[jax-rs-spec users] Re: [jsr339-experts] Re: HEADS-UP, IMPORTANT: Problems with JAX-RS interceptors

From: Martin Matula <>
Date: Mon, 30 Apr 2012 17:05:11 +0200

Hi Bill,

On 4/30/12 4:30 PM, Bill Burke wrote:
>> 2) readEntity() should make an implicit call to bufferEntity() before it
>> does anything. This is just for filters! Not for reading in the resource
>> method or the client.
> Just a thought..Maybe it shouldn't be implicit? Maybe the filter is
> reading the entity, then replacing it with writeEntity(), so a buffer
> is overkill? Or maybe its just better to protect the filter developer
> from himself? I don't know...

OK, not implicitly buffering may provide more flexibility. On the other
hand one poorly written filter can break everybody else. Not sure what's
better. I don't have a strong opinion on this one.

>> 3) maybe - remove get/setEntityStream() from filters (could not find a
>> use-case that could not be covered by interceptors or a combination of
>> an interceptor and a filter that triggers the interception by calling
>> bufferEntity()). Or maybe we want to keep it to be safe. Which leaves us
>> with just the two things above.
>> Here is the rationale:
>> - on the receiving end, you want "decoding" interceptors to work based
>> on the headers, not based on the annotation - i.e. if the entity in the
>> incoming message is zipped, it is not the resource method that tells me
>> it is, it is the sender who should tell me - by the way of the headers.
>> So, typically no annotations processing should be needed to make the
>> stream usable for other consumers. At least I think I would never add a
>> feature that would not have this kind of characteristics.
> hashes or signatures?

Shouldn't the hashes/signatures be verified based on headers then? I.e.
if the sender sends a hash/signature, don't you always want to verify?
And only use the annotation for enforcement? That way your verification
interceptor can be global and the enforcement would be name-bound. And
things would work. Or do you need to read something from the annotations
which is essential for the signature/hash computation?

Otherwise I don't know how to implement it cleanly - I guess you would
have to buffer headers (if you want to buffer the original stream) as
well, since after my gzip interceptor removes the encoding header and
somebody later reads the original stream from the buffer, my gzip
interceptor will no longer know it has to decode - unless it gets the
buffered original headers as well, no? The "mark" in the property bag
would not be enough in this case, as the interceptor does not know when
it works with the original stream as opposed to a new stream created as
a result of writeEntity(). Seems to make things too complicated, no?

>> - given that, with the current API, I can implement gzip/decryption
>> either as a prematching filter (by wrapping the stream using
>> get/setEntityStream() on the filter context) - this is not reusable by
>> the client; or even better (and reusable by the client) as an untyped
>> global (unbound) interceptor. The interceptor can wrap the entity stream
>> and remove the encoding info from the header, to make sure it does not
>> try to unzip an already unzipped stream later in the processing. It may
>> be a good practice to add a "mark" to the request property bag
>> (indicating the message was zipped or encrypted - which can be useful if
>> you want to have encryption enforcement filter somewhere in the chain
>> that ensures that only encrypted messages are allowed).
> FYI, resteasy implements gzip as an interceptor. The code is reusable
> on client and server.

Makes sense.

[skipping part of the message]
> One last issue:
> * If you call writeEntity() what should happen to headers? For
> example, if the original wire bytes are gzip encoded and you call
> writeEntity() what happens to the Content-Encoding header? In this
> case, maybe we writeEntity() should have an additional headers parameter?
> public <T> void writeEntity(
> final MultivalueMap<String, Object> newHeaders,
> final GenericType<T> genericType,
> final Annotation annotations[],
> final MediaType mediaType,
> final T entity);

What would you pass to the header parameter?
writeEntity triggers interceptors, based on the current headers, the
gzip interceptor would either kick in or not, no?

> * BTW I think writeEntity() is the most dangerous method of all.
> readEntity() we can get around potential problems with the workaround
> of buffering the entity. writeEntity() has no such guarantees.

Another thing which would be less error prone if the gzip, encrypt, hash
and signature interceptors are global and only the enforcement
interceptors/filters are name-bound. You would verify everything when
buffering/reading for the first time, add marks to properties and the
enforcement filter/interceptor would later just check that signature was
present and valid in the original stream by the way of checking the mark.
This way even writeEntity should work in most cases (as it would kick in
after these interceptors have done their work).

One more thing - should annotations[] be added to the client API
somewhere (e.g. to the methods that work with entity or to the Entity
class) to make name-bound interceptors reusable on the client side?