（六）分布式通信----MessagePack序列化

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1. .Net Core的序列化方式

1.1 json.Net

常用的工具包，如Newtonsoft.Json， 它是基于json格式的序列化和反序列化的组件

json.net 有以下优点：

       侵入性：可以不添加attribute,就能进行序列化操作

       灵活性：可以灵活性配置，比如允许被序列化的成员自定义名字，屏蔽的非序列化属性成员

       可读性： 数据格式比较简单, 易于读写

       依赖性：可以序列化成JObject，无需依赖对象进行序列化和泛型化。

1.2 protobuf

它是基于二进制格式的序列化和反序列化的组件

protobuf 有以下优点：

  　  性能高 ： 序列化后体积相比Json和XML很小，适合RPC二进制传输
　　 跨语言：支持跨平台多语言
        兼容性：消息格式升级和兼容性还不错
        速度快 ：序列化反序列化速度很快，快于Json的处理速度

1.3 messagepack

它是基于二进制格式的序列化和反序列化的组件

messagepack有以下优点：

  　   性能高：序列化后体积相比Json和XML很小，适合RPC二进制传输
　　 跨语言：支持跨平台多语言
        兼容性：消息格式升级和兼容性还不错
        速度快 ：序列化反序列化速度很快，快于Json的处理速度

messagepack不管是小数据量还是大数据量都保持比较稳定的性能，本文中使用messagepack序列化方式。

2. 项目编码及设计模式

 如下是文件结构：

2.1 工厂模式

抽象接口  工厂负责创建编码器和解码器

1.工厂

    /// <summary>
    /// 一个抽象的传输消息编解码器工厂。
    /// </summary>
    public interface ITransportMessageCodecFactory
    {
        /// <summary>
        /// 获取编码器。
        /// </summary>
        /// <returns>编码器实例。</returns>
        ITransportMessageEncoder GetEncoder();

        /// <summary>
        /// 获取解码器。
        /// </summary>
        /// <returns>解码器实例。</returns>
        ITransportMessageDecoder GetDecoder();
    }

 2.编码器

    /// <summary>
    /// 编码器
    /// </summary>
    public interface ITransportMessageEncoder
    {
        byte[] Encode(TransportMessage message);
    }

 3.解码器

    /// <summary>
    /// 解码器
    /// </summary>
    public interface ITransportMessageDecoder
    {
        TransportMessage Decode(byte[] data);
    }

实现类  工厂、编码器、解码器为MessagePack的实现

1.工厂

　　 public sealed class MessagePackTransportMessageCodecFactory : ITransportMessageCodecFactory
    {
        #region Field
        private readonly ITransportMessageEncoder _transportMessageEncoder = new MessagePackTransportMessageEncoder();
        private readonly ITransportMessageDecoder _transportMessageDecoder = new MessagePackTransportMessageDecoder();
        #endregion Field

        #region Implementation of ITransportMessageCodecFactory

        /// <inheritdoc />
        /// <summary>
        /// 获取编码器 
        /// </summary>
        /// <returns></returns>
        public ITransportMessageEncoder GetEncoder()
        {
            return _transportMessageEncoder;
        }

        /// <inheritdoc />
        /// <summary>
        /// 获取解码器 
        /// </summary>
        /// <returns></returns>
        public ITransportMessageDecoder GetDecoder()
        {
            return _transportMessageDecoder;
        }
        #endregion Implementation of ITransportMessageCodecFactory
    }

 2.编码器

    public sealed class MessagePackTransportMessageEncoder : ITransportMessageEncoder
    {
        #region Implementation of ITransportMessageEncoder

        public byte[] Encode(TransportMessage transportMessage)
        {
            MessagePackTransportMessage messagePackTransportMessage = new MessagePackTransportMessage(transportMessage);
            return MessagePackSerializer.Serialize(messagePackTransportMessage);
        }
        
        #endregion Implementation of ITransportMessageEncoder
    }

 3.解码器

    public sealed class MessagePackTransportMessageDecoder : ITransportMessageDecoder
    {
        #region Implementation of ITransportMessageDecoder

        public TransportMessage Decode(byte[] data)
        {
            MessagePackTransportMessage messagePackTransportMessage = MessagePackSerializer.Deserialize<MessagePackTransportMessage>(data);
            return messagePackTransportMessage.GetTransportMessage();
        }

        #endregion Implementation of ITransportMessageDecoder
    }

2.2 装饰器模式

高层的消息模型：

    public class TransportMessage
    {
        /// <summary>
        /// 消息Id。
        /// </summary>
        public string Id { get; set; }

        /// <summary>
        /// 消息内容。
        /// </summary>
        public object Content { get; set; }

        /// <summary>
        /// 内容类型。
        /// </summary>
        public string ContentType { get; set; }
    }

 由于MessagePack序列化方式具有侵入性，需要添加 MessagePackObjectAttribute 和 KeyAttribute 特性，因此需要对 TransportMessage 做装饰：

using MessagePack;

    [MessagePackObject]
    public class MessagePackTransportMessage
    {
        private TransportMessage _transportMessage;
        public MessagePackTransportMessage(): this(new TransportMessage())
        {
        }

        public MessagePackTransportMessage(TransportMessage transportMessage)
        {
            this._transportMessage = transportMessage;
        }

        public TransportMessage GetTransportMessage()
        {
            return _transportMessage;
        }
        /// <summary>
        /// 消息Id。
        /// </summary>
        [Key(0)]
        public string Id
        {
            get { return _transportMessage.Id; }
            set { _transportMessage.Id = value; }
        }

        /// <summary>
        /// 消息内容。
        /// </summary>
        [Key(1)]
        public object Content
        {
            get { return _transportMessage.Content; }
            set { _transportMessage.Content = value; }
        }

        /// <summary>
        /// 内容类型。
        /// </summary>
        [Key(2)]
        public string ContentType
        {
            get { return _transportMessage.ContentType; }
            set { _transportMessage.ContentType = value; }
        }
    }

2.3 依赖注入

 Autofac 是一个依赖注入工具包，比.net Core 原始的依赖注入拥有更完善的功能，中文官方文档：https://autofaccn.readthedocs.io/zh/latest/index.html

using Autofac;

    public static class ContainerBuilderExtensions
    {
        /// <summary>
        /// 使用messagepack编码解码方式
        /// </summary>
        /// <param name="builder"></param>
        /// <returns></returns>
        public static ContainerBuilder UseMessagePackCodec(this ContainerBuilder builder)
        {
            builder.RegisterType(typeof(MessagePackTransportMessageCodecFactory)).As(typeof(ITransportMessageCodecFactory)).SingleInstance();
            return builder;
        }
    }

 2.4 单元测试

端到端的测试，同时测试编码和解码

using MessagePack;
using Microsoft.VisualStudio.TestTools.UnitTesting;

    [TestClass]
    public class MessagePackTest
    {
        [TestMethod]
        public void TestCodec()
        {
            Person person = new Person
            {
                Name = "张宏伟",
                Age = 18
            };
            TransportMessage transportMessage = new TransportMessage
            {
                Id = "1",
                ContentType = "Person",
                Content = person
            };
            MessagePackTransportMessageCodecFactory factory = new MessagePackTransportMessageCodecFactory();
            ITransportMessageEncoder encoder = factory.GetEncoder();
            ITransportMessageDecoder decoder = factory.GetDecoder();
            byte[] vs = encoder.Encode(transportMessage);
            TransportMessage message =decoder.Decode(vs);
            Assert.AreEqual(message.Id, "1");
            Assert.AreEqual(message.ContentType, "Person");
            Assert.AreEqual(((object[])message.Content)[0].ToString(), "张宏伟" );
            Assert.AreEqual(((object[])message.Content)[1].ToString(), "18");
        }

        [MessagePackObject]
        public class Person
        {
            [Key(0)]
            public string Name { get; set; }
            [Key(1)]
            public int Age { get; set; }
        }
    }