[jax-rs-spec users] Re: Early feedback about JAX-RS 2.1 / SSE specification

From: Sergey Beryozkin <>
Date: Wed, 8 Feb 2017 14:47:25 +0000

Hi Pavel

Thanks for the fast feedback,

SSEContext name is fine IMHO, nearly everything it creates is specific
to a given client SSE connection,
so I'd keep the name,

the only thing that it creates and is not specific to a current
SSEContext is SSEBroadcaster.

The code you typed below is fine, which is what I was implying.
The following code though looks strange:

public Response(@Context SSEContext sseContext) {
      SSEBroadcaster broadcaster = sseContext.newBroadcaster()

It is a valid JAXRS SSE code but it does not make sense given that the
broadcaster is a method local property which indeed defeats the idea of
the broadcaster and if it is made a class level property then it will
have to be synchronized ?

Thus the code you typed below is OK, but the code I typed above is not
hence I suggested to make it invalid by having
sseContext.newBroadcaster() throwing ISE if this method is called from a
SSEContext injected as a method parameter
(same as for example in your code below you'd try to subscribe a
sseContext.newOutput to the broadcaster during the property injection time)

Or may be introduce SSEBroadcaster context

Thanks, Sergey
On 08/02/17 13:37, Pavel Bucek wrote:
> Hi Sergey,
> thanks for digging in your email archive and bringing this up.
> I just tried to write minimal SseBroadcaster usecase and this was the
> result:
> @Singleton @Path("/") public class SseResource { private final
> SseContext sseContext; private final SseBroadcaster sseBroadcaster;
> @Inject public SseResource(SseContext sseContext) { this.sseContext =
> sseContext; this.sseBroadcaster = sseContext.newBroadcaster(); } @GET
> @Path("eventStream") @Produces(MediaType.SERVER_SENT_EVENTS) public
> SseEventOutput eventStream() { final SseEventOutput eventOutput =
> sseContext.newOutput(); sseBroadcaster.subscribe(eventOutput); return
> eventOutput; } public void onEvent(String event) {
> sseBroadcaster.broadcast(sseContext.newDataEvent(event)); } }
> I see what You and Andriy mean about broadcaster not being really
> contextual, but .. I believe that's valid for all methods. Let's
> review SseContext:
> public interface SseContext { SseEventOutput
> newOutput();OutboundSseEvent.Builder newEvent();SseBroadcaster
> newBroadcaster(); // this is not pushed to the public repo yet :)
> default OutboundSseEvent newDataEvent(String data) {}default
> OutboundSseEvent newDataEvent(String data, String name) {}}
> It's not really a context, it feels more like a factory. I don't see
> anything related to current context - thread/request/application. I
> can imagine an app (war) which would create new outbout event and pass
> it to another war. And it would still work.
> Also, the naming of the methods (new*) suggests that the "SseContext"
> always produces new instances, it doesn't do a lookup in thread local
> or any other store, it just creates instances.
> Would rename to SseFactory (or any better name), help with the issue
> raised by Andriy?
> TBH, it doesn't feel right to limit the API in a way you've proposed -
> a method with SseContext as a parameter would work / not work based on
> from where it was called. I'm not saying there are no schemes like
> that already, but here it feels more artificial and doesn't really
> help (the error is still visible in the runtime, not before).
> Also, I belive the sole purpose of having SseContext is to not have
> builders for OutboundEvent, Broadcaster and EventOutput. We might even
> consider removing SseContext and introduce those builders, but it
> would make the connection from the API to the implementation slightly
> more difficult. Or we can improve that, make it a "broadcaster store"
> - something like "SseContext#getOrCreateBroadcaster(String Id)"..
> (that's just me thinking out loud :).
> What do you think?
> Thanks and regards,
> Pavel
> On 08/02/2017 12:47, Sergey Beryozkin wrote:
>> Hi Pavel
>> Can you review the thread text below please (see a note from Marek).
>> SSEContexts can be passed as method parameters, so when one creates a
>> broadcaster it gives the impression the broadcaster is
>> the current SSEContext specific
>> Would it make sense to enforce that SSEBroadcaster can only be
>> created if SSEContext is injected as a thread local proxy as opposed to a
>> case where the broadcaster is created from SSEContext passed as a
>> parameter (SSEContext.newBroadcaster() would throw the
>> IllegalStateException is this case) ?.
>> Thanks, Sergey
>> On 15/08/16 12:58, Sergey Beryozkin wrote:
>>> Hi Marek, Andriy, All
>>> FYI I tried to 'justify' the current design by the spec leads by the
>>> requirement to have an implementation specific
>>> SSEBroadcaster introduced without having to introduce an
>>> SSEBroadcaster Context - the latter would make it possible to pass
>>> SSEBroadcaster as a method parameter which might not be ideal.
>>> I agree with the Andriy's observation though that it does look like
>>> it is a current SSEContext/event stream dependent if SSEContext is
>>> passed
>>> as a method parameter.
>>> Perhaps a neater way to work with broadcasters can be found :-)
>>> Sergey
>>> On 15/08/16 08:49, Marek Potociar wrote:
>>>> Hi Andriy,
>>>> This is a good observation - thank you for spotting this. I’ll give
>>>> it some thought and come up with a fix proposal.
>>>> Cheers,
>>>> Marek
>>>>> On 14 Aug 2016, at 04:36, Andriy Redko <
>>>>> <>> wrote:
>>>>> Early feedback about JAX-RS 2.1 / SSE specification
>>>>> Hey JAX-RS leads,
>>>>> As some of you may already know, the Apache CXF project is one of
>>>>> the early adopters of
>>>>> the JAX-RS 2.1 specification. In particular, we are currently
>>>>> actively working on implementing
>>>>> SSE support, based on drafted JAX-RS 2.1 API. Along the way we
>>>>> stumbled upon some design
>>>>> decisions which may require a bit of clarification or (hopefuly) a
>>>>> second thought. The use case
>>>>> in question is related to SseBroadcaster. Essentially, the idea
>>>>> sounds pretty simple: events
>>>>> into multiple SSE streams could be easily broadcasted. F.e. here
>>>>> is a pseudo-code for typical
>>>>> scenario:
>>>>> SseBroadcaster broadcaster = new SseBroadcasterImlp();
>>>>> broadcaster.register(stream1);
>>>>> broadcaster.register(stream2);
>>>>> ...
>>>>> broadcaster.broadcast(event1);
>>>>> broadcaster.broadcast(event2);
>>>>> In nutshell, current Jersey's SSE implementation does exactly
>>>>> that. However, in JAX-RS 2.1 API
>>>>> draft SseBroadcaster could be created only from SseContext, f.e.:
>>>>> Response stream(@Context SseContext context) {
>>>>> SseBroadcaster broadcaster = context.newBroadcaster();
>>>>> broadcaster.register(context.newOutput());
>>>>> ...
>>>>> }
>>>>> It kind of works but totally defeats the idea of broadcaster as
>>>>> being independent from SseContext or/and
>>>>> streams it serves. Currently, every time new instance of the
>>>>> SseBroadcaster will be created, with no
>>>>> straightforward way to share it across multiple SSE streams. How
>>>>> it could work though may look like that
>>>>> (the implementation details could vary, just trying to present the
>>>>> idea):
>>>>> private SseBroadcaster broadcaster = SseBroadcaster.newBroadcaster();
>>>>> Response stream1(@Context SseContext context) {
>>>>> broadcaster.register(context.newOutput());
>>>>> ...
>>>>> }
>>>>> Response stream2(@Context SseContext context) {
>>>>> broadcaster.register(context.newOutput());
>>>>> ...
>>>>> }
>>>>> In this case, the SseBroadcaster is truly context-independent, and
>>>>> serves it purpose very well. We were trying to
>>>>> come up with some realistic scenarios for SseBroadcaster utilizing
>>>>> the current specification draft but did not really
>>>>> succeeded. Surely, there are a few way to make it work but they do
>>>>> not look good. Does it make sense? Whould you
>>>>> mind guys to give some clarifications/guidance on that?
>>>>> Thank you a lot!
>>>>> Best Regards,
>>>>> Andriy Redko