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moby--moby/pkg/ioutils/fswriters.go

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package ioutils // import "github.com/docker/docker/pkg/ioutils"
import (
"io"
"io/ioutil"
"os"
"path/filepath"
)
// NewAtomicFileWriter returns WriteCloser so that writing to it writes to a
// temporary file and closing it atomically changes the temporary file to
// destination path. Writing and closing concurrently is not allowed.
func NewAtomicFileWriter(filename string, perm os.FileMode) (io.WriteCloser, error) {
f, err := ioutil.TempFile(filepath.Dir(filename), ".tmp-"+filepath.Base(filename))
if err != nil {
return nil, err
}
abspath, err := filepath.Abs(filename)
if err != nil {
return nil, err
}
return &atomicFileWriter{
f: f,
fn: abspath,
perm: perm,
}, nil
}
// AtomicWriteFile atomically writes data to a file named by filename.
func AtomicWriteFile(filename string, data []byte, perm os.FileMode) error {
f, err := NewAtomicFileWriter(filename, perm)
if err != nil {
return err
}
n, err := f.Write(data)
if err == nil && n < len(data) {
err = io.ErrShortWrite
f.(*atomicFileWriter).writeErr = err
}
if err1 := f.Close(); err == nil {
err = err1
}
return err
}
type atomicFileWriter struct {
f *os.File
fn string
writeErr error
perm os.FileMode
}
func (w *atomicFileWriter) Write(dt []byte) (int, error) {
n, err := w.f.Write(dt)
if err != nil {
w.writeErr = err
}
return n, err
}
func (w *atomicFileWriter) Close() (retErr error) {
defer func() {
if retErr != nil || w.writeErr != nil {
os.Remove(w.f.Name())
}
}()
if err := w.f.Sync(); err != nil {
w.f.Close()
return err
}
if err := w.f.Close(); err != nil {
return err
}
if err := os.Chmod(w.f.Name(), w.perm); err != nil {
return err
}
if w.writeErr == nil {
return os.Rename(w.f.Name(), w.fn)
}
return nil
}
// AtomicWriteSet is used to atomically write a set
// of files and ensure they are visible at the same time.
// Must be committed to a new directory.
type AtomicWriteSet struct {
root string
}
// NewAtomicWriteSet creates a new atomic write set to
// atomically create a set of files. The given directory
// is used as the base directory for storing files before
// commit. If no temporary directory is given the system
// default is used.
func NewAtomicWriteSet(tmpDir string) (*AtomicWriteSet, error) {
td, err := ioutil.TempDir(tmpDir, "write-set-")
if err != nil {
return nil, err
}
return &AtomicWriteSet{
root: td,
}, nil
}
// WriteFile writes a file to the set, guaranteeing the file
// has been synced.
func (ws *AtomicWriteSet) WriteFile(filename string, data []byte, perm os.FileMode) error {
f, err := ws.FileWriter(filename, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, perm)
if err != nil {
return err
}
n, err := f.Write(data)
if err == nil && n < len(data) {
err = io.ErrShortWrite
}
if err1 := f.Close(); err == nil {
err = err1
}
return err
}
type syncFileCloser struct {
*os.File
}
func (w syncFileCloser) Close() error {
err := w.File.Sync()
if err1 := w.File.Close(); err == nil {
err = err1
}
return err
}
// FileWriter opens a file writer inside the set. The file
// should be synced and closed before calling commit.
func (ws *AtomicWriteSet) FileWriter(name string, flag int, perm os.FileMode) (io.WriteCloser, error) {
f, err := os.OpenFile(filepath.Join(ws.root, name), flag, perm)
if err != nil {
return nil, err
}
return syncFileCloser{f}, nil
}
// Cancel cancels the set and removes all temporary data
// created in the set.
func (ws *AtomicWriteSet) Cancel() error {
return os.RemoveAll(ws.root)
}
// Commit moves all created files to the target directory. The
// target directory must not exist and the parent of the target
// directory must exist.
func (ws *AtomicWriteSet) Commit(target string) error {
return os.Rename(ws.root, target)
}
// String returns the location the set is writing to.
func (ws *AtomicWriteSet) String() string {
return ws.root
}