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All blog platforms send out pings using the XML-RPC protocol whenever a new post is created or an old one is updated. It is very simple to send out XML-RPC pings using C#, because it is just a normal HTTP request with some XML in the request body. See here how to ping using C#.

To send a ping is the client part of the transaction. There must also be a server to intercept the ping – an endpoint. Feedburner is probably the most widely used by blogs at the moment. What happens is that when you write a post, the blog engine sends a ping to Feedburner’s XML-RPC endpoint. In the XML body of the ping request is the URL of your blog so Feedburner knows who sent the ping. It then retrieves your blog’s RSS feed, parses it, and spits it out to your readers. That’s how simple and powerful it is to use XML-RPC pings.

In an earlier post I showed you how to write the ping client, now let’s look at the server or endpoint. The endpoint can be used by any service that needs to be notified whenever content is updated on a website. That goes for all applications that listen to RSS feeds for instance.

The code

In 100 lines of code including comments, we are able to build an XML-RPC ping server endpoint. All it has to do is to listen for POST requests and parse the XML sent in the request body as shown in my earlier post. By parsing the XML it can find the URL that has been updated. The method HandleUrl is where the URL is passed to and it’s from here you write your logic to handle the ping request.

#region Using

 

using System;

using System.IO;

using System.Net;

using System.Xml;

using System.Web;

 

#endregion

 

public class XML_RPC : IHttpHandler

{

 

  ///<summary>

  ///Handles the URL that was sent by the ping request.

  ///</summary>

  private void HandleUrl(Uri url)

  {

    //This is where you write the code for handing the incoming URL.

    //It is the only place you need to change.

    HttpContext.Current.Response.Write(url);

  }

 

  #region Parse the request

 

  ///<summary>

  ///Parses the request body and returns the URL.

  ///</summary>

  private static string ParseXml(string xml)

  {

    XmlDocument doc = new XmlDocument();

    doc.LoadXml(xml);

 

    string methodName = doc.SelectSingleNode("//methodName").InnerText;

    if (methodName == "weblogUpdates.ping")

    {

      XmlNodeList values = doc.SelectNodes("//value");

      if (values.Count == 2)

      {

        return values[1].InnerText;

      }

    }

 

    throw new NotSupportedException("'" + methodName + "' XML-RPC method not supported");

  }

 

  ///<summary>

  ///Receives this content from the current HTTP request stream.

  ///</summary>

  public static string ReceiveBody()

  {

    using (StreamReader reader = new StreamReader(HttpContext.Current.Request.InputStream))

    {

      return reader.ReadToEnd();

    }

  }

 

  #endregion

 

  #region IHttpHandler members

 

  ///<summary>

  ///Gets a value indicating whether another request can use the<see cref="T:System.Web.IHttpHandler"></see>instance.

  ///</summary>

  ///<value></value>

  ///<returns>true if the<see cref="T:System.Web.IHttpHandler"></see>instance is reusable; otherwise, false.</returns>

  public bool IsReusable

  {

    get { return false; }

  }

 

  ///<summary>

  ///Enables processing of HTTP Web requests by a custom HttpHandler that implements the<see cref="T:System.Web.IHttpHandler"></see>interface.

  ///</summary>

  ///<param name="context">An<see cref="T:System.Web.HttpContext"></see>object that provides references to the intrinsic server objects (for example, Request, Response, Session, and Server) used to service HTTP requests.</param>

  public void ProcessRequest(HttpContext context)

  {

    string body = ReceiveBody();

 

    if (!string.IsNullOrEmpty(body))

    {

      try

      {

        string parsedUrl = ParseXml(body);

        Uri url;

 

        if (Uri.TryCreate(parsedUrl, UriKind.Absolute, out url))

          HandleUrl(url);

      }

      catch (Exception ex)

      {

        // Put whatever error handling you like here.

        context.Response.Write(ex.Message);

      }

    }

  }

 

  #endregion

 

}

Implementation

To use this XML-RPC server class you need to download the class below and put it in your App_Code folder. Then you need to register the handler in the web.config like so:

<httpHandlers>
  <add verb="*" path="xml-rpc.axd" type="XML_RPC" />
</httpHandlers>

The endpoint will then be located at example.com/xml-rpc.axd. The last thing you need is to add some logic to the HandleUrl method of the class and you are ready to go.

XML-RPC.zip (1,18 kb)

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