MCAP

MCAP is a modular container format and logging library for pub/sub messages with arbitrary message serialization. It is primarily intended for use in robotics applications, and works well under various workloads, resource constraints, and durability requirements.

Documentation

• File format specification
  • Kaitai Struct definition
• Motivation
• Support Matrix

Developer quick start

MCAP libraries are provided in the following languages. For guidance on each language, see its corresponding README:

Language	Readme	API docs	Package name	Version
C++	readme	API docs	mcap
Go	readme	API docs		see releases
Python	readme	API docs	mcap
JavaScript/TypeScript	readme	API docs	@mcap/core
Swift	readme	API docs		see releases
Rust	readme	API docs	mcap

To run the conformance tests, you will need to use Git LFS, which is used to store the test logs under tests/conformance/data.

CLI tool

Interact with MCAP files from the command line using the MCAP CLI tool.

Download the latest mcap-cli version from the releases page.

License

MIT License. Contributors are required to accept the Contributor License Agreement.

Release process

Release numbering follows a major.minor.patch format, abbreviated as "X.Y.Z" below.

CI will build the appropriate packages once tags are pushed, as described below.

Go library

1. Update the Version in go/mcap/version.go
2. Tag a release matching the version number go/mcap/vX.Y.Z.

CLI

Tag a release matching releases/mcap-cli/vX.Y.Z.

The version number is set at build time based on the tag.

C++

1. Update the version in all relevant files
   • cpp/bench/conanfile.py
   • cpp/build-docs.sh
   • cpp/build.sh
   • cpp/docs/conanfile.py
   • cpp/examples/conanfile.py
   • cpp/mcap/include/mcap/types.hpp (MCAP_LIBRARY_VERSION)
   • cpp/mcap/include/conanfile.py
   • cpp/test/conanfile.py
2. Tag a release matching the version number releases/cpp/vX.Y.Z

Python

There are several python packages; updating any follows a similar process.

1. Update the version in the appropriate __init.py__ file
2. Tag a release
   • For the core mcap library, match the pattern releases/python/vX.Y.Z
   • For other packages, use releases/python/PACKAGE/vX.Y.Z
     • For example, releases/python/mcap/v1.2.3

TypeScript

There are several TS packages; updating any follows a similar process.

1. Update the version in the appropriate package.json
2. Tag a release matching releases/typescript/PACKAGE/vX.Y.Z
   • For example, releases/typescript/core/v1.2.3

Swift

Tag a release matching the version number releases/swift/vX.Y.Z

Rust

1. Update the version in rust/Cargo.toml
2. Tag a release matching the version number releases/rust/vX.Y.Z