Downloading Files C#

A lot of questions are being asked about downloading a file from the web server to the client in ASP.NET. I have updated this blog post due to the high number of view & comments. You will realize i added a function called "ReturnExtension" which will return the proper content type and set it to the Response.ContentType property. Almost well known file types are supported.

C# Code

   // Get the physical Path of the file(test.doc)
   string filepath = Server.MapPath("test.doc");

   // Create New instance of FileInfo class to get the properties of the file being downloaded
   FileInfo file = new FileInfo(filepath);
 
   // Checking if file exists
   if (file.Exists)
   {
    // Clear the content of the response
    Response.ClearContent();
   
    // LINE1: Add the file name and attachment, which will force the open/cance/save dialog to show, to the header
    Response.AddHeader("Content-Disposition", "attachment; filename=" + file.Name);
   
    // Add the file size into the response header
    Response.AddHeader("Content-Length", file.Length.ToString());

    // Set the ContentType
    Response.ContentType = ReturnExtension(file.Extension.ToLower());

    // Write the file into the response (TransmitFile is for ASP.NET 2.0. In ASP.NET 1.1 you have to use WriteFile instead)
    Response.TransmitFile(file.FullName);

    // End the response
    Response.End();
   }

private string ReturnExtension(string fileExtension)
{
     switch (fileExtension)
            {
                case ".htm":
                case ".html":
                case ".log":
                    return "text/HTML";
                case ".txt":
                    return "text/plain";
                case ".doc":
                    return "application/ms-word";
                case ".tiff":
                case ".tif":
                    return "image/tiff";
                case ".asf":
                    return "video/x-ms-asf";
                case ".avi":
                    return "video/avi";
                case ".zip":
                    return "application/zip";
                case ".xls":
                case ".csv":
                    return "application/vnd.ms-excel";
                case ".gif":
                    return "image/gif";
                case ".jpg":
                case "jpeg":
                    return "image/jpeg";
                case ".bmp":
                    return "image/bmp";
                case ".wav":
                    return "audio/wav";
                case ".mp3":
                    return "audio/mpeg3";
                case ".mpg":
                case "mpeg":
                    return "video/mpeg";
                case ".rtf":
                    return "application/rtf";
                case ".asp":
                    return "text/asp";
                case ".pdf":
                    return "application/pdf";
                case ".fdf":
                    return "application/vnd.fdf";
                case ".ppt":
                    return "application/mspowerpoint";
                case ".dwg":
                    return "image/vnd.dwg";
                case ".msg":
                    return "application/msoutlook";
                case ".xml":
                case ".sdxl":
                    return "application/xml";
                case ".xdp":
                    return "application/vnd.adobe.xdp+xml";
                default:
                    return "application/octet-stream";
}

N.B:  If you want to bypass the Open/Save/Cancel dialog you just need to replace LINE1 by the below code

Response.AddHeader("Content-Disposition", "inline; filename=" + file.Name);

Response.TransmitFile VS Response.WriteFile:
 1- TransmitFile: This method sends the file to the client without loading it to the Application memory on the server. It is the ideal way to use it if the file size being download is large.
 2- WriteFile: This method loads the file being download to the server's memory before sending it to the client. If the file size is large, you might the ASPNET worker process might get restarted.

Hope this helps,