在 Owin 中间件中覆盖响应正文答案

【问题标题】：Overwrite Response Body in Owin Middleware在 Owin 中间件中覆盖响应正文
【发布时间】：2019-09-12 06:12:30
【问题描述】：

我有一个正在使用的 Owin 中间件类。目的是在检测到 401、403 或 405 HTTP 状态代码时覆盖响应正文，并将正文替换为 JSON 对象。到目前为止，这是我的方法：

public override async Task Invoke(IOwinContext context)
        {
            await Next.Invoke(context);

            if (context.Response.StatusCode == 401 || context.Response.StatusCode == 403 || context.Response.StatusCode == 405)
            {

                var owinResponse = context.Response;
                var owinResponseStream = owinResponse.Body;
                var responseBuffer = new MemoryStream();
                owinResponse.Body = responseBuffer;

                string message;

                switch (context.Response.StatusCode)
                {
                    case 401:
                        message = "unauthorized request";
                        break;
                    case 403:
                        message = "forbidden request";
                        break;
                    default:
                        message = "request not allowed";
                        break;
                }
                var newResponse = new ResponseMessage<string>
                {
                    IsError = true,
                    StatusCode = (HttpStatusCode) Enum.Parse(typeof(HttpStatusCode), context.Response.StatusCode.ToString()),
                    Data = null,
                    Message = message
                };

                var customResponseBody = new StringContent(JsonConvert.SerializeObject(newResponse));
                var customResponseStream = await customResponseBody.ReadAsStreamAsync();
                await customResponseStream.CopyToAsync(owinResponseStream);
                owinResponse.ContentType = "application/json";
                owinResponse.ContentLength = customResponseStream.Length;
                owinResponse.StatusCode = 200;
                owinResponse.Body = owinResponseStream;
            }

        }

在大多数情况下它都在工作，但是响应正文被附加而不是替换。比如401错误的情况下，响应体是：

{"message":"Authorization has been denied for this request."}
{"IsError":true,"StatusCode":401,"Data":null,"Message":"unauthorized request"}

代替：

{"IsError":true,"StatusCode":401,"Data":null,"Message":"unauthorized request"}

我确定这与我写给响应正文的方式有关，但到目前为止还没有解决问题。

任何建议将不胜感激。

谢谢

【问题讨论】：

标签： c# asp.net-web-api owin

【解决方案1】：

因为你在await Next.Invoke(context);之后写了下面的代码

await Next.Invoke(context);

            if (context.Response.StatusCode == 401 || context.Response.StatusCode == 403 || context.Response.StatusCode == 405)
            {

                var owinResponse = context.Response;
                var owinResponseStream = owinResponse.Body;
                var responseBuffer = new MemoryStream();
                owinResponse.Body = responseBuffer;

错了。

下一个代码片段可以根据需要工作：

public override async Task Invoke(IOwinContext context)
        {
            var owinResponse = context.Response;
            var owinResponseStream = owinResponse.Body;
            var responseBuffer = new MemoryStream();
            owinResponse.Body = responseBuffer;

            await Next.Invoke(context);

            if (context.Response.StatusCode == 401 || context.Response.StatusCode == 403 || context.Response.StatusCode == 405)
            {

                string message;

                switch (context.Response.StatusCode)
                {
                    case 401:
                        message = "unauthorized request";
                        break;
                    case 403:
                        message = "forbidden request";
                        break;
                    default:
                        message = "request not allowed";
                        break;
                }
                var newResponse = new ResponseMessage<string>
                {
                    IsError = true,
                    StatusCode = (HttpStatusCode) Enum.Parse(typeof(HttpStatusCode), context.Response.StatusCode.ToString()),
                    Data = null,
                    Message = message
                };

                var customResponseBody = new StringContent(JsonConvert.SerializeObject(newResponse));
                var customResponseStream = await customResponseBody.ReadAsStreamAsync();
                await customResponseStream.CopyToAsync(owinResponseStream);
                owinResponse.ContentType = "application/json";
                owinResponse.ContentLength = customResponseStream.Length;
                owinResponse.StatusCode = 200;
                owinResponse.Body = owinResponseStream;
            }

        }

【讨论】：

【解决方案2】：

当您第一次将响应正文设置为内存流时，光标（当前位置）将移动到它的末尾。 owinResponse.Body = responseBuffer; ，结果，我们得到了{"message":"Authorization has been denied for this request."}stored 并且光标指向了末尾。

同样，在方法结束时，您编写新的响应 owinResponse.Body = owinResponseStream;，其中包含消息 {"IsError":true,"StatusCode":401,"Data":null,"Message":"unauthorized request"}

由于当前位置指向流的末尾，因此它会追加。

尝试删除第一组正文~~owinResponse.Body = responseBuffer;~~，因为您不需要原始响应消息。

【讨论】：