package ioutils // import "github.com/docker/docker/pkg/ioutils" import ( "io" "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 := os.CreateTemp(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 := os.MkdirTemp(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 }