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