c# - 无法修改响应标头，因为响应已经开始

Question

我正在使用 Asp.Net 核心 3.1

我已经实现了通过将数据写入 HttpContext Response 来下载 Excel/CSV 文件的功能，并且我能够下载该文件，但我收到错误日志说

[ERR] An unhandled exception has occurred while executing the request. (48a46595)
System.InvalidOperationException: The response headers cannot be modified because the response has already started.

此外，我在服务器上部署了我的应用程序并得到错误代码 502。

下面是代码。

public static class IWorkBookExtensions
    {
        public static void WriteExcelToResponse(this IWorkbook book, HttpContext httpContext, string templateName, ILogger<ExportDataController> _logger)
        {
            try
            {
                var response = httpContext.Response;
                response.ContentType = "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet";
                if (!string.IsNullOrEmpty(templateName))
                {
                    var contentDisposition = new Microsoft.Net.Http.Headers.ContentDispositionHeaderValue("attachment");
                    contentDisposition.SetHttpFileName(templateName);
                    response.Headers[HeaderNames.ContentDisposition] = contentDisposition.ToString();
                }
                book.Write(response.Body);
                
            }
            catch(Exception ex)
            {
                _logger.LogError(ex.InnerException.ToString() + ex.Message);
            }
           
        }
     }

下面是错误日志

2020-10-13T14:45:17.1452752-05:00 80003b-00-fc00-3f-84967bb [ERR] An unhandled exception has occurred while executing the request. (48a46595)
System.InvalidOperationException: The response headers cannot be modified because the response has already started.
   at Microsoft.AspNetCore.HttpSys.Internal.HeaderCollection.ThrowIfReadOnly()
   at Microsoft.AspNetCore.HttpSys.Internal.HeaderCollection.set_Item(String key, StringValues value)
   at Microsoft.AspNetCore.Http.DefaultHttpResponse.set_ContentType(String value)
   --- End of stack trace from previous location where exception was thrown ---
   2020-10-13T14:45:17.1546662-05:00 80003b-00-fc00-3f-84967bb [WRN] The response has already started, the error page middleware will not be executed. (e1dd4c0d)
2020-10-13T14:45:17.2073595-05:00 880003b-00-fc00-3f-84967bb [ERR] Connection ID ""18300129210426"", Request ID ""80003b-00-fc00-3f-84967bb"": An unhandled exception was thrown by the application. (bf3147)
System.InvalidOperationException: The response headers cannot be modified because the response has already started.

标签： c#asp.net-mvcasp.net-core