github.com/mtsmfm/go/src@v0.0.0-20221020090648-44bdcb9f8fde/os/file.go (about) 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/testlog" 46 "io" 47 "io/fs" 48 "runtime" 49 "syscall" 50 "time" 51 "unsafe" 52 ) 53 54 // Name returns the name of the file as presented to Open. 55 func (f *File) Name() string { return f.name } 56 57 // Stdin, Stdout, and Stderr are open Files pointing to the standard input, 58 // standard output, and standard error file descriptors. 59 // 60 // Note that the Go runtime writes to standard error for panics and crashes; 61 // closing Stderr may cause those messages to go elsewhere, perhaps 62 // to a file opened later. 63 var ( 64 Stdin = NewFile(uintptr(syscall.Stdin), "/dev/stdin") 65 Stdout = NewFile(uintptr(syscall.Stdout), "/dev/stdout") 66 Stderr = NewFile(uintptr(syscall.Stderr), "/dev/stderr") 67 ) 68 69 // Flags to OpenFile wrapping those of the underlying system. Not all 70 // flags may be implemented on a given system. 71 const ( 72 // Exactly one of O_RDONLY, O_WRONLY, or O_RDWR must be specified. 73 O_RDONLY int = syscall.O_RDONLY // open the file read-only. 74 O_WRONLY int = syscall.O_WRONLY // open the file write-only. 75 O_RDWR int = syscall.O_RDWR // open the file read-write. 76 // The remaining values may be or'ed in to control behavior. 77 O_APPEND int = syscall.O_APPEND // append data to the file when writing. 78 O_CREATE int = syscall.O_CREAT // create a new file if none exists. 79 O_EXCL int = syscall.O_EXCL // used with O_CREATE, file must not exist. 80 O_SYNC int = syscall.O_SYNC // open for synchronous I/O. 81 O_TRUNC int = syscall.O_TRUNC // truncate regular writable file when opened. 82 ) 83 84 // Seek whence values. 85 // 86 // Deprecated: Use io.SeekStart, io.SeekCurrent, and io.SeekEnd. 87 const ( 88 SEEK_SET int = 0 // seek relative to the origin of the file 89 SEEK_CUR int = 1 // seek relative to the current offset 90 SEEK_END int = 2 // seek relative to the end 91 ) 92 93 // LinkError records an error during a link or symlink or rename 94 // system call and the paths that caused it. 95 type LinkError struct { 96 Op string 97 Old string 98 New string 99 Err error 100 } 101 102 func (e *LinkError) Error() string { 103 return e.Op + " " + e.Old + " " + e.New + ": " + e.Err.Error() 104 } 105 106 func (e *LinkError) Unwrap() error { 107 return e.Err 108 } 109 110 // Read reads up to len(b) bytes from the File and stores them in b. 111 // It returns the number of bytes read and any error encountered. 112 // At end of file, Read returns 0, io.EOF. 113 func (f *File) Read(b []byte) (n int, err error) { 114 if err := f.checkValid("read"); err != nil { 115 return 0, err 116 } 117 n, e := f.read(b) 118 return n, f.wrapErr("read", e) 119 } 120 121 // ReadAt reads len(b) bytes from the File starting at byte offset off. 122 // It returns the number of bytes read and the error, if any. 123 // ReadAt always returns a non-nil error when n < len(b). 124 // At end of file, that error is io.EOF. 125 func (f *File) ReadAt(b []byte, off int64) (n int, err error) { 126 if err := f.checkValid("read"); err != nil { 127 return 0, err 128 } 129 130 if off < 0 { 131 return 0, &PathError{Op: "readat", Path: f.name, Err: errors.New("negative offset")} 132 } 133 134 for len(b) > 0 { 135 m, e := f.pread(b, off) 136 if e != nil { 137 err = f.wrapErr("read", e) 138 break 139 } 140 n += m 141 b = b[m:] 142 off += int64(m) 143 } 144 return 145 } 146 147 // ReadFrom implements io.ReaderFrom. 148 func (f *File) ReadFrom(r io.Reader) (n int64, err error) { 149 if err := f.checkValid("write"); err != nil { 150 return 0, err 151 } 152 n, handled, e := f.readFrom(r) 153 if !handled { 154 return genericReadFrom(f, r) // without wrapping 155 } 156 return n, f.wrapErr("write", e) 157 } 158 159 func genericReadFrom(f *File, r io.Reader) (int64, error) { 160 return io.Copy(onlyWriter{f}, r) 161 } 162 163 type onlyWriter struct { 164 io.Writer 165 } 166 167 // Write writes len(b) bytes from b to the File. 168 // It returns the number of bytes written and an error, if any. 169 // Write returns a non-nil error when n != len(b). 170 func (f *File) Write(b []byte) (n int, err error) { 171 if err := f.checkValid("write"); err != nil { 172 return 0, err 173 } 174 n, e := f.write(b) 175 if n < 0 { 176 n = 0 177 } 178 if n != len(b) { 179 err = io.ErrShortWrite 180 } 181 182 epipecheck(f, e) 183 184 if e != nil { 185 err = f.wrapErr("write", e) 186 } 187 188 return n, err 189 } 190 191 var errWriteAtInAppendMode = errors.New("os: invalid use of WriteAt on file opened with O_APPEND") 192 193 // WriteAt writes len(b) bytes to the File starting at byte offset off. 194 // It returns the number of bytes written and an error, if any. 195 // WriteAt returns a non-nil error when n != len(b). 196 // 197 // If file was opened with the O_APPEND flag, WriteAt returns an error. 198 func (f *File) WriteAt(b []byte, off int64) (n int, err error) { 199 if err := f.checkValid("write"); err != nil { 200 return 0, err 201 } 202 if f.appendMode { 203 return 0, errWriteAtInAppendMode 204 } 205 206 if off < 0 { 207 return 0, &PathError{Op: "writeat", Path: f.name, Err: errors.New("negative offset")} 208 } 209 210 for len(b) > 0 { 211 m, e := f.pwrite(b, off) 212 if e != nil { 213 err = f.wrapErr("write", e) 214 break 215 } 216 n += m 217 b = b[m:] 218 off += int64(m) 219 } 220 return 221 } 222 223 // Seek sets the offset for the next Read or Write on file to offset, interpreted 224 // according to whence: 0 means relative to the origin of the file, 1 means 225 // relative to the current offset, and 2 means relative to the end. 226 // It returns the new offset and an error, if any. 227 // The behavior of Seek on a file opened with O_APPEND is not specified. 228 // 229 // If f is a directory, the behavior of Seek varies by operating 230 // system; you can seek to the beginning of the directory on Unix-like 231 // operating systems, but not on Windows. 232 func (f *File) Seek(offset int64, whence int) (ret int64, err error) { 233 if err := f.checkValid("seek"); err != nil { 234 return 0, err 235 } 236 r, e := f.seek(offset, whence) 237 if e == nil && f.dirinfo != nil && r != 0 { 238 e = syscall.EISDIR 239 } 240 if e != nil { 241 return 0, f.wrapErr("seek", e) 242 } 243 return r, nil 244 } 245 246 // WriteString is like Write, but writes the contents of string s rather than 247 // a slice of bytes. 248 func (f *File) WriteString(s string) (n int, err error) { 249 b := unsafe.Slice(unsafe.StringData(s), len(s)) 250 return f.Write(b) 251 } 252 253 // Mkdir creates a new directory with the specified name and permission 254 // bits (before umask). 255 // If there is an error, it will be of type *PathError. 256 func Mkdir(name string, perm FileMode) error { 257 if runtime.GOOS == "windows" && isWindowsNulName(name) { 258 return &PathError{Op: "mkdir", Path: name, Err: syscall.ENOTDIR} 259 } 260 longName := fixLongPath(name) 261 e := ignoringEINTR(func() error { 262 return syscall.Mkdir(longName, syscallMode(perm)) 263 }) 264 265 if e != nil { 266 return &PathError{Op: "mkdir", Path: name, Err: e} 267 } 268 269 // mkdir(2) itself won't handle the sticky bit on *BSD and Solaris 270 if !supportsCreateWithStickyBit && perm&ModeSticky != 0 { 271 e = setStickyBit(name) 272 273 if e != nil { 274 Remove(name) 275 return e 276 } 277 } 278 279 return nil 280 } 281 282 // setStickyBit adds ModeSticky to the permission bits of path, non atomic. 283 func setStickyBit(name string) error { 284 fi, err := Stat(name) 285 if err != nil { 286 return err 287 } 288 return Chmod(name, fi.Mode()|ModeSticky) 289 } 290 291 // Chdir changes the current working directory to the named directory. 292 // If there is an error, it will be of type *PathError. 293 func Chdir(dir string) error { 294 if e := syscall.Chdir(dir); e != nil { 295 testlog.Open(dir) // observe likely non-existent directory 296 return &PathError{Op: "chdir", Path: dir, Err: e} 297 } 298 if log := testlog.Logger(); log != nil { 299 wd, err := Getwd() 300 if err == nil { 301 log.Chdir(wd) 302 } 303 } 304 return nil 305 } 306 307 // Open opens the named file for reading. If successful, methods on 308 // the returned file can be used for reading; the associated file 309 // descriptor has mode O_RDONLY. 310 // If there is an error, it will be of type *PathError. 311 func Open(name string) (*File, error) { 312 return OpenFile(name, O_RDONLY, 0) 313 } 314 315 // Create creates or truncates the named file. If the file already exists, 316 // it is truncated. If the file does not exist, it is created with mode 0666 317 // (before umask). If successful, methods on the returned File can 318 // be used for I/O; the associated file descriptor has mode O_RDWR. 319 // If there is an error, it will be of type *PathError. 320 func Create(name string) (*File, error) { 321 return OpenFile(name, O_RDWR|O_CREATE|O_TRUNC, 0666) 322 } 323 324 // OpenFile is the generalized open call; most users will use Open 325 // or Create instead. It opens the named file with specified flag 326 // (O_RDONLY etc.). If the file does not exist, and the O_CREATE flag 327 // is passed, it is created with mode perm (before umask). If successful, 328 // methods on the returned File can be used for I/O. 329 // If there is an error, it will be of type *PathError. 330 func OpenFile(name string, flag int, perm FileMode) (*File, error) { 331 testlog.Open(name) 332 f, err := openFileNolog(name, flag, perm) 333 if err != nil { 334 return nil, err 335 } 336 f.appendMode = flag&O_APPEND != 0 337 338 return f, nil 339 } 340 341 // lstat is overridden in tests. 342 var lstat = Lstat 343 344 // Rename renames (moves) oldpath to newpath. 345 // If newpath already exists and is not a directory, Rename replaces it. 346 // OS-specific restrictions may apply when oldpath and newpath are in different directories. 347 // If there is an error, it will be of type *LinkError. 348 func Rename(oldpath, newpath string) error { 349 return rename(oldpath, newpath) 350 } 351 352 // Many functions in package syscall return a count of -1 instead of 0. 353 // Using fixCount(call()) instead of call() corrects the count. 354 func fixCount(n int, err error) (int, error) { 355 if n < 0 { 356 n = 0 357 } 358 return n, err 359 } 360 361 // wrapErr wraps an error that occurred during an operation on an open file. 362 // It passes io.EOF through unchanged, otherwise converts 363 // poll.ErrFileClosing to ErrClosed and wraps the error in a PathError. 364 func (f *File) wrapErr(op string, err error) error { 365 if err == nil || err == io.EOF { 366 return err 367 } 368 if err == poll.ErrFileClosing { 369 err = ErrClosed 370 } 371 return &PathError{Op: op, Path: f.name, Err: err} 372 } 373 374 // TempDir returns the default directory to use for temporary files. 375 // 376 // On Unix systems, it returns $TMPDIR if non-empty, else /tmp. 377 // On Windows, it uses GetTempPath, returning the first non-empty 378 // value from %TMP%, %TEMP%, %USERPROFILE%, or the Windows directory. 379 // On Plan 9, it returns /tmp. 380 // 381 // The directory is neither guaranteed to exist nor have accessible 382 // permissions. 383 func TempDir() string { 384 return tempDir() 385 } 386 387 // UserCacheDir returns the default root directory to use for user-specific 388 // cached data. Users should create their own application-specific subdirectory 389 // within this one and use that. 390 // 391 // On Unix systems, it returns $XDG_CACHE_HOME as specified by 392 // https://specifications.freedesktop.org/basedir-spec/basedir-spec-latest.html if 393 // non-empty, else $HOME/.cache. 394 // On Darwin, it returns $HOME/Library/Caches. 395 // On Windows, it returns %LocalAppData%. 396 // On Plan 9, it returns $home/lib/cache. 397 // 398 // If the location cannot be determined (for example, $HOME is not defined), 399 // then it will return an error. 400 func UserCacheDir() (string, error) { 401 var dir string 402 403 switch runtime.GOOS { 404 case "windows": 405 dir = Getenv("LocalAppData") 406 if dir == "" { 407 return "", errors.New("%LocalAppData% is not defined") 408 } 409 410 case "darwin", "ios": 411 dir = Getenv("HOME") 412 if dir == "" { 413 return "", errors.New("$HOME is not defined") 414 } 415 dir += "/Library/Caches" 416 417 case "plan9": 418 dir = Getenv("home") 419 if dir == "" { 420 return "", errors.New("$home is not defined") 421 } 422 dir += "/lib/cache" 423 424 default: // Unix 425 dir = Getenv("XDG_CACHE_HOME") 426 if dir == "" { 427 dir = Getenv("HOME") 428 if dir == "" { 429 return "", errors.New("neither $XDG_CACHE_HOME nor $HOME are defined") 430 } 431 dir += "/.cache" 432 } 433 } 434 435 return dir, nil 436 } 437 438 // UserConfigDir returns the default root directory to use for user-specific 439 // configuration data. Users should create their own application-specific 440 // subdirectory within this one and use that. 441 // 442 // On Unix systems, it returns $XDG_CONFIG_HOME as specified by 443 // https://specifications.freedesktop.org/basedir-spec/basedir-spec-latest.html if 444 // non-empty, else $HOME/.config. 445 // On Darwin, it returns $HOME/Library/Application Support. 446 // On Windows, it returns %AppData%. 447 // On Plan 9, it returns $home/lib. 448 // 449 // If the location cannot be determined (for example, $HOME is not defined), 450 // then it will return an error. 451 func UserConfigDir() (string, error) { 452 var dir string 453 454 switch runtime.GOOS { 455 case "windows": 456 dir = Getenv("AppData") 457 if dir == "" { 458 return "", errors.New("%AppData% is not defined") 459 } 460 461 case "darwin", "ios": 462 dir = Getenv("HOME") 463 if dir == "" { 464 return "", errors.New("$HOME is not defined") 465 } 466 dir += "/Library/Application Support" 467 468 case "plan9": 469 dir = Getenv("home") 470 if dir == "" { 471 return "", errors.New("$home is not defined") 472 } 473 dir += "/lib" 474 475 default: // Unix 476 dir = Getenv("XDG_CONFIG_HOME") 477 if dir == "" { 478 dir = Getenv("HOME") 479 if dir == "" { 480 return "", errors.New("neither $XDG_CONFIG_HOME nor $HOME are defined") 481 } 482 dir += "/.config" 483 } 484 } 485 486 return dir, nil 487 } 488 489 // UserHomeDir returns the current user's home directory. 490 // 491 // On Unix, including macOS, it returns the $HOME environment variable. 492 // On Windows, it returns %USERPROFILE%. 493 // On Plan 9, it returns the $home environment variable. 494 func UserHomeDir() (string, error) { 495 env, enverr := "HOME", "$HOME" 496 switch runtime.GOOS { 497 case "windows": 498 env, enverr = "USERPROFILE", "%userprofile%" 499 case "plan9": 500 env, enverr = "home", "$home" 501 } 502 if v := Getenv(env); v != "" { 503 return v, nil 504 } 505 // On some geese the home directory is not always defined. 506 switch runtime.GOOS { 507 case "android": 508 return "/sdcard", nil 509 case "ios": 510 return "/", nil 511 } 512 return "", errors.New(enverr + " is not defined") 513 } 514 515 // Chmod changes the mode of the named file to mode. 516 // If the file is a symbolic link, it changes the mode of the link's target. 517 // If there is an error, it will be of type *PathError. 518 // 519 // A different subset of the mode bits are used, depending on the 520 // operating system. 521 // 522 // On Unix, the mode's permission bits, ModeSetuid, ModeSetgid, and 523 // ModeSticky are used. 524 // 525 // On Windows, only the 0200 bit (owner writable) of mode is used; it 526 // controls whether the file's read-only attribute is set or cleared. 527 // The other bits are currently unused. For compatibility with Go 1.12 528 // and earlier, use a non-zero mode. Use mode 0400 for a read-only 529 // file and 0600 for a readable+writable file. 530 // 531 // On Plan 9, the mode's permission bits, ModeAppend, ModeExclusive, 532 // and ModeTemporary are used. 533 func Chmod(name string, mode FileMode) error { return chmod(name, mode) } 534 535 // Chmod changes the mode of the file to mode. 536 // If there is an error, it will be of type *PathError. 537 func (f *File) Chmod(mode FileMode) error { return f.chmod(mode) } 538 539 // SetDeadline sets the read and write deadlines for a File. 540 // It is equivalent to calling both SetReadDeadline and SetWriteDeadline. 541 // 542 // Only some kinds of files support setting a deadline. Calls to SetDeadline 543 // for files that do not support deadlines will return ErrNoDeadline. 544 // On most systems ordinary files do not support deadlines, but pipes do. 545 // 546 // A deadline is an absolute time after which I/O operations fail with an 547 // error instead of blocking. The deadline applies to all future and pending 548 // I/O, not just the immediately following call to Read or Write. 549 // After a deadline has been exceeded, the connection can be refreshed 550 // by setting a deadline in the future. 551 // 552 // If the deadline is exceeded a call to Read or Write or to other I/O 553 // methods will return an error that wraps ErrDeadlineExceeded. 554 // This can be tested using errors.Is(err, os.ErrDeadlineExceeded). 555 // That error implements the Timeout method, and calling the Timeout 556 // method will return true, but there are other possible errors for which 557 // the Timeout will return true even if the deadline has not been exceeded. 558 // 559 // An idle timeout can be implemented by repeatedly extending 560 // the deadline after successful Read or Write calls. 561 // 562 // A zero value for t means I/O operations will not time out. 563 func (f *File) SetDeadline(t time.Time) error { 564 return f.setDeadline(t) 565 } 566 567 // SetReadDeadline sets the deadline for future Read calls and any 568 // currently-blocked Read call. 569 // A zero value for t means Read will not time out. 570 // Not all files support setting deadlines; see SetDeadline. 571 func (f *File) SetReadDeadline(t time.Time) error { 572 return f.setReadDeadline(t) 573 } 574 575 // SetWriteDeadline sets the deadline for any future Write calls and any 576 // currently-blocked Write call. 577 // Even if Write times out, it may return n > 0, indicating that 578 // some of the data was successfully written. 579 // A zero value for t means Write will not time out. 580 // Not all files support setting deadlines; see SetDeadline. 581 func (f *File) SetWriteDeadline(t time.Time) error { 582 return f.setWriteDeadline(t) 583 } 584 585 // SyscallConn returns a raw file. 586 // This implements the syscall.Conn interface. 587 func (f *File) SyscallConn() (syscall.RawConn, error) { 588 if err := f.checkValid("SyscallConn"); err != nil { 589 return nil, err 590 } 591 return newRawConn(f) 592 } 593 594 // isWindowsNulName reports whether name is os.DevNull ('NUL') on Windows. 595 // True is returned if name is 'NUL' whatever the case. 596 func isWindowsNulName(name string) bool { 597 if len(name) != 3 { 598 return false 599 } 600 if name[0] != 'n' && name[0] != 'N' { 601 return false 602 } 603 if name[1] != 'u' && name[1] != 'U' { 604 return false 605 } 606 if name[2] != 'l' && name[2] != 'L' { 607 return false 608 } 609 return true 610 } 611 612 // DirFS returns a file system (an fs.FS) for the tree of files rooted at the directory dir. 613 // 614 // Note that DirFS("/prefix") only guarantees that the Open calls it makes to the 615 // operating system will begin with "/prefix": DirFS("/prefix").Open("file") is the 616 // same as os.Open("/prefix/file"). So if /prefix/file is a symbolic link pointing outside 617 // the /prefix tree, then using DirFS does not stop the access any more than using 618 // os.Open does. Additionally, the root of the fs.FS returned for a relative path, 619 // DirFS("prefix"), will be affected by later calls to Chdir. DirFS is therefore not 620 // a general substitute for a chroot-style security mechanism when the directory tree 621 // contains arbitrary content. 622 // 623 // The result implements fs.StatFS. 624 func DirFS(dir string) fs.FS { 625 return dirFS(dir) 626 } 627 628 func containsAny(s, chars string) bool { 629 for i := 0; i < len(s); i++ { 630 for j := 0; j < len(chars); j++ { 631 if s[i] == chars[j] { 632 return true 633 } 634 } 635 } 636 return false 637 } 638 639 type dirFS string 640 641 func (dir dirFS) Open(name string) (fs.File, error) { 642 if !fs.ValidPath(name) || runtime.GOOS == "windows" && containsAny(name, `\:`) { 643 return nil, &PathError{Op: "open", Path: name, Err: ErrInvalid} 644 } 645 f, err := Open(dir.join(name)) 646 if err != nil { 647 if runtime.GOOS == "windows" { 648 // Undo the backslash conversion done by dir.join. 649 perr := err.(*PathError) 650 if containsAny(perr.Path, `\`) { 651 perr.Path = string(dir) + "/" + name 652 } 653 } 654 return nil, err // nil fs.File 655 } 656 return f, nil 657 } 658 659 func (dir dirFS) Stat(name string) (fs.FileInfo, error) { 660 if !fs.ValidPath(name) || runtime.GOOS == "windows" && containsAny(name, `\:`) { 661 return nil, &PathError{Op: "stat", Path: name, Err: ErrInvalid} 662 } 663 f, err := Stat(dir.join(name)) 664 if err != nil { 665 return nil, err 666 } 667 return f, nil 668 } 669 670 // join returns the path for name in dir. We can't always use "/" 671 // because that fails on Windows for UNC paths. 672 func (dir dirFS) join(name string) string { 673 if runtime.GOOS == "windows" && containsAny(name, "/") { 674 buf := []byte(name) 675 for i, b := range buf { 676 if b == '/' { 677 buf[i] = '\\' 678 } 679 } 680 name = string(buf) 681 } 682 return string(dir) + string(PathSeparator) + name 683 } 684 685 // ReadFile reads the named file and returns the contents. 686 // A successful call returns err == nil, not err == EOF. 687 // Because ReadFile reads the whole file, it does not treat an EOF from Read 688 // as an error to be reported. 689 func ReadFile(name string) ([]byte, error) { 690 f, err := Open(name) 691 if err != nil { 692 return nil, err 693 } 694 defer f.Close() 695 696 var size int 697 if info, err := f.Stat(); err == nil { 698 size64 := info.Size() 699 if int64(int(size64)) == size64 { 700 size = int(size64) 701 } 702 } 703 size++ // one byte for final read at EOF 704 705 // If a file claims a small size, read at least 512 bytes. 706 // In particular, files in Linux's /proc claim size 0 but 707 // then do not work right if read in small pieces, 708 // so an initial read of 1 byte would not work correctly. 709 if size < 512 { 710 size = 512 711 } 712 713 data := make([]byte, 0, size) 714 for { 715 if len(data) >= cap(data) { 716 d := append(data[:cap(data)], 0) 717 data = d[:len(data)] 718 } 719 n, err := f.Read(data[len(data):cap(data)]) 720 data = data[:len(data)+n] 721 if err != nil { 722 if err == io.EOF { 723 err = nil 724 } 725 return data, err 726 } 727 } 728 } 729 730 // WriteFile writes data to the named file, creating it if necessary. 731 // If the file does not exist, WriteFile creates it with permissions perm (before umask); 732 // otherwise WriteFile truncates it before writing, without changing permissions. 733 func WriteFile(name string, data []byte, perm FileMode) error { 734 f, err := OpenFile(name, O_WRONLY|O_CREATE|O_TRUNC, perm) 735 if err != nil { 736 return err 737 } 738 _, err = f.Write(data) 739 if err1 := f.Close(); err1 != nil && err == nil { 740 err = err1 741 } 742 return err 743 }