asp.net - Owin 中间件 vs ExceptionHandler vs HttpMessageHandler (DelegatingHandler)

Question

请任何人告诉我以下三个模块如何在 asp.net Web API 2.1 中协同工作

欧文中间件

HttpMessageHandler(或 DelegatingHandler)

异常处理程序

我正在尝试做的是开发一个 web api，它将提供一个恒定格式的 json 数据，这意味着如果实际数据是

{"Id":1,"UserName":"abc","Email":"abc@xyz.com"}

然后我喜欢将 json 传递为

{__d:{"Id":1,"UserName":"abc","Email":"abc@xyz.com"}, code:200, somekey: "somevalue"}

为此，我尝试使用自定义 Action 过滤器属性 但我觉得(仍然无法确认)如果代码遇到异常，这将无法提供类似格式的数据

请建议我最好的方向。

这是我的自定义属性的简短代码片段。还建议我自定义属性是否适合此目的

[AttributeUsage(AttributeTargets.Method | AttributeTargets.Class, Inherited = true, AllowMultiple = false)]
public class ResponseNormalizationAttribute : ActionFilterAttribute
{
    public override void OnActionExecuted(HttpActionExecutedContext actionExecutedContext)
    {
            base.OnActionExecuted(actionExecutedContext);
            var response = actionExecutedContext.Response;
            object contentValue;
            if (response.TryGetContentValue(out contentValue))
            {
                var nval = new { data=contentValue, status = 200 };


                var newResponse = new HttpResponseMessage { Content = new ObjectContent(nval.GetType(), nval, new JsonMediaTypeFormatter()) };
                newResponse.Content.Headers.ContentType = new MediaTypeHeaderValue("application/json");
                actionContext.Response = newResponse;
            }
     }
}

Answer 1

如果您不使用 Owin 中间件，您可以全局包装所有响应，以便使用委托(delegate)处理程序返回您的常量格式 json 数据。

编写一个继承自 DelegatingHandler 的自定义处理程序:

public class ApiResponseHandler : DelegatingHandler
{
    protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
    {
        var response = await base.SendAsync(request, cancellationToken);

        return BuildResponse(request, response);
    }

    private static HttpResponseMessage BuildResponse(HttpRequestMessage request, HttpResponseMessage response)
    {
        object content;
        string errorMessage = null;

        if (response.TryGetContentValue(out content) && !response.IsSuccessStatusCode)
        {
            HttpError error = content as HttpError;

            if (error != null)
            {
                content = null;
                errorMessage = error.Message;
            }
        }

        var newResponse = request.CreateResponse(response.StatusCode, new ApiResponse((int)response.StatusCode, content, errorMessage));

        foreach (var header in response.Headers)
        {
            newResponse.Headers.Add(header.Key, header.Value);
        }

        return newResponse;
    }
}

//ApiResponse is your constant json response
public class ApiResponse
{

    public ApiResponse(int statusCode, object content, string errorMsg)
    {
        Code = statusCode;
        Content = content;
        Error = errorMsg;
        Id = Guid.NewGuid().ToString();
    }

    public string Error { get; set; }

    //your actual data is mapped to the Content property
    public object Content { get; set; }
    public int Code { get; private set; }
    public string Id { get; set; }
}

在 WebApiConfig.cs 中注册处理程序:

    public static void Register(HttpConfiguration config)
    {
        // Web API routes
        config.MapHttpAttributeRoutes();
        ...

        config.MessageHandlers.Add(new ApiResponseHandler());

        config.Routes.MapHttpRoute(
            name: "DefaultApi",
            routeTemplate: "{controller}/{id}",
            defaults: new { id = RouteParameter.Optional }
        );

        ...
    }

我在 SO 中发布了一个类似的答案，但这是在 .NET Core 中并作为 OWIN 中间件实现(因为 DelegatingHandler 在 .NET Core 中消失了)。 How can I wrap Web API responses(in .net core) for consistency?