在Asp.net核心中间件中访问ModelState

ModelState仅在模型绑定之后可用。只需将ModelState 自动过滤器与动作过滤器一起存储，即可在中间件中使用它。

首先，添加一个动作过滤器以将ModelState设置为功能：

public class ModelStateFeatureFilter : IAsyncActionFilter
{

    public async Task OnActionExecutionAsync(ActionExecutingContext context, ActionExecutionDelegate next)
    {
        var state = context.ModelState;
        context.HttpContext.Features.Set(new ModelStateFeature(state));
        await next();
    }
}

这ModelStateFeature是一个持有ModelState的虚拟类：

public class ModelStateFeature
{
    public ModelStateDictionary ModelState { get; set; }

    public ModelStateFeature(ModelStateDictionary state)
    {
        this.ModelState= state;
    }
}

为了使动作过滤器自动发生，我们需要配置MVC

services.AddMvc(opts=> {
    opts.Filters.Add(typeof(ModelStateFeatureFilter));
})

现在我们可以ModelState在您的中间件中使用，如下所示：

public class ResponseFormatterMiddleware
{
    // ...

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

        using (var respOnseBody= new MemoryStream())
        {
            context.Response.Body = responseBody;
            // Process inner middlewares and return result.
            await _next(context);

            var ModelState = context.Features.Get()?.ModelState;
            if (ModelState==null) {
                return ;      //  if you need pass by , just set another flag in feature .
            }

            responseBody.Seek(0, SeekOrigin.Begin);
            using (var streamReader = new StreamReader(responseBody))
            {
                // Get action result come from mvc pipeline
                var strActiOnResult= streamReader.ReadToEnd();
                var objActiOnResult= JsonConvert.DeserializeObject(strActionResult);
                context.Response.Body = originBody;

               // Create uniuqe shape for all responses.
                var respOnseModel= new GenericResponseModel(objActionResult, (HttpStatusCode)context.Response.StatusCode, context.Items?["Message"]?.ToString());

                // => Get error message
                if (!ModelState.IsValid)
                {
                    var errors= ModelState.Values.Where(v => v.Errors.Count > 0)
                        .SelectMany(v=>v.Errors)
                        .Select(v=>v.ErrorMessage)
                        .ToList();
                    responseModel.Result = null;
                    responseModel.Message = String.Join(" ; ",errors) ;
                } 

                // Set all response code to 200 and keep actual status code inside wrapped object.
                context.Response.StatusCode = (int)HttpStatusCode.OK;
                context.Response.COntentType= "application/json";
                await context.Response.WriteAsync(JsonConvert.SerializeObject(responseModel));
            }
        }
    }
}

让我们用一个简单的模型进行测试

public class MyModel {
    [MinLength(6)]
    [MaxLength(12)]
    public string Name { get; set; }
    public int Age { get; set; }
}

和一个简单的控制器：

public class HomeController : Controller
{

    public IActionResult Index(string name)
    {
        return new JsonResult(new {
            Name=name
        });
    }

    [HttpPost]
    public IActionResult Person([Bind("Age,Name")]MyModel model)
    {
        return new JsonResult(model);
    }
}

如果我们发送带有有效负载的请求：

POST https://localhost:44386/Home/Person HTTP/1.1
content-type: application/x-www-form-urlencoded

name=helloo&age=20

响应将是：

HTTP/1.1 200 OK
Transfer-Encoding: chunked
Content-Type: application/json
Server: Kestrel
X-SourceFiles: =?UTF-8?B?RDpccmVwb3J0XDIwMThcOVw5LTE4XEFwcFxBcHBcQXBwXEhvbWVcUGVyc29u?=
X-Powered-By: ASP.NET

{
  "result": {
    "name": "helloo",
    "age": 20
  },
  "statusCode": 200,
  "message": null,
  "version": "V1.0"
}

如果我们发送的请求的模型无效：

POST https://localhost:44386/Home/Person HTTP/1.1
content-type: application/x-www-form-urlencoded

name=hello&age=i20

响应将是

HTTP/1.1 200 OK
Transfer-Encoding: chunked
Content-Type: application/json
Server: Kestrel
X-SourceFiles: =?UTF-8?B?RDpccmVwb3J0XDIwMThcOVw5LTE4XEFwcFxBcHBcQXBwXEhvbWVcUGVyc29u?=
X-Powered-By: ASP.NET

{
  "result": null,
  "statusCode": 200,
  "message": "The value 'i20' is not valid for Age. ; The field Name must be a string or array type with a minimum length of '6'.",
  "version": "V1.0"
}