code: func (c *Client) WriteBuild(build *pb.Build) error {
  	c.assertInitialized()
  	buf, err := proto.Marshal(build)
  	if err != nil {
  		return err
  	}
  	return c.buildStream.WriteDatagram(buf)
  }
docs: // WriteBuild sends a new version of Build message to the other side
  // of the protocol, that is the host of the LUCI executable.