docker/swarmkit

package ioutils

import (
    "io"
    "os"
    "path/filepath"
)

// todo: split docker/pkg/ioutils into a separate repo

// AtomicWriteFile atomically writes data to a file specified by filename.
func AtomicWriteFile(filename string, data []byte, perm os.FileMode) error {
    f, err := os.CreateTemp(filepath.Dir(filename), ".tmp-"+filepath.Base(filename))
    if err != nil {
        return err
    }
    err = os.Chmod(f.Name(), perm)
    if err != nil {
        f.Close()
        return err
    }
    n, err := f.Write(data)
    if err == nil && n < len(data) {
        f.Close()
        return io.ErrShortWrite
    }
    if err != nil {
        f.Close()
        return err
    }
    if err := f.Sync(); err != nil {
        f.Close()
        return err
    }
    if err := f.Close(); err != nil {
        return err
    }
    return os.Rename(f.Name(), filename)
}