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// 37package os 38 39import ( 40 "io" 41 "syscall" 42) 43 44// Name returns the name of the file as presented to Open. 45func (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. 49var ( 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. 57const ( 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. 69const ( 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. 77type LinkError struct { 78 Op string 79 Old string 80 New string 81 Err error 82} 83 84func (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. 91func (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. 112func (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). 135func (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). 158func (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. 179func (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. 195func (f *File) WriteString(s string) (n 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. 204func Mkdir(name string, perm FileMode) error { 205 e := syscall.Mkdir(name, syscallMode(perm)) 206 207 if e != nil { 208 return &PathError{"mkdir", name, e} 209 } 210 211 // mkdir(2) itself won't handle the sticky bit on *BSD and Solaris 212 if !supportsCreateWithStickyBit && perm&ModeSticky != 0 { 213 Chmod(name, perm) 214 } 215 216 return nil 217} 218 219// Chdir changes the current working directory to the named directory. 220// If there is an error, it will be of type *PathError. 221func Chdir(dir string) error { 222 if e := syscall.Chdir(dir); e != nil { 223 return &PathError{"chdir", dir, e} 224 } 225 return nil 226} 227 228// Chdir changes the current working directory to the file, 229// which must be a directory. 230// If there is an error, it will be of type *PathError. 231func (f *File) Chdir() error { 232 if f == nil { 233 return ErrInvalid 234 } 235 if e := syscall.Fchdir(f.fd); e != nil { 236 return &PathError{"chdir", f.name, e} 237 } 238 return nil 239} 240 241// Open opens the named file for reading. If successful, methods on 242// the returned file can be used for reading; the associated file 243// descriptor has mode O_RDONLY. 244// If there is an error, it will be of type *PathError. 245func Open(name string) (*File, error) { 246 return OpenFile(name, O_RDONLY, 0) 247} 248 249// Create creates the named file with mode 0666 (before umask), truncating 250// it if it already exists. If successful, methods on the returned 251// File can be used for I/O; the associated file descriptor has mode 252// O_RDWR. 253// If there is an error, it will be of type *PathError. 254func Create(name string) (*File, error) { 255 return OpenFile(name, O_RDWR|O_CREATE|O_TRUNC, 0666) 256} 257 258// lstat is overridden in tests. 259var lstat = Lstat 260 261// Rename renames (moves) a file. OS-specific restrictions might apply. 262// If there is an error, it will be of type *LinkError. 263func Rename(oldpath, newpath string) error { 264 return rename(oldpath, newpath) 265} 266 267// Many functions in package syscall return a count of -1 instead of 0. 268// Using fixCount(call()) instead of call() corrects the count. 269func fixCount(n int, err error) (int, error) { 270 if n < 0 { 271 n = 0 272 } 273 return n, err 274} 275