{-# LANGUAGE Trustworthy #-} {-# LANGUAGE NoImplicitPrelude, ExistentialQuantification #-} {-# OPTIONS_GHC -funbox-strict-fields #-} ----------------------------------------------------------------------------- -- | -- Module : GHC.IO.Encoding.Types -- Copyright : (c) The University of Glasgow, 2008-2009 -- License : see libraries/base/LICENSE -- -- Maintainer : libraries@haskell.org -- Stability : internal -- Portability : non-portable -- -- Types for text encoding/decoding -- ----------------------------------------------------------------------------- module GHC.IO.Encoding.Types ( BufferCodec(..), TextEncoding(..), TextEncoder, TextDecoder, CodeBuffer, EncodeBuffer, DecodeBuffer, CodingProgress(..) ) where import GHC.Base import GHC.Word import GHC.Show -- import GHC.IO import GHC.IO.Buffer -- ----------------------------------------------------------------------------- -- Text encoders/decoders data BufferCodec from to state = BufferCodec { encode :: CodeBuffer from to, -- ^ The @encode@ function translates elements of the buffer @from@ -- to the buffer @to@. It should translate as many elements as possible -- given the sizes of the buffers, including translating zero elements -- if there is either not enough room in @to@, or @from@ does not -- contain a complete multibyte sequence. -- -- If multiple CodingProgress returns are possible, OutputUnderflow must be -- preferred to InvalidSequence. This allows GHC's IO library to assume that -- if we observe InvalidSequence there is at least a single element available -- in the output buffer. -- -- The fact that as many elements as possible are translated is used by the IO -- library in order to report translation errors at the point they -- actually occur, rather than when the buffer is translated. recover :: Buffer from -> Buffer to -> IO (Buffer from, Buffer to), -- ^ The @recover@ function is used to continue decoding -- in the presence of invalid or unrepresentable sequences. This includes -- both those detected by @encode@ returning @InvalidSequence@ and those -- that occur because the input byte sequence appears to be truncated. -- -- Progress will usually be made by skipping the first element of the @from@ -- buffer. This function should only be called if you are certain that you -- wish to do this skipping and if the @to@ buffer has at least one element -- of free space. Because this function deals with decoding failure, it assumes -- that the from buffer has at least one element. -- -- @recover@ may raise an exception rather than skipping anything. -- -- Currently, some implementations of @recover@ may mutate the input buffer. -- In particular, this feature is used to implement transliteration. -- -- /Since: 4.4.0.0/ close :: IO (), -- ^ Resources associated with the encoding may now be released. -- The @encode@ function may not be called again after calling -- @close@. getState :: IO state, -- ^ Return the current state of the codec. -- -- Many codecs are not stateful, and in these case the state can be -- represented as '()'. Other codecs maintain a state. For -- example, UTF-16 recognises a BOM (byte-order-mark) character at -- the beginning of the input, and remembers thereafter whether to -- use big-endian or little-endian mode. In this case, the state -- of the codec would include two pieces of information: whether we -- are at the beginning of the stream (the BOM only occurs at the -- beginning), and if not, whether to use the big or little-endian -- encoding. setState :: state -> IO () -- restore the state of the codec using the state from a previous -- call to 'getState'. } type CodeBuffer from to = Buffer from -> Buffer to -> IO (CodingProgress, Buffer from, Buffer to) type DecodeBuffer = CodeBuffer Word8 Char type EncodeBuffer = CodeBuffer Char Word8 type TextDecoder state = BufferCodec Word8 CharBufElem state type TextEncoder state = BufferCodec CharBufElem Word8 state -- | A 'TextEncoding' is a specification of a conversion scheme -- between sequences of bytes and sequences of Unicode characters. -- -- For example, UTF-8 is an encoding of Unicode characters into a sequence -- of bytes. The 'TextEncoding' for UTF-8 is 'utf8'. data TextEncoding = forall dstate estate . TextEncoding { textEncodingName :: String, -- ^ a string that can be passed to 'mkTextEncoding' to -- create an equivalent 'TextEncoding'. mkTextDecoder :: IO (TextDecoder dstate), -- ^ Creates a means of decoding bytes into characters: the result must not -- be shared between several byte sequences or simultaneously across threads mkTextEncoder :: IO (TextEncoder estate) -- ^ Creates a means of encode characters into bytes: the result must not -- be shared between several character sequences or simultaneously across threads } instance Show TextEncoding where -- | Returns the value of 'textEncodingName' show te = textEncodingName te -- | /Since: 4.4.0.0/ data CodingProgress = InputUnderflow -- ^ Stopped because the input contains insufficient available elements, -- or all of the input sequence has been sucessfully translated. | OutputUnderflow -- ^ Stopped because the output contains insufficient free elements | InvalidSequence -- ^ Stopped because there are sufficient free elements in the output -- to output at least one encoded ASCII character, but the input contains -- an invalid or unrepresentable sequence deriving (Eq, Show)