JQuery Ajax code to access external XML data through Handler_jquery

<%@ WebHandler Language="C#" Class="WebApplication1.Stock" %>
namespace WebApplication1
{
using System;
using System.IO;
using System.Net;
using System.Text;
using System.Web;
using System.Collections.Generic;
using System.Linq;
///

/// Asynchronous HTTP handler for rendering external xml source.
///

public class Stock : System.Web.IHttpAsyncHandler
{
private static readonly SafeList safeList = new SafeList();
private HttpContext context;
private WebRequest request;
///

/// Gets a value indicating whether the HTTP handler is reusable.
///

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

/// Verify that the external RSS feed is hosted by a server on the safe list
/// before making an asynchronous HTTP request for it.
///

public IAsyncResult BeginProcessRequest(HttpContext context, AsyncCallback cb, object extraData)
{
var u = context.Request.QueryString["u"];
var uri = new Uri(u);
if (safeList.IsSafe(uri.DnsSafeHost))
{
this.context = context;
this.request = HttpWebRequest.Create(uri);
return this.request.BeginGetResponse(cb, extraData);
}
else
{
throw new HttpException(204, "No content");
}
}
///

/// Render the response from the asynchronous HTTP request for the RSS feed
/// using the response's Expires and Last-Modified headers when caching.
///

public void EndProcessRequest(IAsyncResult result)
{
string expiresHeader;
string lastModifiedHeader;
string rss;
using (var response = this.request.EndGetResponse(result))
{
expiresHeader = response.Headers["Expires"];
lastModifiedHeader = response.Headers["Last-Modified"];
using (var stream = response.GetResponseStream())
using (var reader = new StreamReader(stream, true))
{
rss = reader.ReadToEnd();
}
}
var output = this.context.Response;
output.ContentEncoding = Encoding.UTF8;
output.ContentType = "text/xml;"; // "application/rss xml; charset=utf-8";
output.Write(rss);
var cache = output.Cache;
cache.VaryByParams["u"] = true;
DateTime expires;
var hasExpires = DateTime.TryParse(expiresHeader, out expires);
DateTime lastModified;
var hasLastModified = DateTime.TryParse(lastModifiedHeader, out lastModified);
cache.SetCacheability(HttpCacheability.Public);
cache.SetOmitVaryStar(true);
cache.SetSlidingExpiration(false);
cache.SetValidUntilExpires(true);
DateTime expireBy = DateTime.Now.AddHours(1);
if (hasExpires && expires.CompareTo(expireBy) <= 0)
{
cache.SetExpires(expires);
}
else
{
cache.SetExpires(expireBy);
}
if (hasLastModified)
{
cache.SetLastModified(lastModified);
}
}
///

/// Do not process requests synchronously.
///

public void ProcessRequest(HttpContext context)
{
throw new InvalidOperationException();
}
}
///

/// Methods for matching hostnames to a list of safe hosts.
///

public class SafeList
{
///

/// Hard-coded list of safe hosts.
///

private static readonly IEnumerable hostnames = new string[]
{
"cnblogs.com",
"msn.com",
"163.com",
"csdn.com"
};
///

/// Prefix each safe hostname with a period.
///

private static readonly IEnumerable dottedHostnames =
from hostname in hostnames
select string.Concat(".", hostname);
///

/// Tests if the matches exactly or ends with a
/// hostname from the safe host list.
///

/// Hostname to test
/// True if the hostname matches
public bool IsSafe(string hostname)
{
return MatchesHostname(hostname) || MatchesDottedHostname(hostname);
}
///

/// Tests if the ends with a hostname from the
/// safe host list.
///

/// Hostname to test
/// True if the hostname matches
private static bool MatchesDottedHostname(string hostname)
{
return dottedHostnames.Any(host => hostname.EndsWith(host, StringComparison.InvariantCultureIgnoreCase));
}
///

/// Tests if the matches exactly with a hostname
/// from the safe host list.
///

/// Hostname to test
/// True if the hostname matches
private static bool MatchesHostname(string hostname)
{
return hostnames.Contains(hostname, StringComparer.InvariantCultureIgnoreCase);
}
}
}