c# - QueryStringConverter 因未知原因不工作

Question

我正在编写一个小库，它正在为 WCF 休息服务生成客户端。但是我遇到了可空值的问题:由于未知原因，我的自定义 QueryStringConverter 从未被调用，尽管我在调试器中看到 WCF 调用了它的 CanConvert 方法。这是代码:

public class NullableQueryStringConverter : QueryStringConverter
{
    public static NullableQueryStringConverter Instance { get; } = new NullableQueryStringConverter();
    public override bool CanConvert(Type type)
    {
        if (base.CanConvert(type))
            return true;
        var underlyingType = Nullable.GetUnderlyingType(type);
        var canConvert = underlyingType != null && base.CanConvert(underlyingType);
        return canConvert;
    }

    public override object ConvertStringToValue(string parameter, Type parameterType)
    {
        var underlyingType = Nullable.GetUnderlyingType(parameterType);

        // Handle nullable types
        if (underlyingType != null)
        {
            // Define a null value as being an empty or missing (null) string passed as the query parameter value
            return string.IsNullOrEmpty(parameter) ? null : base.ConvertStringToValue(parameter, underlyingType);
        }

        return base.ConvertStringToValue(parameter, parameterType);
    }
}

这是 WCF 服务打开:

public void Start(Uri baseAddress)
{
    var serviceInterface = _serviceType.GetInterfaces()
                                       .First(i => i.GetCustomAttribute<ServiceContractAttribute>(true) != null);
    var attribute = _serviceType.GetCustomAttribute<ServiceBehaviorAttribute>(true);
    if (attribute?.InstanceContextMode == InstanceContextMode.Single)
    {
        var singleton = Activator.CreateInstance(_serviceType);
        ServiceHost = new WebServiceHost(singleton, baseAddress.Concat(_subAddress));
    }
    else
    {
        ServiceHost = new WebServiceHost(_serviceType, baseAddress.Concat(_subAddress));
    }
    ServiceHost.Description.Behaviors.Add(new ServiceMetadataBehavior { HttpGetEnabled = true });
    var debugBehavior = ServiceHost.Description.Behaviors.OfType<ServiceDebugBehavior>().FirstOrDefault();
    if (debugBehavior != null)
    {
        debugBehavior.IncludeExceptionDetailInFaults = true;
    }
    else
    {
        ServiceHost.Description.Behaviors.Add(new ServiceDebugBehavior { IncludeExceptionDetailInFaults = true });
    }

    var webHttpBinding = new WebHttpBinding
    {
        MaxReceivedMessageSize = int.MaxValue,
        MaxBufferSize = int.MaxValue,
        MaxBufferPoolSize = int.MaxValue,
        ReaderQuotas =
                new XmlDictionaryReaderQuotas
                {
                    MaxArrayLength = int.MaxValue,
                    MaxStringContentLength = int.MaxValue,
                    MaxDepth = 32
                }
    };

    webHttpBinding.ContentTypeMapper = new NewtonsoftJsonContentTypeMapper();
    ServiceHost.AddServiceEndpoint(serviceInterface, webHttpBinding, string.Empty);

    foreach (var endpoint in ServiceHost.Description.Endpoints)
    {
        endpoint.Behaviors.Add(new NullableWebHttpBehavior
        {
            HelpEnabled = false,
            DefaultBodyStyle = WebMessageBodyStyle.Bare,
            DefaultOutgoingRequestFormat = WebMessageFormat.Json,
            DefaultOutgoingResponseFormat = WebMessageFormat.Json,
            FaultExceptionEnabled = true
        });

        endpoint.Behaviors.Add(new NewtonsoftJsonBehavior());
    }

    ServiceHost.Open();
}

如您所见，我正在添加正在调用的 NullableWebHttpBehavior(至少是 CanConvert 方法)，但此后 WCF 仍要求参数可由基类转换.

这是 github 上项目的链接:link .这很奇怪，因为我在另一个工作正常的项目中有非常相似的代码。

也许我遗漏了什么，我不知道。包含所有要检查的逻辑的文件是:NullableWebHttpBehavior.cs 和 ServiceManager.cs。您可以轻松地运行一个测试(这是这里唯一的一个)并面对同样的问题。

Answer 1

经过一些研究，我发现这个方法会导致异常:

    protected override IDispatchMessageFormatter GetRequestDispatchFormatter(OperationDescription operationDescription, ServiceEndpoint endpoint)
    {
        if (operationDescription.IsGetOrDeleteOperation())
        {
            // no change for GET operations
            return base.GetRequestDispatchFormatter(operationDescription, endpoint);
        }

        if (operationDescription.Messages[0].Body.Parts.Count == 0)
        {
            // nothing in the body, still use the default
            return base.GetRequestDispatchFormatter(operationDescription, endpoint);
        }

        return new NewtonsoftJsonDispatchFormatter(operationDescription, true);
    }

出于某种原因，base.GetRequestDispatchFormatter 正在返回原始的 QueryStringConverter，这会引发错误。所以我只是删除了这些 if 并始终使用我的自定义 NewtonsoftJsonDispatchFormatter，它有一些开销但工作正常。