How to download a file in ASP.Net

Introduction

Here is perhaps the simplest, shortest way to download a file in an ASP.Net application.

Response.ContentType = "application/pdf";
Response.AppendHeader("Content-Disposition", "attachment; filename=MyFile.pdf");
Response.TransmitFile(Server.MapPath("~/Files/MyFile.pdf"));
Response.End();

The first step is to set the content type. In the example above, we're downloading a .pdf file. Here are some of the most common content types.

• .htm, .html: Response.ContentType = "text/HTML"
• .txt: Response.ContentType = "text/plain"
• .doc, .rtf, .docx: Response.ContentType = "Application/msword"
• .xls, .xlsx: Response.ContentType = "Application/x-ms excel"
• .jpg, .jpeg: Response.ContentType = "image/jpeg"
• .gif: Response.ContentType = "image/GIF"
• .pdf: Response.ContentType = "application/pdf"

Response.TransmitFile retrieves a file and writes it to the Response. By calling TransmitFile, you ensure that the browser's Open / Save dialog box opens rather than simply opening the file in the browser window.

In some cases, we can't call TransmitFile because we can't map a path to the file. Instead, we'll get the file as a Stream and write it to the Response object:

Response.ContentType = "application/pdf";
Response.AppendHeader("Content-Disposition", "attachment; filename=MyFile.pdf");

// Write the file to the Response
const int bufferLength = 10000;
byte[] buffer = new Byte[bufferLength];
int length = 0;
Stream download = null;

try
{
    download = new FileStream(Server.MapPath("~/Files/Lincoln.txt"),
                            FileMode.Open,
                            FileAccess.Read);

    do
    {
        if (Response.IsClientConnected)
        {
            length = download.Read(buffer, 0, bufferLength);
            Response.OutputStream.Write(buffer, 0, length);
            buffer = new Byte[bufferLength];
        }
        else
        {
            length = -1;
        }
    }
    while (length > 0);

    Response.Flush();
    Response.End();
}
finally
{
    if (download != null)
        download.Close();
}

As before, the Open / Save dialog should open in the browser.

The project download includes working examples of both of these techniques.