Send messages to other systems

In this tutorial we will show how to send messages from one system to another system with channels.

At runtime a channel component is defined to send / receive messages between systems

Define your messages

After creating your system:

click on the import button on the left toolbar,
a dialog is shown,
click on from the library radio button,
select Send messages through a channel from the proposed systems,
click on the Compose button,

Image Alt

This system has now been composed in your system.

on Schemas tab, click on _Channel schema (on the right panel under Schemas),
click on _Channel schema to edit it,
add somethingHappened event:

{
  "_id": "104ad1f48518376",
  "_name": "_Channel",
  "_inherit": [
    "_Component"
  ],
  "send": "event",
  "somethingHappened": "event"
}

on Models tab, click on _Channel model (on the right panel under Models),
click on _Channel model to edit it

{
  "_id": "135c71078810af2",
  "_name": "_Channel",
  "send": {
    "params": [
      {
        "name": "message",
        "type": "message"
      }
  ]
  },
  "somethingHappened": {
    "params": [
      {
        "name": "param",
        "type": "any",
        "mandatory": false,
        "default": ""
      }
    ]
  }
}

We let the default values.

Define how to send the message

on Behaviors tab, click on _Channel model (on the right panel under Models),
click on the send behavior to edit it,

function send(message) { 
  // define here how to send the message to another channel (webRTC, XHR, ...)
  // example
  fetch('url_to_a_server', {
    method: 'POST',
    headers: new Headers({
      'Content-Type': 'application/json',
      'X-System-Id': message.from, // current system id (string value)
      'X-System-Event': message.event // event name (string value)
    }),
    body: message.data // arguments send to the event (array value)
  });
}

Define in this behavior how to send the message to another channel (webRTC, XHR, ...).

Send a message

edit the behavior in which you want to send a message to another channel,
require the channel component,
call the event you have defined, somethingHappened and
pass as parameter a string (as defined in the model).

this.require('channel').somethingHappened('my message');

Listen to a message

create another system,
do all the steps of part Define your messages,
edit the behavior in which you want to listen to a message send from another channel (send via webRTC, XHR, ...),
require runtime component,
call the message method and
pass an object that contains the information send by the other system:

// we suppose that this system runs on a server and
// get the header and body of the request send by the other system

this.require('runtime').message({
  'event': headers['x-system-event'], // 'somethingHappened' (string value)
  'from': headers['x-system-id'], // system id of the system that send the message (string value)
  'data': body // the arguments send by event (array value)
);

then click on channel component (on the right panel under Components),
click on the '+' button on the left toolbar to add a behavior,
select somethingHappened from the list,
click on the Create button,
click on the somethingHappened behavior to edit it,
add this code:

function somethingHappened(param) { 
  // get logger component
  let logger = this.require('logger');

  logger.info('the message ' + param + ' has been send to this system');
}

Now your system is able to listen to an event send by the other system.