This is a WhatsApp messaging API built with Node.js, TypeScript, and Express. The system provides REST endpoints for user authentication, WhatsApp number registration (via QR code), message sending (with scheduling and media support), and user/token management. Architecture follows a layered approach: API controllers delegate to service classes, which use TypeORM repositories for data access. A separate worker process continuously polls the database for pending messages and sends them via WhatsApp using a sophisticated custom client manager that handles multiple WhatsApp sessions, QR code authentication, session persistence, and connection recovery. The WhatsApp client implementation (src/whatsapp/client/index.ts) demonstrates significant skill in managing the complexities of the whatsapp-web.js library, including proper resource cleanup, timeout handling, and state management across multiple concurrent connections.
GoBelieveIO/im_service is an instant messaging (IM) server infrastructure implemented in Go. It provides real-time peer-to-peer messaging, group chat (including super groups for large audiences), and chat rooms. The system is designed for clustered deployment and consists of three separate processes: `im` (access server handling client TCP/WebSocket connections), `ims` (storage server using append-only file logs with in-memory indexes), and `imr` (router server coordinating message delivery between access servers). Authentication is token-based (Redis or JWT). Message storage is per-user file-based with efficient offline message synchronization via sync keys. The codebase includes a custom binary protocol over TCP/WebSocket, a Redis-backed pub/sub mechanism for group events and relationship changes, and MySQL for group and friend data. This is a production-grade system (as indicated by its star count) with comprehensive benchmark tools and Python integration tests. However, the repository appears to be in a maintenance-stale state with no recent commits and some deprecated message types.