94 lines
2.8 KiB
Go
94 lines
2.8 KiB
Go
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// Copyright 2018 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Package renameio writes files atomically by renaming temporary files.
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package renameio
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import (
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"bytes"
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"io"
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"math/rand"
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"os"
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"path/filepath"
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"strconv"
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"honnef.co/go/tools/internal/robustio"
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)
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const patternSuffix = ".tmp"
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// Pattern returns a glob pattern that matches the unrenamed temporary files
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// created when writing to filename.
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func Pattern(filename string) string {
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return filepath.Join(filepath.Dir(filename), filepath.Base(filename)+patternSuffix)
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}
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// WriteFile is like ioutil.WriteFile, but first writes data to an arbitrary
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// file in the same directory as filename, then renames it atomically to the
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// final name.
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//
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// That ensures that the final location, if it exists, is always a complete file.
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func WriteFile(filename string, data []byte, perm os.FileMode) (err error) {
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return WriteToFile(filename, bytes.NewReader(data), perm)
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}
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// WriteToFile is a variant of WriteFile that accepts the data as an io.Reader
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// instead of a slice.
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func WriteToFile(filename string, data io.Reader, perm os.FileMode) (err error) {
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f, err := tempFile(filepath.Dir(filename), filepath.Base(filename), perm)
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if err != nil {
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return err
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}
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defer func() {
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// Only call os.Remove on f.Name() if we failed to rename it: otherwise,
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// some other process may have created a new file with the same name after
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// that.
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if err != nil {
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f.Close()
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os.Remove(f.Name())
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}
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}()
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if _, err := io.Copy(f, data); err != nil {
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return err
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}
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// Sync the file before renaming it: otherwise, after a crash the reader may
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// observe a 0-length file instead of the actual contents.
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// See https://golang.org/issue/22397#issuecomment-380831736.
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if err := f.Sync(); err != nil {
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return err
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}
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if err := f.Close(); err != nil {
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return err
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}
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return robustio.Rename(f.Name(), filename)
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}
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// tempFile creates a new temporary file with given permission bits.
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func tempFile(dir, prefix string, perm os.FileMode) (f *os.File, err error) {
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for i := 0; i < 10000; i++ {
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name := filepath.Join(dir, prefix+strconv.Itoa(rand.Intn(1000000000))+patternSuffix)
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f, err = os.OpenFile(name, os.O_RDWR|os.O_CREATE|os.O_EXCL, perm)
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if os.IsExist(err) {
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continue
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}
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break
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}
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return
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}
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// ReadFile is like ioutil.ReadFile, but on Windows retries spurious errors that
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// may occur if the file is concurrently replaced.
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//
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// Errors are classified heuristically and retries are bounded, so even this
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// function may occasionally return a spurious error on Windows.
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// If so, the error will likely wrap one of:
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// - syscall.ERROR_ACCESS_DENIED
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// - syscall.ERROR_FILE_NOT_FOUND
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// - internal/syscall/windows.ERROR_SHARING_VIOLATION
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func ReadFile(filename string) ([]byte, error) {
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return robustio.ReadFile(filename)
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}
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