59 lines
1.8 KiB
Go
59 lines
1.8 KiB
Go
// package atomic provides functions to atomically change files.
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package atomic
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import (
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"fmt"
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"io"
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"io/ioutil"
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"os"
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"path/filepath"
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)
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// WriteFile atomically writes the contents of r to the specified filepath. If
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// an error occurs, the target file is guaranteed to be either fully written, or
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// not written at all. WriteFile overwrites any file that exists at the
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// location (but only if the write fully succeeds, otherwise the existing file
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// is unmodified).
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func WriteFile(filename string, r io.Reader) (err error) {
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// write to a temp file first, then we'll atomically replace the target file
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// with the temp file.
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dir, file := filepath.Split(filename)
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f, err := ioutil.TempFile(dir, file)
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if err != nil {
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return fmt.Errorf("cannot create temp file: %v", err)
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}
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defer func() {
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if err != nil {
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// Don't leave the temp file lying around on error.
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_ = os.Remove(f.Name()) // yes, ignore the error, not much we can do about it.
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}
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}()
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// ensure we always close f. Note that this does not conflict with the
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// close below, as close is idempotent.
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defer f.Close()
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name := f.Name()
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if _, err := io.Copy(f, r); err != nil {
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return fmt.Errorf("cannot write data to tempfile %q: %v", name, err)
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}
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if err := f.Close(); err != nil {
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return fmt.Errorf("can't close tempfile %q: %v", name, err)
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}
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// get the file mode from the original file and use that for the replacement
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// file, too.
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info, err := os.Stat(filename)
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if os.IsNotExist(err) {
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// no original file
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} else if err != nil {
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return err
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} else {
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if err := os.Chmod(name, info.Mode()); err != nil {
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return fmt.Errorf("can't set filemode on tempfile %q: %v", name, err)
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}
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}
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if err := ReplaceFile(name, filename); err != nil {
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return fmt.Errorf("cannot replace %q with tempfile %q: %v", filename, name, err)
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}
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return nil
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}
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