mv internal lib

lib/osutil/atomic.go

@@ -0,0 +1,101 @@
+// Copyright (C) 2015 The Syncthing Authors.
+//
+// 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 http://mozilla.org/MPL/2.0/.
+
+package osutil
+
+import (
+	"errors"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"runtime"
+)
+
+var (
+	ErrClosed  = errors.New("write to closed writer")
+	TempPrefix = ".syncthing.tmp."
+)
+
+// An AtomicWriter is an *os.File that writes to a temporary file in the same
+// directory as the final path. On successfull Close the file is renamed to
+// it's final path. Any error on Write or during Close is accumulated and
+// returned on Close, so a lazy user can ignore errors until Close.
+type AtomicWriter struct {
+	path string
+	next *os.File
+	err  error
+}
+
+// CreateAtomic is like os.Create with a FileMode, except a temporary file
+// name is used instead of the given name.
+func CreateAtomic(path string, mode os.FileMode) (*AtomicWriter, error) {
+	fd, err := ioutil.TempFile(filepath.Dir(path), TempPrefix)
+	if err != nil {
+		return nil, err
+	}
+
+	if err := os.Chmod(fd.Name(), mode); err != nil {
+		fd.Close()
+		os.Remove(fd.Name())
+		return nil, err
+	}
+
+	w := &AtomicWriter{
+		path: path,
+		next: fd,
+	}
+
+	return w, nil
+}
+
+// Write is like io.Writer, but is a no-op on an already failed AtomicWriter.
+func (w *AtomicWriter) Write(bs []byte) (int, error) {
+	if w.err != nil {
+		return 0, w.err
+	}
+	n, err := w.next.Write(bs)
+	if err != nil {
+		w.err = err
+		w.next.Close()
+	}
+	return n, err
+}
+
+// Close closes the temporary file and renames it to the final path. It is
+// invalid to call Write() or Close() after Close().
+func (w *AtomicWriter) Close() error {
+	if w.err != nil {
+		return w.err
+	}
+
+	// Try to not leave temp file around, but ignore error.
+	defer os.Remove(w.next.Name())
+
+	if err := w.next.Close(); err != nil {
+		w.err = err
+		return err
+	}
+
+	// Remove the destination file, on Windows only. If it fails, and not due
+	// to the file not existing, we won't be able to complete the rename
+	// either. Return this error because it may be more informative. On non-
+	// Windows we want the atomic rename behavior so we don't attempt remove.
+	if runtime.GOOS == "windows" {
+		if err := os.Remove(w.path); err != nil && !os.IsNotExist(err) {
+			return err
+		}
+	}
+
+	if err := os.Rename(w.next.Name(), w.path); err != nil {
+		w.err = err
+		return err
+	}
+
+	// Set w.err to return appropriately for any future operations.
+	w.err = ErrClosed
+
+	return nil
+}