This package is meant to provide an HTTP Push support to WakandaDB / Wakanda via the W3C / WHATWG HTML5 Standard called Server-Sent Events aka Event Source.
This push technology can be used on all modern platforms natively or via the EventSource Polyfill for IE
Start the service on Wakanda Server. A good place for this code is usually a Wakanda bootstrap file.
require('wakanda-eventsource').start();The default listened pattern is "/eventsource".
Default ServerEvent are received by the client as MessageEvent. To send a MessageEventto all client listeners you can simply write:
require('wakanda-eventsource').push('a message from the server');If you want to dispatch on the client a specific Server Event you can use pushEvent()
require('wakanda-eventsource').pushEvent(
'itempurchased',
'5 "DVD" items have been purchased'
);You can push an event to one or more specific session(s), user(s), or group(s) Users and groups can be specified by ids, names, or directly User/Group instances
var sse = require('wakanda-eventsource');
// Important: The client-side EventSource connection need to be redone on login/logout
sse.pushEventToSession(currentSession(), 'itempurchased', '5 "DVD" items have been purchased');
sse.pushEventToUser(currentUser(), 'itempurchased', '5 "DVD" items have been purchased');
sse.pushEventToGroup(['Marketing', 'Engineering'], 'itempurchased', '5 "DVD" items have been purchased');If you want the pushed messaged to be an object message, you can tell the method to encode it in JSON (you could do it yourself but this will make your code lighter). This option works for both push()and pushEvent() methods.
require('wakanda-eventsource').pushEvent(
'itempurchased',
{
nb: 5,
type: 'DVD'
},
true // encode in JSON
);You must first create an EventSource Listener
var sse = new EventSource('/eventsource');You can ask the server to only send you specific events
// ask to receive only "itempurchased" and "ordercancelled" events
// adding onmessage listener or listener for any other events than the listed
// ones will have no effect
var sse = new EventSource('/eventsource/itempurchased,ordercancelled');You can then listen to basic Server Message Events via an onmessage handler
sse.onmessage = function onservermessage(event) {
console.log(event)
};Or you can listen to any specific events using addEventListener()
sse.addEventListener('itempurchased', function onitempurchased(event) {
var
data;
data = JSON.parse(event.data);
console.log(data.nb, '"' + data.type + '"', 'items have been purchased')
});- this implementation should support CORS to allow potential event subscriptions for external web applications
- This implementation use last event ID string for reconnections but needs more tests
- an experimental
pause(delay)method invite clients to reconnect later (we may allow to pause all connections not belonging to important groups) - A parallel client-side lib could help binding such server-sent events to wakanda datasources for live update features
- this module should register itself as a Wakanda service and take benefits of service settings
- W3C Candidate Recommmendation
- WHATWG HTML Living Standard
- HTML5 Rocks tutorial
- Can I use...
- EventSource Polyfill (with IE support)
- Server Sent Events - Who said it's not yet ready? (Wakanda forum)
- Notification Library - Receive server events to update datasources
This package is not a native Wakanda component and 4D gives no guaranty to its usage
This package could not have been done that quick without the preliminary works and involvements from Choisel Fogang and Vegar Ringdal
Copyright (c) 2013 Alexandre Morgaut
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.