如何在ADO.NET Data Service的解决方案中修改最大传输数据量

1.问题描述：

如果你在使用ADO.NET Data Service做应用开发，那么有时候你可能会遇到如下的情况，尤其是你传输的数据量比较大的情况下，例如要上传或者下载一个比较大的文件时。

System.Net.WebException was unhandled by user code
  Message=The underlying connection was closed: An unexpected error occurred on a receive.
  Source=System
  StackTrace:
       at System.Net.HttpWebRequest.GetResponse()
       at System.Data.Services.Client.DataServiceContext.SaveResult.BatchRequest(Boolean replaceOnUpdate)
       at System.Data.Services.Client.DataServiceContext.SaveChanges(SaveChangesOptions options)
       at System.Data.Services.Client.DataServiceContext.SaveChanges()
       at System.Windows.Forms.ToolStripItem.RaiseEvent(Object key, EventArgs e)
       at System.Windows.Forms.ToolStripMenuItem.OnClick(EventArgs e)
       at System.Windows.Forms.ToolStripItem.HandleClick(EventArgs e)
       at System.Windows.Forms.ToolStripItem.HandleMouseUp(MouseEventArgs e)
       at System.Windows.Forms.ToolStripItem.FireEventInteractive(EventArgs e, ToolStripItemEventType met)
       at System.Windows.Forms.ToolStripItem.FireEvent(EventArgs e, ToolStripItemEventType met)
       at System.Windows.Forms.ToolStrip.OnMouseUp(MouseEventArgs mea)
       at System.Windows.Forms.ToolStripDropDown.OnMouseUp(MouseEventArgs mea)
       at System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
       at System.Windows.Forms.Control.WndProc(Message& m)
       at System.Windows.Forms.ScrollableControl.WndProc(Message& m)
       at System.Windows.Forms.ToolStrip.WndProc(Message& m)
       at System.Windows.Forms.ToolStripDropDown.WndProc(Message& m)
       at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
       at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
       at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)
  InnerException: System.IO.IOException
       Message=Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host.
       Source=System
       StackTrace:
            at System.Net.Sockets.NetworkStream.Read(Byte[] buffer, Int32 offset, Int32 size)
            at System.Net.PooledStream.Read(Byte[] buffer, Int32 offset, Int32 size)
            at System.Net.Connection.SyncRead(HttpWebRequest request, Boolean userRetrievedStream, Boolean probeRead)
       InnerException: System.Net.Sockets.SocketException
            Message=An existing connection was forcibly closed by the remote host
            Source=System
            ErrorCode=10054
            NativeErrorCode=10054
            StackTrace:
                 at System.Net.Sockets.Socket.Receive(Byte[] buffer, Int32 offset, Int32 size, SocketFlags socketFlags)
                 at System.Net.Sockets.NetworkStream.Read(Byte[] buffer, Int32 offset, Int32 size)
            InnerException:

如果你无法看到如上的错误消息，那么你需要在服务里面开启一个选项

        public static void InitializeService(DataServiceConfiguration config)
        {
            // TODO: set rules to indicate which entity sets and service operations are visible, updatable, etc.
            // Examples:
            config.SetEntitySetAccessRule("*", EntitySetRights.All);
            config.SetServiceOperationAccessRule("*", ServiceOperationRights.All);
            config.DataServiceBehavior.MaxProtocolVersion = DataServiceProtocolVersion.V2;
            config.UseVerboseErrors = true;

            
        }

2.原因分析：

当然，其实即便你看到了如上的错误消息，估计你也是一头雾水。事实上，上面的错误消息中并没有告诉你问题的真相。（所以我才要写这篇文章的嘛，呵呵）

出现这个问题到底是什么原因呢？

• WCF服务对最大传输的数据量有限制。默认是64KB，即65536BYTE. 因为ADO.NET Data Service说到底是一个WCF服务，只不过它使用的binding是比较特殊的罢
• ASP.NET执行引擎本身对请求数据的长度有限制，默认为4MB(4096KB)。 因为我们的ADO.NET Data Service是宿主在ASP.NET网站中，对它的请求当然首先要能够发送给ASP.NET引擎。（其实，数据发送到了服务器之后，会有两种处理的模式，默认情况下WCF是有一套独立的处理管道，但与此同时也可以设置为所谓的ASP.NET兼容模式。这个话题这里不多展开了）

3.解决方案：

了解了如上的原因，我们就可以设法来解决它

首先，设置WCF的最大消息数据大小为10MB（这里只是举例，你可以根据需要设置为你希望的大小）

  <system.serviceModel>
    <bindings>
      <webHttpBinding>
        <binding  name="my" maxReceivedMessageSize="10485760"></binding>
        <!--最大传输数据量为10MB:10*1024*1024-->
      </webHttpBinding>
    </bindings>
    <behaviors>
      <serviceBehaviors>
        <behavior name="">
          <serviceMetadata httpGetEnabled="true" />
          <serviceDebug includeExceptionDetailInFaults="false" />
        </behavior>
      </serviceBehaviors>
    </behaviors>
    <serviceHostingEnvironment aspNetCompatibilityEnabled="true" multipleSiteBindingsEnabled="true" />
    <services>
      <service name="Web.AdministrationService">
        <endpoint address="" binding="wsHttpBinding" contract="Web.IAdministrationService"></endpoint>
      </service>
      <service name="Web.MyDataService">
        <endpoint address="" binding="webHttpBinding" bindingConfiguration="my" contract="System.Data.Services.IRequestHandler"></endpoint>
      </service>
      
    </services>
  </system.serviceModel>

【注意】大家可以看到,ADO.NET Data Service所使用的binding是webHttpBinding,它的contract是System.Data.Service.IRequestHandler

【注意】这里的maxReceivedMessageSize单位是Byte,所以是10*1024*1024

接下来，我们还需要设置网站级别处理请求的最大长度

<httpRuntime maxRequestLength="10240"/>

【注意】这个参数的单位是KB，所以是10*1024即可(关于单位不统一这一点，我是颇有微词的，很多地方单位都不一样，让你不得不记住那么多东西，例如同样的问题还存在于设置timeout的地方，这里就不多说了）

完成上面两个设置之后，再次运行程序，就不会遇到错误了。然后，整个世界清静了……