Facebook® Application Development For Dummies®

Staying Updated via Real-Time Objects on Facebook

Facebook has its own real-time features. To understand these features, you need two things:

• A callback URL: This is the Web address that Facebook will notify each time it finds new data about the objects you are subscribing to.
• A subscription: You can have multiple subscriptions, and this is where you tell Facebook what data you want to be notified about and where on your Web server Facebook should be notifying.

The following sections show you how this process works.

Creating your callback URL

Facebook requires you to have a script somewhere on your Web server that can handle the requests it sends. Facebook can send two types of requests:

• GET request: Gets sent to your Web servers when Facebook is creating the subscription you set up under the section “Creating your subscription,” later in this chapter.
• POST request: Notifies your Web server that new information is available about an object.

To create your callback URL, you need to set up a subscription responder. This simple script detects that a GET request was sent to your Web server, reads the information that Facebook sends to it, verifies it, and sends some information back to Facebook.

Here's the data Facebook sends:

• hub.mode: This will always be “subscribe.”
• hub.challenge: This is a random string of text that I show you what to do with in a second.
• hub.verify_token: This is (hopefully) the token that you sent to Facebook previously in the verify_token parameter.