What is pingback?

You will notice in many blogs, in the comments section, many comments like this: Pingback from …. What is a pingback and how it differs from regular comments even if they are listed in same section?

I pingback is a pat on the shoulder from one blog to another where first says: Hey, psssst, blog! I mentioned you in a post, care to mention me back? The second blog may choose to post a comment (pingback comment) where it will take the title and a little excerpt from the first blog. The pinback specification can be found here but it's lame and explains nothing technical!

Had to find a solution!

As I built my custom blog engine I wanted to integrate pingback. Pingback relies on XMLRPC and you can read more here and here! I'll explain the concept in a nutshell: XMLRPC allows one to send commands in XML to a remote script by using HTTP POST and have it execute stuff! This is how pingback works. You send a command to the rpc client in the blog and the blog will choose the further steps.

How Pingback works?

These are the steps you have to take:

Step1: Load the page you link to and discover any RPC client. In the HTTP header will look like this:
X-Pingback: http://example.com/pingback/xmlrpc and in the HTML body it will look like this:
<link rel="pingback" href="http://example.com/pingback/xmlrpc" />

Step2: Notify the XMLRPC server of your link by sending a RPC pingback command.

Step3: Pray it'll pass moderation and appear in the blog :)

Warning: This is not a good link spam method unless you have some real content and the pingback passes moderation.

Now the technical PHP part!

I downloaded WordPress and the code inside is really not my type! Not clean and nice formatted as I enjoy PHP scripts. I have no time to see how WordPress works, I'd rather rebuild it myself! So … I kept looking and finally got to the solution I needed which is a two step trick. You have to autodiscover the RPC client and issue the command.

Below is the PHP script which relies on the XMLRPC integrated in PHP. I might make it standalone but I wrote this code yesterday. This code needs PHP cUrl Class previously declared!

<? //--------------------------------------------------- // This is the autodiscovery of XMLRPC client. Can be used alone. function findXmlRpc($target){ $hc=new eHttpClient(); $hc->get($target,0,1); $hdr = $hc->getHeader(); return (isset($hdr['X-Pingback']) ? $hdr['X-Pingback'] : false); } //--------------------------------------------------- // Change $returnbool to 0 to get exact XMLRPC response and error codes function pingBack($target,$source,$returnbool=1){ $xmlrpc = findXmlRpc($target); if($xmlrpc === false) return false; $request = xmlrpc_encode_request("pingback.ping", array($source,$target)); $http_info = array( 'method' => "POST", 'header' => "Content-Type: text/xml", 'content' => $request ); $context = stream_context_create(array('http' => $http_info)); $file = file_get_contents($xmlrpc, false, $context); $response = xmlrpc_decode($file); if($returnbool) return (xmlrpc_is_fault($response) ? false : true); if(xmlrpc_is_fault($response)) return array($response['faultString'],$response['faultCode']); return $response; } //--------------------------------------------------- ?>