code: func (w *lengthDelimitedFrameWriter) Write(data []byte) (int, error) {
  	binary.BigEndian.PutUint32(w.h[:], uint32(len(data)))
  	n, err := w.w.Write(w.h[:])
  	if err != nil {
  		return 0, err
  	}
  	if n != len(w.h) {
  		return 0, io.ErrShortWrite
  	}
  	return w.w.Write(data)
  }
docs: // Write writes a single frame to the nested writer, prepending it with the length in
  // in bytes of data (as a 4 byte, bigendian uint32).