LeetCode Duels

A browser extension that lets you challenge friends to real-time LeetCode duels.

Getting Started

Clone the repository

git clone https://github.com/etbala/LeetCodeDuels.git
cd LeetCodeDuels

Extension

1. Install Dependencies

Install Node.js (v22+) and Angular CLI.

npm install -g @angular/cli

2. Build Extension

cd extension
npm install
ng build

Note: Build using -c local if you are running the server locally:

ng build -c local

3. Load Extension in Browser

Load Unpacked Extension from Directory: /extension/dist/browser

For Chrome, see https://support.google.com/chrome/a/answer/2714278

For Firefox, see https://extensionworkshop.com/documentation/develop/temporary-installation-in-firefox/

Server

1. Install Dependencies

Install Go (v1.24+).

2. Set up .env

Create a .env file in the /server directory by copying the template file: /server/.env.template.

Ensure final file is located at LeetCodeDuels/server/.env

3. Run Server

cd server
go run ./cmd/server

Testing

Server Tests

Install and run Docker.

cd server
go test ./... -v

Server Stress Tests

Install Grafana k6 and Powershell.

cd server/tests/k6
./stress-test.ps1

High Level Architecture

graph TD
    Frontend[Frontend]

    subgraph Cluster [Horizontally Scaled Cluster]
        direction LR
        B1[Backend Instance]
        B2[Backend Instance]
    end

    Postgres[Postgres]
    Redis[Redis]

    Frontend -- "REST API" --> Cluster
    Frontend -- "WebSocket" --> Cluster

    Cluster -- "SQL Queries" --> Postgres

    Cluster --> |"Session & State Storage"| Redis
    Cluster <--> |"Horizontal Communication (Pub/Sub)"| Redis

Loading

Architecture Breakdown

• Frontend: This is the client-side application that the user interacts with. It communicates with the backend via:

  • REST API: Used for standard actions like user login, registration, fetching user profiles, etc. Generally, REST endpoints are used by Angular when loading webpage information.

  • WebSockets: Used for real-time, two-way communication required for gameplay, invitations, and live online status updates.

• Backend Cluster: The core application logic resides in a horizontally scalable cluster of backend instances. Designing the server to be stateless allows us to run multiple instances behind a load balancer so the backend can automatically scale to meet demand.

• Postgres: Long-term storage. Handles account information, game history, and mirrors a simplified version of leetcode's problem database. Generally accessed via REST endpoints.

• Redis:

  • Session & State Storage: Stores temporary data like active game sessions, pending user invites, and which users are currently online (and which server instance they are connected to).

  • Horizontal Communication (Pub/Sub): Redis acts as a message bus for backend instances to communicate with each other. For example, if a user connected to Instance A sends a game invite to a user connected to Instance B, the message is published to a Redis channel, which delivers it to the correct instance.