NPOI export excel directly to frontend without saving it on server - asp.net-core

Question

Is it possible to write an excel file (with NPOI) directly to browser without saving it first on the server.
I tried following in my controller without success:
public async Task<IActionResult> ExportExcel(){
var fs = new MemoryStream();
IWorkbook workbook;
workbook = new XSSFWorkbook();
ISheet excelSheet = workbook.CreateSheet("Test);
IRow row = excelSheet.CreateRow(0);
row.CreateCell(0).SetCellValue("ID");
row.CreateCell(1).SetCellValue("Name");
row = excelSheet.CreateRow(1);
row.CreateCell(0).SetCellValue(1);
row.CreateCell(1).SetCellValue("User 1");
workbook.Write(fs);
byte[] bytes = new byte[fs.Length];
fs.Read(bytes, 0, (int)fs.Length);
return File(bytes, "application/vnd.ms-excel", sampleType.Abbreviation+".xlsx");
}
When executing above method I always get following error:
ObjectDisposedException: Cannot access a closed Stream.
...
System.IO.MemoryStream.get_Length()
byte[] bytes = new byte[fs.Length];
...
Or is their another great nuget package to handle (read and write) excel files without storing files on server?
PS: I am using dotnet core 2.1 en nuget package: https://www.nuget.org/packages/NPOI/

Answer 1

Write directly to the Response.Body.
Because Excel is treated as an attachment, we also need to set the Response.Headers
To make life easy, we can create an extension method firstly:
public static class IWorkBookExtensions {
public static void WriteExcelToResponse(this IWorkbook book, HttpContext httpContext, string templateName)
{
var response = httpContext.Response;
response.ContentType = "application/vnd.ms-excel";
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);
}
}
and now we can export the excel file directly :
public async Task ExportExcel(){
IWorkbook workbook;
workbook = new XSSFWorkbook();
ISheet excelSheet = workbook.CreateSheet("Test");
IRow row = excelSheet.CreateRow(0);
row.CreateCell(0).SetCellValue("ID");
row.CreateCell(1).SetCellValue("Name");
row = excelSheet.CreateRow(1);
row.CreateCell(0).SetCellValue(1);
row.CreateCell(1).SetCellValue("User 1");
workbook.WriteExcelToResponse(HttpContext,"test.xlsx");
}