6-in-a-Row Blitz — Real-Time Multiplayer Strategy Game

I set out to build a complete end-to-end multiplayer experience — a fast-paced 6-in-a-row strategy game inspired by Gomoku and Connect-6 — where two players could compete live on a shared board. The challenge was to synchronize moves, timers, and game logic across clients in real time while handling disconnections and race conditions gracefully. My objective was to architect a performant and reliable real-time system using Socket.IO and Express that ensures fairness, enforces game rules (3 moves per turn, blitz timer), and maintains a consistent authoritative game state, even under concurrent events and unstable networks.

• Desynchronization between clients due to latency or race conditions in socket event order.
• Memory leaks or ghost sessions if disconnected players aren’t cleaned up properly.
• Unvalidated or replayed socket emissions allowing cheating or stale moves.
• Inefficient win-detection loops causing lag on large 15×15 grids.
• Unresponsive UX if the backend fails to broadcast timely state updates.

1. Built a Node.js + Express backend integrated with Socket.IO to manage bidirectional real-time communication. Why: establish a scalable event-driven core for multiplayer sync.
2. Structured the backend into clear layers: Express routes (for lobby + metadata), Socket controllers (for gameplay), and an in-memory game registry keyed by UUID. Why: modular design, easy debugging, and deterministic game state retrieval.
3. Introduced per-game Socket.IO rooms, so only the relevant players receive state updates. Why: reduce network load and prevent event collisions.
4. Engineered custom socket events — createGame, joinGame, makeMove, timerUpdate, gameOver — to maintain a predictable lifecycle. Why: ensure consistent game flow and clear separation of concerns.
5. Implemented authoritative server validation: every move checked server-side for turn order, move count, and time. Why: prevent cheating and preserve fairness.
6. Enabled optimistic rendering on the client with rollback correction on mismatch. Why: preserve responsiveness without breaking state integrity.
7. Used a per-player timer running on the backend, emitting countdown ticks every second. Why: enforce blitz-style urgency with synchronized updates.
8. Developed a dedicated gameLogic.js module performing 8-directional win detection for ‘6 in a row’. Why: isolate compute logic for testing and maintain O(n²) complexity control.
9. Implemented per-turn move limits (3 per player) and automatic turn switching after completion. Why: enforce consistent pacing and prevent spam.
10. Added automatic victory conditions: disconnection = forfeit, timeout = loss. Why: handle edge cases cleanly.
11. Built a responsive frontend using React + Vite + Tailwind CSS. Why: rapid prototyping, reactive state, and lightweight bundle size.
12. Created reusable components: GameBoard (15×15 grid), Lobby (matchmaking), Timer, and MoveIndicator. Why: maintain modular UI and clarity.
13. Integrated Socket.IO client listeners for real-time updates: gameUpdate, moveMade, timerTick, and gameOver. Why: mirror backend state seamlessly.
14. Used TypeScript for all payloads and event types. Why: reduce runtime errors and enforce contract between frontend and backend.
15. Implemented per-player authentication tokens generated on join; validated on every socket emission. Why: prevent spoofed or replayed moves.
16. Added heartbeat checks and disconnect cleanup to reclaim server memory. Why: ensure stability during prolonged sessions.
17. Logged structured socket events and outcomes for testing and observability.
18. Stress-tested concurrent matches (multiple Socket.IO rooms) to validate isolation and throughput. Why: prove scalability of event handling.
19. Profiled win-detection performance — <5 ms average on full board state. Why: maintain smooth gameplay under load.
20. Deployed frontend on Vercel and backend on Render (Node.js service). Why: separate scaling planes for low latency and global reach.

The deployed game consistently achieved sub-100 ms socket round-trip latency in local and cloud tests, maintaining real-time synchronization across multiple matches. Game logic validated moves and win conditions with zero desync or duplication issues. Average backend CPU stayed below 25% under 10 concurrent games, demonstrating stable scaling. Players experienced smooth, near-instant feedback even on mobile connections. The architecture validated my ability to design real-time event systems, concurrency-safe state management, and UX-aligned backend logic.

Designing multiplayer systems taught me that correctness under concurrency is more valuable than raw speed. Socket.IO abstracts WebSocket complexity, but disciplined event flow and clear ownership of state make or break the experience. I learned to think in terms of idempotent updates, time budgets, and latency empathy — optimizing not just code, but communication patterns between human players and machines. This project deepened my understanding of distributed real-time logic and the value of simplicity in synchronized design.