Pingback and TrackBack: ease of implementation (or not)

Finally I managed to implement pingback in addition to TrackBack, and it was interesting to implement both, to compare them from a developer's perspective - as both are technologies that enable other blogs to link back blog entries that link them and this way create a permanent connection between two blogs.

One target of pingback is said to be that it should be "implementable with minimal effort", I also read in a few places that it should not attract spam as easily as TrackBack. The latter has been achieved quite nicely, as the pingback client needs to tell the server the source URL containing the original link as well as its target, and the server needs to verify this link to this target actually exists in the source. TrackBack on the other hand just sends the the URL to link back to and needs no verifications, so strictly according to the spec, a TrackBack server just links back to anything anyone else tells it to link. Of course, most TrackBack servers nowadays do verify that their blog is linked from the source - as does this blog here, like I pointed out in a recent post here.
The ease of implementation was not such a clear win for pingback though in my case. Where it clearly wins over TrackBack is "autodiscovery" (automatically discovering link targets in a blog entry that are able to link back via one of those technologies): While TrackBack uses a rather complicated to detect RDF snippet that needs to be placed in the entry, pingback uses a very easy to read HTTP header (and an also easy to detect HTML <link> tag as a fallback) to detect if some page is pingback-enabled. Telling the other blog that it should link, i.e. actually "pinging" it, is quite simple on the TrackBack side though: do a simple HTTP POST with urlencoded data, get very simple XML as a reply that tells if it was successful or not, and that's it. Pingback on the other hand achieves that part via an XML-RPC call. This might be easy to implement if you have an XML-RPC server running on your site already, but if you don't, it requires you to send a rather deeply structured XML document in a POST request as a client, and as a server, to retrieve the data from that doc (I needed to spend some time to even find out how to get this body of the incoming request in PHP) and send an even more complicated XML reply. So the implementation of the actual ping is (without having working XML-RPC support in place already) much harder for pingback than for TrackBack. I guess there's rarely a technology that has only good sides to it...

BTW, I know that there's some XML-RPC support bundled with PHP (via XMLRPC-EPI), but as there's no good documentation of it anywhere (one case where the else good PHP manual really sucks), I even felt safer to manually deal with that form of communication.

That said, I got both technologies to hopefully work now on this blogging system, including autodiscovery for both of them (if both are supported, pingback is preferred), and I hope users of CBSM and our community system will like them.