Q:

Read an Excel file uploaded using FileUpload Control without saving it on the server

Need to be able to read an Excel file uploaded using FileUploadControl in ASP.NET. The solution will be hosted on a server. I do not want to store the Excel file on the server. I would like to directly convert the excel content into a dataset or a datatable and utilize.
Below are the two solutions I already found but would not work for me.

LINQTOEXCEL - This method works when you have an excel file on your local machine and you are running your code on the local machine. In my case, the user is trying to upload an excel file from his local machine using a webpage hosted on a server. 
ExcelDataReader - I am currently using this one, but this is a third party tool. I cannot move this to our customer. Also if a row/column intersection is carrying a formula, then that row/column intersection's data is not being read into the dataset.

Most of the suggestions i found on google and StackOverflow work when both the excel and the .NET solution are on the same machine. But in mine, I need it to work when the solution is hosted on a server, and users are trying to upload excel using the hosted webpage on their local machine.
If you have any other suggestions, could you please let me know?

A:

You can use the InputStream property of the HttpPostedFile to read the file into memory.
Here's an example which shows how to create a DataTable from the IO.Stream of a HttpPostedFile using EPPlus:
protected void UploadButton_Click(Object sender, EventArgs e)
{
    if (FileUpload1.HasFile && Path.GetExtension(FileUpload1.FileName) == ".xlsx")
    {
        using (var excel = new ExcelPackage(FileUpload1.PostedFile.InputStream))
        {
            var tbl = new DataTable();
            var ws = excel.Workbook.Worksheets.First();
            var hasHeader = true;  // adjust accordingly
            // add DataColumns to DataTable
            foreach (var firstRowCell in ws.Cells[1, 1, 1, ws.Dimension.End.Column])
                tbl.Columns.Add(hasHeader ? firstRowCell.Text
                    : String.Format("Column {0}", firstRowCell.Start.Column));

            // add DataRows to DataTable
            int startRow = hasHeader ? 2 : 1;
            for (int rowNum = startRow; rowNum <= ws.Dimension.End.Row; rowNum++)
            {
                var wsRow = ws.Cells[rowNum, 1, rowNum, ws.Dimension.End.Column];
                DataRow row = tbl.NewRow();
                foreach (var cell in wsRow)
                    row[cell.Start.Column - 1] = cell.Text;
                tbl.Rows.Add(row);
            }
            var msg = String.Format("DataTable successfully created from excel-file. Colum-count:{0} Row-count:{1}",
                                    tbl.Columns.Count, tbl.Rows.Count);
            UploadStatusLabel.Text = msg;
        }
    }
    else 
    {
        UploadStatusLabel.Text = "You did not specify a file to upload.";
    }
}

Here's the VB.NET version:
Sub UploadButton_Click(ByVal sender As Object, ByVal e As System.EventArgs)
    If (FileUpload1.HasFile AndAlso IO.Path.GetExtension(FileUpload1.FileName) = ".xlsx") Then
        Using excel = New ExcelPackage(FileUpload1.PostedFile.InputStream)
            Dim tbl = New DataTable()
            Dim ws = excel.Workbook.Worksheets.First()
            Dim hasHeader = True ' change it if required '
            ' create DataColumns '
            For Each firstRowCell In ws.Cells(1, 1, 1, ws.Dimension.End.Column)
                tbl.Columns.Add(If(hasHeader,
                                   firstRowCell.Text,
                                   String.Format("Column {0}", firstRowCell.Start.Column)))
            Next
            ' add rows to DataTable '
            Dim startRow = If(hasHeader, 2, 1)
            For rowNum = startRow To ws.Dimension.End.Row
                Dim wsRow = ws.Cells(rowNum, 1, rowNum, ws.Dimension.End.Column)
                Dim row = tbl.NewRow()
                For Each cell In wsRow
                    row(cell.Start.Column - 1) = cell.Text
                Next
                tbl.Rows.Add(row)
            Next
            Dim msg = String.Format("DataTable successfully created from excel-file Colum-count:{0} Row-count:{1}",
                                    tbl.Columns.Count, tbl.Rows.Count)
            UploadStatusLabel.Text = msg
        End Using
    Else
        UploadStatusLabel.Text = "You did not specify an excel-file to upload."
    End If
End Sub

For the sake of completeness, here's the aspx:
<div>
   <h4>Select a file to upload:</h4>

   <asp:FileUpload id="FileUpload1"                 
       runat="server">
   </asp:FileUpload>

   <br /><br />

   <asp:Button id="UploadButton" 
       Text="Upload file"
       OnClick="UploadButton_Click"
       runat="server">
   </asp:Button>    

   <hr />

   <asp:Label id="UploadStatusLabel"
       runat="server">
   </asp:Label>        
</div>

