1{-# LANGUAGE Trustworthy #-} 2{-# LANGUAGE CPP 3 , NoImplicitPrelude 4 , ExistentialQuantification 5 #-} 6{-# OPTIONS_GHC -funbox-strict-fields #-} 7{-# OPTIONS_HADDOCK not-home #-} 8 9----------------------------------------------------------------------------- 10-- | 11-- Module : GHC.IO.Handle.Types 12-- Copyright : (c) The University of Glasgow, 1994-2009 13-- License : see libraries/base/LICENSE 14-- 15-- Maintainer : libraries@haskell.org 16-- Stability : internal 17-- Portability : non-portable 18-- 19-- Basic types for the implementation of IO Handles. 20-- 21----------------------------------------------------------------------------- 22 23module GHC.IO.Handle.Types ( 24 Handle(..), Handle__(..), showHandle, 25 checkHandleInvariants, 26 BufferList(..), 27 HandleType(..), 28 isReadableHandleType, isWritableHandleType, isReadWriteHandleType, 29 BufferMode(..), 30 BufferCodec(..), 31 NewlineMode(..), Newline(..), nativeNewline, 32 universalNewlineMode, noNewlineTranslation, nativeNewlineMode 33 ) where 34 35#undef DEBUG 36 37import GHC.Base 38import GHC.MVar 39import GHC.IO 40import GHC.IO.Buffer 41import GHC.IO.BufferedIO 42import GHC.IO.Encoding.Types 43import GHC.IORef 44import GHC.Show 45import GHC.Read 46import GHC.Word 47import GHC.IO.Device 48import Data.Typeable 49#if defined(DEBUG) 50import Control.Monad 51#endif 52 53-- --------------------------------------------------------------------------- 54-- Handle type 55 56-- A Handle is represented by (a reference to) a record 57-- containing the state of the I/O port/device. We record 58-- the following pieces of info: 59 60-- * type (read,write,closed etc.) 61-- * the underlying file descriptor 62-- * buffering mode 63-- * buffer, and spare buffers 64-- * user-friendly name (usually the 65-- FilePath used when IO.openFile was called) 66 67-- Note: when a Handle is garbage collected, we want to flush its buffer 68-- and close the OS file handle, so as to free up a (precious) resource. 69 70-- | Haskell defines operations to read and write characters from and to files, 71-- represented by values of type @Handle@. Each value of this type is a 72-- /handle/: a record used by the Haskell run-time system to /manage/ I\/O 73-- with file system objects. A handle has at least the following properties: 74-- 75-- * whether it manages input or output or both; 76-- 77-- * whether it is /open/, /closed/ or /semi-closed/; 78-- 79-- * whether the object is seekable; 80-- 81-- * whether buffering is disabled, or enabled on a line or block basis; 82-- 83-- * a buffer (whose length may be zero). 84-- 85-- Most handles will also have a current I\/O position indicating where the next 86-- input or output operation will occur. A handle is /readable/ if it 87-- manages only input or both input and output; likewise, it is /writable/ if 88-- it manages only output or both input and output. A handle is /open/ when 89-- first allocated. 90-- Once it is closed it can no longer be used for either input or output, 91-- though an implementation cannot re-use its storage while references 92-- remain to it. Handles are in the 'Show' and 'Eq' classes. The string 93-- produced by showing a handle is system dependent; it should include 94-- enough information to identify the handle for debugging. A handle is 95-- equal according to '==' only to itself; no attempt 96-- is made to compare the internal state of different handles for equality. 97 98data Handle 99 = FileHandle -- A normal handle to a file 100 FilePath -- the file (used for error messages 101 -- only) 102 !(MVar Handle__) 103 104 | DuplexHandle -- A handle to a read/write stream 105 FilePath -- file for a FIFO, otherwise some 106 -- descriptive string (used for error 107 -- messages only) 108 !(MVar Handle__) -- The read side 109 !(MVar Handle__) -- The write side 110 111-- NOTES: 112-- * A 'FileHandle' is seekable. A 'DuplexHandle' may or may not be 113-- seekable. 114 115-- | @since 4.1.0.0 116instance Eq Handle where 117 (FileHandle _ h1) == (FileHandle _ h2) = h1 == h2 118 (DuplexHandle _ h1 _) == (DuplexHandle _ h2 _) = h1 == h2 119 _ == _ = False 120 121data Handle__ 122 = forall dev enc_state dec_state . (IODevice dev, BufferedIO dev, Typeable dev) => 123 Handle__ { 124 haDevice :: !dev, 125 haType :: HandleType, -- type (read/write/append etc.) 126 haByteBuffer :: !(IORef (Buffer Word8)), -- See [note Buffering Implementation] 127 haBufferMode :: BufferMode, 128 haLastDecode :: !(IORef (dec_state, Buffer Word8)), 129 haCharBuffer :: !(IORef (Buffer CharBufElem)), -- See [note Buffering Implementation] 130 haBuffers :: !(IORef (BufferList CharBufElem)), -- spare buffers 131 haEncoder :: Maybe (TextEncoder enc_state), 132 haDecoder :: Maybe (TextDecoder dec_state), 133 haCodec :: Maybe TextEncoding, 134 haInputNL :: Newline, 135 haOutputNL :: Newline, 136 haOtherSide :: Maybe (MVar Handle__) -- ptr to the write side of a 137 -- duplex handle. 138 } 139 140-- we keep a few spare buffers around in a handle to avoid allocating 141-- a new one for each hPutStr. These buffers are *guaranteed* to be the 142-- same size as the main buffer. 143data BufferList e 144 = BufferListNil 145 | BufferListCons (RawBuffer e) (BufferList e) 146 147-- Internally, we classify handles as being one 148-- of the following: 149 150data HandleType 151 = ClosedHandle 152 | SemiClosedHandle 153 | ReadHandle 154 | WriteHandle 155 | AppendHandle 156 | ReadWriteHandle 157 158isReadableHandleType :: HandleType -> Bool 159isReadableHandleType ReadHandle = True 160isReadableHandleType ReadWriteHandle = True 161isReadableHandleType _ = False 162 163isWritableHandleType :: HandleType -> Bool 164isWritableHandleType AppendHandle = True 165isWritableHandleType WriteHandle = True 166isWritableHandleType ReadWriteHandle = True 167isWritableHandleType _ = False 168 169isReadWriteHandleType :: HandleType -> Bool 170isReadWriteHandleType ReadWriteHandle{} = True 171isReadWriteHandleType _ = False 172 173-- INVARIANTS on Handles: 174-- 175-- * A handle *always* has a buffer, even if it is only 1 character long 176-- (an unbuffered handle needs a 1 character buffer in order to support 177-- hLookAhead and hIsEOF). 178-- * In a read Handle, the byte buffer is always empty (we decode when reading) 179-- * In a wriite Handle, the Char buffer is always empty (we encode when writing) 180-- 181checkHandleInvariants :: Handle__ -> IO () 182#if defined(DEBUG) 183checkHandleInvariants h_ = do 184 bbuf <- readIORef (haByteBuffer h_) 185 checkBuffer bbuf 186 cbuf <- readIORef (haCharBuffer h_) 187 checkBuffer cbuf 188 when (isWriteBuffer cbuf && not (isEmptyBuffer cbuf)) $ 189 errorWithoutStackTrace ("checkHandleInvariants: char write buffer non-empty: " ++ 190 summaryBuffer bbuf ++ ", " ++ summaryBuffer cbuf) 191 when (isWriteBuffer bbuf /= isWriteBuffer cbuf) $ 192 errorWithoutStackTrace ("checkHandleInvariants: buffer modes differ: " ++ 193 summaryBuffer bbuf ++ ", " ++ summaryBuffer cbuf) 194 195#else 196checkHandleInvariants _ = return () 197#endif 198 199-- --------------------------------------------------------------------------- 200-- Buffering modes 201 202-- | Three kinds of buffering are supported: line-buffering, 203-- block-buffering or no-buffering. These modes have the following 204-- effects. For output, items are written out, or /flushed/, 205-- from the internal buffer according to the buffer mode: 206-- 207-- * /line-buffering/: the entire output buffer is flushed 208-- whenever a newline is output, the buffer overflows, 209-- a 'System.IO.hFlush' is issued, or the handle is closed. 210-- 211-- * /block-buffering/: the entire buffer is written out whenever it 212-- overflows, a 'System.IO.hFlush' is issued, or the handle is closed. 213-- 214-- * /no-buffering/: output is written immediately, and never stored 215-- in the buffer. 216-- 217-- An implementation is free to flush the buffer more frequently, 218-- but not less frequently, than specified above. 219-- The output buffer is emptied as soon as it has been written out. 220-- 221-- Similarly, input occurs according to the buffer mode for the handle: 222-- 223-- * /line-buffering/: when the buffer for the handle is not empty, 224-- the next item is obtained from the buffer; otherwise, when the 225-- buffer is empty, characters up to and including the next newline 226-- character are read into the buffer. No characters are available 227-- until the newline character is available or the buffer is full. 228-- 229-- * /block-buffering/: when the buffer for the handle becomes empty, 230-- the next block of data is read into the buffer. 231-- 232-- * /no-buffering/: the next input item is read and returned. 233-- The 'System.IO.hLookAhead' operation implies that even a no-buffered 234-- handle may require a one-character buffer. 235-- 236-- The default buffering mode when a handle is opened is 237-- implementation-dependent and may depend on the file system object 238-- which is attached to that handle. 239-- For most implementations, physical files will normally be block-buffered 240-- and terminals will normally be line-buffered. 241 242data BufferMode 243 = NoBuffering -- ^ buffering is disabled if possible. 244 | LineBuffering 245 -- ^ line-buffering should be enabled if possible. 246 | BlockBuffering (Maybe Int) 247 -- ^ block-buffering should be enabled if possible. 248 -- The size of the buffer is @n@ items if the argument 249 -- is 'Just' @n@ and is otherwise implementation-dependent. 250 deriving ( Eq -- ^ @since 4.2.0.0 251 , Ord -- ^ @since 4.2.0.0 252 , Read -- ^ @since 4.2.0.0 253 , Show -- ^ @since 4.2.0.0 254 ) 255 256{- 257[note Buffering Implementation] 258 259Each Handle has two buffers: a byte buffer (haByteBuffer) and a Char 260buffer (haCharBuffer). 261 262[note Buffered Reading] 263 264For read Handles, bytes are read into the byte buffer, and immediately 265decoded into the Char buffer (see 266GHC.IO.Handle.Internals.readTextDevice). The only way there might be 267some data left in the byte buffer is if there is a partial multi-byte 268character sequence that cannot be decoded into a full character. 269 270Note that the buffering mode (haBufferMode) makes no difference when 271reading data into a Handle. When reading, we can always just read all 272the data there is available without blocking, decode it into the Char 273buffer, and then provide it immediately to the caller. 274 275[note Buffered Writing] 276 277Characters are written into the Char buffer by e.g. hPutStr. At the 278end of the operation, or when the char buffer is full, the buffer is 279decoded to the byte buffer (see writeCharBuffer). This is so that we 280can detect encoding errors at the right point. 281 282Hence, the Char buffer is always empty between Handle operations. 283 284[note Buffer Sizing] 285 286The char buffer is always a default size (dEFAULT_CHAR_BUFFER_SIZE). 287The byte buffer size is chosen by the underlying device (via its 288IODevice.newBuffer). Hence the size of these buffers is not under 289user control. 290 291There are certain minimum sizes for these buffers imposed by the 292library (but not checked): 293 294 - we must be able to buffer at least one character, so that 295 hLookAhead can work 296 297 - the byte buffer must be able to store at least one encoded 298 character in the current encoding (6 bytes?) 299 300 - when reading, the char buffer must have room for two characters, so 301 that we can spot the \r\n sequence. 302 303How do we implement hSetBuffering? 304 305For reading, we have never used the user-supplied buffer size, because 306there's no point: we always pass all available data to the reader 307immediately. Buffering would imply waiting until a certain amount of 308data is available, which has no advantages. So hSetBuffering is 309essentially a no-op for read handles, except that it turns on/off raw 310mode for the underlying device if necessary. 311 312For writing, the buffering mode is handled by the write operations 313themselves (hPutChar and hPutStr). Every write ends with 314writeCharBuffer, which checks whether the buffer should be flushed 315according to the current buffering mode. Additionally, we look for 316newlines and flush if the mode is LineBuffering. 317 318[note Buffer Flushing] 319 320** Flushing the Char buffer 321 322We must be able to flush the Char buffer, in order to implement 323hSetEncoding, and things like hGetBuf which want to read raw bytes. 324 325Flushing the Char buffer on a write Handle is easy: it is always empty. 326 327Flushing the Char buffer on a read Handle involves rewinding the byte 328buffer to the point representing the next Char in the Char buffer. 329This is done by 330 331 - remembering the state of the byte buffer *before* the last decode 332 333 - re-decoding the bytes that represent the chars already read from the 334 Char buffer. This gives us the point in the byte buffer that 335 represents the *next* Char to be read. 336 337In order for this to work, after readTextHandle we must NOT MODIFY THE 338CONTENTS OF THE BYTE OR CHAR BUFFERS, except to remove characters from 339the Char buffer. 340 341** Flushing the byte buffer 342 343The byte buffer can be flushed if the Char buffer has already been 344flushed (see above). For a read Handle, flushing the byte buffer 345means seeking the device back by the number of bytes in the buffer, 346and hence it is only possible on a seekable Handle. 347 348-} 349 350-- --------------------------------------------------------------------------- 351-- Newline translation 352 353-- | The representation of a newline in the external file or stream. 354data Newline = LF -- ^ @\'\\n\'@ 355 | CRLF -- ^ @\'\\r\\n\'@ 356 deriving ( Eq -- ^ @since 4.2.0.0 357 , Ord -- ^ @since 4.3.0.0 358 , Read -- ^ @since 4.3.0.0 359 , Show -- ^ @since 4.3.0.0 360 ) 361 362-- | Specifies the translation, if any, of newline characters between 363-- internal Strings and the external file or stream. Haskell Strings 364-- are assumed to represent newlines with the @\'\\n\'@ character; the 365-- newline mode specifies how to translate @\'\\n\'@ on output, and what to 366-- translate into @\'\\n\'@ on input. 367data NewlineMode 368 = NewlineMode { inputNL :: Newline, 369 -- ^ the representation of newlines on input 370 outputNL :: Newline 371 -- ^ the representation of newlines on output 372 } 373 deriving ( Eq -- ^ @since 4.2.0.0 374 , Ord -- ^ @since 4.3.0.0 375 , Read -- ^ @since 4.3.0.0 376 , Show -- ^ @since 4.3.0.0 377 ) 378 379-- | The native newline representation for the current platform: 'LF' 380-- on Unix systems, 'CRLF' on Windows. 381nativeNewline :: Newline 382#if defined(mingw32_HOST_OS) 383nativeNewline = CRLF 384#else 385nativeNewline = LF 386#endif 387 388-- | Map @\'\\r\\n\'@ into @\'\\n\'@ on input, and @\'\\n\'@ to the native newline 389-- represetnation on output. This mode can be used on any platform, and 390-- works with text files using any newline convention. The downside is 391-- that @readFile >>= writeFile@ might yield a different file. 392-- 393-- > universalNewlineMode = NewlineMode { inputNL = CRLF, 394-- > outputNL = nativeNewline } 395-- 396universalNewlineMode :: NewlineMode 397universalNewlineMode = NewlineMode { inputNL = CRLF, 398 outputNL = nativeNewline } 399 400-- | Use the native newline representation on both input and output 401-- 402-- > nativeNewlineMode = NewlineMode { inputNL = nativeNewline 403-- > outputNL = nativeNewline } 404-- 405nativeNewlineMode :: NewlineMode 406nativeNewlineMode = NewlineMode { inputNL = nativeNewline, 407 outputNL = nativeNewline } 408 409-- | Do no newline translation at all. 410-- 411-- > noNewlineTranslation = NewlineMode { inputNL = LF, outputNL = LF } 412-- 413noNewlineTranslation :: NewlineMode 414noNewlineTranslation = NewlineMode { inputNL = LF, outputNL = LF } 415 416-- --------------------------------------------------------------------------- 417-- Show instance for Handles 418 419-- handle types are 'show'n when printing error msgs, so 420-- we provide a more user-friendly Show instance for it 421-- than the derived one. 422 423-- | @since 4.1.0.0 424instance Show HandleType where 425 showsPrec _ t = 426 case t of 427 ClosedHandle -> showString "closed" 428 SemiClosedHandle -> showString "semi-closed" 429 ReadHandle -> showString "readable" 430 WriteHandle -> showString "writable" 431 AppendHandle -> showString "writable (append)" 432 ReadWriteHandle -> showString "read-writable" 433 434-- | @since 4.1.0.0 435instance Show Handle where 436 showsPrec _ (FileHandle file _) = showHandle file 437 showsPrec _ (DuplexHandle file _ _) = showHandle file 438 439showHandle :: FilePath -> String -> String 440showHandle file = showString "{handle: " . showString file . showString "}" 441 442