如何包装 Web API 响应（在 .net 核心中）以保持一致性？

Question

我需要返回一个一致的响应，所有请求都返回一个类似的结构。在之前的 .NET web api 中，我可以使用 DelegatingHandler (MessageHandlers) 来实现这一点。我要返回的对象将被封装在 Result 元素中。所以基本上json响应会是这样的结构：

示例 1：

{
    "RequestId":"some-guid-abcd-1234",
    "StatusCode":200,
    "Result":
    {
        "Id":42,
        "Todo":"Do Hello World"
    }
}

示例 2：

{
    "RequestId":"some-guid-abcd-1235",
    "StatusCode":200,
    "Result":
    {
        [
            {        
                "Id":42,
                "Todo":"Print Hello World"
            },
            {        
                "Id":43,
                "Todo":"Print Thank you"
            }           
        ]

    }
}

在 .NET 核心中，看起来我需要通过中间件来执行此操作。我试过了，但是当您可以调用 HttpResponseMessage.TryGetContentValue 来获取内容并将其包装在全局/通用响应模型中时，我没有看到更好的方法来提取内容，就像在以前的 Web API 中那样。

如何在 .NET core 中实现同样的功能？

Answer 1

对于那些正在寻找现代统包解决方案的人，您现在可以使用AutoWrapper。

它非常易于使用；只需将以下内容添加到您的 Startup.cs 文件中：

app.UseApiResponseAndExceptionWrapper();

Answer 2

这是一个老问题，但也许这会对其他人有所帮助。

在 AspNetCore 2（不确定它是否适用于以前的版本）中，您可以添加自定义 OutputFormatter。下面是使用内置 JsonOutputFormatter 的实现。

请注意，这没有经过彻底测试，我不是 100% 认为更改上下文是可以的。我查看了aspnet源代码，似乎没有关系，但我可能错了。

public class CustomJsonOutputFormatter : JsonOutputFormatter
{
    public CustomJsonOutputFormatter(JsonSerializerSettings serializerSettings, ArrayPool<char> charPool)
        : base(serializerSettings, charPool)
    { }

    public override Task WriteResponseBodyAsync(OutputFormatterWriteContext context, Encoding selectedEncoding)
    {
        if (context.HttpContext.Response.StatusCode == (int)HttpStatusCode.OK)
        {
            var @object = new ApiResponse { Data = context.Object };

            var newContext = new OutputFormatterWriteContext(context.HttpContext, context.WriterFactory, typeof(ApiResponse), @object);
            newContext.ContentType = context.ContentType;
            newContext.ContentTypeIsServerDefined = context.ContentTypeIsServerDefined;

            return base.WriteResponseBodyAsync(newContext, selectedEncoding);
        }

        return base.WriteResponseBodyAsync(context, selectedEncoding);
    }
}

然后在你的 Startup 类中注册它

public void ConfigureServices(IServiceCollection services)
{

        var jsonSettings = new JsonSerializerSettings
        {
            NullValueHandling = Newtonsoft.Json.NullValueHandling.Ignore,
            ContractResolver = new CamelCasePropertyNamesContractResolver()
        };

        options.OutputFormatters.RemoveType<JsonOutputFormatter>();
        options.OutputFormatters.Add(new WrappedJsonOutputFormatter(jsonSettings, ArrayPool<char>.Shared));
}

Answer 3

我创建了一个中间件来包装响应以保持一致性。为了方便注册这个中间件，我还为 IApplicationBuilder 创建了一个扩展方法。所以在 Startup.cs 中，注册中间件：

public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
{
    //code removed for brevity.
    ...
    app.UseResponseWrapper();

    //code removed for brevity.
    ...
}

这是中间件代码：

using System;
using System.IO;
using System.Net;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Http;
using Newtonsoft.Json;

namespace RegistrationWeb.Middleware
{
    public class ResponseWrapper
    {
        private readonly RequestDelegate _next;

        public ResponseWrapper(RequestDelegate next)
        {
            _next = next;
        }

        public async Task Invoke(HttpContext context)
        {
            var currentBody = context.Response.Body;

            using (var memoryStream = new MemoryStream())
            {
                //set the current response to the memorystream.
                context.Response.Body = memoryStream;

                await _next(context);

                //reset the body 
                context.Response.Body = currentBody;
                memoryStream.Seek(0, SeekOrigin.Begin);

                var readToEnd = new StreamReader(memoryStream).ReadToEnd();
                var objResult = JsonConvert.DeserializeObject(readToEnd);
                var result = CommonApiResponse.Create((HttpStatusCode)context.Response.StatusCode, objResult, null);
                await context.Response.WriteAsync(JsonConvert.SerializeObject(result));
            }
        }

    }

    public static class ResponseWrapperExtensions
    {
        public static IApplicationBuilder UseResponseWrapper(this IApplicationBuilder builder)
        {
            return builder.UseMiddleware<ResponseWrapper>();
        }
    }


    public class CommonApiResponse
    {
        public static CommonApiResponse Create(HttpStatusCode statusCode, object result = null, string errorMessage = null)
        {
            return new CommonApiResponse(statusCode, result, errorMessage);
        }

        public string Version => "1.2.3";

        public int StatusCode { get; set; }
        public string RequestId { get; }

        public string ErrorMessage { get; set; }

        public object Result { get; set; }

        protected CommonApiResponse(HttpStatusCode statusCode, object result = null, string errorMessage = null)
        {
            RequestId = Guid.NewGuid().ToString();
            StatusCode = (int)statusCode;
            Result = result;
            ErrorMessage = errorMessage;
        }
    }
}

Answer 4

我至少可以看到两个选项来完成此任务。

首先，如果您想将此包装器添加到项目中的所有 api，您可以通过在项目的 startup.cs 部分中实现中间件来实现。这是通过在“配置”函数中的 app.UseMvc 之前添加一个 app.Use 来完成的，方法如下：

app.Use(async (http, next) =>
{
//remember previous body
var currentBody = http.Response.Body;

using (var memoryStream = new MemoryStream())
{
    //set the current response to the memorystream.
    http.Response.Body = memoryStream;

    await next();

    string requestId = Guid.NewGuid().ToString();

    //reset the body as it gets replace due to https://github.com/aspnet/KestrelHttpServer/issues/940
    http.Response.Body = currentBody;
    memoryStream.Seek(0, SeekOrigin.Begin);

    //build our content wrappter.
    var content = new StringBuilder();
    content.AppendLine("{");
    content.AppendLine("  \"RequestId\":\"" + requestId + "\",");
    content.AppendLine("  \"StatusCode\":" + http.Response.StatusCode + ",");
    content.AppendLine("  \"Result\":");
    //add the original content.
    content.AppendLine(new StreamReader(memoryStream).ReadToEnd());
    content.AppendLine("}");

    await http.Response.WriteAsync(content.ToString());

}
});

您的另一个选择是在控制器中拦截调用。这可以通过覆盖控制器中的OnActionExecuted 函数来完成。类似于以下内容：

    public override void OnActionExecuted(ActionExecutedContext context)
    {
        // 
        // add code to update the context.Result as needed.
        //

        base.OnActionExecuted(context);
    }