synapse-dev mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "Ruwan Linton" <>
Subject Re: Proposal to implement ws-eventing and an event distribution model in Synapse
Date Fri, 12 Sep 2008 09:01:00 GMT

Very nice explanation of the concepts that we have been trying to put
together into the code. Let me add some more to your explanation and refine
the configuration a bit more.

<eventSource name="blah">
        <property name="blah">some xml prop</property>
        <property name="other" value="some text property"/>
        <subscription id="static1">

Here I am getting rid of the wsEventing configuration element where you
specify the subscription service and the event source service. So my idea is
we can extend the proxy services model here and create a new
EventingMessageReceiver, which listens for all the requests coming to this
event source. (I must also say at this point event source is now a service
inside synapse and that fits with the model of extending the proxy service

This EventingMessageReceiver knows how to filter out the the subscription
messages from the notification messages and it uses the specified
subscription manager if it is a subscription request, and if it is a
notification message this receiver will delegate the request to the event
publisher where you find the set of subscribers with matching filter
conditions and execute the mediation sequence and then send the event to the
specified endpoint.

Paul, what do you think about this implementation. I am halfway through the
implementation and can have a look at this in the weekend :-) I have
attached an architecture diagram which explains this concept a little more
and that explains that the event source itself is now exposed as a service
to which you can send subscriptions and notifications.


On Fri, Sep 12, 2008 at 9:15 AM, Paul Fremantle <> wrote:

> Ruwan, AsankaA and I have been building a POC using WS-Eventing this
> week and we think we have come up with a reasonable model. We've
> already iterated several times, and in writing it out I have iterated
> beyond what the three of us discussed, so I am expecting more
> iterations now.
> What we implemented is a mediator that distributes events based on a
> filter. The initial code was almost dead simple:
> for (Subscription subs : manager.getSubscribers()) {
>                        boolean response =
> subs.getFilterMediator().test(mc);
>                        if (response) {
>                                Endpoint ep = subs.getEndpoint();
>                                ep.send(getClonedMessageContext(mc));
>                        }
>                }
> As we implemented the POC it became clear that it was more elegant to
> be able to associate a sequence to a particular subscription, and
> execute that sequence before sending. This goes a bit beyond the
> standard WS-Eventing model, but doesn't seem to contradict it or be a
> bad fit.
> We also implemented a WS-Eventing subscribe model. Now that is
> logically separate, because there might be other ways to subscribe.
> For example, you might subscribe by adding an entry in a registry or
> using WS-Notification or your own interface. We also have allowed
> simple static subscriptions in the synapse.xml model too.
> So the mediator itself is really simple - it only needs to get access
> to some kind of thing that manages the subscriptions that can give it
> a list of subscribers. In WS-Eventing an "Event Source" is something
> that emits events. Effectively our mediator is therefore an event
> source. So effectively the event source name is how you reference the
> manager that gives you the list of subscribers:
> <sequence>
>    <event-source-publisher event-source-name="name"/>
> </sequence>
> Now how do you define these event sources. Well we want a new top
> level child of <definitions> that is configured at start time. And
> this defines an event-source, and also configures how the
> subscriptions can happen.
> <definitions>
>  <eventSource name="blah">
>     <subscriptionManager
> class="">
>        <property name="blah">some xml prop</property>
>        <property name="other" value="some text property"/>
>     </subscriptionManager>
>     <subscription id="static1">
>        <filter....>
>        <sequence...>
>        <endpoint..>
>     </subscription>
>     <subscription...>
>     <wsEventing>
>        <eventSourceService name="myEventSource">
>            <same subchildren of proxy go here>
>        </eventSourceService>
>        <subscriptionManagerService name="myEventSubManager">
>             <same subchildren of proxy go here>
>        </subscriptionManager>
>     </wsEventing>
> <eventSource>
> Lets go through this:
> Each event source has a subscription manager. This is a class that
> keeps track of subscriptions. Here are some examples: a transient in
> memory one. A database backed persistent one. A registry backed
> read-only one. A registry backed read-write one. The class must
> implement a simple interface:
> public interface SubscriptionManager {
>        List<Subscription> getSubscribers();
>        Subscription getSubscription(String id);
>        String addSubscription(Subscription subs);
>        boolean deleteSubscription(String id);
> }
> The subscriptionManager instance is injected with config properties at
> startup just like other things are (tasks, class mediators, etc).
> These might contain the JDBC connection parameters or the URL of the
> registry.
> Next come static subscriptions. These are added into the subscription
> manager by synapse. That happens once at startup.
> The next piece is WSEventing specific, but there could be other
> children for notification etc. Here I'm not 100% sure that we need to
> separate the EventSourceService from the SubscriptionManagerService.
> In WS-Eventing it says these can be the same endpoint or different.
> Basically the configuration of these is the same as a proxy, allowing
> configuration of security etc for this endpoint.
> We certainly haven't done everything. We haven't handled expiry,
> though . We haven't thought about other deliveryModes. We haven't
> dealt with efficiently handling evaluating multiple subscriptions
> against a single message at once. We have simply re-used the existing
> filtermediator code to implement XPath and Xpath/Regex filters as is
> (we can be much more efficient, for Xpaths, by e.g. using DanD's SXC
> code which can evaluate multiple Xpaths on a single message). But its
> not a bad start.
> I'd really appreciate if we have the right overall structure. I did a
> first cut of code, but Ruwan is tidying it up right now, so expect a
> check-in soon.
> Thanks
> Paul
> --
> Paul Fremantle
> Co-Founder and CTO, WSO2
> Apache Synapse PMC Chair
> OASIS WS-RX TC Co-chair
> blog:
> "Oxygenating the Web Service Platform",
> ---------------------------------------------------------------------
> To unsubscribe, e-mail:
> For additional commands, e-mail:

Ruwan Linton - "Oxygenating the Web Services Platform"

View raw message