libgo/go/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 package os
  38
  39 import (
  40         "errors"
  41         "internal/poll"
  42         "io"
  43         "syscall"
  44 )
  45
  46 // Name returns the name of the file as presented to Open.
  47 func (f *File) Name() string { return f.name }
  48
  49 // Stdin, Stdout, and Stderr are open Files pointing to the standard input,
  50 // standard output, and standard error file descriptors.
  51 //
  52 // Note that the Go runtime writes to standard error for panics and crashes;
  53 // closing Stderr may cause those messages to go elsewhere, perhaps
  54 // to a file opened later.
  55 var (
  56         Stdin  = NewFile(uintptr(syscall.Stdin), "/dev/stdin")
  57         Stdout = NewFile(uintptr(syscall.Stdout), "/dev/stdout")
  58         Stderr = NewFile(uintptr(syscall.Stderr), "/dev/stderr")
  59 )
  60
  61 // Flags to OpenFile wrapping those of the underlying system. Not all
  62 // flags may be implemented on a given system.
  63 const (
  64         O_RDONLY int = syscall.O_RDONLY // open the file read-only.
  65         O_WRONLY int = syscall.O_WRONLY // open the file write-only.
  66         O_RDWR   int = syscall.O_RDWR   // open the file read-write.
  67         O_APPEND int = syscall.O_APPEND // append data to the file when writing.
  68         O_CREATE int = syscall.O_CREAT  // create a new file if none exists.
  69         O_EXCL   int = syscall.O_EXCL   // used with O_CREATE, file must not exist
  70         O_SYNC   int = syscall.O_SYNC   // open for synchronous I/O.
  71         O_TRUNC  int = syscall.O_TRUNC  // if possible, truncate file when opened.
  72 )
  73
  74 // Seek whence values.
  75 //
  76 // Deprecated: Use io.SeekStart, io.SeekCurrent, and io.SeekEnd.
  77 const (
  78         SEEK_SET int = 0 // seek relative to the origin of the file
  79         SEEK_CUR int = 1 // seek relative to the current offset
  80         SEEK_END int = 2 // seek relative to the end
  81 )
  82
  83 // LinkError records an error during a link or symlink or rename
  84 // system call and the paths that caused it.
  85 type LinkError struct {
  86         Op  string
  87         Old string
  88         New string
  89         Err error
  90 }
  91
  92 func (e *LinkError) Error() string {
  93         return e.Op + " " + e.Old + " " + e.New + ": " + e.Err.Error()
  94 }
  95
  96 // Read reads up to len(b) bytes from the File.
  97 // It returns the number of bytes read and any error encountered.
  98 // At end of file, Read returns 0, io.EOF.
  99 func (f *File) Read(b []byte) (n int, err error) {
 100         if err := f.checkValid("read"); err != nil {
 101                 return 0, err
 102         }
 103         n, e := f.read(b)
 104         return n, f.wrapErr("read", e)
 105 }
 106
 107 // ReadAt reads len(b) bytes from the File starting at byte offset off.
 108 // It returns the number of bytes read and the error, if any.
 109 // ReadAt always returns a non-nil error when n < len(b).
 110 // At end of file, that error is io.EOF.
 111 func (f *File) ReadAt(b []byte, off int64) (n int, err error) {
 112         if err := f.checkValid("read"); err != nil {
 113                 return 0, err
 114         }
 115
 116         if off < 0 {
 117                 return 0, &PathError{"readat", f.name, errors.New("negative offset")}
 118         }
 119
 120         for len(b) > 0 {
 121                 m, e := f.pread(b, off)
 122                 if e != nil {
 123                         err = f.wrapErr("read", e)
 124                         break
 125                 }
 126                 n += m
 127                 b = b[m:]
 128                 off += int64(m)
 129         }
 130         return
 131 }
 132
 133 // Write writes len(b) bytes to the File.
 134 // It returns the number of bytes written and an error, if any.
 135 // Write returns a non-nil error when n != len(b).
 136 func (f *File) Write(b []byte) (n int, err error) {
 137         if err := f.checkValid("write"); err != nil {
 138                 return 0, err
 139         }
 140         n, e := f.write(b)
 141         if n < 0 {
 142                 n = 0
 143         }
 144         if n != len(b) {
 145                 err = io.ErrShortWrite
 146         }
 147
 148         epipecheck(f, e)
 149
 150         if e != nil {
 151                 err = f.wrapErr("write", e)
 152         }
 153
 154         return n, err
 155 }
 156
 157 // WriteAt writes len(b) bytes to the File starting at byte offset off.
 158 // It returns the number of bytes written and an error, if any.
 159 // WriteAt returns a non-nil error when n != len(b).
 160 func (f *File) WriteAt(b []byte, off int64) (n int, err error) {
 161         if err := f.checkValid("write"); err != nil {
 162                 return 0, err
 163         }
 164
 165         if off < 0 {
 166                 return 0, &PathError{"writeat", f.name, errors.New("negative offset")}
 167         }
 168
 169         for len(b) > 0 {
 170                 m, e := f.pwrite(b, off)
 171                 if e != nil {
 172                         err = f.wrapErr("write", e)
 173                         break
 174                 }
 175                 n += m
 176                 b = b[m:]
 177                 off += int64(m)
 178         }
 179         return
 180 }
 181
 182 // Seek sets the offset for the next Read or Write on file to offset, interpreted
 183 // according to whence: 0 means relative to the origin of the file, 1 means
 184 // relative to the current offset, and 2 means relative to the end.
 185 // It returns the new offset and an error, if any.
 186 // The behavior of Seek on a file opened with O_APPEND is not specified.
 187 func (f *File) Seek(offset int64, whence int) (ret int64, err error) {
 188         if err := f.checkValid("seek"); err != nil {
 189                 return 0, err
 190         }
 191         r, e := f.seek(offset, whence)
 192         if e == nil && f.dirinfo != nil && r != 0 {
 193                 e = syscall.EISDIR
 194         }
 195         if e != nil {
 196                 return 0, f.wrapErr("seek", e)
 197         }
 198         return r, nil
 199 }
 200
 201 // WriteString is like Write, but writes the contents of string s rather than
 202 // a slice of bytes.
 203 func (f *File) WriteString(s string) (n int, err error) {
 204         return f.Write([]byte(s))
 205 }
 206
 207 // Mkdir creates a new directory with the specified name and permission bits.
 208 // If there is an error, it will be of type *PathError.
 209 func Mkdir(name string, perm FileMode) error {
 210         e := syscall.Mkdir(fixLongPath(name), syscallMode(perm))
 211
 212         if e != nil {
 213                 return &PathError{"mkdir", name, e}
 214         }
 215
 216         // mkdir(2) itself won't handle the sticky bit on *BSD and Solaris
 217         if !supportsCreateWithStickyBit && perm&ModeSticky != 0 {
 218                 Chmod(name, perm)
 219         }
 220
 221         return nil
 222 }
 223
 224 // Chdir changes the current working directory to the named directory.
 225 // If there is an error, it will be of type *PathError.
 226 func Chdir(dir string) error {
 227         if e := syscall.Chdir(dir); e != nil {
 228                 return &PathError{"chdir", dir, e}
 229         }
 230         return nil
 231 }
 232
 233 // Open opens the named file for reading. If successful, methods on
 234 // the returned file can be used for reading; the associated file
 235 // descriptor has mode O_RDONLY.
 236 // If there is an error, it will be of type *PathError.
 237 func Open(name string) (*File, error) {
 238         return OpenFile(name, O_RDONLY, 0)
 239 }
 240
 241 // Create creates the named file with mode 0666 (before umask), truncating
 242 // it if it already exists. If successful, methods on the returned
 243 // File can be used for I/O; the associated file descriptor has mode
 244 // O_RDWR.
 245 // If there is an error, it will be of type *PathError.
 246 func Create(name string) (*File, error) {
 247         return OpenFile(name, O_RDWR|O_CREATE|O_TRUNC, 0666)
 248 }
 249
 250 // lstat is overridden in tests.
 251 var lstat = Lstat
 252
 253 // Rename renames (moves) oldpath to newpath.
 254 // If newpath already exists and is not a directory, Rename replaces it.
 255 // OS-specific restrictions may apply when oldpath and newpath are in different directories.
 256 // If there is an error, it will be of type *LinkError.
 257 func Rename(oldpath, newpath string) error {
 258         return rename(oldpath, newpath)
 259 }
 260
 261 // Many functions in package syscall return a count of -1 instead of 0.
 262 // Using fixCount(call()) instead of call() corrects the count.
 263 func fixCount(n int, err error) (int, error) {
 264         if n < 0 {
 265                 n = 0
 266         }
 267         return n, err
 268 }
 269
 270 // wrapErr wraps an error that occurred during an operation on an open file.
 271 // It passes io.EOF through unchanged, otherwise converts
 272 // poll.ErrFileClosing to ErrClosed and wraps the error in a PathError.
 273 func (f *File) wrapErr(op string, err error) error {
 274         if err == nil || err == io.EOF {
 275                 return err
 276         }
 277         if err == poll.ErrFileClosing {
 278                 err = ErrClosed
 279         }
 280         return &PathError{op, f.name, err}
 281 }
 282
 283 // TempDir returns the default directory to use for temporary files.
 284 //
 285 // On Unix systems, it returns $TMPDIR if non-empty, else /tmp.
 286 // On Windows, it uses GetTempPath, returning the first non-empty
 287 // value from %TMP%, %TEMP%, %USERPROFILE%, or the Windows directory.
 288 // On Plan 9, it returns /tmp.
 289 //
 290 // The directory is neither guaranteed to exist nor have accessible
 291 // permissions.
 292 func TempDir() string {
 293         return tempDir()
 294 }
 295
 296 // Chmod changes the mode of the named file to mode.
 297 // If the file is a symbolic link, it changes the mode of the link's target.
 298 // If there is an error, it will be of type *PathError.
 299 //
 300 // A different subset of the mode bits are used, depending on the
 301 // operating system.
 302 //
 303 // On Unix, the mode's permission bits, ModeSetuid, ModeSetgid, and
 304 // ModeSticky are used.
 305 //
 306 // On Windows, the mode must be non-zero but otherwise only the 0200
 307 // bit (owner writable) of mode is used; it controls whether the
 308 // file's read-only attribute is set or cleared. attribute. The other
 309 // bits are currently unused. Use mode 0400 for a read-only file and
 310 // 0600 for a readable+writable file.
 311 //
 312 // On Plan 9, the mode's permission bits, ModeAppend, ModeExclusive,
 313 // and ModeTemporary are used.
 314 func Chmod(name string, mode FileMode) error { return chmod(name, mode) }
 315
 316 // Chmod changes the mode of the file to mode.
 317 // If there is an error, it will be of type *PathError.
 318 func (f *File) Chmod(mode FileMode) error { return f.chmod(mode) }