Update vendor

vendor/github.com/google/renameio/tempfile.go

@@ -0,0 +1,183 @@
+// Copyright 2018 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// +build !windows
+
+package renameio
+
+import (
+	"io/ioutil"
+	"os"
+	"path/filepath"
+)
+
+// TempDir checks whether os.TempDir() can be used as a temporary directory for
+// later atomically replacing files within dest. If no (os.TempDir() resides on
+// a different mount point), dest is returned.
+//
+// Note that the returned value ceases to be valid once either os.TempDir()
+// changes (e.g. on Linux, once the TMPDIR environment variable changes) or the
+// file system is unmounted.
+func TempDir(dest string) string {
+	return tempDir("", filepath.Join(dest, "renameio-TempDir"))
+}
+
+func tempDir(dir, dest string) string {
+	if dir != "" {
+		return dir // caller-specified directory always wins
+	}
+
+	// Chose the destination directory as temporary directory so that we
+	// definitely can rename the file, for which both temporary and destination
+	// file need to point to the same mount point.
+	fallback := filepath.Dir(dest)
+
+	// The user might have overridden the os.TempDir() return value by setting
+	// the TMPDIR environment variable.
+	tmpdir := os.TempDir()
+
+	testsrc, err := ioutil.TempFile(tmpdir, "."+filepath.Base(dest))
+	if err != nil {
+		return fallback
+	}
+	cleanup := true
+	defer func() {
+		if cleanup {
+			os.Remove(testsrc.Name())
+		}
+	}()
+	testsrc.Close()
+
+	testdest, err := ioutil.TempFile(filepath.Dir(dest), "."+filepath.Base(dest))
+	if err != nil {
+		return fallback
+	}
+	defer os.Remove(testdest.Name())
+	testdest.Close()
+
+	if err := os.Rename(testsrc.Name(), testdest.Name()); err != nil {
+		return fallback
+	}
+	cleanup = false // testsrc no longer exists
+	return tmpdir
+}
+
+// PendingFile is a pending temporary file, waiting to replace the destination
+// path in a call to CloseAtomicallyReplace.
+type PendingFile struct {
+	*os.File
+
+	path   string
+	done   bool
+	closed bool
+}
+
+// Cleanup is a no-op if CloseAtomicallyReplace succeeded, and otherwise closes
+// and removes the temporary file.
+func (t *PendingFile) Cleanup() error {
+	if t.done {
+		return nil
+	}
+	// An error occurred. Close and remove the tempfile. Errors are returned for
+	// reporting, there is nothing the caller can recover here.
+	var closeErr error
+	if !t.closed {
+		closeErr = t.Close()
+	}
+	if err := os.Remove(t.Name()); err != nil {
+		return err
+	}
+	return closeErr
+}
+
+// CloseAtomicallyReplace closes the temporary file and atomically replaces
+// the destination file with it, i.e., a concurrent open(2) call will either
+// open the file previously located at the destination path (if any), or the
+// just written file, but the file will always be present.
+func (t *PendingFile) CloseAtomicallyReplace() error {
+	// Even on an ordered file system (e.g. ext4 with data=ordered) or file
+	// systems with write barriers, we cannot skip the fsync(2) call as per
+	// Theodore Ts'o (ext2/3/4 lead developer):
+	//
+	// > data=ordered only guarantees the avoidance of stale data (e.g., the previous
+	// > contents of a data block showing up after a crash, where the previous data
+	// > could be someone's love letters, medical records, etc.). Without the fsync(2)
+	// > a zero-length file is a valid and possible outcome after the rename.
+	if err := t.Sync(); err != nil {
+		return err
+	}
+	t.closed = true
+	if err := t.Close(); err != nil {
+		return err
+	}
+	if err := os.Rename(t.Name(), t.path); err != nil {
+		return err
+	}
+	t.done = true
+	return nil
+}
+
+// TempFile wraps ioutil.TempFile for the use case of atomically creating or
+// replacing the destination file at path.
+//
+// If dir is the empty string, TempDir(filepath.Base(path)) is used. If you are
+// going to write a large number of files to the same file system, store the
+// result of TempDir(filepath.Base(path)) and pass it instead of the empty
+// string.
+//
+// The file's permissions will be 0600 by default. You can change these by
+// explicitly calling Chmod on the returned PendingFile.
+func TempFile(dir, path string) (*PendingFile, error) {
+	f, err := ioutil.TempFile(tempDir(dir, path), "."+filepath.Base(path))
+	if err != nil {
+		return nil, err
+	}
+
+	return &PendingFile{File: f, path: path}, nil
+}
+
+// Symlink wraps os.Symlink, replacing an existing symlink with the same name
+// atomically (os.Symlink fails when newname already exists, at least on Linux).
+func Symlink(oldname, newname string) error {
+	// Fast path: if newname does not exist yet, we can skip the whole dance
+	// below.
+	if err := os.Symlink(oldname, newname); err == nil || !os.IsExist(err) {
+		return err
+	}
+
+	// We need to use ioutil.TempDir, as we cannot overwrite a ioutil.TempFile,
+	// and removing+symlinking creates a TOCTOU race.
+	d, err := ioutil.TempDir(filepath.Dir(newname), "."+filepath.Base(newname))
+	if err != nil {
+		return err
+	}
+	cleanup := true
+	defer func() {
+		if cleanup {
+			os.RemoveAll(d)
+		}
+	}()
+
+	symlink := filepath.Join(d, "tmp.symlink")
+	if err := os.Symlink(oldname, symlink); err != nil {
+		return err
+	}
+
+	if err := os.Rename(symlink, newname); err != nil {
+		return err
+	}
+
+	cleanup = false
+	return os.RemoveAll(d)
+}