CIM is a distributed instant messaging system built for developers using Java and Netty.
CIM solves the problem of building scalable real-time communication infrastructure by providing a complete IM system that developers can deploy, extend, or use as a reference implementation. The architecture separates concerns across multiple components: a Netty-based server handles client connections and message forwarding, a route server manages message routing and user state, and a client SDK enables developers to build their own messaging applications. Communication uses Google Protocol Buffers for efficient encoding and decoding. The system supports both group and private chat, automatic client reconnection, server-side offline client cleanup, and delayed message delivery.
CIM suits developers building instant messaging systems, message push middleware for applications, or IoT scenarios requiring massive concurrent connections. The project provides a complete working system with built-in commands and chat history query capabilities, making it useful both as a deployable solution and as a learning reference for understanding distributed IM architecture. The README does not compare CIM to alternative IM frameworks.
The project maintains active development with recent upgrades to JDK 17 and Spring Boot 3.0, and includes Docker container support. Integration testing support has been added to the codebase. The development roadmap includes planned features such as OpenTelemetry integration, single-node startup mode, replaceable third-party components, WebSocket client support, and Kubernetes operations, indicating ongoing evolution of the platform's capabilities and deployment flexibility.
