (decodeUtf16BE bytes) encodeUtf8 :: Producer ByteString IO (Producer ByteString IO ()) The bytestring producer that is returned begins with where utf16BE decoding failed; if it didn't fail the producer is empty. -} {- $lenses We get a bit more flexibility, particularly in the use of pipes-style "parsers", if we use a lens like @utf8@ or @utf16BE@ that focusses on the text in an appropriately encoded byte stream. > type Lens' a b = forall f . Functor f => (b -> f b) -> (a -> f a) is just an alias for a Prelude type. We abbreviate this further, for our use case, as > type Codec > = forall m r . Monad m => Lens' (Producer ByteString m r) (Producer Text m (Producer ByteString m r)) and call the decoding lenses @utf8@, @utf16BE@ \"codecs\", since they can re-encode what they have decoded. Thus you use any particular codec with the @view@ / @(^.)@ , @zoom@ and @over@ functions from the standard lens libraries; <http://hackage.haskell.org/package/lens lens>, <http://hackage.haskell.org/package/lens-family lens-family>, <http://hackage.haskell.org/package/lens-simple lens-simple>, or one of the and <http://hackage.haskell.org/package/microlens microlens> packages will all work the same, since we already have access to the types they require. Each decoding lens looks into a byte stream that is supposed to contain text. The particular lenses are named in accordance with the expected encoding, 'utf8', 'utf16LE' etc. To turn a such a lens or @Codec@ into an ordinary function, use @view@ / @(^.)@ -- here also called 'decode': > view utf8 :: Producer ByteString m r -> Producer Text m (Producer ByteString m r) > decode utf8 Byte.stdin :: Producer Text IO (Producer ByteString IO r) > Bytes.stdin ^. utf8 :: Producer Text IO (Producer ByteString IO r) Of course, we could always do this with the specialized decoding functions, e.g. > decodeUtf8 :: Producer ByteString m r -> Producer Text m (Producer ByteString m r) > decodeUtf8 Byte.stdin :: Producer Text IO (Producer ByteString IO r) As with these functions, the stream of text that a @Codec@ \'sees\' in the stream of bytes begins at its head. At any point of decoding failure, the stream of text ends and reverts to (returns) the original byte stream. Thus if the first bytes are already un-decodable, the whole ByteString producer will be returned, i.e. > view utf8 bad_bytestream will just come to the same as > return bad_bytestream Where there is no decoding failure, the return value of the text stream will be an empty byte stream followed by its own return value. In all cases you must deal with the fact that it is a /ByteString producer/ that is returned, even if it can be thrown away with @Control.Monad.void@ > void (Bytes.stdin ^. utf8) :: Producer Text IO () The @eof@ lens permits you to pattern match: if there is a Right value, it is the leftover bytestring producer, if there is a Right value, it is the return value of the original bytestring producer: > Bytes.stdin ^. utf8 . eof :: Producer Text IO (Either (Producer ByteString IO IO) ()) Thus for the stream of un-decodable bytes mentioned above, > view (utf8 . eof) bad_bytestream will be the same as > return (Left bad_bytestream) @zoom utf8@ converts a Text parser into a ByteString parser: > zoom utf8 drawChar :: Monad m => StateT (Producer ByteString m r) m (Maybe Char) or, using the type synonymn from @Pipes.Parse@: > zoom utf8 drawChar :: Monad m => Parser ByteString m (Maybe Char) Thus we can define a ByteString parser (in the pipes-parse sense) like this: > charPlusByte :: Parser ByteString m (Maybe Char, Maybe Word8))) > charPlusByte = do char_ <- zoom utf8 Text.drawChar > byte_ <- Bytes.peekByte > return (char_, byte_) Though @charPlusByte@ is partly defined with a Text parser 'drawChar'; but it is a ByteString parser; it will return the first valid utf8-encoded Char in a ByteString, /whatever its byte-length/, and the first byte following, if both exist. Because we \'draw\' one and \'peek\' at the other, the parser as a whole only advances one Char's length along the bytestring, whatever that length may be. See the slightly more complex example \'decode.hs\' in the <http://www.haskellforall.com/2014/02/pipes-parse-30-lens-based-parsing.html#batteries-included haskellforall blog> discussion of this type of byte stream parsing. -} type Lens' a b = forall f . Functor f => (b -> f b) -> (a -> f a) type Codec = forall m r . Monad m => Lens' (Producer ByteString m r) (Producer Text m (Producer ByteString m r)) {- | @decode@ is just the ordinary @view@ or @(^.)@ of the lens libraries; exported here under a name appropriate to the material. Thus given a bytestring producer called @bytes@ we have > decode utf8 bytes :: Producer Text IO (Producer ByteString IO ()) All of these are thus the same: > decode utf8 bytes > view utf8 bytes > bytes ^. utf8 > decodeUtf8 bytes -} decode :: ((b -> Constant b b) -> (a -> Constant b a)) -> a -> b decode codec a = getConstant (codec Constant a) {- | @eof@ tells you explicitly when decoding stops due to bad bytes or instead reaches end-of-file happily. (Without it one just makes an explicit test for emptiness of the resulting bytestring production using next) Thus > decode (utf8 . eof) bytes :: Producer T.Text IO (Either (Producer B.ByteString IO ()) ()) If we hit undecodable bytes, the remaining bytestring producer will be returned as a Left value; in the happy case, a Right value is returned with the anticipated return value for the original bytestring producer. Given a bytestring producer called @bytes@ all of these will be the same: > decode (utf8 . eof) bytes > view (utf8 . eof) bytes > bytes^.utf8.eof -} eof :: (Monad m, Monad (t m), MonadTrans t) => Lens' (t m (Producer ByteString m r)) (t m (Either (Producer ByteString m r) r)) eof k p0 = fmap fromEither (k (toEither p0)) where fromEither = liftM (either id return) toEither pp = do p <- pp check p check p = do e <- lift (next p) case e of Left r -> return (Right r) Right (bs,pb) -> if B.null bs then check pb else return (Left (do yield bs pb)) utf8 :: Codec utf8 = mkCodec decodeUtf8 TE.encodeUtf8 utf8Pure :: Codec utf8Pure = mkCodec decodeUtf8Pure TE.encodeUtf8 utf16LE :: Codec utf16LE = mkCodec decodeUtf16LE TE.encodeUtf16LE utf16BE :: Codec utf16BE = mkCodec decodeUtf16BE TE.encodeUtf16BE utf32LE :: Codec utf32LE = mkCodec decodeUtf32LE TE.encodeUtf32LE utf32BE :: Codec utf32BE = mkCodec decodeUtf32BE TE.encodeUtf32BE decodeStream :: Monad m => (B.ByteString -> DecodeResult) -> Producer ByteString m r -> Producer Text m (Producer ByteString m r) decodeStream = loop where loop dec0 p = do x <- lift (next p) case x of Left r -> return (return r) Right (chunk, p') -> case dec0 chunk of DecodeResultSuccess text dec -> do yield text loop dec p' DecodeResultFailure text bs -> do yield text return (do yield bs p') {-# INLINABLE decodeStream#-} {- $decoders These are functions with the simple type: > decodeUtf8 :: Monad m => Producer ByteString m r -> Producer Text m (Producer ByteString m r) Thus in general > decodeUtf8 = view utf8 > decodeUtf16LE = view utf16LE and so forth, but these forms may be more convenient (and give better type errors!) where lenses are not desired. -} decodeUtf8 :: Monad m => Producer ByteString m r -> Producer Text m (Producer ByteString m r) decodeUtf8 = decodeStream Stream.decodeUtf8 {-# INLINE decodeUtf8 #-} decodeUtf8Pure :: Monad m => Producer ByteString m r -> Producer Text m (Producer ByteString m r) decodeUtf8Pure = decodeStream Stream.decodeUtf8Pure {-# INLINE decodeUtf8Pure #-} decodeUtf16LE :: Monad m => Producer ByteString m r -> Producer Text m (Producer ByteString m r) decodeUtf16LE = decodeStream Stream.decodeUtf16LE {-# INLINE decodeUtf16LE #-} decodeUtf16BE :: Monad m => Producer ByteString m r -> Producer Text m (Producer ByteString m r) decodeUtf16BE = decodeStream Stream.decodeUtf16BE {-# INLINE decodeUtf16BE #-} decodeUtf32LE :: Monad m => Producer ByteString m r -> Producer Text m (Producer ByteString m r) decodeUtf32LE = decodeStream Stream.decodeUtf32LE {-# INLINE decodeUtf32LE #-} decodeUtf32BE :: Monad m => Producer ByteString m r -> Producer Text m (Producer ByteString m r) decodeUtf32BE = decodeStream Stream.decodeUtf32BE {-# INLINE decodeUtf32BE #-} {- $encoders These are simply defined > encodeUtf8 = yield . TE.encodeUtf8 They are intended for use with 'for' > for Text.stdin encodeUtf8 :: Producer ByteString IO () which would have the effect of > Text.stdin >-> Pipes.Prelude.map (TE.encodeUtf8) using the encoding functions from Data.Text.Encoding -} encodeUtf8 :: Monad m => Text -> Producer' ByteString m () encodeUtf8 = yield . TE.encodeUtf8 encodeUtf16LE :: Monad m => Text -> Producer' ByteString m () encodeUtf16LE = yield . TE.encodeUtf16LE encodeUtf16BE :: Monad m => Text -> Producer' ByteString m () encodeUtf16BE = yield . TE.encodeUtf16BE encodeUtf32LE :: Monad m => Text -> Producer' ByteString m () encodeUtf32LE = yield . TE.encodeUtf32LE encodeUtf32BE :: Monad m => Text -> Producer' ByteString m () encodeUtf32BE = yield . TE.encodeUtf32BE mkCodec :: (forall r m . Monad m => Producer ByteString m r -> Producer Text m (Producer ByteString m r )) -> (Text -> ByteString) -> Codec mkCodec dec enc = \k p0 -> fmap (\p -> join (for p (yield . enc))) (k (dec p0)) {- $ascii ascii and latin encodings only use a small number of the characters 'Text' recognizes; thus we cannot use the pipes @Lens@ style to work with them. Rather we simply define functions each way. -} -- | 'encodeAscii' reduces as much of your stream of 'Text' actually is ascii to a byte stream, -- returning the rest of the 'Text' at the first non-ascii 'Char' encodeAscii :: Monad m => Producer Text m r -> Producer ByteString m (Producer Text m r) encodeAscii = go where go p = do e <- lift (next p) case e of Left r -> return (return r) Right (chunk, p') -> if T.null chunk then go p' else let (safe, unsafe) = T.span (\c -> ord c <= 0x7F) chunk in do yield (B8.pack (T.unpack safe)) if T.null unsafe then go p' else return $ do yield unsafe p' {- | Reduce as much of your stream of 'Text' actually is iso8859 or latin1 to a byte stream, returning the rest of the 'Text' upon hitting any non-latin 'Char' -} encodeIso8859_1 :: Monad m => Producer Text m r -> Producer ByteString m (Producer Text m r) encodeIso8859_1 = go where go p = do e <- lift (next p) case e of Left r -> return (return r) Right (txt, p') -> if T.null txt then go p' else let (safe, unsafe) = T.span (\c -> ord c <= 0xFF) txt in do yield (B8.pack (T.unpack safe)) if T.null unsafe then go p' else return $ do yield unsafe p' {- | Reduce a byte stream to a corresponding stream of ascii chars, returning the unused 'ByteString' upon hitting an un-ascii byte. -} decodeAscii :: Monad m => Producer ByteString m r -> Producer Text m (Producer ByteString m r) decodeAscii = go where go p = do e <- lift (next p) case e of Left r -> return (return r) Right (chunk, p') -> if B.null chunk then go p' else let (safe, unsafe) = B.span (<= 0x7F) chunk in do yield (T.pack (B8.unpack safe)) if B.null unsafe then go p' else return (do yield unsafe p') {- | Reduce a byte stream to a corresponding stream of ascii chars, returning the unused 'ByteString' upon hitting the rare un-latinizable byte. -} decodeIso8859_1 :: Monad m => Producer ByteString m r -> Producer Text m (Producer ByteString m r) decodeIso8859_1 = go where go p = do e <- lift (next p) case e of Left r -> return (return r) Right (chunk, p') -> if B.null chunk then go p' else do let (safe, unsafe) = B.span (<= 0xFF) chunk yield (T.pack (B8.unpack safe)) if B.null unsafe then go p' else return (do yield unsafe p')