Scope::UDP

Sends serialized data as a raw UDP packet to a specified address and port.

Syntax

// Send to address and port
emit<Scope::UDP>(std::make_unique<T>(args...), "192.168.1.100", 9000);

// Send specifying source address and port
emit<Scope::UDP>(std::make_unique<T>(args...), "192.168.1.100", 9000, "0.0.0.0", 8000);

Parameters

Parameter	Type	Description
data	std::unique_ptr<T>	The data to serialize and send
to_addr	std::string	Destination address (unicast, broadcast, or multicast)
to_port	in_port_t	Destination port (host endian)
from_addr	std::string	(Optional) Source address, or "" for automatic (default: "")
from_port	in_port_t	(Optional) Source port, or 0 for automatic (default: 0)

Behavior

When data is emitted with Scope::UDP:

1. The data is serialized using util::serialise::Serialise<T>.
2. A UDP socket is opened and the serialized payload is sent as a single datagram.
3. No NUClear-specific framing or headers are added — the raw serialized bytes are the packet payload.

There is no fragmentation, reliability, ordering, or peer discovery. The packet is fire-and-forget.

Example

#include <nuclear>

struct StatusMessage {
    uint32_t id;
    float battery;
};

class Reporter : public NUClear::Reactor {
public:
    explicit Reporter(std::unique_ptr<NUClear::Environment> environment) : Reactor(std::move(environment)) {

        on<Every<5, std::chrono::seconds>>().then([this] {
            emit<Scope::UDP>(std::make_unique<StatusMessage>(StatusMessage{1, 0.85f}),
                             "192.168.1.255", 5000);
        });
    }
};

Notes

• The type must be serializable: either trivially copyable, or provide a util::serialise::Serialise<T> specialization.
• Supports unicast, broadcast, and multicast destination addresses.
• No NUClear protocol wrapping — suitable for interoperating with non-NUClear systems that expect raw data.
• Maximum payload size is limited by the network MTU (typically ~1472 bytes for Ethernet). No fragmentation is performed.
• The socket is opened and closed per emit. For high-frequency sending, consider the UDP DSL word with IO for lower overhead.

See Also

• Network — for communicating with other NUClear peers using the NUClear protocol
• UDP DSL word — receiving UDP packets