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         "io"
  41         "syscall"
  42 )
  43
  44 // Name returns the name of the file as presented to Open.
  45 func (f *File) Name() string { return f.name }
  46
  47 // Stdin, Stdout, and Stderr are open Files pointing to the standard input,
  48 // standard output, and standard error file descriptors.
  49 var (
  50         Stdin  = NewFile(uintptr(syscall.Stdin), "/dev/stdin")
  51         Stdout = NewFile(uintptr(syscall.Stdout), "/dev/stdout")
  52         Stderr = NewFile(uintptr(syscall.Stderr), "/dev/stderr")
  53 )
  54
  55 // Flags to Open wrapping those of the underlying system. Not all flags
  56 // may be implemented on a given system.
  57 const (
  58         O_RDONLY int = syscall.O_RDONLY // open the file read-only.
  59         O_WRONLY int = syscall.O_WRONLY // open the file write-only.
  60         O_RDWR   int = syscall.O_RDWR   // open the file read-write.
  61         O_APPEND int = syscall.O_APPEND // append data to the file when writing.
  62         O_CREATE int = syscall.O_CREAT  // create a new file if none exists.
  63         O_EXCL   int = syscall.O_EXCL   // used with O_CREATE, file must not exist
  64         O_SYNC   int = syscall.O_SYNC   // open for synchronous I/O.
  65         O_TRUNC  int = syscall.O_TRUNC  // if possible, truncate file when opened.
  66 )
  67
  68 // Seek whence values.
  69 const (
  70         SEEK_SET int = 0 // seek relative to the origin of the file
  71         SEEK_CUR int = 1 // seek relative to the current offset
  72         SEEK_END int = 2 // seek relative to the end
  73 )
  74
  75 // LinkError records an error during a link or symlink or rename
  76 // system call and the paths that caused it.
  77 type LinkError struct {
  78         Op  string
  79         Old string
  80         New string
  81         Err error
  82 }
  83
  84 func (e *LinkError) Error() string {
  85         return e.Op + " " + e.Old + " " + e.New + ": " + e.Err.Error()
  86 }
  87
  88 // Read reads up to len(b) bytes from the File.
  89 // It returns the number of bytes read and an error, if any.
  90 // EOF is signaled by a zero count with err set to io.EOF.
  91 func (f *File) Read(b []byte) (n int, err error) {
  92         if f == nil {
  93                 return 0, ErrInvalid
  94         }
  95         n, e := f.read(b)
  96         if n < 0 {
  97                 n = 0
  98         }
  99         if n == 0 && len(b) > 0 && e == nil {
 100                 return 0, io.EOF
 101         }
 102         if e != nil {
 103                 err = &PathError{"read", f.name, e}
 104         }
 105         return n, err
 106 }
 107
 108 // ReadAt reads len(b) bytes from the File starting at byte offset off.
 109 // It returns the number of bytes read and the error, if any.
 110 // ReadAt always returns a non-nil error when n < len(b).
 111 // At end of file, that error is io.EOF.
 112 func (f *File) ReadAt(b []byte, off int64) (n int, err error) {
 113         if f == nil {
 114                 return 0, ErrInvalid
 115         }
 116         for len(b) > 0 {
 117                 m, e := f.pread(b, off)
 118                 if m == 0 && e == nil {
 119                         return n, io.EOF
 120                 }
 121                 if e != nil {
 122                         err = &PathError{"read", f.name, e}
 123                         break
 124                 }
 125                 n += m
 126                 b = b[m:]
 127                 off += int64(m)
 128         }
 129         return
 130 }
 131
 132 // Write writes len(b) bytes to the File.
 133 // It returns the number of bytes written and an error, if any.
 134 // Write returns a non-nil error when n != len(b).
 135 func (f *File) Write(b []byte) (n int, err error) {
 136         if f == nil {
 137                 return 0, ErrInvalid
 138         }
 139         n, e := f.write(b)
 140         if n < 0 {
 141                 n = 0
 142         }
 143         if n != len(b) {
 144                 err = io.ErrShortWrite
 145         }
 146
 147         epipecheck(f, e)
 148
 149         if e != nil {
 150                 err = &PathError{"write", f.name, e}
 151         }
 152         return n, err
 153 }
 154
 155 // WriteAt writes len(b) bytes to the File starting at byte offset off.
 156 // It returns the number of bytes written and an error, if any.
 157 // WriteAt returns a non-nil error when n != len(b).
 158 func (f *File) WriteAt(b []byte, off int64) (n int, err error) {
 159         if f == nil {
 160                 return 0, ErrInvalid
 161         }
 162         for len(b) > 0 {
 163                 m, e := f.pwrite(b, off)
 164                 if e != nil {
 165                         err = &PathError{"write", f.name, e}
 166                         break
 167                 }
 168                 n += m
 169                 b = b[m:]
 170                 off += int64(m)
 171         }
 172         return
 173 }
 174
 175 // Seek sets the offset for the next Read or Write on file to offset, interpreted
 176 // according to whence: 0 means relative to the origin of the file, 1 means
 177 // relative to the current offset, and 2 means relative to the end.
 178 // It returns the new offset and an error, if any.
 179 func (f *File) Seek(offset int64, whence int) (ret int64, err error) {
 180         if f == nil {
 181                 return 0, ErrInvalid
 182         }
 183         r, e := f.seek(offset, whence)
 184         if e == nil && f.dirinfo != nil && r != 0 {
 185                 e = syscall.EISDIR
 186         }
 187         if e != nil {
 188                 return 0, &PathError{"seek", f.name, e}
 189         }
 190         return r, nil
 191 }
 192
 193 // WriteString is like Write, but writes the contents of string s rather than
 194 // a slice of bytes.
 195 func (f *File) WriteString(s string) (ret int, err error) {
 196         if f == nil {
 197                 return 0, ErrInvalid
 198         }
 199         return f.Write([]byte(s))
 200 }
 201
 202 // Mkdir creates a new directory with the specified name and permission bits.
 203 // If there is an error, it will be of type *PathError.
 204 func Mkdir(name string, perm FileMode) error {
 205         e := syscall.Mkdir(name, syscallMode(perm))
 206         if e != nil {
 207                 return &PathError{"mkdir", name, e}
 208         }
 209         return nil
 210 }
 211
 212 // Chdir changes the current working directory to the named directory.
 213 // If there is an error, it will be of type *PathError.
 214 func Chdir(dir string) error {
 215         if e := syscall.Chdir(dir); e != nil {
 216                 return &PathError{"chdir", dir, e}
 217         }
 218         return nil
 219 }
 220
 221 // Chdir changes the current working directory to the file,
 222 // which must be a directory.
 223 // If there is an error, it will be of type *PathError.
 224 func (f *File) Chdir() error {
 225         if f == nil {
 226                 return ErrInvalid
 227         }
 228         if e := syscall.Fchdir(f.fd); e != nil {
 229                 return &PathError{"chdir", f.name, e}
 230         }
 231         return nil
 232 }
 233
 234 // Open opens the named file for reading.  If successful, methods on
 235 // the returned file can be used for reading; the associated file
 236 // descriptor has mode O_RDONLY.
 237 // If there is an error, it will be of type *PathError.
 238 func Open(name string) (file *File, err error) {
 239         return OpenFile(name, O_RDONLY, 0)
 240 }
 241
 242 // Create creates the named file mode 0666 (before umask), truncating
 243 // it if it already exists.  If successful, methods on the returned
 244 // File can be used for I/O; the associated file descriptor has mode
 245 // O_RDWR.
 246 // If there is an error, it will be of type *PathError.
 247 func Create(name string) (file *File, err error) {
 248         return OpenFile(name, O_RDWR|O_CREATE|O_TRUNC, 0666)
 249 }
 250
 251 // lstat is overridden in tests.
 252 var lstat = Lstat
 253
 254 // Rename renames (moves) a file. OS-specific restrictions might apply.
 255 func Rename(oldpath, newpath string) error {
 256         return rename(oldpath, newpath)
 257 }
 258
 259 // Many functions in package syscall return a count of -1 instead of 0.
 260 // Using fixCount(call()) instead of call() corrects the count.
 261 func fixCount(n int, err error) (int, error) {
 262         if n < 0 {
 263                 n = 0
 264         }
 265         return n, err
 266 }