🧑‍💻 Coding Judge Backend

A full-fledged backend system for an online coding judge platform — built with Node.js, Express, MongoDB, and Docker. It supports multi-language code execution (C++, Python, JS), problem management, user authentication, automated evaluation, and plagiarism detection.

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🚀 Features

• 🔐 JWT Authentication with user/admin roles
• 📄 Problem Management with test cases (admin only)
• 📤 Code Submission and result evaluation
• 🧪 Unit Tests for major APIs
• 📊 Leaderboard to showcase top performers
• 🐳 Dockerized Execution for code safety and isolation
• 🚫 Plagiarism Detection via token-based similarity
• 📈 Rate Limiting to prevent abuse

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🛠️ Technologies

• Node.js + Express
• MongoDB + Mongoose
• JWT, bcryptjs
• Docker (with separate images per language)
• Jest + Supertest (unit testing)
• Esprima + string-similarity (for plagiarism)
• Swagger (API docs)

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⚙️ Getting Started

1. Clone the Repo

git clone https://github.com/yourusername/coding-judge-backend.git
cd coding-judge-backend/server

2. Install Dependencies

npm install

3. Create .env

PORT=5000
MONGO_URI=mongodb://127.0.0.1:27017/coding_judge
JWT_SECRET=supersecret123

4. Seed Sample Data

To add a demo admin, user, and a sample problem:

npm run seed

This will create:

• 👤 Admin: admin@example.com / admin123
• 👤 User: student@example.com / user123
• 📘 Problem: Count Vowels

Useful for quickly testing the full judge flow.

5. Start Dev Server

npm run dev

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🐳 Docker Code Runners

Supported Languages:

• cpp
• python
• javascript

Dockerfiles are located at the root level:

.
├── Dockerfile-cpp
├── Dockerfile-python
├── Dockerfile-js

Each submission spins up a temporary container, runs user code in isolation, and returns the output.

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🧪 Running Unit Tests

npm test

Covers:

• Auth (register/login)
• Problem CRUD
• Code submission and fetch APIs

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🔍 Plagiarism Detection

• Tokenization via esprima
• Similarity via string-similarity
• Flags submissions with >80% token match

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📊 Leaderboard API

Ranks users based on:

• Number of problems solved
• Accuracy (accepted submissions / total)

GET /api/leaderboard

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🔐 Rate Limiting

• Limits excessive submission requests
• Implemented using middleware per IP/user

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📚 API Docs (Swagger)

Available at:

http://localhost:5000/api-docs

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🧼 Folder Structure

/server
├── controllers/
├── routes/
├── models/
├── middleware/
├── utils/
├── tests/
├── temp/       ← code + input temp files
├── Dockerfile-* ← Docker sandboxes
├── .env

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🤝 Contributions

PRs welcome for:

• Frontend integration
• Improved judging logic
• Advanced plagiarism

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📜 License

MIT

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👨‍🚀 Author

Made with ❤️ by Shikhar Rai