wcf - 如何以编程方式更改 NetTcp 的 WCF 消息编码？

Question

我有一个没有互操作性要求的自定义 Intranet 应用程序。我们以编程方式在双工模式下构造一个 NetTcp channel 来传递消息。我们想更改消息编码，但无法弄清楚如何实现。

我们采用的方法(未成功)是将 NetTcpBinding 扩展为一个名为 LeanTcpBinding 的新类，如下所示:

internal class LeanTcpBinding : NetTcpBinding
{
    private static readonly ILog _log =
        LogManager.GetLogger(System.Reflection.MethodBase.GetCurrentMethod().DeclaringType);

    public override BindingElementCollection CreateBindingElements()
    {
        BindingElementCollection bindingElementCollection = base.CreateBindingElements();
        BindingElement encodingElement = bindingElementCollection.FirstOrDefault(
            bindingElement => bindingElement is BinaryMessageEncodingBindingElement);
        if (encodingElement != null)
        {
            int index = bindingElementCollection.IndexOf(encodingElement);
            bindingElementCollection.RemoveAt(index);
            bindingElementCollection.Insert(index, new LeanBinaryMessageEncodingBindingElement());
        }
        else
        {
            _log.Warn("Encoding not found");
        }

        return bindingElementCollection;
    }
}

显然，我们正在尝试用我们自己的替换默认的 BinaryMessageEncodingBindingElement。只是为了开始使用，LeanBinaryMessageEncodingBindingElement 是 BinaryMessageEncodingBindingElement 的扩展，如下所示:

 internal class LeanBinaryMessageEncodingBindingElement : MessageEncodingBindingElement
 {
        private readonly BinaryMessageEncodingBindingElement _bindingElement;

        /// 
        /// Initializes a new instance of the  class.
        /// 
        public LeanBinaryMessageEncodingBindingElement()
        {
            _bindingElement = new BinaryMessageEncodingBindingElement();
        }

        /// 
        /// Initializes a new instance of the  class.
        /// 
        /// The binding element.
        public LeanBinaryMessageEncodingBindingElement(BinaryMessageEncodingBindingElement bindingElement)
        {
            _bindingElement = bindingElement;
        }

        /// 
        /// Initializes a new instance of the  class.
        /// 
        /// The element to be cloned.
        /// The binding element.
        public LeanBinaryMessageEncodingBindingElement(MessageEncodingBindingElement elementToBeCloned, BinaryMessageEncodingBindingElement bindingElement)
            : base(elementToBeCloned)
        {
            _bindingElement = bindingElement;
        }

        /// 
        /// When overridden in a derived class, returns a copy of the binding element object.
        /// 
        /// 
        /// A  object that is a deep clone of the original.
        /// 
        public override BindingElement Clone()
        {
            return new LeanBinaryMessageEncodingBindingElement(
                (BinaryMessageEncodingBindingElement)_bindingElement.Clone());
        }

        /// 
        /// When overridden in a derived class, creates a factory for producing message encoders.
        /// 
        /// 
        /// The  used to produce message encoders.
        /// 
        public override MessageEncoderFactory CreateMessageEncoderFactory()
        {
            return new LeanBinaryMessageEncoderFactory(_bindingElement.CreateMessageEncoderFactory());
        }

        /// 
        /// When overridden in a derived class, gets or sets the message version that can be handled by the message encoders produced by the message encoder factory.
        /// 
        /// 
        /// The  used by the encoders produced by the message encoder factory.
        /// 
        public override MessageVersion MessageVersion
        {
            get { return _bindingElement.MessageVersion; }
            set { _bindingElement.MessageVersion = value; }
        }
 }

当我尝试使用绑定(bind)时，它会完全按照我的想法去做......它取代了 BinaryMessageEncodingBindingElement。但是，我从来没有接到过任何对 LeanBinaryMessageEncodingBindingElement.CreateMessageEncoderFactory() 的调用，即使消息正在通过 channel 进行交换。

有人对如何正确执行此操作有任何建议吗？

Answer 1

Kenny Wolf 澄清了遗漏的内容，并记录在下面的博客条目中。

http://kennyw.com/?p=170

对于不耐烦的人，问题在于默认情况下 MessageEncoderBindingElement 不会将自身添加到上下文的绑定(bind)参数中。结果，当传输稍后去查找 MessageEncoderBindingElement 时，它找不到我(或您)创建的那个，并且出现了我在原始帖子中提到的静默失败。

不幸的是，您必须按如下方式覆盖所有 CanBuildXXX 和 BuildXXX 方法，以确保将绑定(bind)元素添加到上下文的绑定(bind)参数中。

public override bool CanBuildChannelFactory(BindingContext context)
{
if (context == null) {
throw new ArgumentNullException("context");
}

context.BindingParameters.Add(this);
return context.CanBuildInnerChannelFactory();
}

public override bool CanBuildChannelListener(BindingContext context)
{
if (context == null) {
throw new ArgumentNullException("context");
}

context.BindingParameters.Add(this);
return context.CanBuildInnerChannelListener();
}

public override IChannelFactory BuildChannelFactory(BindingContext context)
{
if (context == null) {
throw new ArgumentNullException("context");
}

context.BindingParameters.Add(this);
return context.BuildInnerChannelFactory();
}

public override IChannelListener BuildChannelListener(BindingContext context)
{
if (context == null) {
throw new ArgumentNullException("context");
}

context.BindingParameters.Add(this);
return context.BuildInnerChannelListener();
}