syncthing/lib/osutil/osutil.go

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// Copyright (C) 2014 The Syncthing Authors.
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//
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// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this file,
// You can obtain one at https://mozilla.org/MPL/2.0/.
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// Package osutil implements utilities for native OS support.
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package osutil
import (
"errors"
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"io"
"path/filepath"
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"runtime"
"strings"
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"github.com/syncthing/syncthing/lib/fs"
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"github.com/syncthing/syncthing/lib/sync"
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)
// Try to keep this entire operation atomic-like. We shouldn't be doing this
// often enough that there is any contention on this lock.
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var renameLock = sync.NewMutex()
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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(filesystem fs.Filesystem, from, to string) error {
renameLock.Lock()
defer renameLock.Unlock()
return withPreparedTarget(filesystem, from, to, func() error {
return filesystem.Rename(from, to)
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})
}
// Rename moves a temporary file to its final place.
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// Will make sure to delete the from file if the operation fails, so use only
// for situations like committing a temp file to its final location.
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// Tries hard to succeed on various systems by temporarily tweaking directory
// permissions and removing the destination file when necessary.
func Rename(filesystem fs.Filesystem, from, to string) error {
// Don't leave a dangling temp file in case of rename error
if !(runtime.GOOS == "windows" && strings.EqualFold(from, to)) {
defer filesystem.Remove(from)
}
return TryRename(filesystem, from, to)
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}
// 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(filesystem fs.Filesystem, from, to string) (err error) {
return withPreparedTarget(filesystem, from, to, func() error {
return copyFileContents(filesystem, from, to)
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})
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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, fs fs.Filesystem, path string) error {
dir := filepath.Dir(path)
info, err := fs.Stat(dir)
if err != nil {
return err
}
if !info.IsDir() {
return errors.New("Not a directory: " + path)
}
if 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 = fs.Chmod(dir, 0755)
if err == nil {
defer func() {
err = fs.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)
}
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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(filesystem fs.Filesystem, from, to string, f func() error) error {
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// Make sure the destination directory is writeable
toDir := filepath.Dir(to)
if info, err := filesystem.Stat(toDir); err == nil && info.IsDir() && info.Mode()&0200 == 0 {
filesystem.Chmod(toDir, 0755)
defer filesystem.Chmod(toDir, info.Mode())
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}
// On Windows, make sure the destination file is writeable (or we can't delete it)
if runtime.GOOS == "windows" {
filesystem.Chmod(to, 0666)
if !strings.EqualFold(from, to) {
err := filesystem.Remove(to)
if err != nil && !fs.IsNotExist(err) {
return err
}
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}
}
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 its contents will be replaced by the contents
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// of the source file.
func copyFileContents(filesystem fs.Filesystem, src, dst string) (err error) {
in, err := filesystem.Open(src)
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if err != nil {
return
}
defer in.Close()
out, err := filesystem.Create(dst)
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if err != nil {
return
}
defer func() {
cerr := out.Close()
if err == nil {
err = cerr
}
}()
_, err = io.Copy(out, in)
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return
}
func IsDeleted(ffs fs.Filesystem, name string) bool {
if _, err := ffs.Lstat(name); fs.IsNotExist(err) {
return true
}
switch TraversesSymlink(ffs, filepath.Dir(name)).(type) {
case *NotADirectoryError, *TraversesSymlinkError:
return true
}
return false
}