PubSub-over-Webhooks with RabbitHub
It gives every AMQP exchange and queue hosted by a RabbitMQ broker a couple of URLs: one to use for delivering messages to the exchange or queue, and one to use to subscribe to messages forwarded on by the exchange or queue. You subscribe with a callback URL, so when messages arrive, RabbitHub POSTs them on to your callback. For example,
http://dev.rabbitmq.com/rabbithub/endpoint/x/amq.direct is the URL for delivering messages to the "amq.direct" exchange on the public test instance of RabbitMQ, and
http://dev.rabbitmq.com/rabbithub/subscribe/q/some_queue_name is the URL for subscribing to messages from the (hypothetical) queue "some_queue_name" on the broker.
The symmetrical .../subscribe/x/... and .../endpoint/q/... also exist.
The PubSubHubBub protocol specifies some RESTful(ish) operations for establishing subscriptions between message sources (a.k.a "topics") and message sinks. RabbitHub implements these operations as well as a few more for RESTfully creating and deleting exchanges and queues.
While PubSubHubBub is written assuming Atom content, RabbitHub is content-agnostic (just like RabbitMQ): any content at all can be sent using RabbitHub's implementation of the PubSubHubBub protocol. Because RabbitHub is content-agnostic, it doesn't implement any of the Atom-specific parts of the PubSubHubBub protocol, including the "ping" operation that tells a PSHB hub to re-fetch content feeds.
Combining RabbitHub with the AMQP protocol implemented by RabbitMQ
itself and with the other adapters and gateways that form part of the
RabbitMQ universe lets you send messages across different kinds of
message networks - for example, our public RabbitMQ instance,
dev.rabbitmq.com, has RabbitHub running as well as the standard AMQP
adapter, the rabbitmq-xmpp plugin, and a bunch of our other
experimental stuff, so you can do things like this:
become XMPP friends with
email@example.com(the XMPP adapter gives each exchange a JID of its own)
use PubSubHubBub to subscribe the sink http://dev.rabbitmq.com/rabbithub/endpoint/x/pshb to some PubSubHubBub source - perhaps one on the public Google PSHB instance. (Note how the given URL ends in "x/pshb", meaning the "pshb" exchange - which lines up with the JID we just became XMPP friends with.)
wait for changes to be signalled by Google's PSHB hub to RabbitHub
when they are, you get an XMPP IM from
firstname.lastname@example.org the Atom XML that the hub sent out as the body
Again, RabbitHub is content-agnostic, so the fact that Atom appears is an artifact of what Google's public PSHB instance is mailing out, rather than anything intrinsic in pubsub-over-webhooks.
HTTP messaging in the Browser
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