一、One-way MEP V.S. Responsible Service

我们知道MSMQ天生就具有异步的特性，它只能以One-way的MEP（Message Exchange Pattern）进行通信。Client和Service之间采用One-way MEP的话就意味着Client调用Service之后立即返回，它无法获得Service的执行结果，也无法捕捉Service运行的Exception。下图简单表述了基于MSMQ的WCF Service中Client和Service的交互。

但是在有些场景 中，这是无法容忍的。再拿我在上一篇文章的Order Delivery的例子来说。Client向Service提交了Order，却无法确认该Order是否被Service正确处理，这显然是不能接受的。我们今天就来讨论一下，如何创建一个Responsive Service来解决这个问题：Client不再是对Service的执行情况一无所知，它可以获知Order是否被Service正确处理了。

二、 Solution

虽然我们的目的很简单：当Client向Service递交了Order之后，能以某种方式获知Order的执行结果；对于Service端来说，在正确把Order从Message Queue中获取出来、并正确处理之后，能够向Order的递交者发送一个Acknowledge Message。为了简单起见，这个Acknowledge Message包含两组信息：

• Order No.: 被处理的Order的一个能够为一标志它的ID。
• Exception: 如果处理失败的Exception，如果成功处理为null。

要在WCF中实现这样的目的，对于Request/Reply MEP来说是简单而直接的：Client向Service递交Order，并等待Service的Response，Service在处理接收到Order之后直接将处理结果 返回给Client就可以了。但是我们说过MSMQ天生就是异步的，我们只有采取一种间接的方式实现“曲线救国”。

我们的解决方案是：在每个Client Domain也创建一个基于MSMQ的本地的WCF Service，用于接收来自Order处理端发送的Acknowledge Message。对于处理Order 的Service来说，在正确处理Order之后，想对应的Client发送Acknowledge Message。下图简单演示整个过程：

三、Implementation

了解了上面的Solution之后，我们来看看该Solution在真正实现过程中有什么样的困难。对于处理Order的Service来说，在向Client端发送Acknowledge Message的时候，它必须要知道该Order对应的Client的Response Service的MSMQ的Address以及其他和Operation相关的Context信息（在这里我们不需要，不过考虑到扩展性，我们把包括了address的Context的信息 封装到一个了Class中，在这里叫做：OrderResponseContext）。而这些Context却不能在Configuration中进行配置，因为他可以同时面临着很多个Client：比如每个Client用于接收Response 的Message Queue的address都不一样。所以这个OrderResponseContext必须通过对应的Client来提供。基于此，我们具有两面两种解决方式：

方式一、修改Service Contract，把OrderResponseContext当成是Operation的一个参数

这是我们最容易想到的，比如我们原来的Operation这样定义：

namespace Artech.ResponsiveQueuedService.Contract
{
    [ServiceContract]
    [ServiceKnownType(typeof(Order))]
    public interface IOrderProcessor
    {
        [OperationContract(IsOneWay = true)]
        void Submit(Order order);
    }
}

现在变成：

namespace Artech.ResponsiveQueuedService.Contract
{
    [ServiceContract]
    [ServiceKnownType(typeof(Order))]
    public interface IOrderProcessor
    {
        [OperationContract(IsOneWay = true)]
        void Submit(Order order, OrderResponseContext responseContext);
    }
}

虽然这种方式看起来不错，但是却不值得推荐。在一般情况下，我们的Contract需要是很稳定的，一经确定就不能轻易更改，因为Contract是被交互的多方共同支持的，牵一发动全身；此外，从Service Contract代表的是Service的一个Interface，他是对业务逻辑的抽象、和具体实现无关，而对于我们的例子来说，我们仅仅是定义一个递交Order的Operation，从业务逻辑来看，OrderResponseContext和抽象的业务逻辑毫无关系。基于此，我们需要寻求一种和Service Contract无关的解决方式：

方式二、将OrderResponseContext放到Soap Message 的Header中

其实我们要解决的问题很简单，就是要把OrderResponseContext的信息置于Soap Message中发送到Service。而我们知道，Soap的Header具有极强的可伸缩性，原则上，我们可以把任何控制信息置于Header中。基于WCF的编程模式很容易地帮助我们实现对Soap Header的插入和获取：

我们可以通过下面的方式获得当前Operation Context的Incoming Message Headers和Outgoing Message Headers

OperationContext.Current.IncomingMessageHeaders
OperationContext.Current.OutgoingMessageHeaders

如果我们要把一个OrderResponseContext 对象插入到当前Operation Context的Outgoing Message Headers中，我们可以通过下面的代码来实现：

OrderResponseContext context = new OrderResponseContext();
MessageHeader<OrderResponseContext> header = new MessageHeader<OrderResponseContext>( context);
OperationContext.Current.OutgoingMessageHeaders.Add(header.GetUntypedHeader("name", "namespace"));

相应的，我们可以通过下面的代码从Outgoing Message Headers OrderResponseContext的数据获取的内容：

OrderResponseContext context = OperationContext.Current.IncomingMessageHeaders.GetHeader<OrderResponseContext>("name", "namespace"));

四、Sample

我们照例给出一个完整的Sample，下面是整个Solution的结构：

除了一贯使用的4层结构（Contract-Service-Hosting-Client），还为ResponseService增加了下面两层：

• Localservice: 作为Client Domain的ResponseService。
• LocalHosting：Host Localservice。

1．Contract:  Artech.ResponsiveQueuedService.Contract

Service Contract: Artech.ResponsiveQueuedService.Contract. IOrderProcessor

using System;
using System.Collections.Generic;
using System.Text;
using System.ServiceModel;

namespace Artech.ResponsiveQueuedService.Contract
{
    [ServiceContract]
    [ServiceKnownType(typeof(Order))]
    public interface IOrderProcessor
    {
        [OperationContract(IsOneWay = true)]
        void Submit(Order order);
    }
}

Service Contract: Artech.ResponsiveQueuedService.Contract.IOrderRessponse

using System;
using System.Collections.Generic;
using System.Text;
using System.ServiceModel;

namespace Artech.ResponsiveQueuedService.Contract
{
    [ServiceContract]
    public interface  IOrderRessponse
    {
        [OperationContract(IsOneWay =true)]
        void SubmitOrderResponse(Guid orderNo,FaultException exception);
    }
}

接收来自Order processing端的Response：Order No.和Exception。

Data Contract: Artech.ResponsiveQueuedService.Contract.Order

using System;
using System.Collections.Generic;
using System.Text;
using System.Runtime.Serialization;

namespace Artech.ResponsiveQueuedService.Contract
{
    [DataContract]
    public class Order
    {
        Private Fields#region Private Fields
        private Guid _orderNo;
        private DateTime _orderDate;
        private Guid _supplierID;
        private string _supplierName;
        #endregion

        Constructors#region Constructors
        public Order(Guid orderNo, DateTime orderDate, Guid supplierID, string supplierName)
        {
            this._orderNo = orderNo;
            this._orderDate = orderDate;
            this._supplierID = supplierID;
            this._supplierName = supplierName;
        }

        #endregion

        Public Properties#region Public Properties
        [DataMember]
        public Guid OrderNo
        {
            get { return _orderNo; }
            set { _orderNo = value; }
        }

        [DataMember]
        public DateTime OrderDate
        {
            get { return _orderDate; }
            set { _orderDate = value; }
        }

        [DataMember]
        public Guid SupplierID
        {
            get { return _supplierID; }
            set { _supplierID = value; }
        }

        [DataMember]
        public string SupplierName
        {
            get { return _supplierName; }
            set { _supplierName = value; }
        }
        #endregion

        Public Methods#region Public Methods
        public override string ToString()
        {
            string description = string.Format("Order No./t: {0}/n/tOrder Date/t: {1}/n/tSupplier No./t: {2}/n/tSupplier Name/t: {3}", 
                this._orderNo, this._orderDate.ToString("yyyy/MM/dd"), this._supplierID, this._supplierName);
            return description;
        }
        #endregion
    }
}

对Order的封装。

Data Contract：Artech.ResponsiveQueuedService.Contract. OrderResponseContext

using System;
using System.Collections.Generic;
using System.Text;
using System.Runtime.Serialization;
using System.ServiceModel;

namespace Artech.ResponsiveQueuedService.Contract
{    
    [DataContract]
    public class OrderResponseContext
    {
        private Uri _responseAddress;

        [DataMember]
        public Uri ResponseAddress
        {
            get { return _responseAddress; }
            set { _responseAddress = value; }
        }

        public static OrderResponseContext Current
        {
            get
            {
                if (OperationContext.Current == null)
                {
                    return null;
                }

                return OperationContext.Current.IncomingMessageHeaders.GetHeader<OrderResponseContext>("OrderResponseContext", "Artech.ResponsiveQueuedService.Contract");
            }
            set
            {
                MessageHeader<OrderResponseContext> header = new MessageHeader<OrderResponseContext>(value);
                OperationContext.Current.OutgoingMessageHeaders.Add(header.GetUntypedHeader("OrderResponseContext", "Artech.ResponsiveQueuedService.Contract"));
            }
        }
    }
}

ResponseAddress代表Host在Client Domain的Response Service的Address。同过Current把OrderResponseContext插入到Outgoing Message Headers中、以及从Ingoing Message Headers取出OrderResponseContext对象。

2．Order Processing Service：Artech.ResponsiveQueuedService.Service

using System;
using System.Collections.Generic;
using System.Text;
using Artech.ResponsiveQueuedService.Contract;
using System.ServiceModel;
using System.Net.Security;

namespace Artech.ResponsiveQueuedService.Service
{
    public class OrderProcessorService:IOrderProcessor
    {
        private void ProcessOrder(Order order)
        {

            if (order.OrderDate < DateTime.Today)
            {
                throw new Exception();
            }
        }

        IOrderProcessor Members#region IOrderProcessor Members

        public void Submit(Order order)
        {
            Console.WriteLine("Begin to process the order of the order No.: {0}", order.OrderNo);
            FaultException exception= null;
            if (order.OrderDate < DateTime.Today)
            {
                exception = new FaultException(new FaultReason("The order has expried"), new FaultCode("sender"));
                Console.WriteLine("It's fail to process the order./n/tOrder No.: {0}/n/tReason:{1}", order.OrderNo, "The order has expried");
            }
            else
            {
                Console.WriteLine("It's successful to process the order./n/tOrder No.: {0}", order.OrderNo);
            }

            NetMsmqBinding binding = new NetMsmqBinding();
            binding.ExactlyOnce = false;
            binding.Security.Transport.MsmqAuthenticationMode = MsmqAuthenticationMode.None;
            binding.Security.Transport.MsmqProtectionLevel = ProtectionLevel.None;
            ChannelFactory<IOrderRessponse> channelFacotry = new ChannelFactory<IOrderRessponse>(binding);
            OrderResponseContext responseContext = OrderResponseContext.Current;
            IOrderRessponse channel = channelFacotry.CreateChannel(new EndpointAddress(responseContext.ResponseAddress));

            using (OperationContextScope contextScope = new OperationContextScope(channel as IContextChannel))
            {
                channel.SubmitOrderResponse(order.OrderNo, exception);
            }
        }
        #endregion
    }
}

在这里我们模拟了这样的场景：先通过Order Date判断Order是否过期，如果过期创建一个FaultException，否则正确处理该Order，然后通过OrderResponseContext.Current从Incoming Message Header中获取封装在OrderResponseContext对象中的Response Address，创建Binding并调用Response Service.

3. Order Processing Service Hosting: Artech.ResponsiveQueuedService.Hosting

Configuration

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <appSettings>
    <add key="msmqPath" value="./private$/orderprocessor"/>
  </appSettings>
  <system.serviceModel>
    <bindings>
      <netMsmqBinding>
        <binding name="MsmqBinding" exactlyOnce="false" useActiveDirectory="false">
          <security>
            <transport msmqAuthenticationMode="None" msmqProtectionLevel="None" />
          </security>
        </binding>
      </netMsmqBinding>
    </bindings>
    <services>
      <service name="Artech.ResponsiveQueuedService.Service.OrderProcessorService">
        <endpoint address="net.msmq://localhost/private/orderprocessor" binding="netMsmqBinding"
            bindingConfiguration="MsmqBinding" contract="Artech.ResponsiveQueuedService.Contract.IOrderProcessor" />
      </service>
    </services>
  </system.serviceModel>
</configuration>

Program

using System;
using System.Collections.Generic;
using System.Text;
using Artech.ResponsiveQueuedService.Service;
using System.ServiceModel;
using System.Configuration;
using System.Messaging;

namespace Artech.ResponsiveQueuedService.Hosting
{
    class Program
    {
        static void Main(string[] args)
        {
            string path = ConfigurationManager.AppSettings["msmqPath"];
            if (!MessageQueue.Exists(path))
            {
                MessageQueue.Create(path);
            }

            using (ServiceHost host = new ServiceHost(typeof(OrderProcessorService)))
            {
                host.Opened += delegate
                {
                    Console.WriteLine("The Order Processor service has begun to listen");
                };

                host.Open();

                Console.Read();
            }
        }
    }
}

4. Response Service: Artech.ResponsiveQueuedService.LocalService.OrderRessponseService

using System;
using System.Collections.Generic;
using System.Text;
using Artech.ResponsiveQueuedService.Contract;
using System.ServiceModel;

namespace Artech.ResponsiveQueuedService.LocalService
{
    public class OrderRessponseService : IOrderRessponse
    {
        IOrderRessponse Members#region IOrderRessponse Members

        public void SubmitOrderResponse(Guid orderNo, FaultException exception)
        {
            if (exception == null)
            {
                Console.WriteLine("It's successful to process the order!/n/tOrder No.: {0}",orderNo);
            }
            else
            {
                Console.WriteLine("It's fail to process the order!/n/tOrder No.: {0}/n/tReason: {1}", orderNo, exception.Message);
            }
        }

        #endregion
    }
}

5. Response Service Hosting: Artech.ResponsiveQueuedService.LocalhHosting

Configuration

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <appSettings>
    <add key="msmqPath" value="./private$/orderresponse"/>
  </appSettings>
  <system.serviceModel>
    <bindings>
      <netMsmqBinding>
        <binding name="msmqBinding" exactlyOnce="false">
          <security>
            <transport msmqAuthenticationMode="None" msmqProtectionLevel="None" />
          </security>
        </binding>
      </netMsmqBinding>
    </bindings>
    <services>
      <service name="Artech.ResponsiveQueuedService.LocalService.OrderRessponseService">
        <endpoint address="net.msmq://localhost/private/orderresponse" binding="netMsmqBinding"
            bindingConfiguration="msmqBinding" contract="Artech.ResponsiveQueuedService.Contract.IOrderRessponse" />
      </service>
    </services>
  </system.serviceModel>
</configuration>

Program

using System;
using System.Collections.Generic;
using System.Text;
using Artech.ResponsiveQueuedService.LocalService;
using System.Configuration;
using System.ServiceModel;
using System.Messaging;

namespace Artech.ResponsiveQueuedService.LocalhHosting
{
    class Program
    {
        static void Main(string[] args)
        {
            string path = ConfigurationManager.AppSettings["msmqPath"];
            if (!MessageQueue.Exists(path))
            {
                MessageQueue.Create(path);
            }

            using (ServiceHost host = new ServiceHost(typeof(OrderRessponseService)))
            {
                host.Opened += delegate
                {
                    Console.WriteLine("The Order Response service has begun to listen");
                };

                host.Open();

                Console.Read();
            }
        }
    }
}

6. Client: Artech.ResponsiveQueuedService.Client

Configuration:

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <appSettings>
    <add key="msmqPath" value="net.msmq://localhost/private/orderresponse"/>
  </appSettings>
  <system.serviceModel>
    <bindings>
      <netMsmqBinding>
        <binding name="MsmqBinding" exactlyOnce="false" useActiveDirectory="false">
          <security>
            <transport msmqAuthenticationMode="None" msmqProtectionLevel="None" />
          </security>
        </binding>
      </netMsmqBinding>
    </bindings>
    <client>
      <endpoint address="net.msmq://localhost/private/orderprocessor" binding="netMsmqBinding"
            bindingConfiguration="MsmqBinding" contract="Artech.ResponsiveQueuedService.Contract.IOrderProcessor" name="defaultEndpoint" />
    </client>
  </system.serviceModel>
</configuration>

Program:

using System;
using System.Collections.Generic;
using System.Text;
using System.Configuration;
using System.ServiceModel;
using Artech.ResponsiveQueuedService.Contract;
using System.Messaging;

namespace Artech.ResponsiveQueuedService.Clinet
{
    class Program
    {
        static void Main(string[] args)
        {
            Order order1 = new Order(Guid.NewGuid(), DateTime.Today.AddDays(5), Guid.NewGuid(), "Supplier A");
            Order order2 = new Order(Guid.NewGuid(), DateTime.Today.AddDays(-5), Guid.NewGuid(), "Supplier A");

            string path = ConfigurationManager.AppSettings["msmqPath"];
            Uri address = new Uri(path);
            OrderResponseContext context = new OrderResponseContext();
            context.ResponseAddress = address;

            ChannelFactory<IOrderProcessor> channelFactory = new ChannelFactory<IOrderProcessor>("defaultEndpoint");
            IOrderProcessor orderProcessor = channelFactory.CreateChannel();

            using (OperationContextScope contextScope = new OperationContextScope(orderProcessor as IContextChannel))
            {
                Console.WriteLine("Submit the order of order No.: {0}", order1.OrderNo);
                OrderResponseContext.Current = context;
                orderProcessor.Submit(order1);
            }

            using (OperationContextScope contextScope = new OperationContextScope(orderProcessor as IContextChannel))
            {
                Console.WriteLine("Submit the order of order No.: {0}", order2.OrderNo);
                OrderResponseContext.Current = context;
                orderProcessor.Submit(order2);
            }

            Console.Read();
        }
    }
}

我创建了两个Order对象, 其中一个已经过期。从Configuration中取出Response Address并购建一个OrderResponseContext，然后分两次将这两个Order向Order Processing Service递交。在调用Order Processing Order的Operation Context Scope中，通过OrderResponseContext.Current将OrderResponseContext对象插入Outcoming Message Header中。

我们现在运行一下整个程序，看看最终的输出结果：

Client：

Order Processing：

Order Response：

Reference：
Build a Queued WCF Response Service

作者：Artech
出处：http://artech.cnblogs.com
本文版权归作者和博客园共有，欢迎转载，但未经作者同意必须保留此段声明，且在文章页面明显位置给出原文连接，否则保留追究法律责任的权利。