Handler For Writing and Downloading Binary

An ASP.NET HTTP handler is the process (frequently referred to as the "endpoint") that runs in response to a request made to an ASP.NET Web application. The most common handler is an ASP.NET page handler that processes .aspx files. When users request an .aspx file, the request is processed by the page through the page handler. You can create your own HTTP handlers that render custom output to the browser.

The HttpHandler is a pre-processing logic implementation blocks and is the part of the ASP.NET request pipeline. Whenever the IIS Server recieves a request, it looks for an ISAPI filter(looking for the perticuler httphandler to handle a perticuler extension) that is capable of handling web requests.

ASP.NET maps HTTP requests to HttpHandlers. Each HttpHandler enables processing of individual HTTP URLs or groups of URL extensions within an application.

Handlers are considered to be more lightweight object than pages. That's why they are used to serve dynamically-generated images, on-the-fly generated PDF-files and similar content to the web browser.

below is an example (.ashx file)..

<%@ WebHandler Language="C#" Class="DownLoad" %>
using System;
using System.Web;
using System.Data;
using System.Data.SqlClient;

public class DownLoad : IHttpHandler {

  CompCls ObjComp = new CompCls();
  public void ProcessRequest(HttpContext context)
     string conString = ObjComp.strCon;
     SqlConnection con = new SqlConnection(conString);
     string Proj = context.Request["id"];
     SqlDataAdapter Ad = new SqlDataAdapter("SELECT   Attachment,AttachmentFileName FROM tblProjectsAttachment WHERE EntryId=@EntryId", con);
    Ad.SelectCommand.Parameters.AddWithValue("@EntryId", Proj);
    DataSet DS = new DataSet();

    using (con)
        byte[] file = (byte[])DS.Tables[0].Rows[0][0];
        string Filename = DS.Tables[0].Rows[0][1].ToString();
            ("Content-Disposition","inline;attachment; filename=\"" + Filename + "\"");
             context.Response.AddHeader("Content-Length", file.Length.ToString());
             context.Response.ContentType = "application/octet-stream";
        catch (Exception ex)
            context.Response.ContentType = "text/plain";


 public bool IsReusable {
    get {
        return false;

Want to more about http handler and http module go to below link (httphandler and httpmodule in

If We are hosting your application in IIS 7 then you have to do some additional setting in IIS 7 to be register httphandler and httpmodule in IIS 7 take look at this link below. httpmodules-and-httphandlers-in-iis-7.html

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