[asterisk-app-dev] Blinky Lights Proposal

[Ben Merrills]

Hi Matt,

Good idea, it's something that was always a bug-bear of mine in AGI.

One question, what are your ideas for the filtering (you mention by type) but it seems to be this could still be a very large list of returned objects. Just a thought that's all.

Vote +1 :)

From: asterisk-app-dev-bounces at lists.digium.com [mailto:asterisk-app-dev-bounces at lists.digium.com] On Behalf Of Matthew Jordan
Sent: 01 November 2013 00:59
To: Asterisk Application Development discussion
Subject: [asterisk-app-dev] Blinky Lights Proposal

Hey everyone -

At AstriDevCon, we mentioned that two features ARI would need were the ability to raise MWI and the ability to publish state (device state, but theoretically, any event package for some subscribable resource). Initially, we discussed needing two resources in ARI - one that represents the state of mailboxes, and one that represents the state of a "device".

The more we've thought about it, the more it feels like - from ARI's perspective - these are the same concepts. From the perspective of an ARI client, you want the ability to define a resource that someone can subscribe to. You want to be notified when something subscribes to it; when they unsubscribe to it; and when a resource's state changes. In turn, you want to publish state about that resource to the subscribers. The fact that the resource is a mailbox, or a device, or who knows what else - is immaterial. The application itself should determine this.

(Plus, we forgot that in addition to device state and MWI, there's also presence state in Asterisk. So we were already up to 3 things anyway)

We need a more generic concept - a 'blinky light' resource, if you will.

The trick, unfortunately, is that in the guts of Asterisk, these are not the same concepts. MWI and device state (or presence state, for that matter) are all handled very differently. As much as it'd be fun to say "let's unify all the implementations!" - that's unrealistic and potentially harmful. So whatever we choose, there has to be a way to map the generic concept back to the actual implementation inside Asterisk.

The following is a proposal on how I think this might work:

Add a new resource to ARI to represent a generic resource that can be subscribed to/published about, 'topics'. A topic is something that something can subscribe to, that has state, and that the ARI client can publish state about. (Note that I chose the name 'topic' as it's what the XMPP folks used for their publish/subscribe XEP (XEP-0060), and 'resource' isn't a good name as it's a generic term in REST. Hopefully it doesn't get too confusing with Stasis message bus topics.)

Objects:

Topic:
    type: string - Valid types initially would be 'mailbox', 'device', 'presence'
    uri: string - The URI subscribers use to subscribe to the topic
    subscribers: List[Subscriber] - A list of active subscriptions
    id: string - A unique ID for the topic

Subscriber
    id: string - A unique ID for the subscriber
    topic_id: string - The topic ID this subscription refers to
    endpoint: Endpoint - If available, the endpoint that subscribed to this Topic

TopicSubscriptionCreated : Event - Event raised when a new subscription is created for a topic
    subscriber : Subscriber
    topic: Topic

TopicSubscriptionDestroyed : Event - Event raised when a subscription is destroyed for a topic
    subscriber : Subscriber
    topic : Topic

TopicEvent : Event - Event raised in relation to a topic
    topic : Topic
    body : JSON

TopicCreated : Event - Event raised when a new topic is created
    topic : Topic

TopicDestroyed : Event - Event raised when a topic is destroyed
    topic : Topic

Operations:

GET /topics List[Topic] - list all topics, with optional filter for type
GET /topic Topic - get information about a specific topic
DELETE /topic - destroy a topic. This should implicitly unsubscribe all subscribers.
POST /topics Topic - create a new topic. When you create a topic, you are implicitly subscribed to that topic.
    type: The type of topic to create. Valid types initially would be 'mailbox', 'device', 'presence'
    uri: The URI subscribers will use to subscribe to the topic
POST /topics/publish - publish an event to a topic. Events are passed as JSON, and are opaque from the perspective of ARI. It would be up to the specific topic types to understand the  event packages.

/applications/{applicationName}/subscription will be updated to allow for an ARI client to subscribe to any topic in Asterisk.

Note that a topic doesn't have to be something created by ARI - Asterisk will create a *lot* of topics by itself. There would be a topic for all mailboxes created by voicemail providers; a topic for all producers of extension state (at a minimum; devices as well); a topic for all producers of presence state. Much like the Endpoints resource, the Topics resource lets an ARI client subscribe to other things in the system other than what is directly in their application, so that the client can choose to have knowledge of the whole system, even if it only affects a part.

This is quite a big project, but a very necessary one. There's only one thing that has to be fixed in ARI before we can do this - namely the ability to POST JSON (thanks Paul!)  But other than that, I don't think there are any technical barriers to this approach.

Thoughts? Comments?

--
Matthew Jordan
Digium, Inc. | Engineering Manager
445 Jan Davis Drive NW - Huntsville, AL 35806 - USA
Check us out at: http://digium.com & http://asterisk.org
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