github.com/spotify/syslog-redirector-golang@v0.0.0-20140320174030-4859f03d829a/src/pkg/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 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 } 143 144 epipecheck(f, e) 145 146 if e != nil { 147 err = &PathError{"write", f.name, e} 148 } 149 return n, err 150 } 151 152 // WriteAt writes len(b) bytes to the File starting at byte offset off. 153 // It returns the number of bytes written and an error, if any. 154 // WriteAt returns a non-nil error when n != len(b). 155 func (f *File) WriteAt(b []byte, off int64) (n int, err error) { 156 if f == nil { 157 return 0, ErrInvalid 158 } 159 for len(b) > 0 { 160 m, e := f.pwrite(b, off) 161 if e != nil { 162 err = &PathError{"write", f.name, e} 163 break 164 } 165 n += m 166 b = b[m:] 167 off += int64(m) 168 } 169 return 170 } 171 172 // Seek sets the offset for the next Read or Write on file to offset, interpreted 173 // according to whence: 0 means relative to the origin of the file, 1 means 174 // relative to the current offset, and 2 means relative to the end. 175 // It returns the new offset and an error, if any. 176 func (f *File) Seek(offset int64, whence int) (ret int64, err error) { 177 if f == nil { 178 return 0, ErrInvalid 179 } 180 r, e := f.seek(offset, whence) 181 if e == nil && f.dirinfo != nil && r != 0 { 182 e = syscall.EISDIR 183 } 184 if e != nil { 185 return 0, &PathError{"seek", f.name, e} 186 } 187 return r, nil 188 } 189 190 // WriteString is like Write, but writes the contents of string s rather than 191 // a slice of bytes. 192 func (f *File) WriteString(s string) (ret int, err error) { 193 if f == nil { 194 return 0, ErrInvalid 195 } 196 return f.Write([]byte(s)) 197 } 198 199 // Mkdir creates a new directory with the specified name and permission bits. 200 // If there is an error, it will be of type *PathError. 201 func Mkdir(name string, perm FileMode) error { 202 e := syscall.Mkdir(name, syscallMode(perm)) 203 if e != nil { 204 return &PathError{"mkdir", name, e} 205 } 206 return nil 207 } 208 209 // Chdir changes the current working directory to the named directory. 210 // If there is an error, it will be of type *PathError. 211 func Chdir(dir string) error { 212 if e := syscall.Chdir(dir); e != nil { 213 return &PathError{"chdir", dir, e} 214 } 215 return nil 216 } 217 218 // Chdir changes the current working directory to the file, 219 // which must be a directory. 220 // If there is an error, it will be of type *PathError. 221 func (f *File) Chdir() error { 222 if f == nil { 223 return ErrInvalid 224 } 225 if e := syscall.Fchdir(f.fd); e != nil { 226 return &PathError{"chdir", f.name, e} 227 } 228 return nil 229 } 230 231 // Open opens the named file for reading. If successful, methods on 232 // the returned file can be used for reading; the associated file 233 // descriptor has mode O_RDONLY. 234 // If there is an error, it will be of type *PathError. 235 func Open(name string) (file *File, err error) { 236 return OpenFile(name, O_RDONLY, 0) 237 } 238 239 // Create creates the named file mode 0666 (before umask), truncating 240 // it if it already exists. If successful, methods on the returned 241 // File can be used for I/O; the associated file descriptor has mode 242 // O_RDWR. 243 // If there is an error, it will be of type *PathError. 244 func Create(name string) (file *File, err error) { 245 return OpenFile(name, O_RDWR|O_CREATE|O_TRUNC, 0666) 246 } 247 248 // lstat is overridden in tests. 249 var lstat = Lstat