ASP.NET file download from server

Try this set of code to download a CSV file from the server.

byte[] Content= File.ReadAllBytes(FilePath); //missing ;
Response.ContentType = "text/csv";
Response.AddHeader("content-disposition", "attachment; filename=" + fileName + ".csv");
Response.BufferOutput = true;
Response.OutputStream.Write(Content, 0, Content.Length);
Response.End();

Making changes as below and redeploying on server content type as

Response.ContentType = "application/octet-stream";

This worked for me.

Response.Clear(); 
Response.AddHeader("Content-Disposition", "attachment; filename=" + file.Name); 
Response.AddHeader("Content-Length", file.Length.ToString()); 
Response.ContentType = "application/octet-stream"; 
Response.WriteFile(file.FullName); 
Response.End();

You can use an HTTP Handler (.ashx) to download a file, like this:

DownloadFile.ashx:

public class DownloadFile : IHttpHandler 
{
    public void ProcessRequest(HttpContext context)
    {   
        System.Web.HttpResponse response = System.Web.HttpContext.Current.Response;
        response.ClearContent();
        response.Clear();
        response.ContentType = "text/plain";
        response.AddHeader("Content-Disposition", 
                           "attachment; filename=" + fileName + ";");
        response.TransmitFile(Server.MapPath("FileDownload.csv"));
        response.Flush();    
        response.End();
    }

    public bool IsReusable
    {
        get
        {
            return false;
        }
    }
}

Then you can call the HTTP Handler from the button click event handler, like this:

Markup:

<asp:Button ID="btnDownload" runat="server" Text="Download File" 
            OnClick="btnDownload_Click"/>

Code-Behind:

protected void btnDownload_Click(object sender, EventArgs e)
{
    Response.Redirect("PathToHttpHandler/DownloadFile.ashx");
}

---

Passing a parameter to the HTTP Handler:

You can simply append a query string variable to the Response.Redirect(), like this:

Response.Redirect("PathToHttpHandler/DownloadFile.ashx?yourVariable=yourValue");

Then in the actual handler code you can use the Request object in the HttpContext to grab the query string variable value, like this:

System.Web.HttpRequest request = System.Web.HttpContext.Current.Request;
string yourVariableValue = request.QueryString["yourVariable"];

// Use the yourVariableValue here

Note - it is common to pass a filename as a query string parameter to suggest to the user what the file actually is, in which case they can override that name value with Save As...