Hi Kenton,
Thank you for your quick response! It's very helpful because the handler
for the disconnection is another issue actually.
On Tuesday, November 23, 2021 at 1:53:42 AM UTC+9 ken...@cloudflare.com
wrote:
> Hi Mitsuo,
>
> I recommend designing the interface like this:
>
> interface EventPublisher{
> interface Subscriber {
> updateEvent @0 (event: Int32) -> ();
> }
>
> interface Subscription {}
> subscribe @0 (subscriber: Subscriber) -> (result: Int32, subscription:
> Subscription);
> # To unsubscribe, drop the returned `subscription`.
> }
>
>
> Here, subscribe() returns a `subscription` object. This object has no
> methods. But, when the capability is dropped, then the destructor will run
> on the server side. Atn that point, you can remove the subscription.
>
> A big advantage of this approach is that it handles connection failures
> gracefully. If the client randomly disconnects, the `subscription`
> capability is automatically dropped, thus unsubscribing the client. This
> way you don't end up stuck sending messages to a disconnected subscriber.
>
> It also solves your problem because you can remember arbitrary metadata
> about the subscriber within the `Subscription` object, so you know what to
> remove when it's destroyed.
>
> -Kenton
>
> On Mon, Nov 22, 2021 at 12:40 AM mitsuo
> wrote:
>
>> Hi,
>>
>> I'm trying to implement pub/sub like communication model with the
>> following scheme.
>> *pubsub.capnp*
>> *interface EventPublisher{*
>> *interface Subscriber {*
>> *updateEvent @0 (event: Int32) -> ();*
>> *}*
>> *subscribe @0 (subscriber: Subscriber) -> (result: Int32);*
>> *unsubscribe @1 (subscriber: Subscriber) -> (result: Int32);*
>> *}*
>>
>> I'm using *kj::Vector m_subscribers *to
>> store the current subscribers.
>> When I try to implement unsubscribe and remove the Subscriber from the
>> Vector, I couldn't find good method to do that.
>> Could you give me some advice?
>>
>> *server implementation*
>> *class EventPublisherImpl final : public EventPublisher::Server {*
>> * protected:*
>> * ::kj::Promise subscribe(SubscribeContext context) {*
>> *cout << "subscribe request received" << endl;*
>> *m_subscribers.add(context.getParams().getSubscriber());*
>> *return kj::READY_NOW;*
>> * }*
>>
>> * ::kj::Promise unsubscribe(UnsubscribeContext context) {*
>> *cout << "unsubscribe request received" << endl;*
>> *auto unsub = context.getParams().getSubscriber();*
>>
>> *// I want to remove usub from subscribers like
>> m_subscribers[unsub].erase();*
>> *// But I couldn't find a method to compare*
>> *// "EventPublisher::Subscriber::Client" such as == operator or
>> public method*
>> *// to distinguish the client.*
>> *//*
>> *// One solution is having an additional argument(id) for this
>> purpose but*
>> *// that requres additional management of ID.*
>> *// subscribe @0 (subscriber: Subscriber, id: Int32) -> (result:
>> Int32);*
>> *// unsubscribe @1 (id: Int32) -> (result: Int32);*
>>
>> *// what I can do is erase everything but this is not my goal*
>> *m_subscribers.clear();*
>> *return kj::READY_NOW;*
>> * }*
>>
>> * private:*
>> * kj::Vector m_subscribers;*
>> *};*
>> Thank you,
>>
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>
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