Keyvan Nayyeri

One of my yesterday’s blog posts was about implementing a trackback handler in ASP.NET and I stated that I will write a separate post about implementing a pingback handler as well.

Even though trackback and pingback may look like similar concepts to ordinal users but they’re somewhat technically different. However, when reading this post, you will notice some commonalities between these two concepts and their implementations.

Pingback is built on top of XML-RPC web services and its infrastructure is very similar to MetaWeblog API that I had covered before.

Overview

Pingback is a common concept on the web among site owners and bloggers and is used to do the same job as trackback does. Pingback connects a destination site to the source site that has referred to it. This way, readers can find relevance content easily. Pingbacks are stored in the same way as trackbacks and sometimes there may not be any noticeable difference between them like what is provided in Graffiti.

The infrastructure of pingback is built on top of XML-RPC services and there is a workflow behind them that I describe here shortly:

• Content on the source site is published and contains a link to a destination page.
• Source site looks for some specific information in the destination site. Source site has to look for two types of information in a specific order. First of all, it looks for an X-Pingback header in the destination site and if it couldn’t find it then it looks for link information for pingback in the destination page.
• If there isn’t any of these two values provided then the source site gives up.
• If there is any of these two values then the source site sends a pingback request to the XML-RPC service on the destination site.
• Destination site receives this request and stores the URI of the source page in its system.

Like trakcbacks, pingbacks are also commonly implemented by many of the common blogging engines so you wouldn’t worry about anything unless you want to implement your own blogging engine or site.

Before talking about more details of these steps, let me point that you need to download and install XML-RPC.NET library to be able to use the sample code provided in this blog post.

Add the HTTP Header

As you saw, one of the first steps is to add an HTTP header to your site or provide a link with appropriate rel attribute in your pages.

The preferred method is HTTP header and you need to set an X-Pingback header to the URI of your pingback service.

Below code adds such a header to an ASP.NET page.

Add the Link

The other way to provide information about pingback service on your end is, adding a <link /> element to your page headers with a rel attribute set to pingback value and an href attribute set to the URI of your pingback service. Here you can see an example:

Create an HTTP Handler

The next step, as you guess, is creating an ASP.NET HTTP handler that will act as an XML-RPC service. Here I create a PingbackHandler class and derive it from XmlRpcService included in XML-RPC.NET library. This will turn my class to an XML-RPC service.

I also need to define my HTTP handler in Web.Config as is shown below.

Implement the HTTP Handler

But the main part of pingback implementation is, writing the XML-RPC service. Thank to XML-RPC.NET library, this is pretty simple and easy to achieve. You need to provide an XML-RPC method called pingback.ping that gets two string parameters as the URI of the source page and the URI of the target page and returns a string value that usually contains a success text or failure text.

Also you usually need to parse the destination page URI in order to extract some parameters like post identifier or post name to be able to store the pingback request for the relevance local item. Often blog engines try to retrieve the title of the source page and store it among the source page URI in their local storage.

So here is the code for my implementation of this pingback handler:

Note that I have left some code as comments for you to implement it based on your own code. Like trackback, pingback is a good candidate for spammers as well and this is the main reason that you need to check and confirm the existence of the source URI and the inclusion of your destination URI in it.

The final response of this method is a simple text string that doesn’t play a very important role in the process.

That’s all about pingback handling in ASP.NET! You see that they are a little easier to implement than trackbacks. I may write a post about sending trackback and pingback requests from your ASP.NET applications in the near future.

You can grab the source code sample of this post from here.