syncthing/internal/osutil/osutil.go
2014-09-28 01:54:25 +02:00

73 lines
2.2 KiB
Go

// Copyright (C) 2014 Jakob Borg and Contributors (see the CONTRIBUTORS file).
// All rights reserved. Use of this source code is governed by an MIT-style
// license that can be found in the LICENSE file.
// Package osutil implements utilities for native OS support.
package osutil
import (
"os"
"path/filepath"
"runtime"
"sync"
)
// Try to keep this entire operation atomic-like. We shouldn't be doing this
// often enough that there is any contention on this lock.
var renameLock sync.Mutex
// Rename renames a file, while trying hard to succeed on various systems by
// temporarily tweaking directory permissions and removing the destination
// file when necessary. Will make sure to delete the from file if the
// operation fails, so use only for situations like committing a temp file to
// it's final location.
func Rename(from, to string) error {
renameLock.Lock()
defer renameLock.Unlock()
// Make sure the destination directory is writeable
toDir := filepath.Dir(to)
if info, err := os.Stat(toDir); err == nil {
os.Chmod(toDir, 0777)
defer os.Chmod(toDir, info.Mode())
}
// On Windows, make sure the destination file is writeable (or we can't delete it)
if runtime.GOOS == "windows" {
os.Chmod(to, 0666)
err := os.Remove(to)
if err != nil && !os.IsNotExist(err) {
return err
}
}
// Don't leave a dangling temp file in case of rename error
defer os.Remove(from)
return os.Rename(from, to)
}
// InWritableDir calls fn(path), while making sure that the directory
// containing `path` is writable for the duration of the call.
func InWritableDir(fn func(string) error, path string) error {
dir := filepath.Dir(path)
if info, err := os.Stat(dir); err == nil && info.IsDir() && info.Mode()&04 == 0 {
// A non-writeable directory (for this user; we assume that's the
// relevant part). Temporarily change the mode so we can delete the
// file or directory inside it.
err = os.Chmod(dir, 0755)
if err == nil {
defer func() {
err = os.Chmod(dir, info.Mode())
if err != nil {
// We managed to change the permission bits like a
// millisecond ago, so it'd be bizarre if we couldn't
// change it back.
panic(err)
}
}()
}
}
return fn(path)
}