netcore 使用中间件响应文件下载请求

添加以下中间件即可

app.Use(async (context, next) =>
            {
                var token = context.RequestAborted;
                var response = context.Response;

                IFileProvider fileProvider = new PhysicalFileProvider(@"E:"); // 文件所在根目录
                IFileInfo file = fileProvider.GetFileInfo(@"神话26.mp4"); // 文件相对根目录所在地址
                if (!file.Exists)
                {
                    await next();
                    return;
                }

                var suffix = ".mp4";
                var provider = new FileExtensionContentTypeProvider();
                var memi = provider.Mappings[suffix];
                response.ContentType = memi;
                response.Headers.Add(" Content-Disposition ", " attachment;filename= " + "神话26.mp4");
                response.ContentLength = file.Length;

                // 提供文件地址即可发送文件
                //await response.SendFileAsync(@"E:神话26.mp4", token); 
                // 提供文件信息即可发送文件
                //await response.SendFileAsync(file,  token);

                // 基于body发送文件，好处是可以控制下载速度
                var fs = file.CreateReadStream();
                using (System.IO.BinaryReader br = new System.IO.BinaryReader(fs))
                {
                    await response.Body.FlushAsync();
                    var kbs = 1024f * 2 / 10;
                    while (fs.Position < fs.Length)
                    {
                        if (token.IsCancellationRequested) break;
                        byte[] bytes = br.ReadBytes((int)Math.Truncate(1024 * kbs));
                        await response.Body.WriteAsync(bytes, 0, bytes.Length);
                        await response.Body.FlushAsync();
                        System.Threading.Thread.Sleep(100);
                    }
                    await response.Body.FlushAsync();
                }
            });