Proposal: gadgets.rpc.pubsub - a gadget-to-gadget communication API

[Zhen Wang]

Problem:
The gadgets.rpc library enables a gadget to send messages to its container page, and vice versa, yet there is not a standard gadget-to-gadget communication protocol which could open the door to more collaborative gadgets.


Proposed solution:
Add a JavaScript feature named "pubsub" which, based on a publisher-subscriber model, allows gadgets on the same container page to communicate with each other. "Pubsub" utilizes the existing gadget.rpc library for container-mediated message delivery.

To publish a string-type message to a channel, a gadget calls:
    gadgets.rpc.pubsub.publish(channel_name, message);

To subscribe to a message channel, a gadget calls:
    gadgets.rpc.pubsub.subscribe(channel_name, subscriber_callback);
    function subscriber_callback(message, sender) {
      /* Do something with message if sender is a trusted gadget spec URL. */
    }

To unsubscribe from a channel, a gadget calls:
    gadgets.rpc.pubsub.unsubscribe(channel_name);

On the container side, the following function must be called to support "pubsub":
    gadgets.rpc.pubsub.initializeRouter(gadget_id_to_spec_url_callback, {
      onSubscribe: on_subscribe_callback, // optional
      onUnsubscribe: on_unsubscribe_callback, // optional
      onPublish: on_publish_callback // optional
    });
    function gadget_id_to_spec_url_callback(gadget_id) {
      /* Given a gadget id, return the corresponding gadget spec URL. */
    }
    function on_subscribe_callback(gadget_id, channel_name) {
      /* Return true to reject the subscription request; return false to accept it. */
    }
    function on_unsubscribe_callback(gadget_id, channel_name) {
      /* Return true to reject the unsubscription request; return false to accept it. */
    }
    function on_publish_callback(gadget_id, channel_name, message) {
      /* Return true to discard the message; return false to proceed to broadcast it to the channel. */
    }

The "pubsub" library is designed in such a way that all gadgets are allowed to send messages to any message channel without having to register a channel first; containers have full control over message delivery and may choose to discard or throttle messages; and subscribers are given the choice to ignore messages sent from untrusted sources.

Thoughts?

[Kevin Brown]

Why not just gadgets.pubsub? I know it's layered on top of rpc, but it seems a little cleaner to just have it exist as a standalone library. Are there implementation details that make this easier if it's actually an extension of rpc?

--
~Kevin

[Zhen Wang]

gadgets.pubsub sounds good to me.

[Kevin Brown]

And the triggering would be <Require feature="pubsub"/>, right?

--
~Kevin

[Zhen Wang]

Correct.

[Reinoud Elhorst]

+1

[Jun Yang]

+１

[Zhen Wang]

Kevin, Reinoud, Jun, and I are all for it.
Will one more person chime in please?

Thanks!

[Robert Evans]

+1

[Martin Webb]

+1

--
Internet Related Technologies - http://www.irt.org

[Cassie]

approved. thanks.

- cassie