API, REST, SOAP, XML-RPC, WTF?!?!

[eluser]Phil Sturgeon[/eluser]
I had hoped someone with a bit more knowledge on the subject would jump in to clear things up a little, but you might be in for a wait.

When you say "Should I just not worry about it and create a controller that receives post variables and a response to the page? Then sites that rely on the API could just cURL some post data to the controller and scrape the response.", that is all any of these API "methodlogies" use. They just do it in a certain way with certain suggestions.

In much the same way as CodeIgniter's MVC patterns can be followed or ignored, so can these methodoligies. At work we use what we call a REST API, but really it is a mere GET based API. Other than the fact we can make oour URL requests in a certain way, not much sets our REST server apart from any other PHP outputted XML, JSON, etc.

If you basically just want to server up XML to other pages, you can do that with basic CodeIgniter and XML, or take a look at the REST controller I posted above which should show you how to make a very simple XML API. You can use the example controller and all the formats default to XML so you can't go wrong.

I will have a REST client API finished which will accept output created by your REST controllers (or any other REST API). Essentially, my REST client is a tarted up cURL wrapper that handles format convertion and MIME types, so again, you are on the right lines.