Directly transmittign an Excel workbook from an ASP.NET backend to a web client involves transforming object collections into tabular data, serializing the output to a memory buffer, and configuring the apropriate HTTP respnose headers.

public void ExportCollectionAsExcel<T>(IEnumerable<T> sourceCollection, string targetFileName)
{
    var tabularData = ConvertToDataTable(sourceCollection);
    if (tabularData == null || tabularData.Rows.Count == 0) return;

    var workbookInstance = new XlsDocument();
    var activeWorksheet = workbookInstance.Workbook.Worksheets.Add(targetFileName);

    // Map column headers
    for (int colIndex = 0; colIndex < tabularData.Columns.Count; colIndex++)
    {
        activeWorksheet.Cells.Add(1, colIndex + 1, tabularData.Columns[colIndex].ColumnName);
    }

    // Populate cell data
    for (int rowIndex = 0; rowIndex < tabularData.Rows.Count; rowIndex++)
    {
        for (int colIndex = 0; colIndex < tabularData.Columns.Count; colIndex++)
        {
            var cellContent = tabularData.Rows[rowIndex][colIndex]?.ToString() ?? string.Empty;
            activeWorksheet.Cells.Add(rowIndex + 2, colIndex + 1, cellContent);
        }
    }

    using (var memoryStream = new MemoryStream())
    {
        workbookInstance.Save(memoryStream);
        memoryStream.Position = 0;

        var currentResponse = HttpContext.Current.Response;
        currentResponse.Clear();
        currentResponse.ContentType = "application/vnd.ms-excel";
        currentResponse.ContentEncoding = Encoding.UTF8;
        currentResponse.AppendHeader("Content-Disposition", $"attachment; filename={targetFileName}");

        memoryStream.CopyTo(currentResponse.OutputStream);
        currentResponse.End();
    }
}

The covnersion utility maps public properties to a structured grid compatible with the XlsDocument API. Once the workbook is constructed and serialized into a MemoryStream, the HTTP response is cleared, assigned the Excel MIME type, and taggged with a Content-Disposition header to trigger a forced download.

Client-side execution requires a direct navigation request targeting the server endpoint:

window.open('/api/exports/download', '_blank');