Starting a Host

A host can act as either a server or a client. A server binds its UDP socket to the set address, while a client uses that address as its destination. The send and receive loops run on their own std::jthread, while Tick() stays under the application's flow and control!

CelsiusHost host(true, true, this);

host.SetIPv4(L"127.0.0.1");
host.SetHostPort(7777);

if (host.Initialize() == 0) {
    host.DetachReceiver();
    host.DetachSender();
}

while (running) {
    host.Tick();
}

Defining a Packet

Every packet derives from CelsiusPacket. The PACKET_TYPE macro assigns an ID and automatically registers a constructor with CelsiusFactory. This lets the receiver turn the packet ID from the wire back into the correct C++ class later on

class MessagePacket : public CelsiusPacket {
public:
    PACKET_TYPE(MessagePacket, 4);

    std::string message;

    void Write(CelsiusStream& stream) override {
        stream.WriteData<std::string>(message);
    }

    void Read(CelsiusStream& stream) override {
        message = stream.ReadData<std::string>();
    }

    void Handle(void* context) override {
        // React to the packet on the main thread.
    }

    void Reset() override {
        message.clear();
    }

    bool IsReliable() const override {
        return true;
    }
};

Sending the packet is then just a matter of creating the packet and moving it into the outgoing queue

auto packet = std::make_unique<MessagePacket>();
packet->message = "Hello World";
host.QueueOutgoingPacket(std::move(packet));

Bit Packing

My CelsiusStream can write ordinary trivially-copyable values, strings, or a chosen number of bits from an integral value. This is useful for small game-state fields that do not need an entire byte or integer.

// 3 bits allow values from 0 to 7.
stream.WriteBits<uint8_t>(direction, 3);

// A boolean only needs one bit.
stream.WriteBits<uint8_t>(isSprinting ? 1 : 0, 1);

The stream tracks its current bit position and automatically aligns back to the next byte before reading or writing normal data.