MVC Web API：预检响应具有无效的 HTTP 状态代码 404

Question

当我使用它时，我在两个服务器节点上的服务有时运行良好，有时会出错

XMLHttpRequest cannot load.. Response for preflight has invalid HTTP status code 404

我按照stackoverflow上的答案编写了这段代码，但没有解决问题

 protected void Application_BeginRequest()
    {
        if (Request.HttpMethod == "OPTIONS")
        {
            Response.Flush();
        }
    }

Web.config

  <system.webServer>
    <httpProtocol>
      <customHeaders>
        <remove name="X-Powered-By" />
        <add name="Access-Control-Allow-Origin" value="*" />
        <add name="Access-Control-Allow-Headers" value="Accept, Content-Type, Origin" />
        <add name="Access-Control-Allow-Methods" value="GET, PUT, POST, DELETE, OPTIONS" />
      </customHeaders>
    </httpProtocol>
    <security>
      <requestFiltering>
        <requestLimits maxAllowedContentLength="1073741824" />
      </requestFiltering>
    </security>
    <modules>
      <remove name="FormsAuthentication" />
    </modules>
    <handlers>
      <remove name="ExtensionlessUrlHandler-Integrated-4.0" />
      <remove name="OPTIONSVerbHandler" />
      <remove name="TRACEVerbHandler" />
      <add name="ExtensionlessUrlHandler-Integrated-4.0" path="*." verb="*" type="System.Web.Handlers.TransferRequestHandler" preCondition="integratedMode,runtimeVersionv4.0" />
    </handlers>
  </system.webServer>

Answer 1

你可能需要一个带有[WebInvoke(Method = "OPTIONS", UriTemplate = "*")]这个装饰的操作合约，例如：

    [OperationContract]
    [WebInvoke(Method = "OPTIONS", UriTemplate = "*")]
    void GetOptions();

操作实现是：

    public void GetOptions()
    {
        WebOperationContext.Current.OutgoingResponse.Headers.Add("Access-Control-Allow-Origin", "*");
        WebOperationContext.Current.OutgoingResponse.Headers.Add("Access-Control-Allow-Methods", "POST, GET, OPTIONS");
        WebOperationContext.Current.OutgoingResponse.Headers.Add("Access-Control-Allow-Headers", "Content-Type");
    }