Bill the Plumber

As we’re rolling out Resteasy 3.0, we have to pass the JAX-RS TCK.  The good thing about this is that the TCK has grown massively is size and has a lot more test coverage for all old and new features of JAX-RS.  It allowed me to uncover a few bugs I would not have found without the TCK.  An unfortunate downside the TCK also got a lot stricter in some of the weak areas of the JAX-RS specification, particularly the request dispatching algorithm.  I’ll be blunt, the algorithm is poor.  IMO, the old spec leads made a huge mistake in introducing implementation details to the specification and now we have a poor algorithm we are stuck with.  Us vendors cannot innovate and improve it because the TCK has backed us into a corner and the licensing fine print of Java EE makes it really hard for us to ship things that diverge from the spec.  Here are a bunch of problems that used to work in Resteasy, but will no longer work because the TCK tests every fine detail of the JAX-RS matching algorithm.

•  The @Path annotation at the class level is matched first before matching any resource methods.  Only classes with the best and exact regular expressions are picked.  Then the rest of the request is matched with remaining methods.  So this won’t work anymore with a spec compliant algorithm:

Request: OPTIONS /foo

@Path("/foo")
public class Foo {
   @GET
   public String get() {...}
}
@Path("/{.*}")
public class OptionsDefault {
   @OPTIONS
   public String options() {...}
}

Earlier versions of Resteasy would match OptionsDefault.options().  Now, this method will not match according to the spec rules and you’ll get the default JAX-RS OPTIONS behavior.

• Locators are never resolved if there are resource methods that match the request.  For example

PUT /foo/sub

@Path("/foo")
public class Foo {
   @GET
   @Path("sub")
   public String get() {...}

   @Path("{id}")
   public Locator locator() { return new Locator(); }
}

public class Locator{
   @PUT
   public void put() {...}
}

You’d think that the request would resolve to Locator.put() but you’d be wrong! Because there is a resource method whose path matches the request, but not the method you’d get a 405 response from the server. What’s interesting if you flip the expressions, a PUT request would work, but a GET request wouldn’t!

PUT /foo/sub

@Path("/foo")
public class Foo {
   @GET
   @Path("{id}")
   public String get() {...}

   @Path("sub")
   public Locator locator() { return new Locator(); }
}

• It is possible to have poorer matches

GET /fart
Accept: text/plain

  @GET
  @PATH("foo") 
  @Produces("text/plain") 
  public String get1() {} 

  @GET
  @Path("{text}") 
  @Produces("text/plain") 
  public String get2() {} 

  @GET
  @Path("f{text}") 
  @Produces("text/*") 
  public String get3() {}

You would think that GET /fart would match the get3() method because it is more specific path, but you’d be wrong.  Because get3() has a less specific @Produces get2() would match.  This is weird because the spec originally tells you to sort expressions on a best-match basis but then ditches this information to match Accept headers.

Another related note is the default returned media type.Right now the default is dependent on the deployment.  If there is no Produce header, then the returned media type defaults to a union of the Accept header and explicit media types of all available MessageBodyWriters.  There goes your portability!  Instead, implementations should be allowed to specify their own default or even make it configurable.  But, of course we can’t do that!

Granted some of these issues are edge cases, but IMO, some are not.  The specification has 2 pages on english/pseudo-academic algorithm syntax to describe this very complex, but poor algorithm.  Users will get frustrated trying to understand it.  The experts themselves argued for days on interpretation of the specification.  Users will scratch there head wondering why certain classes will match and some won’t and blame the vendor’s implementation.  Resteasy had at least 4 user-reported regression tests that failed as a result of following the specfication matching algorithm religiously.  I know these users will be back complaining that Resteasy 3.0 does not work for them when Resteasy 2.3.x did.