无法修改WCF寻址头a:To元素，添加后被端点地址覆盖

问题场景 #

尝试修改WCF的a:To寻址头，但该元素在ClientMessageInspector的BeforeSendRequest方法中不可用；若在该方法中手动添加a:To头，其值会被端点地址覆盖。添加a:To头的代码如下：

var toHeader = MessageHeader.CreateHeader("To", "http://www.w3.org/2005/08/addressing", "https://toHeaderValue", true);
request.Headers.Add(toHeader);

当前使用的是CustomBinding，配置为SOAP 1.1版本、WS-Addressing 10版本，绑定代码如下：

{
    HttpTransportBindingElement bindingElement;
    var binding = new CustomBinding
    {
        Name = "*******",
        OpenTimeout = TimeSpan.FromMinutes(10),
        CloseTimeout = TimeSpan.FromMinutes(10),
        SendTimeout = TimeSpan.FromMinutes(10),
        ReceiveTimeout = TimeSpan.FromMinutes(10)
    };
    binding.Elements.Add(new TextMessageEncodingBindingElement
    {
        MessageVersion =
            MessageVersion.CreateVersion(EnvelopeVersion.Soap11,
                AddressingVersion.WSAddressing10),
        WriteEncoding = Encoding.UTF8
    });

    bindingElement = GetBindingElement(url);

    bindingElement.ManualAddressing = false;
    bindingElement.MaxReceivedMessageSize = 20000000;
    bindingElement.AllowCookies = false;
    bindingElement.BypassProxyOnLocal = false;
    bindingElement.MaxBufferSize = 20000000;
    bindingElement.TransferMode = TransferMode.Buffered;
    bindingElement.AuthenticationScheme = AuthenticationSchemes.Anonymous;
    bindingElement.ProxyAuthenticationScheme = AuthenticationSchemes.Anonymous;
    bindingElement.UseDefaultWebProxy = true;

    binding.Elements.Add(bindingElement);

    return binding;
}

private HttpTransportBindingElement GetBindingElement(string url)
{
    if (Uri.TryCreate(url, UriKind.Absolute, out var uriResult) && uriResult.Scheme == Uri.UriSchemeHttp)
        return new HttpTransportBindingElement();
    else
        return new HttpsTransportBindingElement();
}

问题原因 #

当HttpTransportBindingElement的ManualAddressing属性设为false时，WCF框架会自动使用端点地址填充a:To头，覆盖你在BeforeSendRequest中手动添加的值；同时，WS-Addressing 10规范下的a:To头由框架自动管理，因此在BeforeSendRequest方法中无法直接访问到该元素。

解决方案 #

将HttpTransportBindingElement的ManualAddressing属性设置为true，关闭WCF自动管理a:To头的行为，这样你就能在ClientMessageInspector的BeforeSendRequest方法中自由添加或修改a:To头，且不会被端点地址覆盖。

修改后的绑定代码关键行如下：

bindingElement.ManualAddressing = true; // 将原false改为true

注意：设置ManualAddressing = true后，需确保手动设置的a:To头值符合服务端要求，框架不再自动填充该字段。

内容的提问来源于stack exchange，提问作者Arjun