CODEWITHSUNDEEP
c#asp.net
Ashish Gupta
Ashish Gupta

Reputation: 15139

ASP.NET how to check type of the file type irrespective of extension

If somebody renames the extension of any file (other than excel) to xls and xlsx (please dont ask me why :-( ), I need to check for its validity (if that is still a valid excel file). I am using mime type and Its not working. Am I missing anything?

const string excel2007MimeType = "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet";
const string excel2003MimeType = "application/vnd.ms-excel";

  string excelExtention = string.Empty;
            excelExtention = System.IO.Path.GetExtension(myFilePath.PostedFile.FileName).ToLower();
            string mimeType = myFilePath.PostedFile.ContentType;
            Response.Write("mime type" + mimeType + Environment.NewLine);
            if( 
                 (
                    !(excelExtention == ".xls" && mimeType == excel2003MimeType)
                    ||
                    !(excelExtention == ".xlsx" && mimeType == excel2007MimeType)
                 )
              )
            {
                Response.Write ("only excel file is permitted");
            }

I rename a jpg file to xlsx file and upload. If I print out variable mimetype, Its value is "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet". I am not sure why because the content is not an excel file. Its an image.

Upvotes: 2

Views: 3617

Answers (2)

Steve Danner
Steve Danner

Reputation: 22158

You could always use the Excel OleDB Database driver and try to open an OleDbConnection against it.

Upvotes: 3

Kieren Johnstone
Kieren Johnstone

Reputation: 42003

To do that you'd need to attempt to open it using an Excel library, or Excel COM object itself. Microsoft doesn't support Office COM object automation in a server environment, unfortunately.

You could just read the first part of the file and check for a binary signature, but it would be a lot of work to support all possible XLS versions; and .XSLX files are simply ZIP files containing the document in several parts.

Hope that helps.

Upvotes: 3

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