firmware/src/mesh/udp/UdpMulticastHandler.h

#pragma once
#if HAS_UDP_MULTICAST
#include "configuration.h"
#include "main.h"
#include "mesh/Router.h"

#if HAS_ETHERNET && defined(ARCH_NRF52)
#include "mesh/eth/ethClient.h"
#else
#include <WiFi.h>
#endif

#include <AsyncUDP.h>

#if HAS_ETHERNET && defined(ARCH_ESP32)
#include <ETH.h>
#endif // HAS_ETHERNET

#define UDP_MULTICAST_DEFAUL_PORT 4403 // Default port for UDP multicast is same as TCP api server

class UdpMulticastHandler final
{
  public:
    UdpMulticastHandler() : isRunning(false) { udpIpAddress = IPAddress(224, 0, 0, 69); }

    void start()
    {
        if (isRunning) {
            LOG_DEBUG("UDP multicast already running");
            return;
        }
        if (udp.listenMulticast(udpIpAddress, UDP_MULTICAST_DEFAUL_PORT, 64)) {
#if defined(ARCH_NRF52) || defined(ARCH_PORTDUINO)
            LOG_DEBUG("UDP Listening on IP: %u.%u.%u.%u:%u", udpIpAddress[0], udpIpAddress[1], udpIpAddress[2], udpIpAddress[3],
                      UDP_MULTICAST_DEFAUL_PORT);
#else
            LOG_DEBUG("UDP Listening on IP: %s", WiFi.localIP().toString().c_str());
#endif
            udp.onPacket([this](AsyncUDPPacket packet) { onReceive(packet); });
            isRunning = true;
        } else {
            LOG_DEBUG("Failed to listen on UDP");
        }
    }

    void stop()
    {
        if (!isRunning) {
            return;
        }
        LOG_DEBUG("Stopping UDP multicast");
#if defined(ARCH_ESP32) || defined(ARCH_NRF52)
        udp.close();
#endif
        isRunning = false;
    }

    void onReceive(AsyncUDPPacket &packet)
    {
        if (!isRunning) {
            return;
        }
        size_t packetLength = packet.length();
#if defined(ARCH_NRF52)
        IPAddress ip = packet.remoteIP();
        LOG_DEBUG("UDP broadcast from: %u.%u.%u.%u, len=%u", ip[0], ip[1], ip[2], ip[3], packetLength);
#elif !defined(ARCH_PORTDUINO)
        // FIXME(PORTDUINO): arduino lacks IPAddress::toString()
        LOG_DEBUG("UDP broadcast from: %s, len=%u", packet.remoteIP().toString().c_str(), packetLength);
#endif
        meshtastic_MeshPacket mp = meshtastic_MeshPacket_init_zero;
        LOG_DEBUG("Decoding MeshPacket from UDP len=%u", packetLength);
        bool isPacketDecoded = pb_decode_from_bytes(packet.data(), packetLength, &meshtastic_MeshPacket_msg, &mp);
        if (isPacketDecoded && router && mp.which_payload_variant == meshtastic_MeshPacket_encrypted_tag) {
            // Drop packets with spoofed local origin — no legitimate LAN node should send from=0 or our own nodeNum
            if (isFromUs(&mp)) {
                LOG_WARN("UDP packet with spoofed local from=0x%x, dropping", mp.from);
                return;
            }
            mp.transport_mechanism = meshtastic_MeshPacket_TransportMechanism_TRANSPORT_MULTICAST_UDP;
            UniquePacketPoolPacket p = packetPool.allocUniqueCopy(mp);
            // Unset received SNR/RSSI
            p->rx_snr = 0;
            p->rx_rssi = 0;
            router->enqueueReceivedMessage(p.release());
        }
    }

    bool onSend(const meshtastic_MeshPacket *mp)
    {
        if (!isRunning || !mp || !udp) {
            return false;
        }
#if defined(ARCH_NRF52)
        if (!isEthernetAvailable()) {
            return false;
        }
#elif !defined(ARCH_PORTDUINO)
        if (WiFi.status() != WL_CONNECTED) {
            return false;
        }
#endif
        if (mp->transport_mechanism == meshtastic_MeshPacket_TransportMechanism_TRANSPORT_MULTICAST_UDP) {
            LOG_ERROR("Attempt to send UDP sourced packet over UDP");
        }
        LOG_DEBUG("Broadcasting packet over UDP (id=%u)", mp->id);
        uint8_t buffer[meshtastic_MeshPacket_size];
        size_t encodedLength = pb_encode_to_bytes(buffer, sizeof(buffer), &meshtastic_MeshPacket_msg, mp);
        return udp.writeTo(buffer, encodedLength, udpIpAddress, UDP_MULTICAST_DEFAUL_PORT);
    }

  private:
    IPAddress udpIpAddress;
    AsyncUDP udp;
    bool isRunning;
};
#endif // HAS_UDP_MULTICAST