inter-widget-communication

The inter-widget-communication library is an npm library providing a simple wrapper around and replacement for the ready, publish, subscribe, and unsubscribe functions of OWF. This library is intended to ease the transition away from OWF by providing a replacement for direct calls to OWF that will function inside or outside OWF. It is not intended as a complete replacement for OWF; OWF capabilities unrelated to OWF's ready, pub and sub are outside the scope of this library.

The library exposes a single class, IWC. IWC contains the following methods:

• subscribe: Subscribes to the topic provided. In OWF, this this is a thin wrapper around OWF.Eventing.subscribe with the same signature. Outside OWF, this will utilize Ozone's ozp-iwc client library to watch a node on ozp-iwc's bus library.
• unsubscribe: Unsubscribes a widget from recieving events from the provided topic. In OWF, this this is a thin wrapper around OWF.Eventing.unsubscribe with the same signature. Outside OWF, this will unwatch a node from the ozp-iwc.
• publish: Publishes data to the given topic. In OWF, this this is a thin wrapper around OWF.Eventing.publish with the same signature. Outside of OWF, this will utilize the create or update a node on the communication bus.
• ready: Fires the callback function when messaging is set up. In OWF, this this is a thin wrapper around OWF.Eventing.ready with the same signature Outside of OWF, the callback function fires after establishing the ozp-iwc bus and client.

Setting up the IWC client

• Download the latest IWC release and copy the client library into your widget's project and refer to it with the script tag.

 <script src="<relative pathing for project>/ozpIwc-client.min.js"></script>

• Create a IWC client. In your application's javascript instantiate a new ozpIwc.Client. The peerUrl is the path to the hosted bus, grunt serve hosts an example bus locally on port 13000.

var client = new ozpIwc.Client({ peerUrl: "http://localhost:13000"});

• When creating the iwc object, pass the ozpIwc client

const iwc = new IWC(client);

Function Based Interface

A simpler API was added. The above API still works. However, with the added API functions, clients do not need to manage the IWC instance. Also, publish and subscribe are wrapped in ready, so they can be called without having to wrap them in a ready call.

Example usage:

import { initialize } from '@moesol/inter-widget-communication'

const myId = initialize({
  provider: 'broadcast',
  busUrl: 'http://bus-host/bus/js'
})

subscribe('topic', (sender, message) => { ... })

publish('topic', 'message'))

Getting Started (ozp-iwc Implementation)

Sample iwc-bus

For testing purposes, you can use the iwc-bus. Below will run a server on port 9090.

cd iwc-bus
npm install
npm start

Sample iwc-example

This example shows how to initialize the IWC and publish and subscribe. After starting the HTTP server, you can visit http://localhost:8080. You should see a text field with a send button next to it. This will publish a message on the test.test topic. Below the text field you will send any messages we receive on the test.test topic (including the ones this page publishes).

Run the server:

cd iwc-example
npm install
npm run build
npm run serve

If you open a second terminal window, you can run

npm start

And a second server will be running on the next available port. For example, http://localhost:8081.

Note that this is not considered the "Same Origin" as http://localhost:8080. Therefore if messages pass between the two pages, you have an example of working around the "Same Origin" restriction that BroadcastChannels impose.

Detailed Client Instructions

The sample client built using these instructions is here: inter-widget-communication/iwc-example.

Clients can use ozp-iwc by installing the required dependencies:

npm install @moesol/inter-widget-communication
npm install @moesol/ozp-iwc

Then in package.json, copying the ozpIwc-client files to where static assets will be served.

"scripts": {
    ...
    "copy": "copyfiles --up 5 node_modules/@moesol/ozp-iwc/dist/js/* public/js/ozp-iwc-1.2.4",
    ...
}

Then running

npm run copy

Then adding in index.html

<head>
    ...
    <script src="js/ozp-iwc-1.2.4/ozpIwc-client.js"></script>
    ...
</head>

Then in index.tsx or initial JavaScript/Typescript entry, adding

import { initialize } from '@moesol/inter-widget-communication'

const myId = initialize({
  busUrl: 'http://localhost:9090/ozp-iwc-1.2.4'
})

And finally, where needed publish or subscribe:

  function handleSend(evt: React.FormEvent) {
    evt.preventDefault()

    const input = inputRef.current as HTMLInputElement
    publish('test.test', input.value)
    input.value = ''
  }

  React.useEffect(() => {
    subscribe('test.test', (sender: string, msg: string) => {
      console.log('sender:', sender, 'msg: ', msg)
      setLastFive(a => [msg, ...a].slice(0, 5))
    })
  }, [])

HTML5 BroadcastChannel/MessageChannel Implementation

This implementation is a good candidate to replace the ozp-iwc implementation because most of the implementation is provided by the browser.

Cross-Origin Support

You can deploy bcst-bus and set busUrl to the reachable URL for bcst-bus. All pages that use the same busUrl will be able to exchange messages.

BroadcastChannel/MessageChannel Cross Origin Sequence Diagram

OWF/BroadcastChannel Interop

When using inter-widget-communication, we can addon OWF/BroadcastChannel inter-operation by creating a background widget hosting the bcst-owf-interop. You can deploy bcst-owf-interop. When this widget is running, subscriptions created with the subscribe function will also subscribe to the same OWF channel. Furthermore, publish will also publish on the same OWF channel. This means that an OWF widget that is not using this facade library for IWC can exchange messages with users of this library, including pages that are running outside of OWF and pages that are "Cross Origin".

Note: the busUrl is currently hard-code to localhost:9090. Hopefully, this will be addressed soon.

In this screenshot, you can see the older OWF test widgets, Channel Shouter and Channel Subscripts are publishing and receiving messages to/from OWF and to/from this IWC facade.

OWF/BroadcastChannel Interop Sequence Diagram