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Source file src/os/file.go

Documentation: os

  // Copyright 2009 The Go Authors. All rights reserved.
  // Use of this source code is governed by a BSD-style
  // license that can be found in the LICENSE file.
  
  // Package os provides a platform-independent interface to operating system
  // functionality. The design is Unix-like, although the error handling is
  // Go-like; failing calls return values of type error rather than error numbers.
  // Often, more information is available within the error. For example,
  // if a call that takes a file name fails, such as Open or Stat, the error
  // will include the failing file name when printed and will be of type
  // *PathError, which may be unpacked for more information.
  //
  // The os interface is intended to be uniform across all operating systems.
  // Features not generally available appear in the system-specific package syscall.
  //
  // Here is a simple example, opening a file and reading some of it.
  //
  //	file, err := os.Open("file.go") // For read access.
  //	if err != nil {
  //		log.Fatal(err)
  //	}
  //
  // If the open fails, the error string will be self-explanatory, like
  //
  //	open file.go: no such file or directory
  //
  // The file's data can then be read into a slice of bytes. Read and
  // Write take their byte counts from the length of the argument slice.
  //
  //	data := make([]byte, 100)
  //	count, err := file.Read(data)
  //	if err != nil {
  //		log.Fatal(err)
  //	}
  //	fmt.Printf("read %d bytes: %q\n", count, data[:count])
  //
  package os
  
  import (
  	"io"
  	"syscall"
  )
  
  // Name returns the name of the file as presented to Open.
  func (f *File) Name() string { return f.name }
  
  // Stdin, Stdout, and Stderr are open Files pointing to the standard input,
  // standard output, and standard error file descriptors.
  //
  // Note that the Go runtime writes to standard error for panics and crashes;
  // closing Stderr may cause those messages to go elsewhere, perhaps
  // to a file opened later.
  var (
  	Stdin  = NewFile(uintptr(syscall.Stdin), "/dev/stdin")
  	Stdout = NewFile(uintptr(syscall.Stdout), "/dev/stdout")
  	Stderr = NewFile(uintptr(syscall.Stderr), "/dev/stderr")
  )
  
  // Flags to OpenFile wrapping those of the underlying system. Not all
  // flags may be implemented on a given system.
  const (
  	O_RDONLY int = syscall.O_RDONLY // open the file read-only.
  	O_WRONLY int = syscall.O_WRONLY // open the file write-only.
  	O_RDWR   int = syscall.O_RDWR   // open the file read-write.
  	O_APPEND int = syscall.O_APPEND // append data to the file when writing.
  	O_CREATE int = syscall.O_CREAT  // create a new file if none exists.
  	O_EXCL   int = syscall.O_EXCL   // used with O_CREATE, file must not exist
  	O_SYNC   int = syscall.O_SYNC   // open for synchronous I/O.
  	O_TRUNC  int = syscall.O_TRUNC  // if possible, truncate file when opened.
  )
  
  // Seek whence values.
  //
  // Deprecated: Use io.SeekStart, io.SeekCurrent, and io.SeekEnd.
  const (
  	SEEK_SET int = 0 // seek relative to the origin of the file
  	SEEK_CUR int = 1 // seek relative to the current offset
  	SEEK_END int = 2 // seek relative to the end
  )
  
  // LinkError records an error during a link or symlink or rename
  // system call and the paths that caused it.
  type LinkError struct {
  	Op  string
  	Old string
  	New string
  	Err error
  }
  
  func (e *LinkError) Error() string {
  	return e.Op + " " + e.Old + " " + e.New + ": " + e.Err.Error()
  }
  
  // Read reads up to len(b) bytes from the File.
  // It returns the number of bytes read and any error encountered.
  // At end of file, Read returns 0, io.EOF.
  func (f *File) Read(b []byte) (n int, err error) {
  	if err := f.checkValid("read"); err != nil {
  		return 0, err
  	}
  	n, e := f.read(b)
  	if n == 0 && len(b) > 0 && e == nil {
  		return 0, io.EOF
  	}
  	if e != nil {
  		err = &PathError{"read", f.name, e}
  	}
  	return n, err
  }
  
  // ReadAt reads len(b) bytes from the File starting at byte offset off.
  // It returns the number of bytes read and the error, if any.
  // ReadAt always returns a non-nil error when n < len(b).
  // At end of file, that error is io.EOF.
  func (f *File) ReadAt(b []byte, off int64) (n int, err error) {
  	if err := f.checkValid("read"); err != nil {
  		return 0, err
  	}
  	for len(b) > 0 {
  		m, e := f.pread(b, off)
  		if m == 0 && e == nil {
  			return n, io.EOF
  		}
  		if e != nil {
  			err = &PathError{"read", f.name, e}
  			break
  		}
  		n += m
  		b = b[m:]
  		off += int64(m)
  	}
  	return
  }
  
  // Write writes len(b) bytes to the File.
  // It returns the number of bytes written and an error, if any.
  // Write returns a non-nil error when n != len(b).
  func (f *File) Write(b []byte) (n int, err error) {
  	if err := f.checkValid("write"); err != nil {
  		return 0, err
  	}
  	n, e := f.write(b)
  	if n < 0 {
  		n = 0
  	}
  	if n != len(b) {
  		err = io.ErrShortWrite
  	}
  
  	epipecheck(f, e)
  
  	if e != nil {
  		err = &PathError{"write", f.name, e}
  	}
  	return n, err
  }
  
  // WriteAt writes len(b) bytes to the File starting at byte offset off.
  // It returns the number of bytes written and an error, if any.
  // WriteAt returns a non-nil error when n != len(b).
  func (f *File) WriteAt(b []byte, off int64) (n int, err error) {
  	if err := f.checkValid("write"); err != nil {
  		return 0, err
  	}
  	for len(b) > 0 {
  		m, e := f.pwrite(b, off)
  		if e != nil {
  			err = &PathError{"write", f.name, e}
  			break
  		}
  		n += m
  		b = b[m:]
  		off += int64(m)
  	}
  	return
  }
  
  // Seek sets the offset for the next Read or Write on file to offset, interpreted
  // according to whence: 0 means relative to the origin of the file, 1 means
  // relative to the current offset, and 2 means relative to the end.
  // It returns the new offset and an error, if any.
  // The behavior of Seek on a file opened with O_APPEND is not specified.
  func (f *File) Seek(offset int64, whence int) (ret int64, err error) {
  	if err := f.checkValid("seek"); err != nil {
  		return 0, err
  	}
  	r, e := f.seek(offset, whence)
  	if e == nil && f.dirinfo != nil && r != 0 {
  		e = syscall.EISDIR
  	}
  	if e != nil {
  		return 0, &PathError{"seek", f.name, e}
  	}
  	return r, nil
  }
  
  // WriteString is like Write, but writes the contents of string s rather than
  // a slice of bytes.
  func (f *File) WriteString(s string) (n int, err error) {
  	return f.Write([]byte(s))
  }
  
  // Mkdir creates a new directory with the specified name and permission bits.
  // If there is an error, it will be of type *PathError.
  func Mkdir(name string, perm FileMode) error {
  	e := syscall.Mkdir(fixLongPath(name), syscallMode(perm))
  
  	if e != nil {
  		return &PathError{"mkdir", name, e}
  	}
  
  	// mkdir(2) itself won't handle the sticky bit on *BSD and Solaris
  	if !supportsCreateWithStickyBit && perm&ModeSticky != 0 {
  		Chmod(name, perm)
  	}
  
  	return nil
  }
  
  // Chdir changes the current working directory to the named directory.
  // If there is an error, it will be of type *PathError.
  func Chdir(dir string) error {
  	if e := syscall.Chdir(dir); e != nil {
  		return &PathError{"chdir", dir, e}
  	}
  	return nil
  }
  
  // Chdir changes the current working directory to the file,
  // which must be a directory.
  // If there is an error, it will be of type *PathError.
  func (f *File) Chdir() error {
  	if err := f.checkValid("chdir"); err != nil {
  		return err
  	}
  	if e := syscall.Fchdir(f.fd); e != nil {
  		return &PathError{"chdir", f.name, e}
  	}
  	return nil
  }
  
  // Open opens the named file for reading. If successful, methods on
  // the returned file can be used for reading; the associated file
  // descriptor has mode O_RDONLY.
  // If there is an error, it will be of type *PathError.
  func Open(name string) (*File, error) {
  	return OpenFile(name, O_RDONLY, 0)
  }
  
  // Create creates the named file with mode 0666 (before umask), truncating
  // it if it already exists. If successful, methods on the returned
  // File can be used for I/O; the associated file descriptor has mode
  // O_RDWR.
  // If there is an error, it will be of type *PathError.
  func Create(name string) (*File, error) {
  	return OpenFile(name, O_RDWR|O_CREATE|O_TRUNC, 0666)
  }
  
  // lstat is overridden in tests.
  var lstat = Lstat
  
  // Rename renames (moves) oldpath to newpath.
  // If newpath already exists and is not a directory, Rename replaces it.
  // OS-specific restrictions may apply when oldpath and newpath are in different directories.
  // If there is an error, it will be of type *LinkError.
  func Rename(oldpath, newpath string) error {
  	return rename(oldpath, newpath)
  }
  
  // Many functions in package syscall return a count of -1 instead of 0.
  // Using fixCount(call()) instead of call() corrects the count.
  func fixCount(n int, err error) (int, error) {
  	if n < 0 {
  		n = 0
  	}
  	return n, err
  }
  
  // checkValid checks whether f is valid for use.
  // If not, it returns an appropriate error, perhaps incorporating the operation name op.
  func (f *File) checkValid(op string) error {
  	if f == nil {
  		return ErrInvalid
  	}
  	if f.fd == badFd {
  		return &PathError{op, f.name, ErrClosed}
  	}
  	return nil
  }
  

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