[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 12:43:31 +0200


On Oct 22, 2012, at 12:37 PM, Marek Potociar wrote:

> On Oct 21, 2012, at 4:47 PM, Jan Algermissen <> wrote:
>> [Top posting because it is really just supportive oif the overall issue]
>> Having gone through the whole thing today, I agree with Markus that there is a severe problem with the overall 2.0 spec.
>> Kudos for pointing at that - its a tricky thing, easily overlooked when looking at the individual features.
>> The problem is the original design of the MessageBodyWriter API (Bill hinted at that already) not the new filter API:
>> MBWs are invoked *after* filters.
>> Filters can (and we need that use case) hook transformers into the output stream.
>> Filters do not see any Content-Length because that is taken from the getSize() of MBWs
>> Once MBWs are reached, they do not know (and should not care) whether the stream they are going to produce will be changed.
>> Hence any result of getSize() that is not -1 is completely useless and error prone because it can lead to wrong Content-Length header value any time.
>> Producing an impossible to find bug from the POV of the API user, BTW.
>> Solutions:
>> 1) describe exactly what JAX-RS implementations have to do. E.g. Ignore getSize() once setOutputStream( ... ) is called.
> This option did not occur to me. I am wondering if it would solve all the issues though? E.g. what if I really only want to log or audit the streamed data? Does it mean that I have to still ignore the MBW.getSize()?

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.

I am not sure though the runtime can do that either.


> 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