// This allows another goroutine to close the reader.
	pr.mu.Lock()
	defer pr.mu.Unlock()
	if pr.rc == nil {
		return 0, io.EOF
	}
	return pr.rc.Read(p)
}

func (pr *syncReadCloser) Close() error {
	pr.mu.Lock()
	defer pr.mu.Unlock()
	if pr.rc != nil {
		err := pr.rc.Close()
		pr.rc = nil
		return err
	}
	return nil