{-# LANGUAGE Trustworthy #-} {-# LANGUAGE CPP , NoImplicitPrelude , RecordWildCards , NondecreasingIndentation #-} {-# OPTIONS_GHC -Wno-unused-matches #-} ----------------------------------------------------------------------------- -- | -- Module : GHC.IO.Handle -- Copyright : (c) The University of Glasgow, 1994-2009 -- License : see libraries/base/LICENSE -- -- Maintainer : libraries@haskell.org -- Stability : provisional -- Portability : non-portable -- -- External API for GHC's Handle implementation -- ----------------------------------------------------------------------------- module GHC.IO.Handle ( Handle, BufferMode(..), mkFileHandle, mkDuplexHandle, hFileSize, hSetFileSize, hIsEOF, isEOF, hLookAhead, hSetBuffering, hSetBinaryMode, hSetEncoding, hGetEncoding, hFlush, hFlushAll, hDuplicate, hDuplicateTo, hClose, hClose_help, LockMode(..), hLock, hTryLock, HandlePosition, HandlePosn(..), hGetPosn, hSetPosn, SeekMode(..), hSeek, hTell, hIsOpen, hIsClosed, hIsReadable, hIsWritable, hGetBuffering, hIsSeekable, hSetEcho, hGetEcho, hIsTerminalDevice, hSetNewlineMode, Newline(..), NewlineMode(..), nativeNewline, noNewlineTranslation, universalNewlineMode, nativeNewlineMode, hShow, hWaitForInput, hGetChar, hGetLine, hGetContents, hGetContents', hPutChar, hPutStr, hGetBuf, hGetBufNonBlocking, hPutBuf, hPutBufNonBlocking ) where import GHC.IO import GHC.IO.Exception import GHC.IO.Encoding import GHC.IO.Buffer import GHC.IO.BufferedIO ( BufferedIO ) import GHC.IO.Device as IODevice import GHC.IO.StdHandles import GHC.IO.SubSystem import GHC.IO.Handle.Lock import GHC.IO.Handle.Types import GHC.IO.Handle.Internals import GHC.IO.Handle.Text import qualified GHC.IO.BufferedIO as Buffered import GHC.Base import GHC.Exception import GHC.MVar import GHC.IORef import GHC.Show import GHC.Num import GHC.Real import Data.Maybe import Data.Typeable -- --------------------------------------------------------------------------- -- Closing a handle -- | Computation 'hClose' @hdl@ makes handle @hdl@ closed. Before the -- computation finishes, if @hdl@ is writable its buffer is flushed as -- for 'hFlush'. -- Performing 'hClose' on a handle that has already been closed has no effect; -- doing so is not an error. All other operations on a closed handle will fail. -- If 'hClose' fails for any reason, any further operations (apart from -- 'hClose') on the handle will still fail as if @hdl@ had been successfully -- closed. -- -- 'hClose' is an /interruptible operation/ in the sense described in -- "Control.Exception". If 'hClose' is interrupted by an asynchronous -- exception in the process of flushing its buffers, then the I/O device -- (e.g., file) will be closed anyway. hClose :: Handle -> IO () hClose = hClose_impl ----------------------------------------------------------------------------- -- Detecting and changing the size of a file -- | For a handle @hdl@ which attached to a physical file, -- 'hFileSize' @hdl@ returns the size of that file in 8-bit bytes. hFileSize :: Handle -> IO Integer hFileSize handle = withHandle_ "hFileSize" handle $ \ handle_@Handle__{haDevice=dev} -> do case haType handle_ of ClosedHandle -> ioe_closedHandle SemiClosedHandle -> ioe_semiclosedHandle _ -> do flushWriteBuffer handle_ r <- IODevice.getSize dev debugIO $ "hFileSize: " ++ show r ++ " " ++ show handle if r /= -1 then return r else ioException (IOError Nothing InappropriateType "hFileSize" "not a regular file" Nothing Nothing) -- | 'hSetFileSize' @hdl@ @size@ truncates the physical file with handle @hdl@ to @size@ bytes. hSetFileSize :: Handle -> Integer -> IO () hSetFileSize handle size = withHandle_ "hSetFileSize" handle $ \ handle_@Handle__{haDevice=dev} -> do case haType handle_ of ClosedHandle -> ioe_closedHandle SemiClosedHandle -> ioe_semiclosedHandle _ -> do flushWriteBuffer handle_ IODevice.setSize dev size return () -- --------------------------------------------------------------------------- -- Detecting the End of Input -- | For a readable handle @hdl@, 'hIsEOF' @hdl@ returns -- 'True' if no further input can be taken from @hdl@ or for a -- physical file, if the current I\/O position is equal to the length of -- the file. Otherwise, it returns 'False'. -- -- NOTE: 'hIsEOF' may block, because it has to attempt to read from -- the stream to determine whether there is any more data to be read. hIsEOF :: Handle -> IO Bool hIsEOF handle = wantReadableHandle_ "hIsEOF" handle $ \Handle__{..} -> do cbuf <- readIORef haCharBuffer if not (isEmptyBuffer cbuf) then return False else do bbuf <- readIORef haByteBuffer if not (isEmptyBuffer bbuf) then return False else do -- NB. do no decoding, just fill the byte buffer; see #3808 (r,bbuf') <- Buffered.fillReadBuffer haDevice bbuf if r == 0 then return True else do writeIORef haByteBuffer bbuf' return False -- --------------------------------------------------------------------------- -- isEOF -- | The computation 'isEOF' is identical to 'hIsEOF', -- except that it works only on 'stdin'. isEOF :: IO Bool isEOF = hIsEOF stdin -- --------------------------------------------------------------------------- -- Looking ahead -- | Computation 'hLookAhead' returns the next character from the handle -- without removing it from the input buffer, blocking until a character -- is available. -- -- This operation may fail with: -- -- * 'System.IO.Error.isEOFError' if the end of file has been reached. hLookAhead :: Handle -> IO Char hLookAhead handle = wantReadableHandle_ "hLookAhead" handle hLookAhead_ -- --------------------------------------------------------------------------- -- Buffering Operations -- Three kinds of buffering are supported: line-buffering, -- block-buffering or no-buffering. See GHC.IO.Handle for definition and -- further explanation of what the type represent. -- | Computation 'hSetBuffering' @hdl mode@ sets the mode of buffering for -- handle @hdl@ on subsequent reads and writes. -- -- If the buffer mode is changed from 'BlockBuffering' or -- 'LineBuffering' to 'NoBuffering', then -- -- * if @hdl@ is writable, the buffer is flushed as for 'hFlush'; -- -- * if @hdl@ is not writable, the contents of the buffer is discarded. -- -- This operation may fail with: -- -- * 'System.IO.Error.isPermissionError' if the handle has already been used -- for reading or writing and the implementation does not allow the -- buffering mode to be changed. hSetBuffering :: Handle -> BufferMode -> IO () hSetBuffering handle mode = withAllHandles__ "hSetBuffering" handle $ \ handle_@Handle__{..} -> do case haType of ClosedHandle -> ioe_closedHandle _ -> do if mode == haBufferMode then return handle_ else do -- See [note Buffer Sizing] in GHC.IO.Handle.Types -- check for errors: case mode of BlockBuffering (Just n) | n <= 0 -> ioe_bufsiz n _ -> return () -- for input terminals we need to put the terminal into -- cooked or raw mode depending on the type of buffering. is_tty <- IODevice.isTerminal haDevice when (is_tty && isReadableHandleType haType) $ case mode of #if !defined(mingw32_HOST_OS) -- 'raw' mode under win32 is a bit too specialised (and troublesome -- for most common uses), so simply disable its use here when not using -- WinIO. NoBuffering -> IODevice.setRaw haDevice True #else NoBuffering -> return () IODevice.setRaw haDevice True #endif _ -> IODevice.setRaw haDevice False -- throw away spare buffers, they might be the wrong size writeIORef haBuffers BufferListNil return Handle__{ haBufferMode = mode,.. } -- ----------------------------------------------------------------------------- -- hSetEncoding -- | The action 'hSetEncoding' @hdl@ @encoding@ changes the text encoding -- for the handle @hdl@ to @encoding@. The default encoding when a 'Handle' is -- created is 'System.IO.localeEncoding', namely the default encoding for the -- current locale. -- -- To create a 'Handle' with no encoding at all, use 'openBinaryFile'. To -- stop further encoding or decoding on an existing 'Handle', use -- 'hSetBinaryMode'. -- -- 'hSetEncoding' may need to flush buffered data in order to change -- the encoding. -- hSetEncoding :: Handle -> TextEncoding -> IO () hSetEncoding hdl encoding = withAllHandles__ "hSetEncoding" hdl $ \h_@Handle__{..} -> do flushCharBuffer h_ closeTextCodecs h_ openTextEncoding (Just encoding) haType $ \ mb_encoder mb_decoder -> do bbuf <- readIORef haByteBuffer ref <- newIORef (errorWithoutStackTrace "last_decode") return (Handle__{ haLastDecode = ref, haDecoder = mb_decoder, haEncoder = mb_encoder, haCodec = Just encoding, .. }) -- | Return the current 'TextEncoding' for the specified 'Handle', or -- 'Nothing' if the 'Handle' is in binary mode. -- -- Note that the 'TextEncoding' remembers nothing about the state of -- the encoder/decoder in use on this 'Handle'. For example, if the -- encoding in use is UTF-16, then using 'hGetEncoding' and -- 'hSetEncoding' to save and restore the encoding may result in an -- extra byte-order-mark being written to the file. -- hGetEncoding :: Handle -> IO (Maybe TextEncoding) hGetEncoding hdl = withHandle_ "hGetEncoding" hdl $ \h_@Handle__{..} -> return haCodec -- ----------------------------------------------------------------------------- -- hFlush -- | The action 'hFlush' @hdl@ causes any items buffered for output -- in handle @hdl@ to be sent immediately to the operating system. -- -- This operation may fail with: -- -- * 'System.IO.Error.isFullError' if the device is full; -- -- * 'System.IO.Error.isPermissionError' if a system resource limit would be -- exceeded. It is unspecified whether the characters in the buffer are -- discarded or retained under these circumstances. hFlush :: Handle -> IO () hFlush handle = wantWritableHandle "hFlush" handle flushWriteBuffer -- | The action 'hFlushAll' @hdl@ flushes all buffered data in @hdl@, -- including any buffered read data. Buffered read data is flushed -- by seeking the file position back to the point before the bufferred -- data was read, and hence only works if @hdl@ is seekable (see -- 'hIsSeekable'). -- -- This operation may fail with: -- -- * 'System.IO.Error.isFullError' if the device is full; -- -- * 'System.IO.Error.isPermissionError' if a system resource limit would be -- exceeded. It is unspecified whether the characters in the buffer are -- discarded or retained under these circumstances; -- -- * 'System.IO.Error.isIllegalOperation' if @hdl@ has buffered read data, and -- is not seekable. hFlushAll :: Handle -> IO () hFlushAll handle = withHandle_ "hFlushAll" handle flushBuffer -- ----------------------------------------------------------------------------- -- Repositioning Handles data HandlePosn = HandlePosn Handle HandlePosition -- | @since 4.1.0.0 instance Eq HandlePosn where (HandlePosn h1 p1) == (HandlePosn h2 p2) = p1==p2 && h1==h2 -- | @since 4.1.0.0 instance Show HandlePosn where showsPrec p (HandlePosn h pos) = showsPrec p h . showString " at position " . shows pos -- HandlePosition is the Haskell equivalent of POSIX' off_t. -- We represent it as an Integer on the Haskell side, but -- cheat slightly in that hGetPosn calls upon a C helper -- that reports the position back via (merely) an Int. type HandlePosition = Integer -- | Computation 'hGetPosn' @hdl@ returns the current I\/O position of -- @hdl@ as a value of the abstract type 'HandlePosn'. hGetPosn :: Handle -> IO HandlePosn hGetPosn handle = do posn <- hTell handle return (HandlePosn handle posn) -- | If a call to 'hGetPosn' @hdl@ returns a position @p@, -- then computation 'hSetPosn' @p@ sets the position of @hdl@ -- to the position it held at the time of the call to 'hGetPosn'. -- -- This operation may fail with: -- -- * 'System.IO.Error.isPermissionError' if a system resource limit would be -- exceeded. hSetPosn :: HandlePosn -> IO () hSetPosn (HandlePosn h i) = hSeek h AbsoluteSeek i -- --------------------------------------------------------------------------- -- hSeek {- Note: - when seeking using `SeekFromEnd', positive offsets (>=0) means seeking at or past EOF. - we possibly deviate from the report on the issue of seeking within the buffer and whether to flush it or not. The report isn't exactly clear here. -} -- | Computation 'hSeek' @hdl mode i@ sets the position of handle -- @hdl@ depending on @mode@. -- The offset @i@ is given in terms of 8-bit bytes. -- -- If @hdl@ is block- or line-buffered, then seeking to a position which is not -- in the current buffer will first cause any items in the output buffer to be -- written to the device, and then cause the input buffer to be discarded. -- Some handles may not be seekable (see 'hIsSeekable'), or only support a -- subset of the possible positioning operations (for instance, it may only -- be possible to seek to the end of a tape, or to a positive offset from -- the beginning or current position). -- It is not possible to set a negative I\/O position, or for -- a physical file, an I\/O position beyond the current end-of-file. -- -- This operation may fail with: -- -- * 'System.IO.Error.isIllegalOperationError' if the Handle is not seekable, -- or does not support the requested seek mode. -- -- * 'System.IO.Error.isPermissionError' if a system resource limit would be -- exceeded. hSeek :: Handle -> SeekMode -> Integer -> IO () hSeek handle mode offset = wantSeekableHandle "hSeek" handle $ \ handle_@Handle__{..} -> do debugIO ("hSeek " ++ show (mode,offset)) cbuf <- readIORef haCharBuffer bbuf <- readIORef haByteBuffer debugIO $ "hSeek - bbuf:" ++ summaryBuffer bbuf debugIO $ "hSeek - cbuf:" ++ summaryBuffer cbuf if isWriteBuffer cbuf then do flushWriteBuffer handle_ new_offset <- IODevice.seek haDevice mode offset -- buffer has been updated, need to re-read it bbuf1 <- readIORef haByteBuffer let bbuf2 = bbuf1{ bufOffset = fromIntegral new_offset } debugIO $ "hSeek - seek:: " ++ show offset ++ " - " ++ show new_offset debugIO $ "hSeek - wr flush bbuf1:" ++ summaryBuffer bbuf2 writeIORef haByteBuffer bbuf2 else do let r = bufL cbuf; w = bufR cbuf if mode == RelativeSeek && isNothing haDecoder && offset >= 0 && offset < fromIntegral (w - r) then writeIORef haCharBuffer cbuf{ bufL = r + fromIntegral offset } else do flushCharReadBuffer handle_ flushByteReadBuffer handle_ -- read the updated values bbuf2 <- readIORef haByteBuffer new_offset <- IODevice.seek haDevice mode offset debugIO $ "hSeek after: " ++ show new_offset writeIORef haByteBuffer bbuf2{ bufOffset = fromIntegral new_offset } -- | Computation 'hTell' @hdl@ returns the current position of the -- handle @hdl@, as the number of bytes from the beginning of -- the file. The value returned may be subsequently passed to -- 'hSeek' to reposition the handle to the current position. -- -- This operation may fail with: -- -- * 'System.IO.Error.isIllegalOperationError' if the Handle is not seekable. -- hTell :: Handle -> IO Integer hTell handle = wantSeekableHandle "hGetPosn" handle $ \ handle_@Handle__{..} -> do -- TODO: Guard these on Windows posn <- if ioSubSystem == IoNative then (fromIntegral . bufOffset) `fmap` readIORef haByteBuffer else IODevice.tell haDevice -- we can't tell the real byte offset if there are buffered -- Chars, so must flush first: flushCharBuffer handle_ bbuf <- readIORef haByteBuffer debugIO ("hTell bbuf (elems=" ++ show (bufferElems bbuf) ++ ")" ++ summaryBuffer bbuf) let real_posn | isWriteBuffer bbuf = posn + fromIntegral (bufferElems bbuf) | otherwise = posn - fromIntegral (bufferElems bbuf) cbuf <- readIORef haCharBuffer debugIO ("\nhGetPosn: (posn, real_posn) = " ++ show (posn, real_posn)) debugIO (" cbuf: " ++ summaryBuffer cbuf ++ " bbuf: " ++ summaryBuffer bbuf) return real_posn -- ----------------------------------------------------------------------------- -- Handle Properties -- A number of operations return information about the properties of a -- handle. Each of these operations returns `True' if the handle has -- the specified property, and `False' otherwise. hIsOpen :: Handle -> IO Bool hIsOpen handle = withHandle_ "hIsOpen" handle $ \ handle_ -> do case haType handle_ of ClosedHandle -> return False SemiClosedHandle -> return False _ -> return True hIsClosed :: Handle -> IO Bool hIsClosed handle = withHandle_ "hIsClosed" handle $ \ handle_ -> do case haType handle_ of ClosedHandle -> return True _ -> return False {- not defined, nor exported, but mentioned here for documentation purposes: hSemiClosed :: Handle -> IO Bool hSemiClosed h = do ho <- hIsOpen h hc <- hIsClosed h return (not (ho || hc)) -} hIsReadable :: Handle -> IO Bool hIsReadable (DuplexHandle _ _ _) = return True hIsReadable handle = withHandle_ "hIsReadable" handle $ \ handle_ -> do case haType handle_ of ClosedHandle -> ioe_closedHandle SemiClosedHandle -> ioe_semiclosedHandle htype -> return (isReadableHandleType htype) hIsWritable :: Handle -> IO Bool hIsWritable (DuplexHandle _ _ _) = return True hIsWritable handle = withHandle_ "hIsWritable" handle $ \ handle_ -> do case haType handle_ of ClosedHandle -> ioe_closedHandle SemiClosedHandle -> ioe_semiclosedHandle htype -> return (isWritableHandleType htype) -- | Computation 'hGetBuffering' @hdl@ returns the current buffering mode -- for @hdl@. hGetBuffering :: Handle -> IO BufferMode hGetBuffering handle = withHandle_ "hGetBuffering" handle $ \ handle_ -> do case haType handle_ of ClosedHandle -> ioe_closedHandle _ -> -- We're being non-standard here, and allow the buffering -- of a semi-closed handle to be queried. -- sof 6/98 return (haBufferMode handle_) -- could be stricter.. hIsSeekable :: Handle -> IO Bool hIsSeekable handle = withHandle_ "hIsSeekable" handle $ \ handle_@Handle__{..} -> do case haType of ClosedHandle -> ioe_closedHandle SemiClosedHandle -> ioe_semiclosedHandle AppendHandle -> return False _ -> IODevice.isSeekable haDevice -- ----------------------------------------------------------------------------- -- Changing echo status -- | Set the echoing status of a handle connected to a terminal. hSetEcho :: Handle -> Bool -> IO () hSetEcho handle on = do isT <- hIsTerminalDevice handle if not isT then return () else withHandle_ "hSetEcho" handle $ \ Handle__{..} -> do case haType of ClosedHandle -> ioe_closedHandle _ -> IODevice.setEcho haDevice on -- | Get the echoing status of a handle connected to a terminal. hGetEcho :: Handle -> IO Bool hGetEcho handle = do isT <- hIsTerminalDevice handle if not isT then return False else withHandle_ "hGetEcho" handle $ \ Handle__{..} -> do case haType of ClosedHandle -> ioe_closedHandle _ -> IODevice.getEcho haDevice -- | Is the handle connected to a terminal? -- -- On Windows the result of 'hIsTerminalDevide' might be misleading, -- because non-native terminals, such as MinTTY used in MSYS and Cygwin environments, -- are implemented via redirection. -- Use @System.Win32.Types.withHandleToHANDLE System.Win32.MinTTY.isMinTTYHandle@ -- to recognise it. Also consider @ansi-terminal@ package for crossplatform terminal -- support. -- hIsTerminalDevice :: Handle -> IO Bool hIsTerminalDevice handle = withHandle_ "hIsTerminalDevice" handle $ \ Handle__{..} -> do case haType of ClosedHandle -> ioe_closedHandle _ -> IODevice.isTerminal haDevice -- ----------------------------------------------------------------------------- -- hSetBinaryMode -- | Select binary mode ('True') or text mode ('False') on a open handle. -- (See also 'openBinaryFile'.) -- -- This has the same effect as calling 'hSetEncoding' with 'char8', together -- with 'hSetNewlineMode' with 'noNewlineTranslation'. -- hSetBinaryMode :: Handle -> Bool -> IO () hSetBinaryMode handle bin = withAllHandles__ "hSetBinaryMode" handle $ \ h_@Handle__{..} -> do flushCharBuffer h_ closeTextCodecs h_ mb_te <- if bin then return Nothing else fmap Just getLocaleEncoding openTextEncoding mb_te haType $ \ mb_encoder mb_decoder -> do -- should match the default newline mode, whatever that is let nl | bin = noNewlineTranslation | otherwise = nativeNewlineMode bbuf <- readIORef haByteBuffer ref <- newIORef (errorWithoutStackTrace "codec_state", bbuf) return Handle__{ haLastDecode = ref, haEncoder = mb_encoder, haDecoder = mb_decoder, haCodec = mb_te, haInputNL = inputNL nl, haOutputNL = outputNL nl, .. } -- ----------------------------------------------------------------------------- -- hSetNewlineMode -- | Set the 'NewlineMode' on the specified 'Handle'. All buffered -- data is flushed first. hSetNewlineMode :: Handle -> NewlineMode -> IO () hSetNewlineMode handle NewlineMode{ inputNL=i, outputNL=o } = withAllHandles__ "hSetNewlineMode" handle $ \h_@Handle__{} -> do flushBuffer h_ return h_{ haInputNL=i, haOutputNL=o } -- ----------------------------------------------------------------------------- -- Duplicating a Handle -- | Returns a duplicate of the original handle, with its own buffer. -- The two Handles will share a file pointer, however. The original -- handle's buffer is flushed, including discarding any input data, -- before the handle is duplicated. hDuplicate :: Handle -> IO Handle hDuplicate h@(FileHandle path m) = withHandle_' "hDuplicate" h m $ \h_ -> dupHandle path h Nothing h_ (Just handleFinalizer) hDuplicate h@(DuplexHandle path r w) = do write_side@(FileHandle _ write_m) <- withHandle_' "hDuplicate" h w $ \h_ -> dupHandle path h Nothing h_ (Just handleFinalizer) read_side@(FileHandle _ read_m) <- withHandle_' "hDuplicate" h r $ \h_ -> dupHandle path h (Just write_m) h_ Nothing return (DuplexHandle path read_m write_m) dupHandle :: FilePath -> Handle -> Maybe (MVar Handle__) -> Handle__ -> Maybe HandleFinalizer -> IO Handle dupHandle filepath h other_side h_@Handle__{..} mb_finalizer = do -- flush the buffer first, so we don't have to copy its contents flushBuffer h_ case other_side of Nothing -> do new_dev <- IODevice.dup haDevice dupHandle_ new_dev filepath other_side h_ mb_finalizer Just r -> withHandle_' "dupHandle" h r $ \Handle__{haDevice=dev} -> dupHandle_ dev filepath other_side h_ mb_finalizer dupHandle_ :: (RawIO dev, IODevice dev, BufferedIO dev, Typeable dev) => dev -> FilePath -> Maybe (MVar Handle__) -> Handle__ -> Maybe HandleFinalizer -> IO Handle dupHandle_ new_dev filepath other_side h_@Handle__{..} mb_finalizer = do -- XXX wrong! mb_codec <- if isJust haEncoder then fmap Just getLocaleEncoding else return Nothing mkHandle new_dev filepath haType True{-buffered-} mb_codec NewlineMode { inputNL = haInputNL, outputNL = haOutputNL } mb_finalizer other_side -- ----------------------------------------------------------------------------- -- Replacing a Handle {- | Makes the second handle a duplicate of the first handle. The second handle will be closed first, if it is not already. This can be used to retarget the standard Handles, for example: > do h <- openFile "mystdout" WriteMode > hDuplicateTo h stdout -} hDuplicateTo :: Handle -> Handle -> IO () hDuplicateTo h1@(FileHandle path m1) h2@(FileHandle _ m2) = withHandle__' "hDuplicateTo" h2 m2 $ \h2_ -> do try $ flushWriteBuffer h2_ withHandle_' "hDuplicateTo" h1 m1 $ \h1_ -> dupHandleTo path h1 Nothing h2_ h1_ (Just handleFinalizer) hDuplicateTo h1@(DuplexHandle path r1 w1) h2@(DuplexHandle _ r2 w2) = do withHandle__' "hDuplicateTo" h2 w2 $ \w2_ -> do try $ flushWriteBuffer w2_ withHandle_' "hDuplicateTo" h1 w1 $ \w1_ -> dupHandleTo path h1 Nothing w2_ w1_ (Just handleFinalizer) withHandle__' "hDuplicateTo" h2 r2 $ \r2_ -> do try $ flushWriteBuffer r2_ withHandle_' "hDuplicateTo" h1 r1 $ \r1_ -> dupHandleTo path h1 (Just w1) r2_ r1_ Nothing hDuplicateTo h1 _ = ioe_dupHandlesNotCompatible h1 try :: IO () -> IO () try io = io `catchException` (const (pure ()) :: SomeException -> IO ()) ioe_dupHandlesNotCompatible :: Handle -> IO a ioe_dupHandlesNotCompatible h = ioException (IOError (Just h) IllegalOperation "hDuplicateTo" "handles are incompatible" Nothing Nothing) dupHandleTo :: FilePath -> Handle -> Maybe (MVar Handle__) -> Handle__ -> Handle__ -> Maybe HandleFinalizer -> IO Handle__ dupHandleTo filepath h other_side hto_@Handle__{haDevice=devTo} h_@Handle__{haDevice=dev} mb_finalizer = do flushBuffer h_ case cast devTo of Nothing -> ioe_dupHandlesNotCompatible h Just dev' -> do _ <- IODevice.dup2 dev dev' FileHandle _ m <- dupHandle_ dev' filepath other_side h_ mb_finalizer takeMVar m -- --------------------------------------------------------------------------- -- showing Handles. -- -- | 'hShow' is in the 'IO' monad, and gives more comprehensive output -- than the (pure) instance of 'Show' for 'Handle'. hShow :: Handle -> IO String hShow h@(FileHandle path _) = showHandle' path False h hShow h@(DuplexHandle path _ _) = showHandle' path True h showHandle' :: String -> Bool -> Handle -> IO String showHandle' filepath is_duplex h = withHandle_ "showHandle" h $ \hdl_ -> let showType | is_duplex = showString "duplex (read-write)" | otherwise = shows (haType hdl_) in return (( showChar '{' . showHdl (haType hdl_) (showString "loc=" . showString filepath . showChar ',' . showString "type=" . showType . showChar ',' . showString "buffering=" . showBufMode (unsafePerformIO (readIORef (haCharBuffer hdl_))) (haBufferMode hdl_) . showString "}" ) ) "") where showHdl :: HandleType -> ShowS -> ShowS showHdl ht cont = case ht of ClosedHandle -> shows ht . showString "}" _ -> cont showBufMode :: Buffer e -> BufferMode -> ShowS showBufMode buf bmo = case bmo of NoBuffering -> showString "none" LineBuffering -> showString "line" BlockBuffering (Just n) -> showString "block " . showParen True (shows n) BlockBuffering Nothing -> showString "block " . showParen True (shows def) where def :: Int def = bufSize buf