https://github.com/cafjs/caf_pubsub
CAF extra lib to a publish/subscribe service
https://github.com/cafjs/caf_pubsub
Last synced: 5 months ago
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CAF extra lib to a publish/subscribe service
- Host: GitHub
- URL: https://github.com/cafjs/caf_pubsub
- Owner: cafjs
- Created: 2013-01-13T22:03:33.000Z (over 13 years ago)
- Default Branch: master
- Last Pushed: 2023-04-18T22:34:14.000Z (about 3 years ago)
- Last Synced: 2025-09-02T08:48:07.511Z (10 months ago)
- Language: JavaScript
- Size: 73.2 KB
- Stars: 1
- Watchers: 1
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
- Changelog: CHANGES.md
- Contributing: CONTRIBUTING.md
- License: LICENSE-2.0.txt
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README
# Caf.js
Co-design cloud assistants with your web app and IoT devices.
See https://www.cafjs.com
## Library to Access a Publish/Subscribe Bus
[](https://github.com/cafjs/caf_pubsub/actions/workflows/push.yml)
This repository contains a `Caf.js` library that implements a publish/subscribe bus using, for example, a `Redis` backend.
There are two types of channels:
* A *private channel* name is prefixed by the CA name, i.e., `-`, and only that CA can publish messages.
* A *forum channel* has a name of the form `forum-`, and anybody can publish to it. However, subscribers can filter publishers using method ACLs, since pubsub messages are always processed by invoking a CA method. This method is chosen by the subscriber.
Anybody can subscribe to a channel if they know its name, and we recommend to use hard to guess channel names to limit visibility.
The delivery guarantees depend on the pubsub backend service. `Redis`, for example, is best effort. However, when the plugin has committed to publish a message, it will retry after a CA or node.js process crash.
A pubsub service complements well a `SharedMap` (see {@link external:caf_sharing}). `SharedMaps` are silently updated, and this makes them very efficient when shared by many CAs. Messages generated by a pubsub service are processed by subscribed CAs and, for example, can trigger external actions. By combining them, we can get the right mix of silent updates vs external actions.
`Caf.js` discourages `point-to-point` communication between CAs. At the network infrastructure level, `point-to-point` becomes `all-to-all` very quickly, limiting the scalability of the system.
However, if you really need `point-to-point`, you can always use a *private pubsub channel*, or write a new plugin...
Instead, applications should expose higher-level communication patterns to improve scalability. These patterns can then be implemented efficiently with specialized services, such as `SharedMap` or `pubsub`. This approach is common for HPC applications that, for example, use MPI collective communication calls.
### Hello World (see `examples/helloworld`)
The following example has a privileged CA, i.e., `admin`, that regularly publishes messages in a private channel. CAs with the same owner subscribe to this channel, and the handler function notifies clients using sessions (see {@link external:caf_session}).
```
exports.methods = {
async __ca_init__() {
this.state.counter = 0;
this.$.pubsub.subscribe(mainChannel(this), '__ca_handle__');
this.$.security.addRule(this.$.security.newSimpleRule(
'__ca_handle__', this.$.security.SELF, ADMIN_CA
));
return [];
},
async __ca_pulse__() {
if (isAdmin(this)) {
this.state.counter = this.state.counter + 1;
this.$.pubsub.publish(mainChannel(this),
'Counter: ' + this.state.counter);
}
return [];
},
async __ca_handle__(topic, msg, from) {
this.$.log && this.$.log.debug('Got ' + msg);
this.$.session.notify([msg]);
return [];
}
}
```
A couple of helper functions for naming:
```
const ADMIN_CA = 'admin';
const ADMIN_CHANNEL = 'myNews';
const isAdmin = function(self) {
const name = self.__ca_getName__();
return (caf.splitName(name)[1] === ADMIN_CA);
};
const mainChannel = function(self) {
const name = self.__ca_getName__();
return caf.joinName(caf.splitName(name)[0], ADMIN_CA, ADMIN_CHANNEL);
};
```
See the client code in `examples/helloworld/client1.js`
## API
See {@link module:caf_pubsub/proxy_pubsub}
## Configuration
### framework.json
See {@link module:caf_pubsub/plug_pubsub}
### ca.json
See {@link module:caf_pubsub/plug_ca_pubsub}