Source file src/os/file.go
Documentation: os
1 // Copyright 2009 The Go Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style 3 // license that can be found in the LICENSE file. 4 5 // Package os provides a platform-independent interface to operating system 6 // functionality. The design is Unix-like, although the error handling is 7 // Go-like; failing calls return values of type error rather than error numbers. 8 // Often, more information is available within the error. For example, 9 // if a call that takes a file name fails, such as Open or Stat, the error 10 // will include the failing file name when printed and will be of type 11 // *PathError, which may be unpacked for more information. 12 // 13 // The os interface is intended to be uniform across all operating systems. 14 // Features not generally available appear in the system-specific package syscall. 15 // 16 // Here is a simple example, opening a file and reading some of it. 17 // 18 // file, err := os.Open("file.go") // For read access. 19 // if err != nil { 20 // log.Fatal(err) 21 // } 22 // 23 // If the open fails, the error string will be self-explanatory, like 24 // 25 // open file.go: no such file or directory 26 // 27 // The file's data can then be read into a slice of bytes. Read and 28 // Write take their byte counts from the length of the argument slice. 29 // 30 // data := make([]byte, 100) 31 // count, err := file.Read(data) 32 // if err != nil { 33 // log.Fatal(err) 34 // } 35 // fmt.Printf("read %d bytes: %q\n", count, data[:count]) 36 // 37 // Note: The maximum number of concurrent operations on a File may be limited by 38 // the OS or the system. The number should be high, but exceeding it may degrade 39 // performance or cause other issues. 40 // 41 package os 42 43 import ( 44 "errors" 45 "internal/poll" 46 "internal/testlog" 47 "io" 48 "runtime" 49 "syscall" 50 "time" 51 ) 52 53 // Name returns the name of the file as presented to Open. 54 func (f *File) Name() string { return f.name } 55 56 // Stdin, Stdout, and Stderr are open Files pointing to the standard input, 57 // standard output, and standard error file descriptors. 58 // 59 // Note that the Go runtime writes to standard error for panics and crashes; 60 // closing Stderr may cause those messages to go elsewhere, perhaps 61 // to a file opened later. 62 var ( 63 Stdin = NewFile(uintptr(syscall.Stdin), "/dev/stdin") 64 Stdout = NewFile(uintptr(syscall.Stdout), "/dev/stdout") 65 Stderr = NewFile(uintptr(syscall.Stderr), "/dev/stderr") 66 ) 67 68 // Flags to OpenFile wrapping those of the underlying system. Not all 69 // flags may be implemented on a given system. 70 const ( 71 // Exactly one of O_RDONLY, O_WRONLY, or O_RDWR must be specified. 72 O_RDONLY int = syscall.O_RDONLY // open the file read-only. 73 O_WRONLY int = syscall.O_WRONLY // open the file write-only. 74 O_RDWR int = syscall.O_RDWR // open the file read-write. 75 // The remaining values may be or'ed in to control behavior. 76 O_APPEND int = syscall.O_APPEND // append data to the file when writing. 77 O_CREATE int = syscall.O_CREAT // create a new file if none exists. 78 O_EXCL int = syscall.O_EXCL // used with O_CREATE, file must not exist. 79 O_SYNC int = syscall.O_SYNC // open for synchronous I/O. 80 O_TRUNC int = syscall.O_TRUNC // truncate regular writable file when opened. 81 ) 82 83 // Seek whence values. 84 // 85 // Deprecated: Use io.SeekStart, io.SeekCurrent, and io.SeekEnd. 86 const ( 87 SEEK_SET int = 0 // seek relative to the origin of the file 88 SEEK_CUR int = 1 // seek relative to the current offset 89 SEEK_END int = 2 // seek relative to the end 90 ) 91 92 // LinkError records an error during a link or symlink or rename 93 // system call and the paths that caused it. 94 type LinkError struct { 95 Op string 96 Old string 97 New string 98 Err error 99 } 100 101 func (e *LinkError) Error() string { 102 return e.Op + " " + e.Old + " " + e.New + ": " + e.Err.Error() 103 } 104 105 func (e *LinkError) Unwrap() error { 106 return e.Err 107 } 108 109 // Read reads up to len(b) bytes from the File. 110 // It returns the number of bytes read and any error encountered. 111 // At end of file, Read returns 0, io.EOF. 112 func (f *File) Read(b []byte) (n int, err error) { 113 if err := f.checkValid("read"); err != nil { 114 return 0, err 115 } 116 n, e := f.read(b) 117 return n, f.wrapErr("read", e) 118 } 119 120 // ReadAt reads len(b) bytes from the File starting at byte offset off. 121 // It returns the number of bytes read and the error, if any. 122 // ReadAt always returns a non-nil error when n < len(b). 123 // At end of file, that error is io.EOF. 124 func (f *File) ReadAt(b []byte, off int64) (n int, err error) { 125 if err := f.checkValid("read"); err != nil { 126 return 0, err 127 } 128 129 if off < 0 { 130 return 0, &PathError{"readat", f.name, errors.New("negative offset")} 131 } 132 133 for len(b) > 0 { 134 m, e := f.pread(b, off) 135 if e != nil { 136 err = f.wrapErr("read", e) 137 break 138 } 139 n += m 140 b = b[m:] 141 off += int64(m) 142 } 143 return 144 } 145 146 // ReadFrom implements io.ReaderFrom. 147 func (f *File) ReadFrom(r io.Reader) (n int64, err error) { 148 if err := f.checkValid("write"); err != nil { 149 return 0, err 150 } 151 n, handled, e := f.readFrom(r) 152 if !handled { 153 return genericReadFrom(f, r) // without wrapping 154 } 155 return n, f.wrapErr("write", e) 156 } 157 158 func genericReadFrom(f *File, r io.Reader) (int64, error) { 159 return io.Copy(onlyWriter{f}, r) 160 } 161 162 type onlyWriter struct { 163 io.Writer 164 } 165 166 // Write writes len(b) bytes to the File. 167 // It returns the number of bytes written and an error, if any. 168 // Write returns a non-nil error when n != len(b). 169 func (f *File) Write(b []byte) (n int, err error) { 170 if err := f.checkValid("write"); err != nil { 171 return 0, err 172 } 173 n, e := f.write(b) 174 if n < 0 { 175 n = 0 176 } 177 if n != len(b) { 178 err = io.ErrShortWrite 179 } 180 181 epipecheck(f, e) 182 183 if e != nil { 184 err = f.wrapErr("write", e) 185 } 186 187 return n, err 188 } 189 190 var errWriteAtInAppendMode = errors.New("os: invalid use of WriteAt on file opened with O_APPEND") 191 192 // WriteAt writes len(b) bytes to the File starting at byte offset off. 193 // It returns the number of bytes written and an error, if any. 194 // WriteAt returns a non-nil error when n != len(b). 195 // 196 // If file was opened with the O_APPEND flag, WriteAt returns an error. 197 func (f *File) WriteAt(b []byte, off int64) (n int, err error) { 198 if err := f.checkValid("write"); err != nil { 199 return 0, err 200 } 201 if f.appendMode { 202 return 0, errWriteAtInAppendMode 203 } 204 205 if off < 0 { 206 return 0, &PathError{"writeat", f.name, errors.New("negative offset")} 207 } 208 209 for len(b) > 0 { 210 m, e := f.pwrite(b, off) 211 if e != nil { 212 err = f.wrapErr("write", e) 213 break 214 } 215 n += m 216 b = b[m:] 217 off += int64(m) 218 } 219 return 220 } 221 222 // Seek sets the offset for the next Read or Write on file to offset, interpreted 223 // according to whence: 0 means relative to the origin of the file, 1 means 224 // relative to the current offset, and 2 means relative to the end. 225 // It returns the new offset and an error, if any. 226 // The behavior of Seek on a file opened with O_APPEND is not specified. 227 // 228 // If f is a directory, the behavior of Seek varies by operating 229 // system; you can seek to the beginning of the directory on Unix-like 230 // operating systems, but not on Windows. 231 func (f *File) Seek(offset int64, whence int) (ret int64, err error) { 232 if err := f.checkValid("seek"); err != nil { 233 return 0, err 234 } 235 r, e := f.seek(offset, whence) 236 if e == nil && f.dirinfo != nil && r != 0 { 237 e = syscall.EISDIR 238 } 239 if e != nil { 240 return 0, f.wrapErr("seek", e) 241 } 242 return r, nil 243 } 244 245 // WriteString is like Write, but writes the contents of string s rather than 246 // a slice of bytes. 247 func (f *File) WriteString(s string) (n int, err error) { 248 return f.Write([]byte(s)) 249 } 250 251 // Mkdir creates a new directory with the specified name and permission 252 // bits (before umask). 253 // If there is an error, it will be of type *PathError. 254 func Mkdir(name string, perm FileMode) error { 255 if runtime.GOOS == "windows" && isWindowsNulName(name) { 256 return &PathError{"mkdir", name, syscall.ENOTDIR} 257 } 258 e := syscall.Mkdir(fixLongPath(name), syscallMode(perm)) 259 260 if e != nil { 261 return &PathError{"mkdir", name, e} 262 } 263 264 // mkdir(2) itself won't handle the sticky bit on *BSD and Solaris 265 if !supportsCreateWithStickyBit && perm&ModeSticky != 0 { 266 e = setStickyBit(name) 267 268 if e != nil { 269 Remove(name) 270 return e 271 } 272 } 273 274 return nil 275 } 276 277 // setStickyBit adds ModeSticky to the permission bits of path, non atomic. 278 func setStickyBit(name string) error { 279 fi, err := Stat(name) 280 if err != nil { 281 return err 282 } 283 return Chmod(name, fi.Mode()|ModeSticky) 284 } 285 286 // Chdir changes the current working directory to the named directory. 287 // If there is an error, it will be of type *PathError. 288 func Chdir(dir string) error { 289 if e := syscall.Chdir(dir); e != nil { 290 testlog.Open(dir) // observe likely non-existent directory 291 return &PathError{"chdir", dir, e} 292 } 293 if log := testlog.Logger(); log != nil { 294 wd, err := Getwd() 295 if err == nil { 296 log.Chdir(wd) 297 } 298 } 299 return nil 300 } 301 302 // Open opens the named file for reading. If successful, methods on 303 // the returned file can be used for reading; the associated file 304 // descriptor has mode O_RDONLY. 305 // If there is an error, it will be of type *PathError. 306 func Open(name string) (*File, error) { 307 return OpenFile(name, O_RDONLY, 0) 308 } 309 310 // Create creates or truncates the named file. If the file already exists, 311 // it is truncated. If the file does not exist, it is created with mode 0666 312 // (before umask). If successful, methods on the returned File can 313 // be used for I/O; the associated file descriptor has mode O_RDWR. 314 // If there is an error, it will be of type *PathError. 315 func Create(name string) (*File, error) { 316 return OpenFile(name, O_RDWR|O_CREATE|O_TRUNC, 0666) 317 } 318 319 // OpenFile is the generalized open call; most users will use Open 320 // or Create instead. It opens the named file with specified flag 321 // (O_RDONLY etc.). If the file does not exist, and the O_CREATE flag 322 // is passed, it is created with mode perm (before umask). If successful, 323 // methods on the returned File can be used for I/O. 324 // If there is an error, it will be of type *PathError. 325 func OpenFile(name string, flag int, perm FileMode) (*File, error) { 326 testlog.Open(name) 327 f, err := openFileNolog(name, flag, perm) 328 if err != nil { 329 return nil, err 330 } 331 f.appendMode = flag&O_APPEND != 0 332 333 return f, nil 334 } 335 336 // lstat is overridden in tests. 337 var lstat = Lstat 338 339 // Rename renames (moves) oldpath to newpath. 340 // If newpath already exists and is not a directory, Rename replaces it. 341 // OS-specific restrictions may apply when oldpath and newpath are in different directories. 342 // If there is an error, it will be of type *LinkError. 343 func Rename(oldpath, newpath string) error { 344 return rename(oldpath, newpath) 345 } 346 347 // Many functions in package syscall return a count of -1 instead of 0. 348 // Using fixCount(call()) instead of call() corrects the count. 349 func fixCount(n int, err error) (int, error) { 350 if n < 0 { 351 n = 0 352 } 353 return n, err 354 } 355 356 // wrapErr wraps an error that occurred during an operation on an open file. 357 // It passes io.EOF through unchanged, otherwise converts 358 // poll.ErrFileClosing to ErrClosed and wraps the error in a PathError. 359 func (f *File) wrapErr(op string, err error) error { 360 if err == nil || err == io.EOF { 361 return err 362 } 363 if err == poll.ErrFileClosing { 364 err = ErrClosed 365 } 366 return &PathError{op, f.name, err} 367 } 368 369 // TempDir returns the default directory to use for temporary files. 370 // 371 // On Unix systems, it returns $TMPDIR if non-empty, else /tmp. 372 // On Windows, it uses GetTempPath, returning the first non-empty 373 // value from %TMP%, %TEMP%, %USERPROFILE%, or the Windows directory. 374 // On Plan 9, it returns /tmp. 375 // 376 // The directory is neither guaranteed to exist nor have accessible 377 // permissions. 378 func TempDir() string { 379 return tempDir() 380 } 381 382 // UserCacheDir returns the default root directory to use for user-specific 383 // cached data. Users should create their own application-specific subdirectory 384 // within this one and use that. 385 // 386 // On Unix systems, it returns $XDG_CACHE_HOME as specified by 387 // https://specifications.freedesktop.org/basedir-spec/basedir-spec-latest.html if 388 // non-empty, else $HOME/.cache. 389 // On Darwin, it returns $HOME/Library/Caches. 390 // On Windows, it returns %LocalAppData%. 391 // On Plan 9, it returns $home/lib/cache. 392 // 393 // If the location cannot be determined (for example, $HOME is not defined), 394 // then it will return an error. 395 func UserCacheDir() (string, error) { 396 var dir string 397 398 switch runtime.GOOS { 399 case "windows": 400 dir = Getenv("LocalAppData") 401 if dir == "" { 402 return "", errors.New("%LocalAppData% is not defined") 403 } 404 405 case "darwin": 406 dir = Getenv("HOME") 407 if dir == "" { 408 return "", errors.New("$HOME is not defined") 409 } 410 dir += "/Library/Caches" 411 412 case "plan9": 413 dir = Getenv("home") 414 if dir == "" { 415 return "", errors.New("$home is not defined") 416 } 417 dir += "/lib/cache" 418 419 default: // Unix 420 dir = Getenv("XDG_CACHE_HOME") 421 if dir == "" { 422 dir = Getenv("HOME") 423 if dir == "" { 424 return "", errors.New("neither $XDG_CACHE_HOME nor $HOME are defined") 425 } 426 dir += "/.cache" 427 } 428 } 429 430 return dir, nil 431 } 432 433 // UserConfigDir returns the default root directory to use for user-specific 434 // configuration data. Users should create their own application-specific 435 // subdirectory within this one and use that. 436 // 437 // On Unix systems, it returns $XDG_CONFIG_HOME as specified by 438 // https://specifications.freedesktop.org/basedir-spec/basedir-spec-latest.html if 439 // non-empty, else $HOME/.config. 440 // On Darwin, it returns $HOME/Library/Application Support. 441 // On Windows, it returns %AppData%. 442 // On Plan 9, it returns $home/lib. 443 // 444 // If the location cannot be determined (for example, $HOME is not defined), 445 // then it will return an error. 446 func UserConfigDir() (string, error) { 447 var dir string 448 449 switch runtime.GOOS { 450 case "windows": 451 dir = Getenv("AppData") 452 if dir == "" { 453 return "", errors.New("%AppData% is not defined") 454 } 455 456 case "darwin": 457 dir = Getenv("HOME") 458 if dir == "" { 459 return "", errors.New("$HOME is not defined") 460 } 461 dir += "/Library/Application Support" 462 463 case "plan9": 464 dir = Getenv("home") 465 if dir == "" { 466 return "", errors.New("$home is not defined") 467 } 468 dir += "/lib" 469 470 default: // Unix 471 dir = Getenv("XDG_CONFIG_HOME") 472 if dir == "" { 473 dir = Getenv("HOME") 474 if dir == "" { 475 return "", errors.New("neither $XDG_CONFIG_HOME nor $HOME are defined") 476 } 477 dir += "/.config" 478 } 479 } 480 481 return dir, nil 482 } 483 484 // UserHomeDir returns the current user's home directory. 485 // 486 // On Unix, including macOS, it returns the $HOME environment variable. 487 // On Windows, it returns %USERPROFILE%. 488 // On Plan 9, it returns the $home environment variable. 489 func UserHomeDir() (string, error) { 490 env, enverr := "HOME", "$HOME" 491 switch runtime.GOOS { 492 case "windows": 493 env, enverr = "USERPROFILE", "%userprofile%" 494 case "plan9": 495 env, enverr = "home", "$home" 496 } 497 if v := Getenv(env); v != "" { 498 return v, nil 499 } 500 // On some geese the home directory is not always defined. 501 switch runtime.GOOS { 502 case "android": 503 return "/sdcard", nil 504 case "darwin": 505 if runtime.GOARCH == "arm64" { 506 return "/", nil 507 } 508 } 509 return "", errors.New(enverr + " is not defined") 510 } 511 512 // Chmod changes the mode of the named file to mode. 513 // If the file is a symbolic link, it changes the mode of the link's target. 514 // If there is an error, it will be of type *PathError. 515 // 516 // A different subset of the mode bits are used, depending on the 517 // operating system. 518 // 519 // On Unix, the mode's permission bits, ModeSetuid, ModeSetgid, and 520 // ModeSticky are used. 521 // 522 // On Windows, only the 0200 bit (owner writable) of mode is used; it 523 // controls whether the file's read-only attribute is set or cleared. 524 // The other bits are currently unused. For compatibility with Go 1.12 525 // and earlier, use a non-zero mode. Use mode 0400 for a read-only 526 // file and 0600 for a readable+writable file. 527 // 528 // On Plan 9, the mode's permission bits, ModeAppend, ModeExclusive, 529 // and ModeTemporary are used. 530 func Chmod(name string, mode FileMode) error { return chmod(name, mode) } 531 532 // Chmod changes the mode of the file to mode. 533 // If there is an error, it will be of type *PathError. 534 func (f *File) Chmod(mode FileMode) error { return f.chmod(mode) } 535 536 // SetDeadline sets the read and write deadlines for a File. 537 // It is equivalent to calling both SetReadDeadline and SetWriteDeadline. 538 // 539 // Only some kinds of files support setting a deadline. Calls to SetDeadline 540 // for files that do not support deadlines will return ErrNoDeadline. 541 // On most systems ordinary files do not support deadlines, but pipes do. 542 // 543 // A deadline is an absolute time after which I/O operations fail with an 544 // error instead of blocking. The deadline applies to all future and pending 545 // I/O, not just the immediately following call to Read or Write. 546 // After a deadline has been exceeded, the connection can be refreshed 547 // by setting a deadline in the future. 548 // 549 // If the deadline is exceeded a call to Read or Write or to other I/O 550 // methods will return an error that wraps ErrDeadlineExceeded. 551 // This can be tested using errors.Is(err, os.ErrDeadlineExceeded). 552 // That error implements the Timeout method, and calling the Timeout 553 // method will return true, but there are other possible errors for which 554 // the Timeout will return true even if the deadline has not been exceeded. 555 // 556 // An idle timeout can be implemented by repeatedly extending 557 // the deadline after successful Read or Write calls. 558 // 559 // A zero value for t means I/O operations will not time out. 560 func (f *File) SetDeadline(t time.Time) error { 561 return f.setDeadline(t) 562 } 563 564 // SetReadDeadline sets the deadline for future Read calls and any 565 // currently-blocked Read call. 566 // A zero value for t means Read will not time out. 567 // Not all files support setting deadlines; see SetDeadline. 568 func (f *File) SetReadDeadline(t time.Time) error { 569 return f.setReadDeadline(t) 570 } 571 572 // SetWriteDeadline sets the deadline for any future Write calls and any 573 // currently-blocked Write call. 574 // Even if Write times out, it may return n > 0, indicating that 575 // some of the data was successfully written. 576 // A zero value for t means Write will not time out. 577 // Not all files support setting deadlines; see SetDeadline. 578 func (f *File) SetWriteDeadline(t time.Time) error { 579 return f.setWriteDeadline(t) 580 } 581 582 // SyscallConn returns a raw file. 583 // This implements the syscall.Conn interface. 584 func (f *File) SyscallConn() (syscall.RawConn, error) { 585 if err := f.checkValid("SyscallConn"); err != nil { 586 return nil, err 587 } 588 return newRawConn(f) 589 } 590 591 // isWindowsNulName reports whether name is os.DevNull ('NUL') on Windows. 592 // True is returned if name is 'NUL' whatever the case. 593 func isWindowsNulName(name string) bool { 594 if len(name) != 3 { 595 return false 596 } 597 if name[0] != 'n' && name[0] != 'N' { 598 return false 599 } 600 if name[1] != 'u' && name[1] != 'U' { 601 return false 602 } 603 if name[2] != 'l' && name[2] != 'L' { 604 return false 605 } 606 return true 607 } 608