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// 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.
// +build aix darwin dragonfly freebsd js,wasm linux netbsd openbsd solaris
package os
import (
// fixLongPath is a noop on non-Windows platforms.
func fixLongPath(path string) string {
return path
func rename(oldname, newname string) error {
fi, err := Lstat(newname)
if err == nil && fi.IsDir() {
// There are two independent errors this function can return:
// one for a bad oldname, and one for a bad newname.
// At this point we've determined the newname is bad.
// But just in case oldname is also bad, prioritize returning
// the oldname error because that's what we did historically.
// However, if the old name and new name are not the same, yet
// they refer to the same file, it implies a case-only
// rename on a case-insensitive filesystem, which is ok.
if ofi, err := Lstat(oldname); err != nil {
if pe, ok := err.(*PathError); ok {
err = pe.Err
return &LinkError{"rename", oldname, newname, err}
} else if newname == oldname || !SameFile(fi, ofi) {
return &LinkError{"rename", oldname, newname, syscall.EEXIST}
err = syscall.Rename(oldname, newname)
if err != nil {
return &LinkError{"rename", oldname, newname, err}
return nil
// file is the real representation of *File.
// The extra level of indirection ensures that no clients of os
// can overwrite this data, which could cause the finalizer
// to close the wrong file descriptor.
type file struct {
pfd poll.FD
name string
dirinfo *dirInfo // nil unless directory being read
nonblock bool // whether we set nonblocking mode
stdoutOrErr bool // whether this is stdout or stderr
appendMode bool // whether file is opened for appending
// Fd returns the integer Unix file descriptor referencing the open file.
// The file descriptor is valid only until f.Close is called or f is garbage collected.
// On Unix systems this will cause the SetDeadline methods to stop working.
func (f *File) Fd() uintptr {
if f == nil {
return ^(uintptr(0))
// If we put the file descriptor into nonblocking mode,
// then set it to blocking mode before we return it,
// because historically we have always returned a descriptor
// opened in blocking mode. The File will continue to work,
// but any blocking operation will tie up a thread.
if f.nonblock {
return uintptr(f.pfd.Sysfd)
// NewFile returns a new File with the given file descriptor and
// name. The returned value will be nil if fd is not a valid file
// descriptor. On Unix systems, if the file descriptor is in
// non-blocking mode, NewFile will attempt to return a pollable File
// (one for which the SetDeadline methods work).
func NewFile(fd uintptr, name string) *File {
kind := kindNewFile
if nb, err := unix.IsNonblock(int(fd)); err == nil && nb {
kind = kindNonBlock
return newFile(fd, name, kind)
// newFileKind describes the kind of file to newFile.
type newFileKind int
const (
kindNewFile newFileKind = iota
// newFile is like NewFile, but if called from OpenFile or Pipe
// (as passed in the kind parameter) it tries to add the file to
// the runtime poller.
func newFile(fd uintptr, name string, kind newFileKind) *File {
fdi := int(fd)
if fdi < 0 {
return nil
f := &File{&file{
pfd: poll.FD{
Sysfd: fdi,
IsStream: true,
ZeroReadIsEOF: true,
name: name,
stdoutOrErr: fdi == 1 || fdi == 2,
pollable := kind == kindOpenFile || kind == kindPipe || kind == kindNonBlock
// If the caller passed a non-blocking filedes (kindNonBlock),
// we assume they know what they are doing so we allow it to be
// used with kqueue.
if kind == kindOpenFile {
switch runtime.GOOS {
case "darwin", "dragonfly", "freebsd", "netbsd", "openbsd":
var st syscall.Stat_t
err := syscall.Fstat(fdi, &st)
typ := st.Mode & syscall.S_IFMT
// Don't try to use kqueue with regular files on *BSDs.
// On FreeBSD a regular file is always
// reported as ready for writing.
// On Dragonfly, NetBSD and OpenBSD the fd is signaled
// only once as ready (both read and write).
// Issue 19093.
// Also don't add directories to the netpoller.
if err == nil && (typ == syscall.S_IFREG || typ == syscall.S_IFDIR) {
pollable = false
// In addition to the behavior described above for regular files,
// on Darwin, kqueue does not work properly with fifos:
// closing the last writer does not cause a kqueue event
// for any readers. See issue #24164.
if runtime.GOOS == "darwin" && typ == syscall.S_IFIFO {
pollable = false
if err := f.pfd.Init("file", pollable); err != nil {
// An error here indicates a failure to register
// with the netpoll system. That can happen for
// a file descriptor that is not supported by
// epoll/kqueue; for example, disk files on
// GNU/Linux systems. We assume that any real error
// will show up in later I/O.
} else if pollable {
// We successfully registered with netpoll, so put
// the file into nonblocking mode.
if err := syscall.SetNonblock(fdi, true); err == nil {
f.nonblock = true
runtime.SetFinalizer(f.file, (*file).close)
return f
// epipecheck raises SIGPIPE if we get an EPIPE error on standard
// output or standard error. See the SIGPIPE docs in os/signal, and
// issue 11845.
func epipecheck(file *File, e error) {
if e == syscall.EPIPE && file.stdoutOrErr {
// DevNull is the name of the operating system's ``null device.''
// On Unix-like systems, it is "/dev/null"; on Windows, "NUL".
const DevNull = "/dev/null"
// openFileNolog is the Unix implementation of OpenFile.
// Changes here should be reflected in openFdAt, if relevant.
func openFileNolog(name string, flag int, perm FileMode) (*File, error) {
setSticky := false
if !supportsCreateWithStickyBit && flag&O_CREATE != 0 && perm&ModeSticky != 0 {
if _, err := Stat(name); IsNotExist(err) {
setSticky = true
var r int
for {
var e error
r, e = syscall.Open(name, flag|syscall.O_CLOEXEC, syscallMode(perm))
if e == nil {
// On OS X, sigaction(2) doesn't guarantee that SA_RESTART will cause
// open(2) to be restarted for regular files. This is easy to reproduce on
// fuse file systems (see
if runtime.GOOS == "darwin" && e == syscall.EINTR {
return nil, &PathError{"open", name, e}
// open(2) itself won't handle the sticky bit on *BSD and Solaris
if setSticky {
// There's a race here with fork/exec, which we are
// content to live with. See ../syscall/exec_unix.go.
if !supportsCloseOnExec {
return newFile(uintptr(r), name, kindOpenFile), nil
// Close closes the File, rendering it unusable for I/O.
// On files that support SetDeadline, any pending I/O operations will
// be canceled and return immediately with an error.
// Close will return an error if it has already been called.
func (f *File) Close() error {
if f == nil {
return ErrInvalid
return f.file.close()
func (file *file) close() error {
if file == nil {
return syscall.EINVAL
if file.dirinfo != nil {
var err error
if e := file.pfd.Close(); e != nil {
if e == poll.ErrFileClosing {
e = ErrClosed
err = &PathError{"close",, e}
// no need for a finalizer anymore
runtime.SetFinalizer(file, nil)
return err
// read reads up to len(b) bytes from the File.
// It returns the number of bytes read and an error, if any.
func (f *File) read(b []byte) (n int, err error) {
n, err = f.pfd.Read(b)
return n, err
// pread reads len(b) bytes from the File starting at byte offset off.
// It returns the number of bytes read and the error, if any.
// EOF is signaled by a zero count with err set to nil.
func (f *File) pread(b []byte, off int64) (n int, err error) {
n, err = f.pfd.Pread(b, off)
return n, err
// write writes len(b) bytes to the File.
// It returns the number of bytes written and an error, if any.
func (f *File) write(b []byte) (n int, err error) {
n, err = f.pfd.Write(b)
return n, err
// pwrite writes len(b) bytes to the File starting at byte offset off.
// It returns the number of bytes written and an error, if any.
func (f *File) pwrite(b []byte, off int64) (n int, err error) {
n, err = f.pfd.Pwrite(b, off)
return n, err
// 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.
func (f *File) seek(offset int64, whence int) (ret int64, err error) {
ret, err = f.pfd.Seek(offset, whence)
return ret, err
// Truncate changes the size of the named file.
// If the file is a symbolic link, it changes the size of the link's target.
// If there is an error, it will be of type *PathError.
func Truncate(name string, size int64) error {
if e := syscall.Truncate(name, size); e != nil {
return &PathError{"truncate", name, e}
return nil
// Remove removes the named file or (empty) directory.
// If there is an error, it will be of type *PathError.
func Remove(name string) error {
// System call interface forces us to know
// whether name is a file or directory.
// Try both: it is cheaper on average than
// doing a Stat plus the right one.
e := syscall.Unlink(name)
if e == nil {
return nil
e1 := syscall.Rmdir(name)
if e1 == nil {
return nil
// Both failed: figure out which error to return.
// OS X and Linux differ on whether unlink(dir)
// returns EISDIR, so can't use that. However,
// both agree that rmdir(file) returns ENOTDIR,
// so we can use that to decide which error is real.
// Rmdir might also return ENOTDIR if given a bad
// file path, like /etc/passwd/foo, but in that case,
// both errors will be ENOTDIR, so it's okay to
// use the error from unlink.
if e1 != syscall.ENOTDIR {
e = e1
return &PathError{"remove", name, e}
func tempDir() string {
dir := Getenv("TMPDIR")
if dir == "" {
if runtime.GOOS == "android" {
dir = "/data/local/tmp"
} else {
dir = "/tmp"
return dir
// Link creates newname as a hard link to the oldname file.
// If there is an error, it will be of type *LinkError.
func Link(oldname, newname string) error {
e := syscall.Link(oldname, newname)
if e != nil {
return &LinkError{"link", oldname, newname, e}
return nil
// Symlink creates newname as a symbolic link to oldname.
// If there is an error, it will be of type *LinkError.
func Symlink(oldname, newname string) error {
e := syscall.Symlink(oldname, newname)
if e != nil {
return &LinkError{"symlink", oldname, newname, e}
return nil
func (f *File) readdir(n int) (fi []FileInfo, err error) {
dirname :=
if dirname == "" {
dirname = "."
names, err := f.Readdirnames(n)
fi = make([]FileInfo, 0, len(names))
for _, filename := range names {
fip, lerr := lstat(dirname + "/" + filename)
if IsNotExist(lerr) {
// File disappeared between readdir + stat.
// Just treat it as if it didn't exist.
if lerr != nil {
return fi, lerr
fi = append(fi, fip)
if len(fi) == 0 && err == nil && n > 0 {
// Per File.Readdir, the slice must be non-empty or err
// must be non-nil if n > 0.
err = io.EOF
return fi, err
// Readlink returns the destination of the named symbolic link.
// If there is an error, it will be of type *PathError.
func Readlink(name string) (string, error) {
for len := 128; ; len *= 2 {
b := make([]byte, len)
n, e := fixCount(syscall.Readlink(name, b))
// buffer too small
if runtime.GOOS == "aix" && e == syscall.ERANGE {
if e != nil {
return "", &PathError{"readlink", name, e}
if n < len {
return string(b[0:n]), nil