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

From: Jan Algermissen <>
Date: Mon, 22 Oct 2012 16:18:01 +0200

On Oct 22, 2012, at 2:29 PM, Marek Potociar wrote:

> Hi Jan,
> When you say the overall design is broken, do you specifically mean the MBW.getSize() not fitting well into the picture

Yes, that is what I meant. Sorry.

> or is there anything else?
> Also, when you say that the problem cannot be fixed by the developers, do you think that (given most MBWs already return -1 anyway) a workaround where a user would need to override a particular MBW with it's own (perhaps wrapper or extension) implementation that returns -1 from getSize() is not possible? Again, most MBWs already are "compatible", so we're talking about marginal use cases here...

Agreed (as I said, I never use getSize() anyhow, hence never occurred to me). However, in Markus' case the non -1 return value seems to come from a Jersey build-in MBW. That is what I mean when I say that it is a very hard to find 'bug'.

> FWIW, I agree that we need to fix the getSize() issue in the spec. It just seems to me we need a longer discussion about this and I'm not sure if we can agree on a solution in time for 2.0.

I am +1 on Bill's suggestion to deprecate it and require ignoring it from 2.0 on. This will not break existing apps as they would silently default to chinked transfer encoding.

JAX-RS implementations could be required to issue a warning if they find an MBW that overwrites getSize() *and* filters or interceptors.


> Marek
> On Oct 22, 2012, at 12:45 PM, Jan Algermissen <> wrote:
>> 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 ...'
>> Jan
>>> 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