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// Copyright (c) Tailscale Inc & AUTHORS
// SPDX-License-Identifier: BSD-3-Clause
// Package atomicfile contains code related to writing to filesystems
// atomically.
//
// This package should be considered internal; its API is not stable.
package atomicfile // import "tailscale.com/atomicfile"
import (
"fmt"
"os"
"path/filepath"
"runtime"
)
// WriteFile writes data to filename+some suffix, then renames it into filename.
// The perm argument is ignored on Windows. If the target filename already
// exists but is not a regular file, WriteFile returns an error.
func WriteFile(filename string, data []byte, perm os.FileMode) (err error) {
fi, err := os.Stat(filename)
if err == nil && !fi.Mode().IsRegular() {
return fmt.Errorf("%s already exists and is not a regular file", filename)
}
f, err := os.CreateTemp(filepath.Dir(filename), filepath.Base(filename)+".tmp")
if err != nil {
return err
}
tmpName := f.Name()
defer func() {
if err != nil {
f.Close() //nolint:errcheck
os.Remove(tmpName) //nolint:errcheck
}
}()
if _, err := f.Write(data); err != nil {
return err
}
if runtime.GOOS != "windows" {
if err := f.Chmod(perm); err != nil {
return err
}
}
if err := f.Sync(); err != nil {
return err
}
if err := f.Close(); err != nil {
return err
}
return os.Rename(tmpName, filename)
}
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