Quick links

Download extension | Trello board | Googlegroups forum

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1. Reliable Nepali news

Khabardar is a native chrome extension that warns against unreliable news websites by displaying a popup in the top of the browser window.

1.1 A thin extension

The only job of the extension is to call the API on every page load and display any message received from the API.

Dissecting the manifest.json file:

"browser_action":{
	"default_icon": "khabardar128.png",
	"default_title": "Khabardar settings",
	"default_popup": "settings.html"
}

The browser action controls what happens when the extension icon (in the top right) is clicked. In this case, settings.html will be shown. Also, some icons are being set.

"content_scripts":[
	{
		"matches": ["http://*/*"],
		"js":["content_script.js"],
		"css":["content_script.css"]
	}
],

A content script is being injected on every page that corresponds a match (in this case all sites starting with http://, e.g. not https). The js and the css specified will be injected on every page load.

"permissions":[
	"activeTab",
	"storage",
	"http://parewalabs.com:5000/reputation"
],

The permissions section specifies that the extension needs access to the current tab, the local storage and a custom url which is our api.

1.2 A simple API

Backend written in sails.js

installed node_modules:

• moment parses dates
• whois retrieves whois information for a domain
• node-cache caches whois information on server in order to speed up whois lookup

important files:

• config/routes.js A single route "POST /reputation" used by the extension. Sends and receives json.
• api/controllers/ApiController.js Defines the priority in which checks are performed for the current website. Check first against the blacklist, then against the "unreputable" list, then check for too young age of website.
• api/services/ApiService.js Each "check" is an independent blackbox, so that it can be run in any order or stack onto each other.
• config/locales/en.json Defines messages to be sent to, and displayed by, the client. This prepares the app for messages not only in English, if the Accept-Header tells so. More on locales.
• config/bootstrap.js Starts the cache on every server restart.

the blackbox approach:

As the number of blackbox filters will grow, this approach enables scalability.

// api/services/ApiService.js
...
checkBlacklistedSite: function(obj){
	var BlacklistedDomains = [
		'funnysite.com'
	];
	return new Promise(function (resolve, reject){
		if (BlacklistedDomains.indexOf(obj.data.domain_name) > -1){
			obj.data.errorType = 'MsgBlacklistedSite';
			return reject(obj);
		}
		resolve(obj);
	});
}

The function takes in an obj and returns the same obj, possibly with altered contents. This makes it easy to stack independent blackboxes onto each other, which can be seen in the controller that is consuming the blackboxes:

// api/controllers/ApiController.js
...
ApiService.checkBlacklistedSite(obj)
.then(function (obj){
	return ApiService.checkUnverifiedIdentity(obj);
})
.then(function (obj){
	return ApiService.checkInvalidDate(obj);
})

The behavior is the same for all blackboxes: on failure, an errorType is set and the blackbox is "rejected", otherwise it is "resolved". The errorType is a key in the locale file which translates into a message for the user.

2. Use

To try it out, just install the extension from the Chrome Webstore and visit some sites.

3. Develop

To contribute, clone/check out the code from https://github.com/parewalabs/khabardar. Don't forget to have a look at what's hot in our issue tracker on Trello. If you have any questions, ping us in googlegroups.

3.1 Developing the extension

This means that you will use the live version of the api (and that is great). To develop the extension, the chrome extension tutorial is a good start.

To try your changes first time in the browser:

1. goto chrome://extensions
2. enable "Developer mode" in upper right corner
3. click "Load unpacked extension"
4. select the khabardar/extensions/chrome folder

Et voilà, you have just loaded the extension. Now, after making any changes to the extension code:

1. goto chrome://extensions
2. click "Reload" on the extension

3.2 Developing the backend

This means that you will develop with a local copy of the backend. For the local copy to run, you will need to install node.js v4 or higher.

Below is the folder structure, with the most used folders and files marked for the backend.

khabardar/
	backend/
		...
		api/
		config/
		app.js
		...
	extensions/
		chrome/
			...

A typical workflow would be to first start the server with cd khabardar/backend && nodemon app.js and then change the code in either backend/ or chrome/. The npm module nodemon tracks any changes you make to the code and restarts the server.

To host the extension for a longer period of time, use the npm module forever like so forever start app.js.