code: func sendFile(conn *wire.SyncConn, path string, mode os.FileMode, mtime time.Time) (io.WriteCloser, error) {
  	if err := conn.SendOctetString("SEND"); err != nil {
  		return nil, err
  	}
  
  	pathAndMode := encodePathAndMode(path, mode)
  	if err := conn.SendBytes(pathAndMode); err != nil {
  		return nil, err
  	}
  
  	return newSyncFileWriter(conn, mtime), nil
  }
docs: // sendFile returns a WriteCloser than will write to the file at path on device.
  // The file will be created with permissions specified by mode.
  // The file's modified time will be set to mtime, unless mtime is 0, in which case the time the writer is
  // closed will be used.