CXF-7860: Ensure @FormParam parms are consistent with Form entities

[andymc12]

This addresses an issue surfaced by the Jakarta JAX-RS API community in Issue 659 where a parameter marked as @FormParam may be injected with a value that is inconsistent with an entity Form parameter. The latter will have the latest contents of the HTTP form body stream whereas the former will not - modifications made to the HTTP form body during filters or interceptors will be lost, thus it is possible that the following code would fail:

@POST
public Response processForm(@FormParam("value") String value, Form form) {
    assertEquals(value, form.asMap().getFirst("value"));
}

This change ensures that the @FormParam parameters will match the values in the Form parameter. There is probably an optimization that I am missing that would only perform this logic if the input stream were modified - suggestions welcome on how I could best do this. Thanks!

[reta]

@andymc12 Thanks a lot for addressing this very edgy case. I was looking how the current implementation works and basically I was trying to understand if we could defer the evaluation of the HTTP parameters (like @FormParam) to a later phase. In general, I think it would be feasible but would significantly impact the existing design.

However, I think I found a simple trick to make it work: reordering parameters initialization. Here is an interesting exercise:

• Response processForm(@FormParam("value") String value, Form form) -> does not work
• Response processForm(Form form, @FormParam("value") String value) -> works just fine

So the idea in the nutshell is to a modify JAXRSUtils::processParameters to initialize parameters in a different order. In this case, the Form should be initialized before any @FormParam, it triggers the reader interceptors and the right values are propagated in Form and @FromParam arguments. It should also work in case of constructors or class members.

What do you think?
Thanks!

[andymc12]

@reta Thanks so much! That is a much better solution that what I had originally proposed. I had also considered that the "right approach" would be to refactor the phase when parameters were processed, but I think this solution is cleaner - and should not disrupt normal cases.

I've left the test cases unaltered, but I removed my changes from JAXRSInvoker and instead changed JAXRSUtils as you suggested. This passes all of the unit tests and the systests (including my new one). Can you take a look at the latest changes?

Thanks again!

[reta]

Looks good, thanks @andymc12 !