Coding Arena

Self-hosted competitive programming judge built for GCET's open source program. Submit code, get it graded against test cases in a sandboxed environment. Runs entirely in Docker with no external dependencies.

Setup

git clone https://github.com/GCET-Open-Source-Foundation/coding_arena.git
cd coding_arena
docker compose up --build

First build takes a while (judge image compiles Rust toolchain, fetches Kotlin/Dart SDKs). Subsequent builds are cached.

Once all three containers are up:

• http://localhost — frontend
• http://localhost:8080/health — {"status":"ok","judge":"connected"}

Smoke test the full pipeline:

./scripts/test-judge.sh

How it works

Three containers:

• Frontend — React + TypeScript + Vite, served via nginx on port 80. Monaco editor, problem browser, submission results.
• Backend — Go (Gin) on port 8080. Accepts submissions, manages a TCP bridge on port 9999 that the judge connects to.
• Judge — DMOJ judge-server in a custom debian:trixie-slim image (arena). Connects outbound to the backend bridge, receives submissions, runs them sandboxed, returns verdicts.

No database. Problems are flat files (init.yml + .in/.out pairs) mounted into the judge container from judge-config/problems/.

Project layout

backend/               Go API + bridge (see backend/ for details)
frontend/              React SPA (see frontend/README.md)
judge-server/          DMOJ source + custom Dockerfile at .docker/arena/
judge-config/          .dmojrc + problems/
scripts/               test-judge.sh (e2e smoke test)
docker-compose.yml

Adding problems

Create judge-config/problems/<slug>/:

init.yml
1.in   1.out
2.in   2.out

test_cases:
- {in: 1.in, out: 1.out, points: 5}
- {in: 2.in, out: 2.out, points: 5}

time_limit: 1.0
memory_limit: 262144

Restart the judge to pick them up. Output comparison is byte-exact, so trailing newlines matter.

Configuration

Environment variables on the backend (defaults in docker-compose.yml):

• PORT — HTTP port (8080)
• BRIDGE_ADDR — bridge listen address (:9999)
• JUDGE_ID / JUDGE_KEY — judge auth credentials
• API_KEYS — comma-separated API keys, auth disabled if unset
• CORS_ORIGINS — allowed origins
• JUDGE_TIME_LIMIT — per-case time override (Go duration, e.g. 5s)
• JUDGE_MEMORY_LIMIT — memory override in MB

Development

cd backend && go test ./...          # backend tests
cd frontend && npm run dev           # frontend dev server on :5173

Contributing

Fork, branch, PR against main on Aerosane/coding_arena, not the GCET org repo. Commits follow type(scope): description. Backend changes should pass go test ./.... Problem PRs should include properly formatted test data (look at existing problems for reference).

License

MIT