This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.

MessagePack-Java is a binary serialization library that provides a fast and compact alternative to JSON. The project consists of two main modules:

• msgpack-core: Standalone MessagePack implementation with no external dependencies
• msgpack-jackson: Jackson integration for object mapping capabilities

./sbt compile              # Compile source code
./sbt "Test / compile"     # Compile source and test code
./sbt package              # Create JAR files

./sbt test                 # Run all tests
./sbt ~test                # Run tests continuously on file changes
./sbt testOnly *TestClass  # Run specific test class
./sbt "testOnly *TestClass -- -z pattern"  # Run tests matching pattern

# Test with universal buffer mode (for compatibility testing)
./sbt test -J-Dmsgpack.universal-buffer=true

./sbt jcheckStyle          # Run checkstyle (Facebook Presto style)
./sbt scalafmtAll          # Format all Scala and sbt code

./sbt publishLocal         # Install to local .ivy2 repository
./sbt publishM2            # Install to local .m2 Maven repository

The main entry point is the MessagePack factory class which creates:

• MessagePacker: Serializes objects to MessagePack binary format
• MessageUnpacker: Deserializes MessagePack binary data

Key locations:

• Core interfaces: msgpack-core/src/main/java/org/msgpack/core/
• Jackson integration: msgpack-jackson/src/main/java/org/msgpack/jackson/dataformat/

MessagePack uses an efficient buffer abstraction layer:

• MessageBuffer: Platform-optimized buffer implementations
  • Uses sun.misc.Unsafe for performance when available
  • Falls back to ByteBuffer on restricted platforms
• MessageBufferInput/Output: Manages buffer sequences for streaming

The msgpack-jackson module provides:

• MessagePackFactory: Jackson JsonFactory implementation
• MessagePackMapper: Pre-configured ObjectMapper for MessagePack
• Support for field IDs (integer keys) for compact serialization
• Extension type support including timestamps

• msgpack-core tests: Written in Scala (always use the latest Scala 3 version) using AirSpec framework
  • Location: msgpack-core/src/test/scala/
• msgpack-jackson tests: Written in Java using JUnit
  • Location: msgpack-jackson/src/test/java/

For JDK 17+ compatibility, these options are automatically added:

--add-opens=java.base/java.nio=ALL-UNNAMED
--add-opens=java.base/sun.nio.ch=ALL-UNNAMED

• Java code follows Facebook Presto style (enforced by checkstyle)
• Scala test code uses Scalafmt with Scala 3 dialect and 100 character line limit
• Checkstyle runs automatically during compilation
• No external dependencies allowed in msgpack-core

1. Zero Dependencies: msgpack-core has no external dependencies
2. Platform Optimization: Uses platform-specific optimizations when available
3. Streaming Support: Both streaming and object-based APIs
4. Type Safety: Immutable Value hierarchy for type-safe data handling
5. Extension Support: Extensible type system for custom data types