This module implements the msgpack_ext behaviour for (un)packing Elixir DateTimes as MessagePack ext -1 types. Use by adding {:ext, MsgpackDateTime} to :msgpack.unpack(_, options), and (un)wrap your DateTimes as {MsgpackDateTime, dt}.

Packing DateTimes directly cannot be implemented because :msgpack only considers erlang structs (so, tuples: {module, ...}) to be extendable and serialises Elixir structs (so, maps: %{__struct__: DateTime, ...}) as maps. Thus, the wrapping.

iex> dt = ~U[2025-12-10 12:53:25Z]
...> assert :msgpack.pack({MsgpackDateTime, dt}, [{:ext, MsgpackDateTime}])
...>        === <<214, 255, 105, 57, 109, 69>>
...> assert :msgpack.unpack("\x93\xC4\x06record\xD6\xFFi9mE\xCD\x01\xA4", [{:ext, MsgpackDateTime}])
...>        === {:ok, ["record", {MsgpackDateTime, dt}, 420]}

Elixir DateTimes have microsecond precision, but MessagePack provides nanosecond precision, so an unpack+pack won't round-trip if the packed timestamp had a non-zero nanosecond component.