Dynamic Flash

I find it shocking that the Flash Player still lacks the ability to properly interact with RESTful web services. I keep running into this issue, and every time I scour the Internet hoping that someone, somewhere has found a solution. Every time I return disappointed, hating the Flash Player just a little bit more.

REST stands for REpresentational State Transfer, and describes a technique to organise a web service into resources that can be uniquely identified by a URI. The actions that can be performed on that resource map directly to the standard HTTP methods: GET, POST, PUT, DELETE, HEAD and OPTIONS. With properly organised resources it’s possible to do virtually everything you can do with an RPC-style web service with REST. The benefit of REST is that it goes with the grain of the web, not against it.

The problem with the Flash Player is that the URLRequest class, which is the basis for all HTTP requests, only supports GET and POST operations¹. This is due to a limitation in the NPAPI pseudo-standard used by non-IE browsers that only exposes the ability to make GET and POST requests. Unless NPAPI is updated to allow other HTTP methods, and browser vendors and plugin authors update their implementations to match that new API, we need to find other ways of interacting with RESTful web services.

Now, If you’re lucky, the web service you’re trying to interact with will support some way of overriding the request method, such as a X-HTTP-Method-Override header. If this is the case, you can use the requestHeaders property of your URLRequest object to set the appropriate method:

// Create request object with appropriate resource URL
var req:URLRequest = new URLRequest( 'http://rest.example.com/v1/book/1234' );
 
// Use POST because DELETE is non-idempotent
req.method = URLRequestMethod.POST;
 
// Specify DELETE method in X-HTTP-Method-Override header
req.requestHeaders = [ new URLRequestHeader( 'X-HTTP-Method-Override', 'DELETE') ];

If your web service isn’t quite so forgiving, the only option you have is to use the ExternalInferface class and some JavaScript magic to make requests on behalf of your Flash project and send the response back. It’s an ugly hack, but a developer’s gotta do what a developer’s gotta do. If you’re interested in this workaround, leave a comment and I’ll knock up a simple example.

For what it’s worth, Silverlight fares no better in this regard. This is not surprising since Microsoft are stuck with the same browser plug-in APIs as Adobe, but that doesn’t make it any less annoying for developers on both sides of the fence.