sioxx — a modern C++ socket.io client (nlohmann/json + Boost.Beast, JSON or MessagePack)

If you've ever tried to use

What changed vs. the original

The public API keeps the same shape you'd expect from socket.io — client, socket("/namespace"), on(event, handler), emit(event, data), ack callbacks — but almost everything under the hood is new.

The JSON value problem, solved by not solving it

The original library has a whole sio::message class hierarchy — int_message, string_message, object_message, array_message, binary_message — basically reimplementing a JSON value type from scratch. But nlohmann::json is a JSON value type, and it already handles null/bool/int/double/string/array/object and raw binary via json::binary_t. So sioxx::message is just:

namespace sioxx {

using json = nlohmann::json;

using message = json;          // that's it

using message_list = json;     // always a JSON array

}

That one decision deletes an entire subsystem. Building event args is just building a json array:

sock->emit("hello", sioxx::json{"world"});

sock->emit("ping_ack", sioxx::json::array({1, 2, 3}), [](sioxx::message reply) {

    std::cout << "ack: " << reply.dump() << "\n";

});

Two wire protocols behind one interface

socket.io actually has two parsers in the wild: the default text protocol, and