TouK Hackathon – March 2019

Hackathons are prone to fail. It’s because we have very little time to create something useful, actually working and making a wow!-effect.

So this time we wanted to run “THE HACKATHON”, a well-prepared event with a very high success rate. We called it “Ship IT!” to ensure that we will focus on delivering a working product, not only on having fun while making it. We formed an organising team responsible for internal communication, collecting the needs, removing obstacles and buying some snacks and pizza for the event itself.

We thought that if we want to succeed, we’ll have to prepare well. So each team gathered before the event and talked about their plans, the technologies they intend to use and what hardware they need to order. The organizers met with all teams, exchanged details and gave some good advice.

And finally, the day has come! Seven teams started the two-day hacking session at 9AM, continued until 5PM, and showed the demos of all seven projects after 4.30PM on the second day. We gathered 25 participants total.

Here is a quick presentation of the projects we delivered.

Lidar/ROS.org based robot

robot image We always wanted to build a fully autonomous vehicle to transport sandwiches and monitor the Wi-Fi quality over the whole office space. The first step we took was creating a remote controlled platform with Lidar, which allowed to build the office map and made a foundation for future experiments. We reached this goal with ROS.org and mapped a few corridors and rooms in our office at the end of the hackathon. Now we’re almost ready to conquer Mars :D

Quak Liero-like Game

quak team Quak is a PvP platform game inspired by Liero or Soldat. We used a mix of Kotlin, libGDX and box2d (physics) to build a good-looking 2D game in less than 2 days. Destructible level as a mesh of boxes are generated from provided png layers. Additionally, we implemented some extras to diversify the player experience, such as multiple weapons, double jump, blood effects and explosions.

Quiz Game

quiz game DuckQuiz is a game we wanted to use at public event, e.g. conferences. It’s a little bit similar to the legendary Flappy Bird. Your goal is to make the title hero – a duck – go as far as possible! Correct answers give the duck a bump, so the more questions you answer correctly, the further the duck will go. Be careful, though! Three wrong answers will make a brick fall on the duck’s head! To spice things up a little, we decided to introduce a score threshold, which – once achieved – guaranteed a prize. Plus, of course, if you beat the highest score, you will make history as the reigning champion Duck Flyer. The quiz application is written in Kotlin for Android. We used RxJava and Retrofit for communication with the server. For the back-end side, we chose SpringBoot along with Kotlin. There is also a web-based “Hall of Fame” panel and a simple CMS which allows the management of the quiz questions, written in ReactJS.

Own Card Authorization system

demo4 We’re waiting for our private brand new vending machine which we’re going to use for distribution of snacks in Touk. We’ve noticed that we can communicate with it using MDB protocol. We’d like to authenticate in the machine with RFID cards which are commonly used in TouK to open doors. As a first step, we wanted to create authorization system based on RFID cards, but with additional PIN verification part added. Our system should be integrated with internal LDAP. We’ve separated our project into 4 modules: backend (spring boot), web frontend (scalajs-react), mobile app (android) and hardware device (arduino yun). Backend part connects all modules and allows matching RFID cards UID with LDAP logins. Web frontend is designed for users to set and manage their PINs. The mobile app at the moment is dedicated for our administrator to make pairing existing cards with LDAP logins easier. Finally, hardware device was created to read data from card, get PIN from user and check if PIN is correct (via backend). In the next step, we’d like to integrate our system with mentioned vending machine and make payments using it. There is also a plan to enhance mobile app and use it as mobile payment terminal and integrate web UI with Touk SelfCare system.

Notification lights

lights hackers Three suites (3 lights in red, yellow and blue) controlled by Raspberry Pi Zero W communicating with the managing service via MQTT protocol. The service handles messages from Rocket’s (our chat) outgoing web hooks and notifications from GitLab (e.g. opened merge requests).

Team gathering app (e.g. for football matches)

Team gathering app We regularly play football and volleyball after work, but we sometimes struggle with completing the teams. So far, we used a sign-up system based on Confluence pages, which is not mobile-friendly. We also wanted to allow registration for “reserve” players from outside the company. That’s why we built a simple mobile app with a sign-up form, game history and basic player ranking. The app was built with Dart using the Flutter framework and Firebase for storage and authorization.

Internal time reporting API

hr This HR project’s goal was to integrate and simplify the way we log time in our company. We’ve achieved that with a Google Calendar-like GUI and multiple microservices written in TypeScript, Python, Java and Scala!

The Grand Finale

demo1 At the end of “Ship IT!”, the teams had demonstrated the effects of their work. They shared some successes and other stories :) about the used software and hardware and the lessons learned during those two intensive days. The audience were amused when the robot started to explore the room. The Quak team had a bloody battle in their game. The lights were blinking when one of the team members wrote “kanapki” on our internal TouK chat.

demo2 demo3 demo5 demo6

It was very impressive that each team managed to deliver a viable result and show their projects in action. We can’t wait to run the next edition of The TouK Hackahton and hope there will be even more participants and surprising ideas to see.

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Grails session timeout without XML

This article shows clean, non hacky way of configuring featureful event listeners for Grails application servlet context. Feat. HttpSessionListener as a Spring bean example with session timeout depending on whether user account is premium or not.

Common approaches

Speaking of session timeout config in Grails, a default approach is to install templates with a command. This way we got direct access to web.xml file. Also more unnecessary files are created. Despite that unnecessary files are unnecessary, we should also remember some other common knowledge: XML is not for humans.

Another, a bit more hacky, way is to create mysterious scripts/_Events.groovy file. Inside of which, by using not less enigmatic closure: eventWebXmlEnd = { filename -> ... }we can parse and hack into web.xml with a help of XmlSlurper.
Even though lot of Grails plugins do it similar way, still it’s not really straightforward, is it? Besides, where’s the IDE support? Hello!?

Examples of both above ways can be seen on StackOverflow.

Simpler and cleaner way

By adding just a single line to the already generated init closure we have it done:
class BootStrap {

def init = { servletContext ->
servletContext.addListener(OurListenerClass)
}
}

Allrighty, this is enough to avoid XML. Sweets are served after the main course though :)

Listener as a Spring bean

Let us assume we have a requirement. Set a longer session timeout for premium user account.
Users are authenticated upon session creation through SSO.

To easy meet the requirements just instantiate the CustomTimeoutSessionListener as Spring bean at resources.groovy. We also going to need some source of the user custom session timeout. Let say a ConfigService.
beans = {    
customTimeoutSessionListener(CustomTimeoutSessionListener) {
configService = ref('configService')
}
}

With such approach BootStrap.groovy has to by slightly modified. To keep control on listener instantation, instead of passing listener class type, Spring bean is injected by Grails and the instance passed:
class BootStrap {

def customTimeoutSessionListener

def init = { servletContext ->
servletContext.addListener(customTimeoutSessionListener)
}
}

An example CustomTimeoutSessionListener implementation can look like:
import javax.servlet.http.HttpSessionEvent    
import javax.servlet.http.HttpSessionListener
import your.app.ConfigService

class CustomTimeoutSessionListener implements HttpSessionListener {

ConfigService configService

@Override
void sessionCreated(HttpSessionEvent httpSessionEvent) {
httpSessionEvent.session.maxInactiveInterval = configService.sessionTimeoutSeconds
}

@Override
void sessionDestroyed(HttpSessionEvent httpSessionEvent) { /* nothing to implement */ }
}
Having at hand all power of the Spring IoC this is surely a good place to load some persisted user’s account stuff into the session or to notify any other adequate bean about user presence.

Wait, what about the user context?

Honest answer is: that depends on your case. Yet here’s an example of getSessionTimeoutMinutes() implementation using Spring Security:
import org.springframework.security.core.context.SecurityContextHolder    

class ConfigService {

static final int 3H = 3 * 60 * 60
static final int QUARTER = 15 * 60

int getSessionTimeoutSeconds() {

String username = SecurityContextHolder.context?.authentication?.principal
def account = Account.findByUsername(username)

return account?.premium ? 3H : QUARTER
}
}
This example is simplified. Does not contain much of defensive programming. Just an assumption that principal is already set and is a String - unique username. Thanks to Grails convention our ConfigService is transactional so the Account domain class can use GORM dynamic finder.
OK, config fetching implementation details are out of scope here anyway. You can get, load, fetch, obtain from wherever you like to. Domain persistence, principal object, role config, external file and so on...

Any gotchas?

There is one. When running grails test command, servletContext comes as some mocked class instance without addListener method. Thus we going to have a MissingMethodException when running tests :(

Solution is typical:
def init = { servletContext ->
if (Environment.current != Environment.TEST) {
servletContext.addListener(customTimeoutSessionListener)
}
}
An unnecessary obstacle if you ask me. Should I submit a Jira issue about that?

TL;DR

Just implement a HttpSessionListener. Create a Spring bean of the listener. Inject it into BootStrap.groovy and call servletContext.addListener(injectedListener).