CTF Backend

A high-performance, concurrent Go backend for Capture The Flag (CTF) competitions.

Features

• Real-time leaderboard with intelligent caching
• Atomic flag validation preventing race conditions
• User progress tracking across multiple challenge levels
• Optimized performance with prefetching and in-memory caching
• Graceful shutdown and signal handling

Tech Stack

• Go - Backend server
• MongoDB - Database
• CORS-enabled REST API

Prerequisites

• Go 1.16+
• MongoDB instance

Setup

1. Install dependencies

   go mod download

2. Set environment variables

   export MONGODB_URI="your_mongodb_connection_string"
   export PORT=10000  # Optional, defaults to 10000

3. Run the server

   go run main.go

API Endpoints

Method	Endpoint	Description
GET	/api/test	Health check
GET	/getLevel?userId={id}	Get user's current level
POST	/checkFlag	Submit a flag
POST	/resetUser	Reset user progress
POST	/deleteUser	Delete a user
GET	/api/leaderboard	Get top 100 players
GET	/api/challenges	List all challenges

Request Examples

Check Flag

curl -X POST http://localhost:10000/checkFlag \
  -H "Content-Type: application/json" \
  -d '{"userId": "player1", "flag": "CTF{...}"}'

Get Leaderboard

curl http://localhost:10000/api/leaderboard

Performance Features

• O(1) challenge lookups via hash maps
• User data prefetching for reduced latency
• Leaderboard caching with background refresh
• Database indexes for optimized queries
• Atomic operations for thread-safety

Development

Run with race detector:

go run -race main.go

Build for production:

go build -o ctf-server main.go

License

MIT