Broadcaster for dual-protocol 

Fan-out dual-protocol messages.

Construct a broadcasting domain

dual-protocol domains may be extended with the dual-broadcast module:
``javascript
var dual = require('dual-protocol').use(require('dual-broadcast'));
`

Domains with this extension can create broadcast objects:
`javascript
var domain = dual();
var broadcaster = domain.broadcast(['b']);
`

Here we've provided a specific mount point for the broadcaster at
['b']. newListener and removeListener events will be emitted
below that endpoint. By default, the broadcaster is mounted at
['broadcast'].




Register a broadcast recipient

To register a mount point ['client', xxxxx] as potential recipient
of broadcasts:
`javascript
broadcaster.register(['client', xxxxx]);
`

A map of subscriptions is created for each client. The subscriptions
will be removed when the ['disconnect', 'client', xxxx] event is
emitted on the domain.

Subscribe a registered client to a broadcast channel

To subscribe the registered ['client', xxxxx] to the broadcast point ['bbc',
'eight']:
`javascript
broadcaster.subscribe(['client', xxxxx], ['bbc', 'eight']);
`
The registered client ['client', xxxxx] would now receive broadcasts from ['bbc', 'eight'].




Broadcasting

Broadcast a message to every subscribed recipient by
`javascript
broadcaster.send(['bbc', 'eight'], 'hello', { optional: 'metadata' });
`
All subscribers would receive a message from ['bbc', 'eight'] with body 'hello', and the given dualapi options.

Unsubscribing

Broadcast clients may be unsubscribed from specific subscriptions:
`javascript
broadcaster.unsubscribe(['client', xxxxx], ['bbc', 'eight']);
`

Disconnecting

A client is unsubscribed from all subscriptions, and removed as a
potential subscription host, when the domain emits a disconnect event:
`javascript
domain.send(['disconnect', 'client', xxxxx]);
`

Auto-registering clients

Clients may be automatically registered on ['connect', '**'] events
by using the autoregister function.

`javascript
broadcaster.autoregister(['client', '*']);
domain.send(['connect', 'client', 'zzz']);
`
At this point, ['client', 'zzz'] would be registered, as would any other client matching ['client', '*'] when they
connect.

newListener events


When a subscriber is added to a broadcast channel, the domain emits a newListener event
`javascript
domain.mount(['b', 'newListener'], function (body, ctxt) {
console.log(body.join('/'), ' is now a subscriber to ', ctxt.from.join('/'));
});
`
New subscribers on specific broadcast channels are are emitted below the newListener endpoint:
`javascript
domain.mount(['b', 'newListener', 'bbc', 'eight'], function (body, ctxt) {
console.log(body.join('/'), ' is now a subscriber to ', ctxt.from.join('/'));
});
`

removeListener events

When a subscriber is removed from a broadcast channel, either by
unsubscribe or disconnecting, the domain emits a removeListener
event
`javascript
domain.mount(['b', 'removeListener'], function (body, ctxt) {
console.log(body.join('/'), ' is no longer a subscriber to ', ctxt.from.join('/'));
});
`
Subscribers leaving a specific broadcast channel are emitted below the removeListener endpoint:
`javascript
domain.mount(['b', 'removeListener', 'bbc', 'eight'], function (body, ctxt) {
console.log(body.join('/'), ' is no longer a subscriber to ', ctxt.from.join('/'));
});
``