content: {-# LANGUAGE Trustworthy #-}
  {-# LANGUAGE CPP
             , NoImplicitPrelude
             , RecordWildCards
             , BangPatterns
             , PatternGuards
             , NondecreasingIndentation
             , MagicHash
             , ForeignFunctionInterface
    #-}
  {-# OPTIONS_GHC -fno-warn-name-shadowing #-}
  {-# OPTIONS_GHC -fno-warn-unused-matches #-}
  {-# OPTIONS_HADDOCK hide #-}
  
  -----------------------------------------------------------------------------
  -- |
  -- 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
  --
  -----------------------------------------------------------------------------
  
  -- #hide
  module GHC.IO.Handle.Text ( 
          hWaitForInput, hGetChar, hGetLine, hGetContents, hPutChar, hPutStr,
          commitBuffer',       -- hack, see below
          hGetBuf, hGetBufSome, hGetBufNonBlocking, hPutBuf, hPutBufNonBlocking,
          memcpy, hPutStrLn,
      ) 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.Maybe
  import Control.Monad
  
  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 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
    = Exception.catch
       (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
  #ifdef 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 'hClose'.
  -- A semi-closed handle becomes closed:
  --
  --  * if '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
            ClosedHandle     -> return (handle_, "")
            SemiClosedHandle -> lazyReadBuffered handle handle_
            _ -> 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
  
  -- ---------------------------------------------------------------------------
  -- 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.
  
  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, error "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 '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
  
    -- enough room in handle buffer?
    if (size - w > count)
          -- 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
                  writeIORef haByteBuffer old_buf{ bufR = w + count }
                  return count
  
          -- else, we have to flush
          else do debugIO "hPutBuf: flushing first"
                  old_buf' <- Buffered.flushWriteBuffer haDevice old_buf
                          -- TODO: we should do a non-blocking flush here
                  writeIORef haByteBuffer old_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 '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 '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 if count > sz  -- large read?
                      then do RawIO.read (haFD h_) (castPtr ptr) count
                      else 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__ -> FD
  haFD h_@Handle__{..} =
     case cast haDevice of
               Nothing -> error "not an FD"
               Just fd -> fd
  
  -- | '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 '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)
  
  