code: function encode() {
    var data = this.data;
    var length = 11;
    var sender = this.sender;
    var target = this.target;
    var header = new Buffer(9);
    var content = !data || isBuffer(data) ? data : this.encode(data);
  
    if (content) length += content.length;
  
    header.writeUInt8(length, 0);
    header.writeUInt8(sender.subnet, 1);
    header.writeUInt8(sender.id, 2);
    header.writeUInt16BE(sender.type, 3);
    header.writeUInt16BE(this.code, 5);
    header.writeUInt8(target.subnet, 7);
    header.writeUInt8(target.id, 8);
  
    return content ? Buffer.concat([header, content]) : header;
  }
docs: Return compiled command message
  
  @param  {Object|Buffer} data
  @return {Buffer}