[jax-rs-spec users] [jsr339-experts] Re: Re: Re: Re: Heads Up: Severe problem when rewriting responses! Is our Filter API suitable?

From: Jan Algermissen <>
Date: Mon, 22 Oct 2012 12:45:26 +0200

On Oct 22, 2012, at 12:43 PM, Jan Algermissen wrote:
> I think the overall design is now broken because the original MBW API does not fit with the filter concept.
> The problem must be taken care of by the runtime because a developer alone cannot ensure correct Content-Length settings.

Sorry, should have added '..taken care of until getSize() is removed from the API ...'


> I am not sure though the runtime can do that either.
> Jan
>> Marek
>>> or
>>> 2) depricate getSize()
>>> I guess 1) needs to be added and implemented by every container in any case given that we cannot deprecate getSize immediately.
>>> It never struck me as an issue, because I never use built-in MBWs and mine allways return -1 from getSize() but looking at this, the original design of MBWs deciding upon Content-Length vs. Chunked-Encoding as simply wrong. This is an HTTP-connector issue and should be left to that layer.
>>> Bottom line: +1 to Markus saying that 2.0 cannot be shipped without that being fixed.
>>> Jan
>>> On Oct 20, 2012, at 6:09 PM, Markus KARG wrote:
>>>> Marek,
>>>>>> Sorry for repeating myself, but, whether to use chunked encoding or
>>>>> set a content-length header should be left up to the underlying HTTP
>>>>> engine (i.e. the servlet container). I know for a fact that Jetty and
>>>>> Tomcat use a buffered output stream. If you finish a request within
>>>>> the limits of the buffer (without calling flush), then Content-length
>>>>> is set, otherwise chunk encoding is used.
>>>> ...not just "should" but MUST! And that underlying "engine" for a JAX-RS
>>>> filter (hence the layer that the filter relies on to manage this) is the
>>>> JAX-RS implementation (independend of whether it does it on its own or
>>>> instead relies on a deeper layer to do it), as that "engine" is defined
>>>> solely by means of an API -- JAX RS 2.0! (I think we all agree that a filter
>>>> has to work in Java SE environments, too, as in the opposite case we do not
>>>> need to define JAX-RS filter API at all: If we enforce Servlets, we can just
>>>> use Servlet Filters!).
>>>>> Ok, sorry for confusion. What I meant to say is that if you remove
>>>>> manually set Content-Lenght header as well as return -1 from
>>>>> MBW.getSize(), the IO container will take care of it. Since the
>>>>> solution is IO container dependent it would be hard to enforce a single
>>>>> standard behavior in JAX-RS IMO.
>>>> This does not work as the Content-Length header is not manually set, but is
>>>> set by Jersey. See below.
>>>>>> getSize() should also be deprecated and ignored. With the ability to
>>>>> wrap streams to do things like GZip encoding, getSize() is often wrong
>>>>> and should never be relied upon.
>>>> Exactly!
>>>> BTW, agreed, even for a simple log recorder *both*, getEntityStream *and*
>>>> setEntityStream are needed, otherwise the recorded content will never be
>>>> transferred. You are right; I missed this side effect.
>>>> But, frankly spoken, I still think (basing on what I experienced in the past
>>>> with Servlet Filters I came across, and basing on the filters I contributed
>>>> to) many of the future JAX-RS filters will be representational
>>>> *transformers* (hence: change Content-Length) in some way (not Java entity
>>>> modifiers or MBR/MBW caches, which surely are good for *different*
>>>> purposes), hence will enforce a "correctly working" underlying *automatic*
>>>> processing of Content-Length / Chunking in the JAX-RS provider (which may
>>>> itself offload this burden to the Servlet Container or implement it directly
>>>> in a Java SE case, in its sole discretion), adjusting the Content-Length
>>>> information according to the transformation *result* (not *source*) in its
>>>> representational form (hence: modify JSON or XML without knowledge or care
>>>> of neither the used MBR / MBW, nor Java Entity Class, nor JAX-RS Resource).
>>>> In the case of ISVs -like me- the problem is getting rather worse: The
>>>> filters we provide to the open market not only are purely representational
>>>> transformers, but are provided in binary form to anybody that has the need
>>>> to enable the particular functionality (hence "feature") of that filter to
>>>> any representational form produced by any completely unknown combination of
>>>> MBR / MBW, Java Entity Class, JAX-RS Resource *and JAX-RS implementation*.
>>>> Due to that, any proposed solution to the mentioned problem will "not exist
>>>> by definition" (i. e. are to be ignored by the designers), as that solution
>>>> is *Jersey* and / or *Servlet* specific! Neither does an ISV know whether or
>>>> not the filter will be used in a Servlet container or on a Java SE
>>>> environment, nor would it be wise to rely on one particular JAX-RS product.
>>>> Hence, ISVs can and will *only* rely on solutions guaranteed to work by pure
>>>> JAX-RS 2.0 API. So a Jersey-only solution is "not existing by definition" in
>>>> the context of a *spec* discussion.
>>>> Moreover I think you maybe missed the fact the a filter *cannot* remove the
>>>> false Content-Length header, as at time of filtering that header is actually
>>>> *not set* --- because it is *not* the JAX-RS Resource nor an earlier filter
>>>> that has set that header, but it is the JAX-RS 2.0 implementation (here:
>>>> Jersey 2.0 M08-1) itself which had set that header *automatically* basing on
>>>> the *original* representation (maybe it is a MBW inside of Jersey, I don't
>>>> know, it just is not there at .filter() time, but it is there in the
>>>> representation received by the client)! THAT DOES SIMPLY NOT WORK AND LEADS
>>>> As a result, there is *no* solution to the problem I have so far, which
>>>> unfortunately *enforces* a vote for "NO GO!" for the current draft of the
>>>> spec!
>>>> Potentially (and even worse: such easily) opening the doors to
>>>> *unexpectedly* induce such severe problems is a definitive no-go situation
>>>> for the complete specification, unfortunately! And the sole existing
>>>> workaround (using a filter to inspect request headers to enable / disable
>>>> the transformer, store them as a context property, check this in an entity
>>>> listener and then apply the transformation *there* as this runs *before* the
>>>> JAX-RS implementation auto-adds the Content-Length header), is such overly
>>>> complicated and error-prone that it simply looks as a design fault of the
>>>> specification to the average reader (as one sees the getEntityStream /
>>>> setEntityStream combination and will think that he can simply inline a
>>>> FilterStream, which, again, will result in the wrong Content-Length). Also
>>>> it will induce the next problem: What if that transformer must be the *last*
>>>> step in the filter chain (to ensure that another filter does not ruin the
>>>> transformed result again) - which currently simply is impossible as by
>>>> definition entity listeners MUST run *before* the very first filter will
>>>> run? As you see, all currently proposed "solutions" are just NOT COMPLETE OR
>>>> WORKING STABLE in any way!
>>>> Maybe you see a working solution with the current draft. I do not. The only
>>>> solution I see is that the spec has to be changed.
>>>> My solution proposal is: The spec must mandate that if a compliant JAX-RS
>>>> 2.0 implementation is setting the Content-Length header, then it MUST
>>>> calcuate its value from the *transformed* representation, but not from the
>>>> *original* representation provided by the MBW. Moreover, I would even
>>>> mandate that a compliant implementation MUST OVERWRITE the Content-Length
>>>> (to the correct value, certainly) always, as neither the JAX-RS resource,
>>>> nor a MBW, nor another filter, will know whether the deployer might add a
>>>> filter that changes the length of the representation! At last, JAX-RS must
>>>> not allow that a JAX-RS 2.0 implementation is providing a false value to
>>>> Content-Length just like Jersey does it at the moment (better to have NO
>>>> Content-Length set by Jersey than to have it set a wrong one)!
>>>> This is a very severe issue, and we MUST have a solution for that before
>>>> final release. I see absolutely no chance for a "GO!" to a draft that
>>>> provides the possibility to modify the representation using an inlined
>>>> FilterStream while the JAX-RS implementation is allowed to add a *false*
>>>> Content-Length header at the same time.
>>>> Regards
>>>> Markus