c# - 从 OWIN 中间件返回异常

Question

我有一个 OWIN 中间件类来根据一些自定义 token 进行一些身份验证。一切正常。但是我想向客户端返回一个有用的错误响应。我的理由是，如果客户要求“application/json”响应并且他们期望序列化对象，那么这就是他们应该得到的，即使它是 401 状态代码。

这是我的中间件的调用部分:

    public override async Task Invoke(IOwinContext context)
    {
        try
        {
            this.DoAuthorization(context);
            await this.Next.Invoke(context);
        }
        catch (UnauthorizedAccessException ex)
        {
            this.GenerateErrorResult(context, HttpStatusCode.Unauthorized, this.ExceptionToString(ex));
        }
        catch (Exception ex)
        {
            this.GenerateErrorResult(context, HttpStatusCode.InternalServerError, this.ExceptionToString(ex));
        }
    }

    private void GenerateErrorResult(IOwinContext context, HttpStatusCode code, string errorMessage)
    {
        var result = new Result { Status = Result.EStatus.Error, ErrorText = errorMessage };

        context.Response.StatusCode = (int)code;
        context.Response.ContentType = "application/json";
        context.Response.Write(JsonConvert.SerializeObject(result));
    }

这一切都很好，但是:

• 这是“正确”的方式吗？
• 如果客户端要求'application/xml'怎么办，这显然是 Web API 能够支持的

是否有更好的方法来返回按客户期望序列化的自定义响应对象(在我的例子中为“结果”)？

Answer 1

这似乎可行，首先使用一个额外的 OwinMiddleware:

   public override async Task Invoke(IOwinContext context)
    {
        try
        {
            await Next.Invoke(context);
        }
        catch (UnauthorizedAccessException ex)
        {
            var result = new Result { Status = Result.EStatus.Error, ErrorText = ExceptionToString(ex) };

            this.ReturnFormattedResult(result, HttpStatusCode.Unauthorized, context);
        }
        catch (Exception ex)
        {
            var result = new Result { Status = Result.EStatus.Error, ErrorText = ExceptionToString(ex) };

            this.ReturnFormattedResult(result, HttpStatusCode.InternalServerError, context);
        }
    }

    private void ReturnFormattedResult(Result result, HttpStatusCode code, IOwinContext context)
    {
        // what should our response be?
        var mediaType = context.Request.MediaType ?? context.Request.ContentType;

        // use the accept header (unless it is empty or '*/*' in which case use the content-type
        if (!string.IsNullOrEmpty(context.Request.Accept) && !context.Request.Accept.Contains("*/*"))
        {
            mediaType = context.Request.Accept;
        }

        // find a formatter for this media type, if no match then use the first one
        var formatter = this.config.Formatters.FindWriter(typeof(Result), new MediaTypeHeaderValue(mediaType));
        if (formatter == null)
        {
            formatter = this.config.Formatters.First();
            mediaType = formatter.SupportedMediaTypes.First().MediaType;
        }

        context.Response.StatusCode = (int)code;
        context.Response.ContentType = mediaType;
        formatter.WriteToStreamAsync(typeof(Result), result, context.Response.Body, null, null).Wait();
    }