How to: Create a WCF Service that Communicates over WebSockets

Article
09/15/2021

WCF services and clients can use the NetHttpBinding binding to communicate over WebSockets. WebSockets will be used when the NetHttpBinding determines the service contract defines a callback contract. This topic describes how to implement a WCF service and client that uses the NetHttpBinding to communicate over WebSockets.

Define the Service

Define a callback contract

[ServiceContract]  
    public interface IStockQuoteCallback  
    {  
        [OperationContract(IsOneWay = true)]  
        Task SendQuote(string code, double value);  
    }

This contract will be implemented by the client application to allow the service to send messages back to the client.

Define the service contract and specify the IStockQuoteCallback interface as the callback contract.

[ServiceContract(CallbackContract = typeof(IStockQuoteCallback))]  
    public interface IStockQuoteService  
    {  
        [OperationContract(IsOneWay = true)]  
        Task StartSendingQuotes();  
    }

Implement the service contract.

public class StockQuoteService : IStockQuoteService  
{  
    public async Task StartSendingQuotes()  
    {  
        var callback = OperationContext.Current.GetCallbackChannel<IStockQuoteCallback>();  
        var random = new Random();  
        double price = 29.00;  

        while (((IChannel)callback).State == CommunicationState.Opened)  
        {  
            await callback.SendQuote("MSFT", price);  
            price += random.NextDouble();  
            await Task.Delay(1000);  
        }  
    }  
}

The service operation StartSendingQuotes is implemented as an asynchronous call. We retrieve the callback channel using the OperationContext and if the channel is open, we make an async call on the callback channel.

Configure the service

<configuration>  
    <appSettings>  
      <add key="aspnet:UseTaskFriendlySynchronizationContext" value="true" />
    </appSettings>  
    <system.web>  
      <compilation debug="true" targetFramework="4.5" />
    </system.web>  
    <system.serviceModel>  
        <protocolMapping>  
          <add scheme="http" binding="netHttpBinding"/>  
          <add scheme="https" binding="netHttpsBinding"/>  
        </protocolMapping>  
        <behaviors>  
            <serviceBehaviors>  
                <behavior name="">  
                    <serviceMetadata httpGetEnabled="true" httpsGetEnabled="true" />  
                    <serviceDebug includeExceptionDetailInFaults="false" />  
                </behavior>  
            </serviceBehaviors>  
        </behaviors>  
        <serviceHostingEnvironment aspNetCompatibilityEnabled="true"  
            multipleSiteBindingsEnabled="true" />  
    </system.serviceModel>  
</configuration>

The service’s configuration file relies on WCF’s default endpoints. The <protocolMapping> section is used to specify that the NetHttpBinding should be used for the default endpoints created.

Define the Client

Implement the callback contract.

private class CallbackHandler : StockQuoteServiceReference.IStockQuoteServiceCallback  
        {  
            public async Task SendQuoteAsync(string code, double value)  
            {  
                Console.WriteLine("{0}: {1:f2}", code, value);  
            }  
        }

The callback contract operation is implemented as an asynchronous method.

Implement the client code.

class Program  
{  
    static void Main(string[] args)  
    {  
        var context = new InstanceContext(new CallbackHandler());  
        var client = new StockQuoteServiceReference.StockQuoteServiceClient(context);  
        client.StartSendingQuotes();
        Console.ReadLine();  
    }  

    private class CallbackHandler : StockQuoteServiceReference.IStockQuoteServiceCallback  
    {  
        public async Task SendQuoteAsync(string code, double value)  
        {  
            Console.WriteLine("{0}: {1:f2}", code, value);  
        }  
    }  
}

The CallbackHandler is repeated here for clarity. The client application creates a new InstanceContext and specifies the implementation of the callback interface. Next it creates an instance of the proxy class sending a reference to the newly created InstanceContext. When the client calls the service, the service will call the client using the callback contract specified.

Configure the client

<?xml version="1.0" encoding="utf-8" ?>  
<configuration>  
    <startup>
        <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.5" />  
    </startup>  
    <system.serviceModel>  
        <bindings>  
            <netHttpBinding>  
                <binding name="NetHttpBinding_IStockQuoteService">  
                    <webSocketSettings transportUsage="Always" />  
                </binding>  
            </netHttpBinding>  
        </bindings>  
        <client>  
            <endpoint address="ws://localhost/NetHttpSampleServer/StockQuoteService.svc"  
                binding="netHttpBinding" bindingConfiguration="NetHttpBinding_IStockQuoteService"  
                contract="StockQuoteServiceReference.IStockQuoteService" name="NetHttpBinding_IStockQuoteService" />  
        </client>  
    </system.serviceModel>  
</configuration>

There is nothing special you need to do in the client configuration, just specify the client side endpoint using the NetHttpBinding.

Example

The following is the complete code used in this topic.

// IStockQuoteService.cs  
using System;  
using System.Collections.Generic;  
using System.Linq;  
using System.Runtime.Serialization;  
using System.ServiceModel;  
using System.Text;  
using System.Threading.Tasks;  
  
namespace Server  
{  
    [ServiceContract(CallbackContract = typeof(IStockQuoteCallback))]  
    public interface IStockQuoteService  
    {  
        [OperationContract(IsOneWay = true)]  
        Task StartSendingQuotes();  
    }  
  
    [ServiceContract]  
    public interface IStockQuoteCallback  
    {  
        [OperationContract(IsOneWay = true)]  
        Task SendQuote(string code, double value);  
    }  
}

// StockQuoteService.svc.cs  
using System;  
using System.Collections.Generic;  
using System.Linq;  
using System.Runtime.Serialization;  
using System.ServiceModel;  
using System.ServiceModel.Channels;  
using System.Text;  
using System.Threading.Tasks;  
  
namespace Server  
{  
    public class StockQuoteService : IStockQuoteService  
    {  
        public async Task StartSendingQuotes()  
        {  
            var callback = OperationContext.Current.GetCallbackChannel<IStockQuoteCallback>();  
            var random = new Random();  
            double price = 29.00;  
  
            while (((IChannel)callback).State == CommunicationState.Opened)  
            {  
                await callback.SendQuote("MSFT", price);  
                price += random.NextDouble();  
                await Task.Delay(1000);  
            }  
        }  
    }  
}

<?xml version="1.0"?>  
  
<!--  
  For more information on how to configure your ASP.NET application, please visit  
  https://go.microsoft.com/fwlink/?LinkId=169433  
  -->  
  
<configuration>  
    <appSettings>  
      <add key="aspnet:UseTaskFriendlySynchronizationContext" value="true" />
    </appSettings>  
    <system.web>  
      <compilation debug="true" targetFramework="4.5" />
    </system.web>  
    <system.serviceModel>  
        <protocolMapping>  
          <add scheme="http" binding="netHttpBinding"/>  
          <add scheme="https" binding="netHttpsBinding"/>  
        </protocolMapping>  
        <behaviors>  
            <serviceBehaviors>  
                <behavior name="">  
                    <serviceMetadata httpGetEnabled="true" httpsGetEnabled="true" />  
                    <serviceDebug includeExceptionDetailInFaults="false" />  
                </behavior>  
            </serviceBehaviors>  
        </behaviors>  
        <serviceHostingEnvironment aspNetCompatibilityEnabled="true"  
            multipleSiteBindingsEnabled="true" />  
    </system.serviceModel>  
</configuration>

<!-- StockQuoteService.svc -->  
<%@ ServiceHost Language="C#" Debug="true" Service="Server.StockQuoteService" CodeBehind="StockQuoteService.svc.cs" %>

// Client.cs  
using System;  
using System.Collections.Generic;  
using System.Linq;  
using System.ServiceModel;  
using System.Text;  
using System.Threading.Tasks;  
  
namespace Client  
{  
    class Program  
    {  
        static void Main(string[] args)  
        {  
            var context = new InstanceContext(new CallbackHandler());  
            var client = new StockQuoteServiceReference.StockQuoteServiceClient(context);  
            client.StartSendingQuotes();
            Console.ReadLine();  
        }  
  
        private class CallbackHandler : StockQuoteServiceReference.IStockQuoteServiceCallback  
        {  
            public async Task SendQuoteAsync(string code, double value)  
            {  
                Console.WriteLine("{0}: {1:f2}", code, value);  
            }  
        }  
    }  
}

<!--App.config -->  
<?xml version="1.0" encoding="utf-8" ?>  
<configuration>  
    <startup>
        <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.5" />  
    </startup>  
    <system.serviceModel>  
        <bindings>  
            <netHttpBinding>  
                <binding name="NetHttpBinding_IStockQuoteService">  
                    <webSocketSettings transportUsage="Always" />  
                </binding>  
            </netHttpBinding>  
        </bindings>  
        <client>  
            <endpoint address="ws://localhost/NetHttpSampleServer/StockQuoteService.svc"  
                binding="netHttpBinding" bindingConfiguration="NetHttpBinding_IStockQuoteService"  
                contract="StockQuoteServiceReference.IStockQuoteService" name="NetHttpBinding_IStockQuoteService" />  
        </client>  
    </system.serviceModel>  
</configuration>

How to: Create a WCF Service that Communicates over WebSockets

Define the Service

Define the Client

Example

See also

Additional resources