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 package os 41 42 import ( 43 "errors" 44 "internal/poll" 45 "internal/safefilepath" 46 "internal/testlog" 47 "io" 48 "io/fs" 49 "runtime" 50 "syscall" 51 "time" 52 "unsafe" 53 ) 54 55 // Name returns the name of the file as presented to Open. 56 func (f *File) Name() string { return f.name } 57 58 // Stdin, Stdout, and Stderr are open Files pointing to the standard input, 59 // standard output, and standard error file descriptors. 60 // 61 // Note that the Go runtime writes to standard error for panics and crashes; 62 // closing Stderr may cause those messages to go elsewhere, perhaps 63 // to a file opened later. 64 var ( 65 Stdin = NewFile(uintptr(syscall.Stdin), "/dev/stdin") 66 Stdout = NewFile(uintptr(syscall.Stdout), "/dev/stdout") 67 Stderr = NewFile(uintptr(syscall.Stderr), "/dev/stderr") 68 ) 69 70 // Flags to OpenFile wrapping those of the underlying system. Not all 71 // flags may be implemented on a given system. 72 const ( 73 // Exactly one of O_RDONLY, O_WRONLY, or O_RDWR must be specified. 74 O_RDONLY int = syscall.O_RDONLY // open the file read-only. 75 O_WRONLY int = syscall.O_WRONLY // open the file write-only. 76 O_RDWR int = syscall.O_RDWR // open the file read-write. 77 // The remaining values may be or'ed in to control behavior. 78 O_APPEND int = syscall.O_APPEND // append data to the file when writing. 79 O_CREATE int = syscall.O_CREAT // create a new file if none exists. 80 O_EXCL int = syscall.O_EXCL // used with O_CREATE, file must not exist. 81 O_SYNC int = syscall.O_SYNC // open for synchronous I/O. 82 O_TRUNC int = syscall.O_TRUNC // truncate regular writable file when opened. 83 ) 84 85 // Seek whence values. 86 // 87 // Deprecated: Use io.SeekStart, io.SeekCurrent, and io.SeekEnd. 88 const ( 89 SEEK_SET int = 0 // seek relative to the origin of the file 90 SEEK_CUR int = 1 // seek relative to the current offset 91 SEEK_END int = 2 // seek relative to the end 92 ) 93 94 // LinkError records an error during a link or symlink or rename 95 // system call and the paths that caused it. 96 type LinkError struct { 97 Op string 98 Old string 99 New string 100 Err error 101 } 102 103 func (e *LinkError) Error() string { 104 return e.Op + " " + e.Old + " " + e.New + ": " + e.Err.Error() 105 } 106 107 func (e *LinkError) Unwrap() error { 108 return e.Err 109 } 110 111 // Read reads up to len(b) bytes from the File and stores them in b. 112 // It returns the number of bytes read and any error encountered. 113 // At end of file, Read returns 0, io.EOF. 114 func (f *File) Read(b []byte) (n int, err error) { 115 if err := f.checkValid("read"); err != nil { 116 return 0, err 117 } 118 n, e := f.read(b) 119 return n, f.wrapErr("read", e) 120 } 121 122 // ReadAt reads len(b) bytes from the File starting at byte offset off. 123 // It returns the number of bytes read and the error, if any. 124 // ReadAt always returns a non-nil error when n < len(b). 125 // At end of file, that error is io.EOF. 126 func (f *File) ReadAt(b []byte, off int64) (n int, err error) { 127 if err := f.checkValid("read"); err != nil { 128 return 0, err 129 } 130 131 if off < 0 { 132 return 0, &PathError{Op: "readat", Path: f.name, Err: errors.New("negative offset")} 133 } 134 135 for len(b) > 0 { 136 m, e := f.pread(b, off) 137 if e != nil { 138 err = f.wrapErr("read", e) 139 break 140 } 141 n += m 142 b = b[m:] 143 off += int64(m) 144 } 145 return 146 } 147 148 // ReadFrom implements io.ReaderFrom. 149 func (f *File) ReadFrom(r io.Reader) (n int64, err error) { 150 if err := f.checkValid("write"); err != nil { 151 return 0, err 152 } 153 n, handled, e := f.readFrom(r) 154 if !handled { 155 return genericReadFrom(f, r) // without wrapping 156 } 157 return n, f.wrapErr("write", e) 158 } 159 160 // noReadFrom can be embedded alongside another type to 161 // hide the ReadFrom method of that other type. 162 type noReadFrom struct{} 163 164 // ReadFrom hides another ReadFrom method. 165 // It should never be called. 166 func (noReadFrom) ReadFrom(io.Reader) (int64, error) { 167 panic("can't happen") 168 } 169 170 // fileWithoutReadFrom implements all the methods of *File other 171 // than ReadFrom. This is used to permit ReadFrom to call io.Copy 172 // without leading to a recursive call to ReadFrom. 173 type fileWithoutReadFrom struct { 174 noReadFrom 175 *File 176 } 177 178 func genericReadFrom(f *File, r io.Reader) (int64, error) { 179 return io.Copy(fileWithoutReadFrom{File: f}, r) 180 } 181 182 // Write writes len(b) bytes from b to the File. 183 // It returns the number of bytes written and an error, if any. 184 // Write returns a non-nil error when n != len(b). 185 func (f *File) Write(b []byte) (n int, err error) { 186 if err := f.checkValid("write"); err != nil { 187 return 0, err 188 } 189 n, e := f.write(b) 190 if n < 0 { 191 n = 0 192 } 193 if n != len(b) { 194 err = io.ErrShortWrite 195 } 196 197 epipecheck(f, e) 198 199 if e != nil { 200 err = f.wrapErr("write", e) 201 } 202 203 return n, err 204 } 205 206 var errWriteAtInAppendMode = errors.New("os: invalid use of WriteAt on file opened with O_APPEND") 207 208 // WriteAt writes len(b) bytes to the File starting at byte offset off. 209 // It returns the number of bytes written and an error, if any. 210 // WriteAt returns a non-nil error when n != len(b). 211 // 212 // If file was opened with the O_APPEND flag, WriteAt returns an error. 213 func (f *File) WriteAt(b []byte, off int64) (n int, err error) { 214 if err := f.checkValid("write"); err != nil { 215 return 0, err 216 } 217 if f.appendMode { 218 return 0, errWriteAtInAppendMode 219 } 220 221 if off < 0 { 222 return 0, &PathError{Op: "writeat", Path: f.name, Err: errors.New("negative offset")} 223 } 224 225 for len(b) > 0 { 226 m, e := f.pwrite(b, off) 227 if e != nil { 228 err = f.wrapErr("write", e) 229 break 230 } 231 n += m 232 b = b[m:] 233 off += int64(m) 234 } 235 return 236 } 237 238 // WriteTo implements io.WriterTo. 239 func (f *File) WriteTo(w io.Writer) (n int64, err error) { 240 if err := f.checkValid("read"); err != nil { 241 return 0, err 242 } 243 n, handled, e := f.writeTo(w) 244 if handled { 245 return n, f.wrapErr("read", e) 246 } 247 return genericWriteTo(f, w) // without wrapping 248 } 249 250 // noWriteTo can be embedded alongside another type to 251 // hide the WriteTo method of that other type. 252 type noWriteTo struct{} 253 254 // WriteTo hides another WriteTo method. 255 // It should never be called. 256 func (noWriteTo) WriteTo(io.Writer) (int64, error) { 257 panic("can't happen") 258 } 259 260 // fileWithoutWriteTo implements all the methods of *File other 261 // than WriteTo. This is used to permit WriteTo to call io.Copy 262 // without leading to a recursive call to WriteTo. 263 type fileWithoutWriteTo struct { 264 noWriteTo 265 *File 266 } 267 268 func genericWriteTo(f *File, w io.Writer) (int64, error) { 269 return io.Copy(w, fileWithoutWriteTo{File: f}) 270 } 271 272 // Seek sets the offset for the next Read or Write on file to offset, interpreted 273 // according to whence: 0 means relative to the origin of the file, 1 means 274 // relative to the current offset, and 2 means relative to the end. 275 // It returns the new offset and an error, if any. 276 // The behavior of Seek on a file opened with O_APPEND is not specified. 277 func (f *File) Seek(offset int64, whence int) (ret int64, err error) { 278 if err := f.checkValid("seek"); err != nil { 279 return 0, err 280 } 281 r, e := f.seek(offset, whence) 282 if e == nil && f.dirinfo != nil && r != 0 { 283 e = syscall.EISDIR 284 } 285 if e != nil { 286 return 0, f.wrapErr("seek", e) 287 } 288 return r, nil 289 } 290 291 // WriteString is like Write, but writes the contents of string s rather than 292 // a slice of bytes. 293 func (f *File) WriteString(s string) (n int, err error) { 294 b := unsafe.Slice(unsafe.StringData(s), len(s)) 295 return f.Write(b) 296 } 297 298 // Mkdir creates a new directory with the specified name and permission 299 // bits (before umask). 300 // If there is an error, it will be of type *PathError. 301 func Mkdir(name string, perm FileMode) error { 302 longName := fixLongPath(name) 303 e := ignoringEINTR(func() error { 304 return syscall.Mkdir(longName, syscallMode(perm)) 305 }) 306 307 if e != nil { 308 return &PathError{Op: "mkdir", Path: name, Err: e} 309 } 310 311 // mkdir(2) itself won't handle the sticky bit on *BSD and Solaris 312 if !supportsCreateWithStickyBit && perm&ModeSticky != 0 { 313 e = setStickyBit(name) 314 315 if e != nil { 316 Remove(name) 317 return e 318 } 319 } 320 321 return nil 322 } 323 324 // setStickyBit adds ModeSticky to the permission bits of path, non atomic. 325 func setStickyBit(name string) error { 326 fi, err := Stat(name) 327 if err != nil { 328 return err 329 } 330 return Chmod(name, fi.Mode()|ModeSticky) 331 } 332 333 // Chdir changes the current working directory to the named directory. 334 // If there is an error, it will be of type *PathError. 335 func Chdir(dir string) error { 336 if e := syscall.Chdir(dir); e != nil { 337 testlog.Open(dir) // observe likely non-existent directory 338 return &PathError{Op: "chdir", Path: dir, Err: e} 339 } 340 if log := testlog.Logger(); log != nil { 341 wd, err := Getwd() 342 if err == nil { 343 log.Chdir(wd) 344 } 345 } 346 return nil 347 } 348 349 // Open opens the named file for reading. If successful, methods on 350 // the returned file can be used for reading; the associated file 351 // descriptor has mode O_RDONLY. 352 // If there is an error, it will be of type *PathError. 353 func Open(name string) (*File, error) { 354 return OpenFile(name, O_RDONLY, 0) 355 } 356 357 // Create creates or truncates the named file. If the file already exists, 358 // it is truncated. If the file does not exist, it is created with mode 0666 359 // (before umask). If successful, methods on the returned File can 360 // be used for I/O; the associated file descriptor has mode O_RDWR. 361 // If there is an error, it will be of type *PathError. 362 func Create(name string) (*File, error) { 363 return OpenFile(name, O_RDWR|O_CREATE|O_TRUNC, 0666) 364 } 365 366 // OpenFile is the generalized open call; most users will use Open 367 // or Create instead. It opens the named file with specified flag 368 // (O_RDONLY etc.). If the file does not exist, and the O_CREATE flag 369 // is passed, it is created with mode perm (before umask). If successful, 370 // methods on the returned File can be used for I/O. 371 // If there is an error, it will be of type *PathError. 372 func OpenFile(name string, flag int, perm FileMode) (*File, error) { 373 testlog.Open(name) 374 f, err := openFileNolog(name, flag, perm) 375 if err != nil { 376 return nil, err 377 } 378 f.appendMode = flag&O_APPEND != 0 379 380 return f, nil 381 } 382 383 // lstat is overridden in tests. 384 var lstat = Lstat 385 386 // Rename renames (moves) oldpath to newpath. 387 // If newpath already exists and is not a directory, Rename replaces it. 388 // OS-specific restrictions may apply when oldpath and newpath are in different directories. 389 // Even within the same directory, on non-Unix platforms Rename is not an atomic operation. 390 // If there is an error, it will be of type *LinkError. 391 func Rename(oldpath, newpath string) error { 392 return rename(oldpath, newpath) 393 } 394 395 // Readlink returns the destination of the named symbolic link. 396 // If there is an error, it will be of type *PathError. 397 // 398 // If the link destination is relative, Readlink returns the relative path 399 // without resolving it to an absolute one. 400 func Readlink(name string) (string, error) { 401 return readlink(name) 402 } 403 404 // Many functions in package syscall return a count of -1 instead of 0. 405 // Using fixCount(call()) instead of call() corrects the count. 406 func fixCount(n int, err error) (int, error) { 407 if n < 0 { 408 n = 0 409 } 410 return n, err 411 } 412 413 // checkWrapErr is the test hook to enable checking unexpected wrapped errors of poll.ErrFileClosing. 414 // It is set to true in the export_test.go for tests (including fuzz tests). 415 var checkWrapErr = false 416 417 // wrapErr wraps an error that occurred during an operation on an open file. 418 // It passes io.EOF through unchanged, otherwise converts 419 // poll.ErrFileClosing to ErrClosed and wraps the error in a PathError. 420 func (f *File) wrapErr(op string, err error) error { 421 if err == nil || err == io.EOF { 422 return err 423 } 424 if err == poll.ErrFileClosing { 425 err = ErrClosed 426 } else if checkWrapErr && errors.Is(err, poll.ErrFileClosing) { 427 panic("unexpected error wrapping poll.ErrFileClosing: " + err.Error()) 428 } 429 return &PathError{Op: op, Path: f.name, Err: err} 430 } 431 432 // TempDir returns the default directory to use for temporary files. 433 // 434 // On Unix systems, it returns $TMPDIR if non-empty, else /tmp. 435 // On Windows, it uses GetTempPath, returning the first non-empty 436 // value from %TMP%, %TEMP%, %USERPROFILE%, or the Windows directory. 437 // On Plan 9, it returns /tmp. 438 // 439 // The directory is neither guaranteed to exist nor have accessible 440 // permissions. 441 func TempDir() string { 442 return tempDir() 443 } 444 445 // UserCacheDir returns the default root directory to use for user-specific 446 // cached data. Users should create their own application-specific subdirectory 447 // within this one and use that. 448 // 449 // On Unix systems, it returns $XDG_CACHE_HOME as specified by 450 // https://specifications.freedesktop.org/basedir-spec/basedir-spec-latest.html if 451 // non-empty, else $HOME/.cache. 452 // On Darwin, it returns $HOME/Library/Caches. 453 // On Windows, it returns %LocalAppData%. 454 // On Plan 9, it returns $home/lib/cache. 455 // 456 // If the location cannot be determined (for example, $HOME is not defined), 457 // then it will return an error. 458 func UserCacheDir() (string, error) { 459 var dir string 460 461 switch runtime.GOOS { 462 case "windows": 463 dir = Getenv("LocalAppData") 464 if dir == "" { 465 return "", errors.New("%LocalAppData% is not defined") 466 } 467 468 case "darwin", "ios": 469 dir = Getenv("HOME") 470 if dir == "" { 471 return "", errors.New("$HOME is not defined") 472 } 473 dir += "/Library/Caches" 474 475 case "plan9": 476 dir = Getenv("home") 477 if dir == "" { 478 return "", errors.New("$home is not defined") 479 } 480 dir += "/lib/cache" 481 482 default: // Unix 483 dir = Getenv("XDG_CACHE_HOME") 484 if dir == "" { 485 dir = Getenv("HOME") 486 if dir == "" { 487 return "", errors.New("neither $XDG_CACHE_HOME nor $HOME are defined") 488 } 489 dir += "/.cache" 490 } 491 } 492 493 return dir, nil 494 } 495 496 // UserConfigDir returns the default root directory to use for user-specific 497 // configuration data. Users should create their own application-specific 498 // subdirectory within this one and use that. 499 // 500 // On Unix systems, it returns $XDG_CONFIG_HOME as specified by 501 // https://specifications.freedesktop.org/basedir-spec/basedir-spec-latest.html if 502 // non-empty, else $HOME/.config. 503 // On Darwin, it returns $HOME/Library/Application Support. 504 // On Windows, it returns %AppData%. 505 // On Plan 9, it returns $home/lib. 506 // 507 // If the location cannot be determined (for example, $HOME is not defined), 508 // then it will return an error. 509 func UserConfigDir() (string, error) { 510 var dir string 511 512 switch runtime.GOOS { 513 case "windows": 514 dir = Getenv("AppData") 515 if dir == "" { 516 return "", errors.New("%AppData% is not defined") 517 } 518 519 case "darwin", "ios": 520 dir = Getenv("HOME") 521 if dir == "" { 522 return "", errors.New("$HOME is not defined") 523 } 524 dir += "/Library/Application Support" 525 526 case "plan9": 527 dir = Getenv("home") 528 if dir == "" { 529 return "", errors.New("$home is not defined") 530 } 531 dir += "/lib" 532 533 default: // Unix 534 dir = Getenv("XDG_CONFIG_HOME") 535 if dir == "" { 536 dir = Getenv("HOME") 537 if dir == "" { 538 return "", errors.New("neither $XDG_CONFIG_HOME nor $HOME are defined") 539 } 540 dir += "/.config" 541 } 542 } 543 544 return dir, nil 545 } 546 547 // UserHomeDir returns the current user's home directory. 548 // 549 // On Unix, including macOS, it returns the $HOME environment variable. 550 // On Windows, it returns %USERPROFILE%. 551 // On Plan 9, it returns the $home environment variable. 552 // 553 // If the expected variable is not set in the environment, UserHomeDir 554 // returns either a platform-specific default value or a non-nil error. 555 func UserHomeDir() (string, error) { 556 env, enverr := "HOME", "$HOME" 557 switch runtime.GOOS { 558 case "windows": 559 env, enverr = "USERPROFILE", "%userprofile%" 560 case "plan9": 561 env, enverr = "home", "$home" 562 } 563 if v := Getenv(env); v != "" { 564 return v, nil 565 } 566 // On some geese the home directory is not always defined. 567 switch runtime.GOOS { 568 case "android": 569 return "/sdcard", nil 570 case "ios": 571 return "/", nil 572 } 573 return "", errors.New(enverr + " is not defined") 574 } 575 576 // Chmod changes the mode of the named file to mode. 577 // If the file is a symbolic link, it changes the mode of the link's target. 578 // If there is an error, it will be of type *PathError. 579 // 580 // A different subset of the mode bits are used, depending on the 581 // operating system. 582 // 583 // On Unix, the mode's permission bits, ModeSetuid, ModeSetgid, and 584 // ModeSticky are used. 585 // 586 // On Windows, only the 0200 bit (owner writable) of mode is used; it 587 // controls whether the file's read-only attribute is set or cleared. 588 // The other bits are currently unused. For compatibility with Go 1.12 589 // and earlier, use a non-zero mode. Use mode 0400 for a read-only 590 // file and 0600 for a readable+writable file. 591 // 592 // On Plan 9, the mode's permission bits, ModeAppend, ModeExclusive, 593 // and ModeTemporary are used. 594 func Chmod(name string, mode FileMode) error { return chmod(name, mode) } 595 596 // Chmod changes the mode of the file to mode. 597 // If there is an error, it will be of type *PathError. 598 func (f *File) Chmod(mode FileMode) error { return f.chmod(mode) } 599 600 // SetDeadline sets the read and write deadlines for a File. 601 // It is equivalent to calling both SetReadDeadline and SetWriteDeadline. 602 // 603 // Only some kinds of files support setting a deadline. Calls to SetDeadline 604 // for files that do not support deadlines will return ErrNoDeadline. 605 // On most systems ordinary files do not support deadlines, but pipes do. 606 // 607 // A deadline is an absolute time after which I/O operations fail with an 608 // error instead of blocking. The deadline applies to all future and pending 609 // I/O, not just the immediately following call to Read or Write. 610 // After a deadline has been exceeded, the connection can be refreshed 611 // by setting a deadline in the future. 612 // 613 // If the deadline is exceeded a call to Read or Write or to other I/O 614 // methods will return an error that wraps ErrDeadlineExceeded. 615 // This can be tested using errors.Is(err, os.ErrDeadlineExceeded). 616 // That error implements the Timeout method, and calling the Timeout 617 // method will return true, but there are other possible errors for which 618 // the Timeout will return true even if the deadline has not been exceeded. 619 // 620 // An idle timeout can be implemented by repeatedly extending 621 // the deadline after successful Read or Write calls. 622 // 623 // A zero value for t means I/O operations will not time out. 624 func (f *File) SetDeadline(t time.Time) error { 625 return f.setDeadline(t) 626 } 627 628 // SetReadDeadline sets the deadline for future Read calls and any 629 // currently-blocked Read call. 630 // A zero value for t means Read will not time out. 631 // Not all files support setting deadlines; see SetDeadline. 632 func (f *File) SetReadDeadline(t time.Time) error { 633 return f.setReadDeadline(t) 634 } 635 636 // SetWriteDeadline sets the deadline for any future Write calls and any 637 // currently-blocked Write call. 638 // Even if Write times out, it may return n > 0, indicating that 639 // some of the data was successfully written. 640 // A zero value for t means Write will not time out. 641 // Not all files support setting deadlines; see SetDeadline. 642 func (f *File) SetWriteDeadline(t time.Time) error { 643 return f.setWriteDeadline(t) 644 } 645 646 // SyscallConn returns a raw file. 647 // This implements the syscall.Conn interface. 648 func (f *File) SyscallConn() (syscall.RawConn, error) { 649 if err := f.checkValid("SyscallConn"); err != nil { 650 return nil, err 651 } 652 return newRawConn(f) 653 } 654 655 // DirFS returns a file system (an fs.FS) for the tree of files rooted at the directory dir. 656 // 657 // Note that DirFS("/prefix") only guarantees that the Open calls it makes to the 658 // operating system will begin with "/prefix": DirFS("/prefix").Open("file") is the 659 // same as os.Open("/prefix/file"). So if /prefix/file is a symbolic link pointing outside 660 // the /prefix tree, then using DirFS does not stop the access any more than using 661 // os.Open does. Additionally, the root of the fs.FS returned for a relative path, 662 // DirFS("prefix"), will be affected by later calls to Chdir. DirFS is therefore not 663 // a general substitute for a chroot-style security mechanism when the directory tree 664 // contains arbitrary content. 665 // 666 // The directory dir must not be "". 667 // 668 // The result implements [io/fs.StatFS], [io/fs.ReadFileFS] and 669 // [io/fs.ReadDirFS]. 670 func DirFS(dir string) fs.FS { 671 return dirFS(dir) 672 } 673 674 type dirFS string 675 676 func (dir dirFS) Open(name string) (fs.File, error) { 677 fullname, err := dir.join(name) 678 if err != nil { 679 return nil, &PathError{Op: "open", Path: name, Err: err} 680 } 681 f, err := Open(fullname) 682 if err != nil { 683 // DirFS takes a string appropriate for GOOS, 684 // while the name argument here is always slash separated. 685 // dir.join will have mixed the two; undo that for 686 // error reporting. 687 err.(*PathError).Path = name 688 return nil, err 689 } 690 return f, nil 691 } 692 693 // The ReadFile method calls the [ReadFile] function for the file 694 // with the given name in the directory. The function provides 695 // robust handling for small files and special file systems. 696 // Through this method, dirFS implements [io/fs.ReadFileFS]. 697 func (dir dirFS) ReadFile(name string) ([]byte, error) { 698 fullname, err := dir.join(name) 699 if err != nil { 700 return nil, &PathError{Op: "readfile", Path: name, Err: err} 701 } 702 b, err := ReadFile(fullname) 703 if err != nil { 704 if e, ok := err.(*PathError); ok { 705 // See comment in dirFS.Open. 706 e.Path = name 707 } 708 return nil, err 709 } 710 return b, nil 711 } 712 713 // ReadDir reads the named directory, returning all its directory entries sorted 714 // by filename. Through this method, dirFS implements [io/fs.ReadDirFS]. 715 func (dir dirFS) ReadDir(name string) ([]DirEntry, error) { 716 fullname, err := dir.join(name) 717 if err != nil { 718 return nil, &PathError{Op: "readdir", Path: name, Err: err} 719 } 720 entries, err := ReadDir(fullname) 721 if err != nil { 722 if e, ok := err.(*PathError); ok { 723 // See comment in dirFS.Open. 724 e.Path = name 725 } 726 return nil, err 727 } 728 return entries, nil 729 } 730 731 func (dir dirFS) Stat(name string) (fs.FileInfo, error) { 732 fullname, err := dir.join(name) 733 if err != nil { 734 return nil, &PathError{Op: "stat", Path: name, Err: err} 735 } 736 f, err := Stat(fullname) 737 if err != nil { 738 // See comment in dirFS.Open. 739 err.(*PathError).Path = name 740 return nil, err 741 } 742 return f, nil 743 } 744 745 // join returns the path for name in dir. 746 func (dir dirFS) join(name string) (string, error) { 747 if dir == "" { 748 return "", errors.New("os: DirFS with empty root") 749 } 750 if !fs.ValidPath(name) { 751 return "", ErrInvalid 752 } 753 name, err := safefilepath.FromFS(name) 754 if err != nil { 755 return "", ErrInvalid 756 } 757 if IsPathSeparator(dir[len(dir)-1]) { 758 return string(dir) + name, nil 759 } 760 return string(dir) + string(PathSeparator) + name, nil 761 } 762 763 // ReadFile reads the named file and returns the contents. 764 // A successful call returns err == nil, not err == EOF. 765 // Because ReadFile reads the whole file, it does not treat an EOF from Read 766 // as an error to be reported. 767 func ReadFile(name string) ([]byte, error) { 768 f, err := Open(name) 769 if err != nil { 770 return nil, err 771 } 772 defer f.Close() 773 774 var size int 775 if info, err := f.Stat(); err == nil { 776 size64 := info.Size() 777 if int64(int(size64)) == size64 { 778 size = int(size64) 779 } 780 } 781 size++ // one byte for final read at EOF 782 783 // If a file claims a small size, read at least 512 bytes. 784 // In particular, files in Linux's /proc claim size 0 but 785 // then do not work right if read in small pieces, 786 // so an initial read of 1 byte would not work correctly. 787 if size < 512 { 788 size = 512 789 } 790 791 data := make([]byte, 0, size) 792 for { 793 n, err := f.Read(data[len(data):cap(data)]) 794 data = data[:len(data)+n] 795 if err != nil { 796 if err == io.EOF { 797 err = nil 798 } 799 return data, err 800 } 801 802 if len(data) >= cap(data) { 803 d := append(data[:cap(data)], 0) 804 data = d[:len(data)] 805 } 806 } 807 } 808 809 // WriteFile writes data to the named file, creating it if necessary. 810 // If the file does not exist, WriteFile creates it with permissions perm (before umask); 811 // otherwise WriteFile truncates it before writing, without changing permissions. 812 // Since WriteFile requires multiple system calls to complete, a failure mid-operation 813 // can leave the file in a partially written state. 814 func WriteFile(name string, data []byte, perm FileMode) error { 815 f, err := OpenFile(name, O_WRONLY|O_CREATE|O_TRUNC, perm) 816 if err != nil { 817 return err 818 } 819 _, err = f.Write(data) 820 if err1 := f.Close(); err1 != nil && err == nil { 821 err = err1 822 } 823 return err 824 } 825