contest-platform

Competitive Coding Contest Platform with Judge0 Client

Full Setup Guide for Ubuntu 24.04

---

OVERVIEW

• Flask backend (Python)
• Monaco Editor (VS Code editor in browser)
• Judge0 for code execution (self-hosted via Docker)
• SQLite database (zero-config)
• Users connect via LAN — no separate installation needed on client PCs

---

STEP 1 — Install Dependencies (on YOUR laptop only)

# Python + pip
sudo apt update
sudo apt install python3 python3-pip -y

# Install Flask, dotenv and requests
cd ~/contest-platform
pip3 install flask python-dotenv requests --break-system-packages

---

STEP 2 — Set Up Judge0 (run code in browser)

Judge0 runs in Docker. Your laptop is the server.

# Install Docker if not already installed
sudo apt install docker.io docker-compose -y
sudo usermod -aG docker $USER
newgrp docker

# Download Judge0
cd ~
wget https://github.com/judge0/judge0/releases/download/v1.13.1/judge0-v1.13.1.zip
unzip judge0-v1.13.1.zip
cd judge0-v1.13.1

# Fix Docker credential error (if it appears)
# Edit ~/.docker/config.json and replace entire contents with: {}

# Start Judge0
docker-compose up -d db redis
sleep 15
docker-compose up -d

# Verify Judge0 is running (should return JSON)
curl http://localhost:2358/system_info

Judge0 takes ~2 minutes to fully start the first time.

---

STEP 3 — Configure the Platform

Open .env and change these lines near the top:

JUDGE0_URL=
ADMIN_PASSWORD=
CONTEST_DURATION_SECONDS=
DB_PATH=
SECRET_KEY=

---

STEP 4 — Find Your LAN IP

ip addr show | grep "inet " | grep -v 127

Your IP will look like 192.168.1.42 or 10.0.0.5. This is the address participants will open in their browser.

---

STEP 5 — Start the Contest Server

cd routes/ && mvn spring-boot:run &

cd ~/contest_platform
python3 app.py

The server starts on port 5000.

---

STEP 6 — During Contest

Admin flow:

1. Open http://localhost:5000/admin on YOUR PC
2. Login with the admin password
3. When ready to start the contest → click ▶ Start Contest
4. This starts the shared 1-hour timer for everyone simultaneously
5. During the contest, watch the participant list refresh every 15 seconds
6. After contest → click View Code to see each participant’s submissions

Participant flow:

1. Open http://YOUR_LAPTOP_IP:5000 on any lab PC
2. Fill in name, college, system number, phone → Enter the Ship
3. Select a task from the left sidebar
4. Choose language (Python/C/C++/Java)
5. Fix the intentionally broken code
6. Click ▶ Run to test visible test cases
7. Click ✓ Submit to run all test cases (including hidden)
8. Green tick appears when all test cases pass
9. End Test button appears in the last 10 minutes
10. Test auto-ends after time-limit is up

---

EDITING QUESTIONS

Edit data/problems.json to change problems, test cases, or boilerplate code.

Structure per problem:

• title, subtitle, description — displayed to participants
• required_complexity — shown as a hint chip
• visible_test_cases — shown to participants
• hidden_test_cases — run on submit, not shown
• boilerplate — the wrong code shown in editor per language
• hidden_main — injected invisibly for execution

---

ANTI-CHEAT FEATURES

• Tab switching detection — warning overlay appears, violations logged
• Window blur detection — same warning
• Fullscreen enforcement — prompts on first click
• Keyboard shortcut blocking — Ctrl+T, Ctrl+W, Alt+Tab blocked
• Right-click disabled
• Auto-save every 30 seconds — code preserved even if browser closes
• One submission per phone number — can’t re-register after ending

---

JUDGE0 LANGUAGE IDs USED

Language	ID	Version
Python	71	Python 3.8
C++	54	GCC 9.2 (C++17)
C	50	GCC 9.2
Java	62	OpenJDK 13

---

TROUBLESHOOTING

Judge0 not responding:

cd ~/judge0-v1.13.1
docker-compose ps          # Check all containers are Up
docker-compose logs worker # Check for errors

Port 5000 blocked on LAN:

sudo ufw allow 5000

Participants can’t reach your IP:

# Make sure you're on the same network/switch as lab PCs
# Try pinging your laptop from a lab PC:
ping YOUR_LAPTOP_IP

Reset database (clear all participants):

rm contest.db
python3 app.py   # Auto-recreates fresh DB

---

FILE STRUCTURE

contest_platform/
├── app.py                   
├── .env                      
├── .gitignore                
├── requirements.txt
│
├── core/
│   ├── __init__.py
│   ├── config.py             
│   ├── database.py          
│   └── problems.py           
│
├── routes/
│   ├── __init__.py
│   ├── participant.py        
│   ├── admin.py              
│   └── judge.py              
│
├── templates/
│   ├── register.html         
│   ├── contest.html
│   ├── admin.html
│   ├── admin_login.html
│   └── ended.html
│
├── static/
│   ├── css/
│   │   ├── register.css
│   │   ├── contest.css
│   │   ├── admin.css
│   │   ├── admin_login.css
│   │   └── ended.css
│   └── js/
│       ├── register.js
│       ├── contest.js
│       ├── admin.js
│       └── admin_login.js
│
└── data/
    └── problems.json