C# ETagCacheMiddleware

 public class ETagCacheMiddleware
    {
        private readonly RequestDelegate _next;

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

        public async Task InvokeAsync(HttpContext context)
        {
            var originalResponseStream = context.Response.Body;
            var etag = "";
            if (context.Request.Headers.ContainsKey("etag"))
            {
                etag = context.Request.Headers["etag"].ToString();
                var response = await _redisCacheClient.Value.GetOrDefault<string>(etag);

                if (response == null)
                {
                    using (var ms = new MemoryStream())
                    {
                        context.Response.Body = ms;
                        context.Response.Headers.Add("etag", etag);
                        await _next(context);

                        ms.Seek(0,SeekOrigin.Begin);

                        var responseReader = new StreamReader(ms);
                        var responseContent = responseReader.ReadToEnd();

                        ms.Seek(0, SeekOrigin.Begin);

                        await ms.CopyToAsync(originalResponseStream);
                        context.Response.Body = originalResponseStream;
　　　　　　　　　　　　　　
　　　　　　　　　　　　　　//可根据具体需求操作已获得的etag和请求返回内容responseContent


                    }
                }
                else
                {
                    //返回response
                    context.Response.Headers.Add("etag",etag);
                    context.Response.ContentType = "application/json";
                    using (var ms = new MemoryStream())
                    {
                        var orgBodyStream = context.Response.Body;
                        context.Response.Body = ms;

                        ms.Seek(0, SeekOrigin.Begin);
                        byte[] responseArray = Encoding.ASCII.GetBytes(response);
                        ms.Write(responseArray, 0, responseArray.Length);
                        ms.Seek(0, SeekOrigin.Begin);
                        await ms.CopyToAsync(orgBodyStream);
                        context.Response.Body = orgBodyStream;
                    }
                }
            }
            else
            {
                await _next(context);
            }
        }
    }