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
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).