path: root/libraries/base/GHC/IO/Handle/Text.hs

{-# LANGUAGE Trustworthy #-}
{-# LANGUAGE CPP
           , NoImplicitPrelude
           , RecordWildCards
           , BangPatterns
           , NondecreasingIndentation
           , MagicHash
  #-}
{-# OPTIONS_GHC -Wno-name-shadowing #-}
{-# OPTIONS_GHC -Wno-unused-matches #-}
{-# OPTIONS_HADDOCK not-home #-}

-----------------------------------------------------------------------------
-- |
-- Module      :  GHC.IO.Text
-- Copyright   :  (c) The University of Glasgow, 1992-2008
-- License     :  see libraries/base/LICENSE
--
-- Maintainer  :  libraries@haskell.org
-- Stability   :  internal
-- Portability :  non-portable
--
-- String I\/O functions
--
-----------------------------------------------------------------------------

module GHC.IO.Handle.Text (
        hWaitForInput, hGetChar, hGetLine, hGetContents, hPutChar, hPutStr,
        commitBuffer',       -- hack, see below
        hGetBuf, hGetBufSome, hGetBufNonBlocking, hPutBuf, hPutBufNonBlocking,
        memcpy, hPutStrLn, hGetContents',
    ) where

import GHC.IO
import GHC.IO.FD
import GHC.IO.Buffer
import qualified GHC.IO.BufferedIO as Buffered
import GHC.IO.Exception
import GHC.Exception
import GHC.IO.Handle.Types
import GHC.IO.Handle.Internals
import qualified GHC.IO.Device as IODevice
import qualified GHC.IO.Device as RawIO

import Foreign
import Foreign.C

import qualified Control.Exception as Exception
import Data.Typeable
import System.IO.Error
import Data.Either (Either(..))
import Data.Maybe

import GHC.IORef
import GHC.Base
import GHC.Real
import GHC.Num
import GHC.Show
import GHC.List

-- ---------------------------------------------------------------------------
-- Simple input operations

-- If hWaitForInput finds anything in the Handle's buffer, it
-- immediately returns.  If not, it tries to read from the underlying
-- OS handle. Notice that for buffered Handles connected to terminals
-- this means waiting until a complete line is available.

-- | Computation 'hWaitForInput' @hdl t@
-- waits until input is available on handle @hdl@.
-- It returns 'True' as soon as input is available on @hdl@,
-- or 'False' if no input is available within @t@ milliseconds.  Note that
-- 'hWaitForInput' waits until one or more full /characters/ are available,
-- which means that it needs to do decoding, and hence may fail
-- with a decoding error.
--
-- If @t@ is less than zero, then @hWaitForInput@ waits indefinitely.
--
-- This operation may fail with:
--
--  * 'isEOFError' if the end of file has been reached.
--
--  * a decoding error, if the input begins with an invalid byte sequence
--    in this Handle's encoding.
--
-- NOTE for GHC users: unless you use the @-threaded@ flag,
-- @hWaitForInput hdl t@ where @t >= 0@ will block all other Haskell
-- threads for the duration of the call.  It behaves like a
-- @safe@ foreign call in this respect.
--

hWaitForInput :: Handle -> Int -> IO Bool
hWaitForInput h msecs = do
  wantReadableHandle_ "hWaitForInput" h $ \ handle_@Handle__{..} -> do
  cbuf <- readIORef haCharBuffer

  if not (isEmptyBuffer cbuf) then return True else do

  if msecs < 0
        then do cbuf' <- readTextDevice handle_ cbuf
                writeIORef haCharBuffer cbuf'
                return True
        else do
               -- there might be bytes in the byte buffer waiting to be decoded
               cbuf' <- decodeByteBuf handle_ cbuf
               writeIORef haCharBuffer cbuf'

               if not (isEmptyBuffer cbuf') then return True else do

                r <- IODevice.ready haDevice False{-read-} msecs
                if r then do -- Call hLookAhead' to throw an EOF
                             -- exception if appropriate
                             _ <- hLookAhead_ handle_
                             return True
                     else return False
                -- XXX we should only return when there are full characters
                -- not when there are only bytes.  That would mean looping
                -- and re-running IODevice.ready if we don't have any full
                -- characters; but we don't know how long we've waited
                -- so far.

-- ---------------------------------------------------------------------------
-- hGetChar

-- | Computation 'hGetChar' @hdl@ reads a character from the file or
-- channel managed by @hdl@, blocking until a character is available.
--
-- This operation may fail with:
--
--  * 'isEOFError' if the end of file has been reached.

hGetChar :: Handle -> IO Char
hGetChar handle =
  wantReadableHandle_ "hGetChar" handle $ \handle_@Handle__{..} -> do

  -- buffering mode makes no difference: we just read whatever is available
  -- from the device (blocking only if there is nothing available), and then
  -- return the first character.
  -- See [note Buffered Reading] in GHC.IO.Handle.Types
  buf0 <- readIORef haCharBuffer

  buf1 <- if isEmptyBuffer buf0
             then readTextDevice handle_ buf0
             else return buf0

  (c1,i) <- readCharBuf (bufRaw buf1) (bufL buf1)
  let buf2 = bufferAdjustL i buf1

  if haInputNL == CRLF && c1 == '\r'
     then do
            mbuf3 <- if isEmptyBuffer buf2
                      then maybeFillReadBuffer handle_ buf2
                      else return (Just buf2)

            case mbuf3 of
               -- EOF, so just return the '\r' we have
               Nothing -> do
                  writeIORef haCharBuffer buf2
                  return '\r'
               Just buf3 -> do
                  (c2,i2) <- readCharBuf (bufRaw buf2) (bufL buf2)
                  if c2 == '\n'
                     then do
                       writeIORef haCharBuffer (bufferAdjustL i2 buf3)
                       return '\n'
                     else do
                       -- not a \r\n sequence, so just return the \r
                       writeIORef haCharBuffer buf3
                       return '\r'
     else do
            writeIORef haCharBuffer buf2
            return c1

-- ---------------------------------------------------------------------------
-- hGetLine

-- | Computation 'hGetLine' @hdl@ reads a line from the file or
-- channel managed by @hdl@.
--
-- This operation may fail with:
--
--  * 'isEOFError' if the end of file is encountered when reading
--    the /first/ character of the line.
--
-- If 'hGetLine' encounters end-of-file at any other point while reading
-- in a line, it is treated as a line terminator and the (partial)
-- line is returned.

hGetLine :: Handle -> IO String
hGetLine h =
  wantReadableHandle_ "hGetLine" h $ \ handle_ -> do
     hGetLineBuffered handle_

hGetLineBuffered :: Handle__ -> IO String
hGetLineBuffered handle_@Handle__{..} = do
  buf <- readIORef haCharBuffer
  hGetLineBufferedLoop handle_ buf []

hGetLineBufferedLoop :: Handle__
                     -> CharBuffer -> [String]
                     -> IO String
hGetLineBufferedLoop handle_@Handle__{..}
        buf@Buffer{ bufL=r0, bufR=w, bufRaw=raw0 } xss =
  let
        -- find the end-of-line character, if there is one
        loop raw r
           | r == w = return (False, w)
           | otherwise =  do
                (c,r') <- readCharBuf raw r
                if c == '\n'
                   then return (True, r) -- NB. not r': don't include the '\n'
                   else loop raw r'
  in do
  (eol, off) <- loop raw0 r0

  debugIO ("hGetLineBufferedLoop: r=" ++ show r0 ++ ", w=" ++ show w ++ ", off=" ++ show off)

  (xs,r') <- if haInputNL == CRLF
                then unpack_nl raw0 r0 off ""
                else do xs <- unpack raw0 r0 off ""
                        return (xs,off)

  -- if eol == True, then off is the offset of the '\n'
  -- otherwise off == w and the buffer is now empty.
  if eol -- r' == off
        then do writeIORef haCharBuffer (bufferAdjustL (off+1) buf)
                return (concat (reverse (xs:xss)))
        else do
             let buf1 = bufferAdjustL r' buf
             maybe_buf <- maybeFillReadBuffer handle_ buf1
             case maybe_buf of
                -- Nothing indicates we caught an EOF, and we may have a
                -- partial line to return.
                Nothing -> do
                     -- we reached EOF.  There might be a lone \r left
                     -- in the buffer, so check for that and
                     -- append it to the line if necessary.
                     --
                     let pre = if not (isEmptyBuffer buf1) then "\r" else ""
                     writeIORef haCharBuffer buf1{ bufL=0, bufR=0 }
                     let str = concat (reverse (pre:xs:xss))
                     if not (null str)
                        then return str
                        else ioe_EOF
                Just new_buf ->
                     hGetLineBufferedLoop handle_ new_buf (xs:xss)

maybeFillReadBuffer :: Handle__ -> CharBuffer -> IO (Maybe CharBuffer)
maybeFillReadBuffer handle_ buf
  = catchException
     (do buf' <- getSomeCharacters handle_ buf
         return (Just buf')
     )
     (\e -> do if isEOFError e
                  then return Nothing
                  else ioError e)

-- See GHC.IO.Buffer
#define CHARBUF_UTF32
-- #define CHARBUF_UTF16

-- NB. performance-critical code: eyeball the Core.
unpack :: RawCharBuffer -> Int -> Int -> [Char] -> IO [Char]
unpack !buf !r !w acc0
 | r == w    = return acc0
 | otherwise =
  withRawBuffer buf $ \pbuf ->
    let
        unpackRB acc !i
         | i < r  = return acc
         | otherwise = do
              -- Here, we are rather careful to only put an *evaluated* character
              -- in the output string. Due to pointer tagging, this allows the consumer
              -- to avoid ping-ponging between the actual consumer code and the thunk code
#if defined(CHARBUF_UTF16)
              -- reverse-order decoding of UTF-16
              c2 <- peekElemOff pbuf i
              if (c2 < 0xdc00 || c2 > 0xdffff)
                 then unpackRB (unsafeChr (fromIntegral c2) : acc) (i-1)
                 else do c1 <- peekElemOff pbuf (i-1)
                         let c = (fromIntegral c1 - 0xd800) * 0x400 +
                                 (fromIntegral c2 - 0xdc00) + 0x10000
                         case desurrogatifyRoundtripCharacter (unsafeChr c) of
                           { C# c# -> unpackRB (C# c# : acc) (i-2) }
#else
              c <- peekElemOff pbuf i
              unpackRB (c : acc) (i-1)
#endif
     in
     unpackRB acc0 (w-1)

-- NB. performance-critical code: eyeball the Core.
unpack_nl :: RawCharBuffer -> Int -> Int -> [Char] -> IO ([Char],Int)
unpack_nl !buf !r !w acc0
 | r == w    =  return (acc0, 0)
 | otherwise =
  withRawBuffer buf $ \pbuf ->
    let
        unpackRB acc !i
         | i < r  = return acc
         | otherwise = do
              c <- peekElemOff pbuf i
              if (c == '\n' && i > r)
                 then do
                         c1 <- peekElemOff pbuf (i-1)
                         if (c1 == '\r')
                            then unpackRB ('\n':acc) (i-2)
                            else unpackRB ('\n':acc) (i-1)
                 else do
                         unpackRB (c : acc) (i-1)
     in do
     c <- peekElemOff pbuf (w-1)
     if (c == '\r')
        then do
                -- If the last char is a '\r', we need to know whether or
                -- not it is followed by a '\n', so leave it in the buffer
                -- for now and just unpack the rest.
                str <- unpackRB acc0 (w-2)
                return (str, w-1)
        else do
                str <- unpackRB acc0 (w-1)
                return (str, w)

-- Note [#5536]
--
-- We originally had
--
--    let c' = desurrogatifyRoundtripCharacter c in
--    c' `seq` unpackRB (c':acc) (i-1)
--
-- but this resulted in Core like
--
--    case (case x <# y of True -> C# e1; False -> C# e2) of c
--      C# _ -> unpackRB (c:acc) (i-1)
--
-- which compiles into a continuation for the outer case, with each
-- branch of the inner case building a C# and then jumping to the
-- continuation.  We'd rather not have this extra jump, which makes
-- quite a difference to performance (see #5536) It turns out that
-- matching on the C# directly causes GHC to do the case-of-case,
-- giving much straighter code.

-- -----------------------------------------------------------------------------
-- hGetContents

-- hGetContents on a DuplexHandle only affects the read side: you can
-- carry on writing to it afterwards.

-- | Computation 'hGetContents' @hdl@ returns the list of characters
-- corresponding to the unread portion of the channel or file managed
-- by @hdl@, which is put into an intermediate state, /semi-closed/.
-- In this state, @hdl@ is effectively closed,
-- but items are read from @hdl@ on demand and accumulated in a special
-- list returned by 'hGetContents' @hdl@.
--
-- Any operation that fails because a handle is closed,
-- also fails if a handle is semi-closed.  The only exception is
-- 'System.IO.hClose'.  A semi-closed handle becomes closed:
--
--  * if 'System.IO.hClose' is applied to it;
--
--  * if an I\/O error occurs when reading an item from the handle;
--
--  * or once the entire contents of the handle has been read.
--
-- Once a semi-closed handle becomes closed, the contents of the
-- associated list becomes fixed.  The contents of this final list is
-- only partially specified: it will contain at least all the items of
-- the stream that were evaluated prior to the handle becoming closed.
--
-- Any I\/O errors encountered while a handle is semi-closed are simply
-- discarded.
--
-- This operation may fail with:
--
--  * 'isEOFError' if the end of file has been reached.

hGetContents :: Handle -> IO String
hGetContents handle =
   wantReadableHandle "hGetContents" handle $ \handle_ -> do
      xs <- lazyRead handle
      return (handle_{ haType=SemiClosedHandle}, xs )

-- Note that someone may close the semi-closed handle (or change its
-- buffering), so each time these lazy read functions are pulled on,
-- they have to check whether the handle has indeed been closed.

lazyRead :: Handle -> IO String
lazyRead handle =
   unsafeInterleaveIO $
        withHandle "hGetContents" handle $ \ handle_ -> do
        case haType handle_ of
          SemiClosedHandle -> lazyReadBuffered handle handle_
          ClosedHandle
            -> ioException
                  (IOError (Just handle) IllegalOperation "hGetContents"
                        "delayed read on closed handle" Nothing Nothing)
          _ -> ioException
                  (IOError (Just handle) IllegalOperation "hGetContents"
                        "illegal handle type" Nothing Nothing)

lazyReadBuffered :: Handle -> Handle__ -> IO (Handle__, [Char])
lazyReadBuffered h handle_@Handle__{..} = do
   buf <- readIORef haCharBuffer
   Exception.catch
        (do
            buf'@Buffer{..} <- getSomeCharacters handle_ buf
            lazy_rest <- lazyRead h
            (s,r) <- if haInputNL == CRLF
                         then unpack_nl bufRaw bufL bufR lazy_rest
                         else do s <- unpack bufRaw bufL bufR lazy_rest
                                 return (s,bufR)
            writeIORef haCharBuffer (bufferAdjustL r buf')
            return (handle_, s)
        )
        (\e -> do (handle_', _) <- hClose_help handle_
                  debugIO ("hGetContents caught: " ++ show e)
                  -- We might have a \r cached in CRLF mode.  So we
                  -- need to check for that and return it:
                  let r = if isEOFError e
                             then if not (isEmptyBuffer buf)
                                     then "\r"
                                     else ""
                             else
                                  throw (augmentIOError e "hGetContents" h)

                  return (handle_', r)
        )

-- ensure we have some characters in the buffer
getSomeCharacters :: Handle__ -> CharBuffer -> IO CharBuffer
getSomeCharacters handle_@Handle__{..} buf@Buffer{..} =
  case bufferElems buf of

    -- buffer empty: read some more
    0 -> readTextDevice handle_ buf

    -- if the buffer has a single '\r' in it and we're doing newline
    -- translation: read some more
    1 | haInputNL == CRLF -> do
      (c,_) <- readCharBuf bufRaw bufL
      if c == '\r'
         then do -- shuffle the '\r' to the beginning.  This is only safe
                 -- if we're about to call readTextDevice, otherwise it
                 -- would mess up flushCharBuffer.
                 -- See [note Buffer Flushing], GHC.IO.Handle.Types
                 _ <- writeCharBuf bufRaw 0 '\r'
                 let buf' = buf{ bufL=0, bufR=1 }
                 readTextDevice handle_ buf'
         else do
                 return buf

    -- buffer has some chars in it already: just return it
    _otherwise ->
      return buf

-- -----------------------------------------------------------------------------
-- hGetContents'

-- We read everything into a list of CharBuffer chunks, and convert it lazily
-- to a string, which minimizes memory usage.
-- In the worst case, space usage is at most that of the complete String,
-- as the chunks can be garbage collected progressively.
-- For streaming consumers, space usage is at most that of the list of chunks.

-- | The 'hGetContents'' operation reads all input on the given handle
-- before returning it as a 'String' and closing the handle.
--
-- @since 4.14.0.0

hGetContents' :: Handle -> IO String
hGetContents' handle = do
    es <- wantReadableHandle "hGetContents'" handle (strictRead handle)
    case es of
      Right s -> return s
      Left e ->
          case fromException e of
            Just ioe -> throwIO (augmentIOError ioe "hGetContents'" handle)
            Nothing -> throwIO e

strictRead :: Handle -> Handle__ -> IO (Handle__, Either SomeException String)
strictRead h handle_@Handle__{..} = do
    cbuf <- readIORef haCharBuffer
    cbufs <- strictReadLoop' handle_ [] cbuf
    (handle_', me) <- hClose_help handle_
    case me of
      Just e -> return (handle_', Left e)
      Nothing -> do
        s <- lazyBuffersToString haInputNL cbufs ""
        return (handle_', Right s)

strictReadLoop :: Handle__ -> [CharBuffer] -> CharBuffer -> IO [CharBuffer]
strictReadLoop handle_ cbufs cbuf0 = do
    mcbuf <- Exception.catch
        (do r <- readTextDevice handle_ cbuf0
            return (Just r))
        (\e -> if isEOFError e
                  then return Nothing
                  else throw e)
    case mcbuf of
      Nothing -> return (cbuf0 : cbufs)
      Just cbuf1 -> strictReadLoop' handle_ cbufs cbuf1

-- If 'cbuf' is full, allocate a new buffer.
strictReadLoop' :: Handle__ -> [CharBuffer] -> CharBuffer -> IO [CharBuffer]
strictReadLoop' handle_ cbufs cbuf
    | isFullCharBuffer cbuf = do
        cbuf' <- newCharBuffer dEFAULT_CHAR_BUFFER_SIZE ReadBuffer
        strictReadLoop handle_ (cbuf : cbufs) cbuf'
    | otherwise = strictReadLoop handle_ cbufs cbuf

-- Lazily convert a list of buffers to a String. The buffers are
-- in reverse order: the first buffer is the end of the String.
lazyBuffersToString :: Newline -> [CharBuffer] -> String -> IO String
lazyBuffersToString LF = loop where
    loop [] s = return s
    loop (Buffer{..} : cbufs) s = do
        s' <- unsafeInterleaveIO (unpack bufRaw bufL bufR s)
        loop cbufs s'
lazyBuffersToString CRLF = loop '\0' where
    loop before [] s = return s
    loop before (Buffer{..} : cbufs) s
        | bufL == bufR = loop before cbufs s  -- skip empty buffers
        | otherwise = do
            -- When a CRLF is broken across two buffers, we already have a newline
            -- from decoding the LF, so we ignore the CR in the current buffer.
            s1 <- if before == '\n'
                     then return s
                     else do
                       -- We restore trailing CR not followed by LF.
                       c <- peekCharBuf bufRaw (bufR - 1)
                       if c == '\r'
                          then return ('\r' : s)
                          else return s
            s2 <- unsafeInterleaveIO (do
                (s2, _) <- unpack_nl bufRaw bufL bufR s1
                return s2)
            c0 <- peekCharBuf bufRaw bufL
            loop c0 cbufs s2

-- ---------------------------------------------------------------------------
-- hPutChar

-- | Computation 'hPutChar' @hdl ch@ writes the character @ch@ to the
-- file or channel managed by @hdl@.  Characters may be buffered if
-- buffering is enabled for @hdl@.
--
-- This operation may fail with:
--
--  * 'isFullError' if the device is full; or
--
--  * 'isPermissionError' if another system resource limit would be exceeded.

hPutChar :: Handle -> Char -> IO ()
hPutChar handle c = do
    c `seq` return ()
    wantWritableHandle "hPutChar" handle $ \ handle_  -> do
     hPutcBuffered handle_ c

hPutcBuffered :: Handle__ -> Char -> IO ()
hPutcBuffered handle_@Handle__{..} c = do
  buf <- readIORef haCharBuffer
  if c == '\n'
     then do buf1 <- if haOutputNL == CRLF
                        then do
                          buf1 <- putc buf '\r'
                          putc buf1 '\n'
                        else do
                          putc buf '\n'
             writeCharBuffer handle_ buf1
             when is_line $ flushByteWriteBuffer handle_
      else do
          buf1 <- putc buf c
          writeCharBuffer handle_ buf1
          return ()
  where
    is_line = case haBufferMode of
                LineBuffering -> True
                _             -> False

    putc buf@Buffer{ bufRaw=raw, bufR=w } c = do
       debugIO ("putc: " ++ summaryBuffer buf)
       w'  <- writeCharBuf raw w c
       return buf{ bufR = w' }

-- ---------------------------------------------------------------------------
-- hPutStr

-- We go to some trouble to avoid keeping the handle locked while we're
-- evaluating the string argument to hPutStr, in case doing so triggers another
-- I/O operation on the same handle which would lead to deadlock.  The classic
-- case is
--
--              putStr (trace "hello" "world")
--
-- so the basic scheme is this:
--
--      * copy the string into a fresh buffer,
--      * "commit" the buffer to the handle.
--
-- Committing may involve simply copying the contents of the new
-- buffer into the handle's buffer, flushing one or both buffers, or
-- maybe just swapping the buffers over (if the handle's buffer was
-- empty).  See commitBuffer below.

-- | Computation 'hPutStr' @hdl s@ writes the string
-- @s@ to the file or channel managed by @hdl@.
--
-- This operation may fail with:
--
--  * 'isFullError' if the device is full; or
--
--  * 'isPermissionError' if another system resource limit would be exceeded.

hPutStr :: Handle -> String -> IO ()
hPutStr handle str = hPutStr' handle str False

-- | The same as 'hPutStr', but adds a newline character.
hPutStrLn :: Handle -> String -> IO ()
hPutStrLn handle str = hPutStr' handle str True
  -- An optimisation: we treat hPutStrLn specially, to avoid the
  -- overhead of a single putChar '\n', which is quite high now that we
  -- have to encode eagerly.

{-# NOINLINE hPutStr' #-}
hPutStr' :: Handle -> String -> Bool -> IO ()
hPutStr' handle str add_nl =
  do
    (buffer_mode, nl) <-
         wantWritableHandle "hPutStr" handle $ \h_ -> do
                       bmode <- getSpareBuffer h_
                       return (bmode, haOutputNL h_)

    case buffer_mode of
       (NoBuffering, _) -> do
            hPutChars handle str        -- v. slow, but we don't care
            when add_nl $ hPutChar handle '\n'
       (LineBuffering, buf) -> do
            writeBlocks handle True  add_nl nl buf str
       (BlockBuffering _, buf) -> do
            writeBlocks handle False add_nl nl buf str

hPutChars :: Handle -> [Char] -> IO ()
hPutChars _      [] = return ()
hPutChars handle (c:cs) = hPutChar handle c >> hPutChars handle cs

getSpareBuffer :: Handle__ -> IO (BufferMode, CharBuffer)
getSpareBuffer Handle__{haCharBuffer=ref,
                        haBuffers=spare_ref,
                        haBufferMode=mode}
 = do
   case mode of
     NoBuffering -> return (mode, errorWithoutStackTrace "no buffer!")
     _ -> do
          bufs <- readIORef spare_ref
          buf  <- readIORef ref
          case bufs of
            BufferListCons b rest -> do
                writeIORef spare_ref rest
                return ( mode, emptyBuffer b (bufSize buf) WriteBuffer)
            BufferListNil -> do
                new_buf <- newCharBuffer (bufSize buf) WriteBuffer
                return (mode, new_buf)


-- NB. performance-critical code: eyeball the Core.
writeBlocks :: Handle -> Bool -> Bool -> Newline -> Buffer CharBufElem -> String -> IO ()
writeBlocks hdl line_buffered add_nl nl
            buf@Buffer{ bufRaw=raw, bufSize=len } s =
  let
   shoveString :: Int -> [Char] -> [Char] -> IO ()
   shoveString !n [] [] = do
        commitBuffer hdl raw len n False{-no flush-} True{-release-}
   shoveString !n [] rest = do
        shoveString n rest []
   shoveString !n (c:cs) rest
     -- n+1 so we have enough room to write '\r\n' if necessary
     | n + 1 >= len = do
        commitBuffer hdl raw len n False{-flush-} False
        shoveString 0 (c:cs) rest
     | c == '\n'  =  do
        n' <- if nl == CRLF
                 then do
                    n1 <- writeCharBuf raw n  '\r'
                    writeCharBuf raw n1 '\n'
                 else do
                    writeCharBuf raw n c
        if line_buffered
           then do
                -- end of line, so write and flush
               commitBuffer hdl raw len n' True{-flush-} False
               shoveString 0 cs rest
           else do
               shoveString n' cs rest
     | otherwise = do
        n' <- writeCharBuf raw n c
        shoveString n' cs rest
  in
  shoveString 0 s (if add_nl then "\n" else "")

-- -----------------------------------------------------------------------------
-- commitBuffer handle buf sz count flush release
--
-- Write the contents of the buffer 'buf' ('sz' bytes long, containing
-- 'count' bytes of data) to handle (handle must be block or line buffered).

commitBuffer
        :: Handle                       -- handle to commit to
        -> RawCharBuffer -> Int         -- address and size (in bytes) of buffer
        -> Int                          -- number of bytes of data in buffer
        -> Bool                         -- True <=> flush the handle afterward
        -> Bool                         -- release the buffer?
        -> IO ()

commitBuffer hdl !raw !sz !count flush release =
  wantWritableHandle "commitBuffer" hdl $ \h_@Handle__{..} -> do
      debugIO ("commitBuffer: sz=" ++ show sz ++ ", count=" ++ show count
            ++ ", flush=" ++ show flush ++ ", release=" ++ show release)

      writeCharBuffer h_ Buffer{ bufRaw=raw, bufState=WriteBuffer,
                                 bufL=0, bufR=count, bufSize=sz }

      when flush $ flushByteWriteBuffer h_

      -- release the buffer if necessary
      when release $ do
          -- find size of current buffer
          old_buf@Buffer{ bufSize=size } <- readIORef haCharBuffer
          when (sz == size) $ do
               spare_bufs <- readIORef haBuffers
               writeIORef haBuffers (BufferListCons raw spare_bufs)

      return ()

-- backwards compatibility; the text package uses this
commitBuffer' :: RawCharBuffer -> Int -> Int -> Bool -> Bool -> Handle__
              -> IO CharBuffer
commitBuffer' raw sz@(I# _) count@(I# _) flush release h_@Handle__{..}
   = do
      debugIO ("commitBuffer: sz=" ++ show sz ++ ", count=" ++ show count
            ++ ", flush=" ++ show flush ++ ", release=" ++ show release)

      let this_buf = Buffer{ bufRaw=raw, bufState=WriteBuffer,
                             bufL=0, bufR=count, bufSize=sz }

      writeCharBuffer h_ this_buf

      when flush $ flushByteWriteBuffer h_

      -- release the buffer if necessary
      when release $ do
          -- find size of current buffer
          old_buf@Buffer{ bufSize=size } <- readIORef haCharBuffer
          when (sz == size) $ do
               spare_bufs <- readIORef haBuffers
               writeIORef haBuffers (BufferListCons raw spare_bufs)

      return this_buf

-- ---------------------------------------------------------------------------
-- Reading/writing sequences of bytes.

-- ---------------------------------------------------------------------------
-- hPutBuf

-- | 'hPutBuf' @hdl buf count@ writes @count@ 8-bit bytes from the
-- buffer @buf@ to the handle @hdl@.  It returns ().
--
-- 'hPutBuf' ignores any text encoding that applies to the 'Handle',
-- writing the bytes directly to the underlying file or device.
--
-- 'hPutBuf' ignores the prevailing 'System.IO.TextEncoding' and
-- 'NewlineMode' on the 'Handle', and writes bytes directly.
--
-- This operation may fail with:
--
--  * 'ResourceVanished' if the handle is a pipe or socket, and the
--    reading end is closed.  (If this is a POSIX system, and the program
--    has not asked to ignore SIGPIPE, then a SIGPIPE may be delivered
--    instead, whose default action is to terminate the program).

hPutBuf :: Handle                       -- handle to write to
        -> Ptr a                        -- address of buffer
        -> Int                          -- number of bytes of data in buffer
        -> IO ()
hPutBuf h ptr count = do _ <- hPutBuf' h ptr count True
                         return ()

hPutBufNonBlocking
        :: Handle                       -- handle to write to
        -> Ptr a                        -- address of buffer
        -> Int                          -- number of bytes of data in buffer
        -> IO Int                       -- returns: number of bytes written
hPutBufNonBlocking h ptr count = hPutBuf' h ptr count False

hPutBuf':: Handle                       -- handle to write to
        -> Ptr a                        -- address of buffer
        -> Int                          -- number of bytes of data in buffer
        -> Bool                         -- allow blocking?
        -> IO Int
hPutBuf' handle ptr count can_block
  | count == 0 = return 0
  | count <  0 = illegalBufferSize handle "hPutBuf" count
  | otherwise =
    wantWritableHandle "hPutBuf" handle $
      \ h_@Handle__{..} -> do
          debugIO ("hPutBuf count=" ++ show count)

          r <- bufWrite h_ (castPtr ptr) count can_block

          -- we must flush if this Handle is set to NoBuffering.  If
          -- it is set to LineBuffering, be conservative and flush
          -- anyway (we didn't check for newlines in the data).
          case haBufferMode of
             BlockBuffering _      -> do return ()
             _line_or_no_buffering -> do flushWriteBuffer h_
          return r

bufWrite :: Handle__-> Ptr Word8 -> Int -> Bool -> IO Int
bufWrite h_@Handle__{..} ptr count can_block =
  seq count $ do  -- strictness hack
  old_buf@Buffer{ bufRaw=old_raw, bufR=w, bufSize=size }
     <- readIORef haByteBuffer

  -- TODO: Possible optimisation:
  --       If we know that `w + count > size`, we should write both the
  --       handle buffer and the `ptr` in a single `writev()` syscall.

  -- Need to buffer and enough room in handle buffer?
  -- There's no need to buffer if the data to be written is larger than
  -- the handle buffer (`count >= size`).
  if (count < size && count <= size - w)
        -- We need to buffer and there's enough room in the buffer:
        -- just copy the data in and update bufR.
        then do debugIO ("hPutBuf: copying to buffer, w=" ++ show w)
                copyToRawBuffer old_raw w ptr count
                let copied_buf = old_buf{ bufR = w + count }
                -- If the write filled the buffer completely, we need to flush,
                -- to maintain the "INVARIANTS on Buffers" from
                -- GHC.IO.Buffer.checkBuffer: "a write buffer is never full".
                if (count == size - w)
                  then do
                    debugIO "hPutBuf: flushing full buffer after writing"
                    flushed_buf <- Buffered.flushWriteBuffer haDevice copied_buf
                            -- TODO: we should do a non-blocking flush here
                    writeIORef haByteBuffer flushed_buf
                  else do
                    writeIORef haByteBuffer copied_buf
                return count

        -- else, we have to flush any existing handle buffer data
        -- and can then write out the data in `ptr` directly.
        else do -- No point flushing when there's nothing in the buffer.
                when (w > 0) $ do
                  debugIO "hPutBuf: flushing first"
                  flushed_buf <- Buffered.flushWriteBuffer haDevice old_buf
                          -- TODO: we should do a non-blocking flush here
                  writeIORef haByteBuffer flushed_buf
                -- if we can fit in the buffer, then just loop
                if count < size
                   then bufWrite h_ ptr count can_block
                   else if can_block
                           then do writeChunk h_ (castPtr ptr) count
                                   return count
                           else writeChunkNonBlocking h_ (castPtr ptr) count

writeChunk :: Handle__ -> Ptr Word8 -> Int -> IO ()
writeChunk h_@Handle__{..} ptr bytes
  | Just fd <- cast haDevice  =  RawIO.write (fd::FD) ptr bytes
  | otherwise = error "Todo: hPutBuf"

writeChunkNonBlocking :: Handle__ -> Ptr Word8 -> Int -> IO Int
writeChunkNonBlocking h_@Handle__{..} ptr bytes
  | Just fd <- cast haDevice  =  RawIO.writeNonBlocking (fd::FD) ptr bytes
  | otherwise = error "Todo: hPutBuf"

-- ---------------------------------------------------------------------------
-- hGetBuf

-- | 'hGetBuf' @hdl buf count@ reads data from the handle @hdl@
-- into the buffer @buf@ until either EOF is reached or
-- @count@ 8-bit bytes have been read.
-- It returns the number of bytes actually read.  This may be zero if
-- EOF was reached before any data was read (or if @count@ is zero).
--
-- 'hGetBuf' never raises an EOF exception, instead it returns a value
-- smaller than @count@.
--
-- If the handle is a pipe or socket, and the writing end
-- is closed, 'hGetBuf' will behave as if EOF was reached.
--
-- 'hGetBuf' ignores the prevailing 'System.IO.TextEncoding' and 'NewlineMode'
-- on the 'Handle', and reads bytes directly.

hGetBuf :: Handle -> Ptr a -> Int -> IO Int
hGetBuf h !ptr count
  | count == 0 = return 0
  | count <  0 = illegalBufferSize h "hGetBuf" count
  | otherwise =
      wantReadableHandle_ "hGetBuf" h $ \ h_@Handle__{..} -> do
         flushCharReadBuffer h_
         buf@Buffer{ bufRaw=raw, bufR=w, bufL=r, bufSize=sz }
            <- readIORef haByteBuffer
         if isEmptyBuffer buf
            then bufReadEmpty    h_ buf (castPtr ptr) 0 count
            else bufReadNonEmpty h_ buf (castPtr ptr) 0 count

-- small reads go through the buffer, large reads are satisfied by
-- taking data first from the buffer and then direct from the file
-- descriptor.

bufReadNonEmpty :: Handle__ -> Buffer Word8 -> Ptr Word8 -> Int -> Int -> IO Int
bufReadNonEmpty h_@Handle__{..}
                buf@Buffer{ bufRaw=raw, bufR=w, bufL=r, bufSize=sz }
                ptr !so_far !count
 = do
        let avail = w - r
        if (count < avail)
           then do
                copyFromRawBuffer ptr raw r count
                writeIORef haByteBuffer buf{ bufL = r + count }
                return (so_far + count)
           else do

        copyFromRawBuffer ptr raw r avail
        let buf' = buf{ bufR=0, bufL=0 }
        writeIORef haByteBuffer buf'
        let remaining = count - avail
            so_far' = so_far + avail
            ptr' = ptr `plusPtr` avail

        if remaining == 0
           then return so_far'
           else bufReadEmpty h_ buf' ptr' so_far' remaining


bufReadEmpty :: Handle__ -> Buffer Word8 -> Ptr Word8 -> Int -> Int -> IO Int
bufReadEmpty h_@Handle__{..}
             buf@Buffer{ bufRaw=raw, bufR=w, bufL=r, bufSize=sz }
             ptr so_far count
 | count > sz, Just fd <- cast haDevice = loop fd 0 count
 | otherwise = do
     (r,buf') <- Buffered.fillReadBuffer haDevice buf
     if r == 0
        then return so_far
        else do writeIORef haByteBuffer buf'
                bufReadNonEmpty h_ buf' ptr so_far count
 where
  loop :: FD -> Int -> Int -> IO Int
  loop fd off bytes | bytes <= 0 = return (so_far + off)
  loop fd off bytes = do
    r <- RawIO.read (fd::FD) (ptr `plusPtr` off) bytes
    if r == 0
        then return (so_far + off)
        else loop fd (off + r) (bytes - r)

-- ---------------------------------------------------------------------------
-- hGetBufSome

-- | 'hGetBufSome' @hdl buf count@ reads data from the handle @hdl@
-- into the buffer @buf@.  If there is any data available to read,
-- then 'hGetBufSome' returns it immediately; it only blocks if there
-- is no data to be read.
--
-- It returns the number of bytes actually read.  This may be zero if
-- EOF was reached before any data was read (or if @count@ is zero).
--
-- 'hGetBufSome' never raises an EOF exception, instead it returns a value
-- smaller than @count@.
--
-- If the handle is a pipe or socket, and the writing end
-- is closed, 'hGetBufSome' will behave as if EOF was reached.
--
-- 'hGetBufSome' ignores the prevailing 'System.IO.TextEncoding' and
-- 'NewlineMode' on the 'Handle', and reads bytes directly.

hGetBufSome :: Handle -> Ptr a -> Int -> IO Int
hGetBufSome h !ptr count
  | count == 0 = return 0
  | count <  0 = illegalBufferSize h "hGetBufSome" count
  | otherwise =
      wantReadableHandle_ "hGetBufSome" h $ \ h_@Handle__{..} -> do
         flushCharReadBuffer h_
         buf@Buffer{ bufSize=sz } <- readIORef haByteBuffer
         if isEmptyBuffer buf
            then case count > sz of  -- large read? optimize it with a little special case:
                    True | Just fd <- haFD h_ -> do RawIO.read fd (castPtr ptr) count
                    _ -> do (r,buf') <- Buffered.fillReadBuffer haDevice buf
                            if r == 0
                               then return 0
                               else do writeIORef haByteBuffer buf'
                                       bufReadNBNonEmpty h_ buf' (castPtr ptr) 0 (min r count)
                                        -- new count is  (min r count), so
                                        -- that bufReadNBNonEmpty will not
                                        -- issue another read.
            else
              let count' = min count (bufferElems buf)
              in bufReadNBNonEmpty h_ buf (castPtr ptr) 0 count'

haFD :: Handle__ -> Maybe FD
haFD h_@Handle__{..} = cast haDevice

-- | 'hGetBufNonBlocking' @hdl buf count@ reads data from the handle @hdl@
-- into the buffer @buf@ until either EOF is reached, or
-- @count@ 8-bit bytes have been read, or there is no more data available
-- to read immediately.
--
-- 'hGetBufNonBlocking' is identical to 'hGetBuf', except that it will
-- never block waiting for data to become available, instead it returns
-- only whatever data is available.  To wait for data to arrive before
-- calling 'hGetBufNonBlocking', use 'hWaitForInput'.
--
-- If the handle is a pipe or socket, and the writing end
-- is closed, 'hGetBufNonBlocking' will behave as if EOF was reached.
--
-- 'hGetBufNonBlocking' ignores the prevailing 'System.IO.TextEncoding' and
-- 'NewlineMode' on the 'Handle', and reads bytes directly.
--
-- NOTE: on Windows, this function does not work correctly; it
-- behaves identically to 'hGetBuf'.

hGetBufNonBlocking :: Handle -> Ptr a -> Int -> IO Int
hGetBufNonBlocking h !ptr count
  | count == 0 = return 0
  | count <  0 = illegalBufferSize h "hGetBufNonBlocking" count
  | otherwise =
      wantReadableHandle_ "hGetBufNonBlocking" h $ \ h_@Handle__{..} -> do
         flushCharReadBuffer h_
         buf@Buffer{ bufRaw=raw, bufR=w, bufL=r, bufSize=sz }
            <- readIORef haByteBuffer
         if isEmptyBuffer buf
            then bufReadNBEmpty    h_ buf (castPtr ptr) 0 count
            else bufReadNBNonEmpty h_ buf (castPtr ptr) 0 count

bufReadNBEmpty :: Handle__ -> Buffer Word8 -> Ptr Word8 -> Int -> Int -> IO Int
bufReadNBEmpty   h_@Handle__{..}
                 buf@Buffer{ bufRaw=raw, bufR=w, bufL=r, bufSize=sz }
                 ptr so_far count
  | count > sz,
    Just fd <- cast haDevice = do
       m <- RawIO.readNonBlocking (fd::FD) ptr count
       case m of
         Nothing -> return so_far
         Just n  -> return (so_far + n)

 | otherwise = do
     buf <- readIORef haByteBuffer
     (r,buf') <- Buffered.fillReadBuffer0 haDevice buf
     case r of
       Nothing -> return so_far
       Just 0  -> return so_far
       Just r  -> do
         writeIORef haByteBuffer buf'
         bufReadNBNonEmpty h_ buf' ptr so_far (min count r)
                          -- NOTE: new count is    min count r
                          -- so we will just copy the contents of the
                          -- buffer in the recursive call, and not
                          -- loop again.


bufReadNBNonEmpty :: Handle__ -> Buffer Word8 -> Ptr Word8 -> Int -> Int -> IO Int
bufReadNBNonEmpty h_@Handle__{..}
                  buf@Buffer{ bufRaw=raw, bufR=w, bufL=r, bufSize=sz }
                  ptr so_far count
  = do
        let avail = w - r
        if (count < avail)
           then do
                copyFromRawBuffer ptr raw r count
                writeIORef haByteBuffer buf{ bufL = r + count }
                return (so_far + count)
           else do

        copyFromRawBuffer ptr raw r avail
        let buf' = buf{ bufR=0, bufL=0 }
        writeIORef haByteBuffer buf'
        let remaining = count - avail
            so_far' = so_far + avail
            ptr' = ptr `plusPtr` avail

        if remaining == 0
           then return so_far'
           else bufReadNBEmpty h_ buf' ptr' so_far' remaining

-- ---------------------------------------------------------------------------
-- memcpy wrappers

copyToRawBuffer :: RawBuffer e -> Int -> Ptr e -> Int -> IO ()
copyToRawBuffer raw off ptr bytes =
 withRawBuffer raw $ \praw ->
   do _ <- memcpy (praw `plusPtr` off) ptr (fromIntegral bytes)
      return ()

copyFromRawBuffer :: Ptr e -> RawBuffer e -> Int -> Int -> IO ()
copyFromRawBuffer ptr raw off bytes =
 withRawBuffer raw $ \praw ->
   do _ <- memcpy ptr (praw `plusPtr` off) (fromIntegral bytes)
      return ()

foreign import ccall unsafe "memcpy"
   memcpy :: Ptr a -> Ptr a -> CSize -> IO (Ptr ())

-----------------------------------------------------------------------------
-- Internal Utils

illegalBufferSize :: Handle -> String -> Int -> IO a
illegalBufferSize handle fn sz =
        ioException (IOError (Just handle)
                            InvalidArgument  fn
                            ("illegal buffer size " ++ showsPrec 9 sz [])
                            Nothing Nothing)