FactPub chrome extension is a browser extension that helps fact donors to extract facts from PDF files on chrome browser and upload them to FactPub website – http://factpub.org FactPub project aims to break down the paywall for academic papers by uploading ‘facts’, not original copy-right protected PDF papers.

1. FactPub Chrome Extension
- Developer’s Guide -
Genome Institute of Singapore
Sun Sagong 2017Feb27

2. What is FactPub Chrome Extension ?
• FactPub chrome extension is a browser extension that helps fact
donors to extract facts from PDF files on chrome browser and upload
them to FactPub website – http://factpub.org/
• FactPub aims to break down the paywall for academic papers by
uploading ‘facts’, not original copy-right protected PDF papers.
• A Java program, released under the name of Factify, is used to extract
facts from PDF. Thus the extension is designed to interact with it.

3. Factify - invisible process
Upload JSON file
FactPub Chrome Extension
background.js
- calls FactifyChrome.jar
General Architecture
Local User PC
FactPub - http://factpub.org/
Server side process
Extract facts
Passing PDF file
Send status notifications
Generate Page in WikiReturn page URL

4. Folder structure for FactPub chrome extension
Manifest file (JSON file)
Main code (JavaScript)

5. Manifest file – manifest.json (1/2)
https://github.com/pauline-ng/factify_chrome_extension/blob/master/manifest.json#12-34
• Every chrome extension has a JSON-formatted manifest file that provides
important information to configure the extension.
Detailed explanation is given by Google - https://developer.chrome.com/extensions/manifest
Specify the files that are used when the extension icon is clicked.
Chose ‘background.js’ file as a main JavaScript code file.
Grant necessary permissions because chrome extension works
with limited API control for security reason.

6. Manifest file – manifest.json (2/2)
https://github.com/pauline-ng/factify_chrome_extension/blob/master/manifest.json#1-15
• The first field of the manifest.json file - ‘key’ – is critical for modifying windows
registry to launch external program (Java) from chrome browser.
This hash value generate the folder name where
extension is going to be saved.
It must be always the same because installer – will be
explained later – need to write a folder location into
windows registry key.

7. Main code – background.js (1/7)
https://github.com/pauline-ng/factify_chrome_extension/blob/master/background.js#26-41
• Upon installation, the instruction page is displayed and downloading of the Factify installer starts.

8. Main code – background.js (2/7)
https://github.com/pauline-ng/factify_chrome_extension/blob/master/background.js#77-87
• Code to check whether the page being browsed is PDF file or not.
Get header information
Analyze header information

9. Main code – background.js (3/7)
https://github.com/pauline-ng/factify_chrome_extension/blob/master/background.js#140-172
• Load page information whenever user browses a web page.
Using XMLHttpRequest background to handle page data
Detecting PDF
Sending user activity data to
server – e.g. page url

10. Main code – background.js (4/7)
https://github.com/pauline-ng/factify_chrome_extension/blob/master/background.js#174-200
• Show desktop notification if the page is PDF
Creating desktop notification
message with some properties.
Detailed explanation is given by Google
https://developer.chrome.com/apps/notifications

11. Main code – background.js (5/7)
https://github.com/pauline-ng/factify_chrome_extension/blob/master/background.js#245-270
• If user click the first button (Yes), starting extraction process by calling Factify
Serialize PDF data into JSON
format so Factify can
process it.
Pass data
Update desktop notification
message.

12. Main code – background.js (6/7)
https://github.com/pauline-ng/factify_chrome_extension/blob/master/background.js#312-328
• The code within connectNativeApp() function – Establishing port with Chrome Extension
Establishing connection with Factify
Add an event listener for the time when
connection is closed.
Detailed explanation is given by Google
https://developer.chrome.com/extensions/nativeMessaging

13. Main code – background.js (7/7)
https://github.com/pauline-ng/factify_chrome_extension/blob/master/background.js#376-401
• Adding event listener for receiving messages from Factify – This part is called when Factify send messages
Update desktop notification
messages based on statuses
resopnded by Factify

14. Installer
https://github.com/pauline-ng/factify_chrome_installer
• An extra step must be taken to call external program (Java) from chrome browser due to its security policy.
• This installer makes a necessary modification for windows registry to allow Native Messaging protocol between the extension and Java.
Codes for windows installer
Factify - it must be built as an external .jar
format and put under the root of
factify_chrome_installer folder as _factify.jar.
Main code for installer
Configuration files required to
run .jar from chrome browser

15. Installer – setup.nsi
https://github.com/pauline-ng/factify_chrome_installer/blob/master/install_scripts_win/setup.nsi
• Use NSIS (Nullsoft Scriptable Install System) for an windows installer builder - http://nsis.sourceforge.net/Simple_tutorials
Define registry key name and its values
Detailed explanation is given by Google
https://developer.chrome.com/extensions/nativeMessaging
The installer, including necessary
configuration files and _factify.jar.
Write necessary registry value to
specified registry key following
documents by Google.

16. Installer – setup.exe (How to build)
https://github.com/pauline-ng/factify_chrome_installer/blob/master/install_scripts_win/setup.nsi
• Just drug and drop NSI script file on NSI scripts compiler, then executable file will be created.

17. References for codes
• FactPub Chrome Extension – [JavaScript]
https://github.com/pauline-ng/factify_chrome_extension
• Installer of Factify – [Windows bat script & NSI script]
https://github.com/pauline-ng/factify_chrome_installer
• Factify – [Java]
https://github.com/pauline-ng/factify/blob/master/src/main/java/org/factpub/factify/ui/extension/chrome/FactifyChromeMain.java

18. Useful References for Chrome Extension
• Getting Started Tutorial for Chrome Extension Development
https://developer.chrome.com/extensions/getstarted
• Desktop Notifications
https://developer.chrome.com/apps/notifications
• Native Messaging Protocol
https://developer.chrome.com/extensions/nativeMessaging