RESTEasy Interceptors (Proposed Feature)

A number of new ideas have cropped up on the RESTEasy developers list that indicate that adding some type of request/response interceptor API to RESTEasy could aid in adding these features. Such features include:

1. RESTEasy Server-Side Caching API Ideas
   
2. Content Negotiation customization
   
3. GZip Input/Output streams
   
4. Security
   

There could more, but you get the point. Below are a few approaches we could take.

Filter-Style Interceptor

This type of interceptor looks similar to a Servelt Filter and provides access to the raw request and response. more details TDB.

Annotation-based Interceptor

The annotation approach allows the developer to define specific points in the request/response lifecycle where we can alter the process. There are a few directions we could take this such as having really broad point cuts like @BeforeRequest and @AfterRequest. Or, we could have more fine grained pointcuts such as:

• @BeforeResresource: executes after the request has been processed, but before the resource method has been invoked
• @AfterResource: executes after the resource method has been executed, but before the MessageBodyWriter is invoked
• @BeforeWriter: after the request has been provecces and the resource method has been executed, but before the invocation of the MessgaeBodyWriter
  
• @AfterWriter: executed after the message body reader
  
• @BeforeReader: executed before the MessageBodyReader is executed
  
• @AfterReader: executed after the MessageBodyReade, but before the resource method
  
• Perhaps more? (some of these maybe redundant, but we'll work that out)

An interceptor might end up looking something like this:

@Provider

@Interceptor

public class CacheControlInterceptor

{

   @BeforeResource

   public Response checkCache(@Context HttpRequest request,

              @Context HttpResponse response,

              @Context RequestContext ctx)

   {

      ...check the cache...

   }

   @BeforeWriter

   public void addCacheControlHeaders(@Context HttpResponse response

                                      @Context RequestContext ctx)

   {

      ... write some cache control headers...

   }

   @AfterWriter

   public void grabBytesToMarshall(@Context HttpResponse response

                                   @Context RequestContext) {

   }

}

Unresolved Issues

One thing that still needs to get worked out if how to declare precedence of interceptors, what gets executed first, etc.