syncthing/internal/osutil/osutil.go

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// Copyright (C) 2014 The Syncthing Authors.
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//
// This program is free software: you can redistribute it and/or modify it
// under the terms of the GNU General Public License as published by the Free
// Software Foundation, either version 3 of the License, or (at your option)
// any later version.
//
// This program is distributed in the hope that it will be useful, but WITHOUT
// ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
// FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
// more details.
//
// You should have received a copy of the GNU General Public License along
// with this program. If not, see <http://www.gnu.org/licenses/>.
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// Package osutil implements utilities for native OS support.
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package osutil
import (
"errors"
"fmt"
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"io"
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"os"
"path/filepath"
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"runtime"
"strings"
"sync"
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)
var ErrNoHome = errors.New("No home directory found - set $HOME (or the platform equivalent).")
// 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
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// TryRename renames a file, leaving source file intact in case of failure.
// Tries hard to succeed on various systems by temporarily tweaking directory
// permissions and removing the destination file when necessary.
func TryRename(from, to string) error {
renameLock.Lock()
defer renameLock.Unlock()
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return withPreparedTarget(to, func() error {
return os.Rename(from, to)
})
}
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// Rename moves a temporary file to it's final place.
// 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.
// Tries hard to succeed on various systems by temporarily tweaking directory
// permissions and removing the destination file when necessary.
func Rename(from, to string) error {
// Don't leave a dangling temp file in case of rename error
defer os.Remove(from)
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return TryRename(from, to)
}
// Copy copies the file content from source to destination.
// Tries hard to succeed on various systems by temporarily tweaking directory
// permissions and removing the destination file when necessary.
func Copy(from, to string) (err error) {
return withPreparedTarget(to, func() error {
return copyFileContents(from, to)
})
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}
// 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()&0200 == 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)
}
func ExpandTilde(path string) (string, error) {
if path == "~" {
return getHomeDir()
}
path = filepath.FromSlash(path)
if !strings.HasPrefix(path, fmt.Sprintf("~%c", os.PathSeparator)) {
return path, nil
}
home, err := getHomeDir()
if err != nil {
return "", err
}
return filepath.Join(home, path[2:]), nil
}
func getHomeDir() (string, error) {
var home string
switch runtime.GOOS {
case "windows":
home = filepath.Join(os.Getenv("HomeDrive"), os.Getenv("HomePath"))
if home == "" {
home = os.Getenv("UserProfile")
}
default:
home = os.Getenv("HOME")
}
if home == "" {
return "", ErrNoHome
}
return home, nil
}
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// Tries hard to succeed on various systems by temporarily tweaking directory
// permissions and removing the destination file when necessary.
func withPreparedTarget(to string, f func() error) error {
// Make sure the destination directory is writeable
toDir := filepath.Dir(to)
if info, err := os.Stat(toDir); err == nil && info.IsDir() && info.Mode()&0200 == 0 {
os.Chmod(toDir, 0755)
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
}
}
return f()
}
// copyFileContents copies the contents of the file named src to the file named
// by dst. The file will be created if it does not already exist. If the
// destination file exists, all it's contents will be replaced by the contents
// of the source file.
func copyFileContents(src, dst string) (err error) {
in, err := os.Open(src)
if err != nil {
return
}
defer in.Close()
out, err := os.Create(dst)
if err != nil {
return
}
defer func() {
cerr := out.Close()
if err == nil {
err = cerr
}
}()
if _, err = io.Copy(out, in); err != nil {
return
}
err = out.Sync()
return
}