{-# LANGUAGE Trustworthy #-} {-# LANGUAGE CPP, NoImplicitPrelude #-} ----------------------------------------------------------------------------- -- | -- Module : System.IO -- Copyright : (c) The University of Glasgow 2001 -- License : BSD-style (see the file libraries/base/LICENSE) -- -- Maintainer : libraries@haskell.org -- Stability : stable -- Portability : portable -- -- The standard IO library. -- ----------------------------------------------------------------------------- module System.IO ( -- * The IO monad IO, fixIO, -- * Files and handles FilePath, Handle, -- abstract, instance of: Eq, Show. -- | GHC note: a 'Handle' will be automatically closed when the garbage -- collector detects that it has become unreferenced by the program. -- However, relying on this behaviour is not generally recommended: -- the garbage collector is unpredictable. If possible, use -- an explicit 'hClose' to close 'Handle's when they are no longer -- required. GHC does not currently attempt to free up file -- descriptors when they have run out, it is your responsibility to -- ensure that this doesn't happen. -- ** Standard handles -- | Three handles are allocated during program initialisation, -- and are initially open. stdin, stdout, stderr, -- * Opening and closing files -- ** Opening files withFile, openFile, IOMode(ReadMode,WriteMode,AppendMode,ReadWriteMode), -- ** Closing files hClose, -- ** Special cases -- | These functions are also exported by the "Prelude". readFile, writeFile, appendFile, -- ** File locking -- $locking -- * Operations on handles -- ** Determining and changing the size of a file hFileSize, hSetFileSize, -- ** Detecting the end of input hIsEOF, isEOF, -- ** Buffering operations BufferMode(NoBuffering,LineBuffering,BlockBuffering), hSetBuffering, hGetBuffering, hFlush, -- ** Repositioning handles hGetPosn, hSetPosn, HandlePosn, -- abstract, instance of: Eq, Show. hSeek, SeekMode(AbsoluteSeek,RelativeSeek,SeekFromEnd), hTell, -- ** Handle properties hIsOpen, hIsClosed, hIsReadable, hIsWritable, hIsSeekable, -- ** Terminal operations (not portable: GHC only) hIsTerminalDevice, hSetEcho, hGetEcho, -- ** Showing handle state (not portable: GHC only) hShow, -- * Text input and output -- ** Text input hWaitForInput, hReady, hGetChar, hGetLine, hLookAhead, hGetContents, -- ** Text output hPutChar, hPutStr, hPutStrLn, hPrint, -- ** Special cases for standard input and output -- | These functions are also exported by the "Prelude". interact, putChar, putStr, putStrLn, print, getChar, getLine, getContents, readIO, readLn, -- * Binary input and output withBinaryFile, openBinaryFile, hSetBinaryMode, hPutBuf, hGetBuf, hGetBufSome, hPutBufNonBlocking, hGetBufNonBlocking, -- * Temporary files openTempFile, openBinaryTempFile, openTempFileWithDefaultPermissions, openBinaryTempFileWithDefaultPermissions, -- * Unicode encoding\/decoding -- | A text-mode 'Handle' has an associated 'TextEncoding', which -- is used to decode bytes into Unicode characters when reading, -- and encode Unicode characters into bytes when writing. -- -- The default 'TextEncoding' is the same as the default encoding -- on your system, which is also available as 'localeEncoding'. -- (GHC note: on Windows, we currently do not support double-byte -- encodings; if the console\'s code page is unsupported, then -- 'localeEncoding' will be 'latin1'.) -- -- Encoding and decoding errors are always detected and reported, -- except during lazy I/O ('hGetContents', 'getContents', and -- 'readFile'), where a decoding error merely results in -- termination of the character stream, as with other I/O errors. hSetEncoding, hGetEncoding, -- ** Unicode encodings TextEncoding, latin1, utf8, utf8_bom, utf16, utf16le, utf16be, utf32, utf32le, utf32be, localeEncoding, char8, mkTextEncoding, -- * Newline conversion -- | In Haskell, a newline is always represented by the character -- '\n'. However, in files and external character streams, a -- newline may be represented by another character sequence, such -- as '\r\n'. -- -- A text-mode 'Handle' has an associated 'NewlineMode' that -- specifies how to transate newline characters. The -- 'NewlineMode' specifies the input and output translation -- separately, so that for instance you can translate '\r\n' -- to '\n' on input, but leave newlines as '\n' on output. -- -- The default 'NewlineMode' for a 'Handle' is -- 'nativeNewlineMode', which does no translation on Unix systems, -- but translates '\r\n' to '\n' and back on Windows. -- -- Binary-mode 'Handle's do no newline translation at all. -- hSetNewlineMode, Newline(..), nativeNewline, NewlineMode(..), noNewlineTranslation, universalNewlineMode, nativeNewlineMode, ) where import Control.Exception.Base import Data.Bits import Data.List import Data.Maybe import Foreign.C.Error #ifdef mingw32_HOST_OS import Foreign.C.String #endif import Foreign.C.Types import System.Posix.Internals import System.Posix.Types import GHC.Base import GHC.IO hiding ( bracket, onException ) import GHC.IO.IOMode import GHC.IO.Handle.FD import qualified GHC.IO.FD as FD import GHC.IO.Handle import GHC.IO.Handle.Text ( hGetBufSome, hPutStrLn ) import GHC.IO.Exception ( userError ) import GHC.IO.Encoding import GHC.Num import Text.Read import GHC.Show import GHC.MVar -- ----------------------------------------------------------------------------- -- Standard IO -- | Write a character to the standard output device -- (same as 'hPutChar' 'stdout'). putChar :: Char -> IO () putChar c = hPutChar stdout c -- | Write a string to the standard output device -- (same as 'hPutStr' 'stdout'). putStr :: String -> IO () putStr s = hPutStr stdout s -- | The same as 'putStr', but adds a newline character. putStrLn :: String -> IO () putStrLn s = hPutStrLn stdout s -- | The 'print' function outputs a value of any printable type to the -- standard output device. -- Printable types are those that are instances of class 'Show'; 'print' -- converts values to strings for output using the 'show' operation and -- adds a newline. -- -- For example, a program to print the first 20 integers and their -- powers of 2 could be written as: -- -- > main = print ([(n, 2^n) | n <- [0..19]]) print :: Show a => a -> IO () print x = putStrLn (show x) -- | Read a character from the standard input device -- (same as 'hGetChar' 'stdin'). getChar :: IO Char getChar = hGetChar stdin -- | Read a line from the standard input device -- (same as 'hGetLine' 'stdin'). getLine :: IO String getLine = hGetLine stdin -- | The 'getContents' operation returns all user input as a single string, -- which is read lazily as it is needed -- (same as 'hGetContents' 'stdin'). getContents :: IO String getContents = hGetContents stdin -- | The 'interact' function takes a function of type @String->String@ -- as its argument. The entire input from the standard input device is -- passed to this function as its argument, and the resulting string is -- output on the standard output device. interact :: (String -> String) -> IO () interact f = do s <- getContents putStr (f s) -- | The 'readFile' function reads a file and -- returns the contents of the file as a string. -- The file is read lazily, on demand, as with 'getContents'. readFile :: FilePath -> IO String readFile name = openFile name ReadMode >>= hGetContents -- | The computation 'writeFile' @file str@ function writes the string @str@, -- to the file @file@. writeFile :: FilePath -> String -> IO () writeFile f txt = withFile f WriteMode (\ hdl -> hPutStr hdl txt) -- | The computation 'appendFile' @file str@ function appends the string @str@, -- to the file @file@. -- -- Note that 'writeFile' and 'appendFile' write a literal string -- to a file. To write a value of any printable type, as with 'print', -- use the 'show' function to convert the value to a string first. -- -- > main = appendFile "squares" (show [(x,x*x) | x <- [0,0.1..2]]) appendFile :: FilePath -> String -> IO () appendFile f txt = withFile f AppendMode (\ hdl -> hPutStr hdl txt) -- | The 'readLn' function combines 'getLine' and 'readIO'. readLn :: Read a => IO a readLn = do l <- getLine r <- readIO l return r -- | The 'readIO' function is similar to 'read' except that it signals -- parse failure to the 'IO' monad instead of terminating the program. readIO :: Read a => String -> IO a readIO s = case (do { (x,t) <- reads s ; ("","") <- lex t ; return x }) of [x] -> return x [] -> ioError (userError "Prelude.readIO: no parse") _ -> ioError (userError "Prelude.readIO: ambiguous parse") -- | The Unicode encoding of the current locale -- -- This is the initial locale encoding: if it has been subsequently changed by -- 'GHC.IO.Encoding.setLocaleEncoding' this value will not reflect that change. localeEncoding :: TextEncoding localeEncoding = initLocaleEncoding -- | Computation 'hReady' @hdl@ indicates whether at least one item is -- available for input from handle @hdl@. -- -- This operation may fail with: -- -- * 'System.IO.Error.isEOFError' if the end of file has been reached. hReady :: Handle -> IO Bool hReady h = hWaitForInput h 0 -- | Computation 'hPrint' @hdl t@ writes the string representation of @t@ -- given by the 'shows' function to the file or channel managed by @hdl@ -- and appends a newline. -- -- This operation may fail with: -- -- * 'System.IO.Error.isFullError' if the device is full; or -- -- * 'System.IO.Error.isPermissionError' if another system resource limit would be exceeded. hPrint :: Show a => Handle -> a -> IO () hPrint hdl = hPutStrLn hdl . show -- | @'withFile' name mode act@ opens a file using 'openFile' and passes -- the resulting handle to the computation @act@. The handle will be -- closed on exit from 'withFile', whether by normal termination or by -- raising an exception. If closing the handle raises an exception, then -- this exception will be raised by 'withFile' rather than any exception -- raised by 'act'. withFile :: FilePath -> IOMode -> (Handle -> IO r) -> IO r withFile name mode = bracket (openFile name mode) hClose -- | @'withBinaryFile' name mode act@ opens a file using 'openBinaryFile' -- and passes the resulting handle to the computation @act@. The handle -- will be closed on exit from 'withBinaryFile', whether by normal -- termination or by raising an exception. withBinaryFile :: FilePath -> IOMode -> (Handle -> IO r) -> IO r withBinaryFile name mode = bracket (openBinaryFile name mode) hClose -- --------------------------------------------------------------------------- -- fixIO fixIO :: (a -> IO a) -> IO a fixIO k = do m <- newEmptyMVar ans <- unsafeInterleaveIO (takeMVar m) result <- k ans putMVar m result return result -- NOTE: we do our own explicit black holing here, because GHC's lazy -- blackholing isn't enough. In an infinite loop, GHC may run the IO -- computation a few times before it notices the loop, which is wrong. -- -- NOTE2: the explicit black-holing with an IORef ran into trouble -- with multiple threads (see #5421), so now we use an MVar. I'm -- actually wondering whether we should use readMVar rather than -- takeMVar, just in case it ends up being executed multiple times, -- but even then it would have to be masked to protect against async -- exceptions. Ugh. What we really need here is an IVar, or an -- atomic readMVar, or even STM. All these seem like overkill. -- -- See also System.IO.Unsafe.unsafeFixIO. -- -- | The function creates a temporary file in ReadWrite mode. -- The created file isn\'t deleted automatically, so you need to delete it manually. -- -- The file is creates with permissions such that only the current -- user can read\/write it. -- -- With some exceptions (see below), the file will be created securely -- in the sense that an attacker should not be able to cause -- openTempFile to overwrite another file on the filesystem using your -- credentials, by putting symbolic links (on Unix) in the place where -- the temporary file is to be created. On Unix the @O_CREAT@ and -- @O_EXCL@ flags are used to prevent this attack, but note that -- @O_EXCL@ is sometimes not supported on NFS filesystems, so if you -- rely on this behaviour it is best to use local filesystems only. -- openTempFile :: FilePath -- ^ Directory in which to create the file -> String -- ^ File name template. If the template is \"foo.ext\" then -- the created file will be \"fooXXX.ext\" where XXX is some -- random number. -> IO (FilePath, Handle) openTempFile tmp_dir template = openTempFile' "openTempFile" tmp_dir template False 0o600 -- | Like 'openTempFile', but opens the file in binary mode. See 'openBinaryFile' for more comments. openBinaryTempFile :: FilePath -> String -> IO (FilePath, Handle) openBinaryTempFile tmp_dir template = openTempFile' "openBinaryTempFile" tmp_dir template True 0o600 -- | Like 'openTempFile', but uses the default file permissions openTempFileWithDefaultPermissions :: FilePath -> String -> IO (FilePath, Handle) openTempFileWithDefaultPermissions tmp_dir template = openTempFile' "openBinaryTempFile" tmp_dir template False 0o666 -- | Like 'openBinaryTempFile', but uses the default file permissions openBinaryTempFileWithDefaultPermissions :: FilePath -> String -> IO (FilePath, Handle) openBinaryTempFileWithDefaultPermissions tmp_dir template = openTempFile' "openBinaryTempFile" tmp_dir template True 0o666 openTempFile' :: String -> FilePath -> String -> Bool -> CMode -> IO (FilePath, Handle) openTempFile' loc tmp_dir template binary mode = do pid <- c_getpid findTempName pid where -- We split off the last extension, so we can use .foo.ext files -- for temporary files (hidden on Unix OSes). Unfortunately we're -- below filepath in the hierarchy here. (prefix,suffix) = case break (== '.') $ reverse template of -- First case: template contains no '.'s. Just re-reverse it. (rev_suffix, "") -> (reverse rev_suffix, "") -- Second case: template contains at least one '.'. Strip the -- dot from the prefix and prepend it to the suffix (if we don't -- do this, the unique number will get added after the '.' and -- thus be part of the extension, which is wrong.) (rev_suffix, '.':rest) -> (reverse rest, '.':reverse rev_suffix) -- Otherwise, something is wrong, because (break (== '.')) should -- always return a pair with either the empty string or a string -- beginning with '.' as the second component. _ -> error "bug in System.IO.openTempFile" findTempName x = do r <- openNewFile filepath binary mode case r of FileExists -> findTempName (x + 1) OpenNewError errno -> ioError (errnoToIOError loc errno Nothing (Just tmp_dir)) NewFileCreated fd -> do (fD,fd_type) <- FD.mkFD fd ReadWriteMode Nothing{-no stat-} False{-is_socket-} True{-is_nonblock-} enc <- getLocaleEncoding h <- mkHandleFromFD fD fd_type filepath ReadWriteMode False{-set non-block-} (Just enc) return (filepath, h) where filename = prefix ++ show x ++ suffix filepath = tmp_dir `combine` filename -- XXX bits copied from System.FilePath, since that's not available here combine a b | null b = a | null a = b | last a == pathSeparator = a ++ b | otherwise = a ++ [pathSeparator] ++ b data OpenNewFileResult = NewFileCreated CInt | FileExists | OpenNewError Errno openNewFile :: FilePath -> Bool -> CMode -> IO OpenNewFileResult openNewFile filepath binary mode = do let oflags1 = rw_flags .|. o_EXCL binary_flags | binary = o_BINARY | otherwise = 0 oflags = oflags1 .|. binary_flags fd <- withFilePath filepath $ \ f -> c_open f oflags mode if fd < 0 then do errno <- getErrno case errno of _ | errno == eEXIST -> return FileExists #ifdef mingw32_HOST_OS -- If c_open throws EACCES on windows, it could mean that filepath is a -- directory. In this case, we want to return FileExists so that the -- enclosing openTempFile can try again instead of failing outright. -- See bug #4968. _ | errno == eACCES -> do withCString filepath $ \path -> do -- There is a race here: the directory might have been moved or -- deleted between the c_open call and the next line, but there -- doesn't seem to be any direct way to detect that the c_open call -- failed because of an existing directory. exists <- c_fileExists path return $ if exists then FileExists else OpenNewError errno #endif _ -> return (OpenNewError errno) else return (NewFileCreated fd) #ifdef mingw32_HOST_OS foreign import ccall "file_exists" c_fileExists :: CString -> IO Bool #endif -- XXX Should use filepath library pathSeparator :: Char #ifdef mingw32_HOST_OS pathSeparator = '\\' #else pathSeparator = '/' #endif -- XXX Copied from GHC.Handle std_flags, output_flags, rw_flags :: CInt std_flags = o_NONBLOCK .|. o_NOCTTY output_flags = std_flags .|. o_CREAT rw_flags = output_flags .|. o_RDWR -- $locking -- Implementations should enforce as far as possible, at least locally to the -- Haskell process, multiple-reader single-writer locking on files. -- That is, /there may either be many handles on the same file which manage input, or just one handle on the file which manages output/. If any -- open or semi-closed handle is managing a file for output, no new -- handle can be allocated for that file. If any open or semi-closed -- handle is managing a file for input, new handles can only be allocated -- if they do not manage output. Whether two files are the same is -- implementation-dependent, but they should normally be the same if they -- have the same absolute path name and neither has been renamed, for -- example. -- -- /Warning/: the 'readFile' operation holds a semi-closed handle on -- the file until the entire contents of the file have been consumed. -- It follows that an attempt to write to a file (using 'writeFile', for -- example) that was earlier opened by 'readFile' will usually result in -- failure with 'System.IO.Error.isAlreadyInUseError'.