This is the OpenIM SDK Core, a cross-platform instant messaging client SDK written in Go. It provides the core messaging functionality—send/receive messages, manage conversations, groups, friends, user profiles, and file uploads—for the OpenIM ecosystem. The SDK communicates with an OpenIM server via HTTP REST and WebSocket long connections, and persists data locally using SQLite (native) or IndexedDB (WebAssembly). It features robust incremental synchronization, a callback-driven architecture for event handling, and extensive support for multiple platforms (iOS, Android, Windows, macOS, Linux, Web). The codebase demonstrates solid engineering practices with generic sync engines, caching utilities, and a comprehensive integration test suite. However, it also contains notable code duplication (dual native/WASM storage implementations), incomplete WASM stubs, some panic-based error handling, and alpha-stage dependencies, which prevent it from being exceptional. Overall, it is a functional, actively maintained SDK with reusable patterns for incremental sync and WebSocket connection management.