libmpack

Introduction

libmpack is a small binary serialization/RPC library that implements both the msgpack and msgpack-rpc specifications.

Concepts

See libmpack-python for an overview, in particular the RPC section explains the lifecycle of a libmpack Session.

Rationale

While there's already a msgpack-c implementation, it has a few problems that libmpack aims to address:

• It couples msgpack serialization format with a set of predefined C typedefs. This means the user almost always has to recursively convert the allocated structures into some other application-specific format, especially if binding to another language. libmpack serialization/deserialization API is callback-based, making it simple to serialize/deserialize directly from/to application-specific objects.

• It is not trivial to simply include its files into another project(eg: a lua C module) since it relies too much on C99 features and compilation with -Wconversion issues a bunch of warnings. You need to build the library and link against it, which can be cumbersome for a simple serialization library that is being embedded into other projects(lua or node.js modules for example). libmpack provides an amalgamation build(single source file containing all code that can be #included) and should compile cleanly as part of any C89 project. It won't produce any warnings for -Wall/-Wextra/-Wconversion.

• msgpack-c doesn't work without allocating memory. For example, you can't send/receive simple primitives without a msgpack_sbuffer_t(which is then dynamically extended by msgpack internal functions). libmpack does no allocation at all, and provides some helpers to simplify dynamic allocation by the user, if required.

• There's no msgpack-rpc implementation for C(much less one that can be reused in other languages). libmpack has a simple and flexible msgpack-rpc implementation that can be used to easily create distributed applications across any kind of transport. Unlike some msgpack-rpc libraries(ruby official implementation for example), libmpack has no coupling with any network sink/source, allowing it to be used with any event loop library or system-specific networking APIs.

Here's a few extras that may or not overlap with what msgpack-c provides:

• Fully incremental/iterative parse/serialization API with no backtracking, which simplifies working with split buffers.

• Portable C89 library with zero system dependencies. In fact, it only uses one function from C standard library: memcpy. libmpack can be used even in OS/kernel development(eg: communicate with userspace using netlink/msgpack-rpc).

• Endian aware: it should work unmodified regardless of the system's byte order, and its CI infrastructure automatically tests it on a big endian platform.

• Well tested, it should always have about 100% code coverage: https://coveralls.io/github/libmpack/libmpack?branch=master

• Relatively small footprint: The amalgamation(headers + code) is less than 2k lines of C. The whole library can be inlined when compiled with -O3(Though this depends on compiler and usage, eg: how many call sites for certain functions).