UDP Unicast for Meshtasticd

src/main.cpp

@@ -186,6 +186,11 @@ extern void tftSetup(void);
 UdpMulticastHandler *udpHandler = nullptr;
 #endif
 
+#ifdef ARCH_PORTDUINO
+#include "mesh/udp/UdpUnicastConnector.h"
+UdpUnicastConnector *udpUnicastConnector = nullptr;
+#endif
+
 #if defined(TCXO_OPTIONAL)
 float tcxoVoltage = SX126X_DIO3_TCXO_VOLTAGE; // if TCXO is optional, put this here so it can be changed further down.
 #endif
@@ -1037,6 +1042,20 @@ void setup()
     }
 #endif
 #endif
+
+#ifdef ARCH_PORTDUINO
+    // Native unicast-UDP connector to the meshswitch routing daemon, enabled by setting a peer
+    // address in config.yaml (General -> UDPUnicastPeer). Independent of UDP multicast.
+    if (!portduino_config.udp_unicast_peer.empty()) {
+        LOG_DEBUG("Start UDP unicast connector");
+        udpUnicastConnector = new UdpUnicastConnector();
+        if (!udpUnicastConnector->start(portduino_config.udp_unicast_peer)) {
+            delete udpUnicastConnector;
+            udpUnicastConnector = nullptr;
+        }
+    }
+#endif
+
     service = new MeshService();
     service->init();
 

src/main.h

@@ -67,6 +67,11 @@ extern AudioThread *audioThread;
 extern UdpMulticastHandler *udpHandler;
 #endif
 
+#ifdef ARCH_PORTDUINO
+#include "mesh/udp/UdpUnicastConnector.h"
+extern UdpUnicastConnector *udpUnicastConnector;
+#endif
+
 // Global Screen singleton.
 extern graphics::Screen *screen;
 

src/mesh/Channels.h

@@ -112,13 +112,13 @@ class Channels
 
     int16_t getHash(ChannelIndex i) { return hashes[i]; }
 
-  private:
     /** Given a channel index, change to use the crypto key specified by that index
      *
      * @eturn the (0 to 255) hash for that channel - if no suitable channel could be found, return -1
      */
     int16_t setCrypto(ChannelIndex chIndex);
 
+  private:
     /** Return the channel index for the specified channel hash, or -1 for not found */
     int8_t getIndexByHash(ChannelHash channelHash);
 

src/mesh/Router.cpp

@@ -421,6 +421,13 @@ ErrorCode Router::send(meshtastic_MeshPacket *p)
     }
 #endif
 
+#ifdef ARCH_PORTDUINO
+    // Mirror every outbound packet to the meshswitch routing daemon, if a unicast peer is configured.
+    if (udpUnicastConnector) {
+        udpUnicastConnector->onSend(p);
+    }
+#endif
+
     assert(iface); // This should have been detected already in sendLocal (or we just received a packet from outside)
     return iface->send(p);
 }
@@ -451,6 +458,33 @@ void Router::sniffReceived(const meshtastic_MeshPacket *p, const meshtastic_Rout
     // FIXME, update nodedb here for any packet that passes through us
 }
 
+bool attemptAESDecrypt(meshtastic_MeshPacket *p, size_t rawSize)
+{
+    memcpy(bytes, p->encrypted.bytes, rawSize);
+    // Try to decrypt the packet if we can
+    crypto->decrypt(p->from, p->id, rawSize, bytes);
+
+    // printBytes("plaintext", bytes, p->encrypted.size);
+
+    // Take those raw bytes and convert them back into a well structured protobuf we can understand
+    meshtastic_Data decodedtmp;
+    memset(&decodedtmp, 0, sizeof(decodedtmp));
+    if (!pb_decode_from_bytes(bytes, rawSize, &meshtastic_Data_msg, &decodedtmp)) {
+        LOG_DEBUG("Invalid protobufs in received mesh packet id=0x%08x (bad psk?)", p->id);
+    } else if (decodedtmp.portnum == meshtastic_PortNum_UNKNOWN_APP) {
+        LOG_DEBUG("Invalid portnum (bad psk?)");
+#if !(MESHTASTIC_EXCLUDE_PKI)
+    } else if (!owner.is_licensed && isToUs(p) && decodedtmp.portnum == meshtastic_PortNum_TEXT_MESSAGE_APP) {
+        LOG_WARN("Rejecting legacy DM");
+        return false;
+#endif
+    } else {
+        p->decoded = decodedtmp;
+        p->which_payload_variant = meshtastic_MeshPacket_decoded_tag; // change type to decoded
+        return true;
+    }
+    return false;
+}
 #if !(MESHTASTIC_EXCLUDE_PKI) && !(MESHTASTIC_EXCLUDE_XEDDSA)
 bool checkXeddsaReceivePolicy(meshtastic_MeshPacket *p)
 {
@@ -588,30 +622,26 @@ DecodeState perhapsDecode(meshtastic_MeshPacket *p)
         for (chIndex = 0; chIndex < channels.getNumChannels(); chIndex++) {
             // Try to use this hash/channel pair
             if (channels.decryptForHash(chIndex, p->channel)) {
-                // we have to copy into a scratch buffer, because these bytes are a union with the decoded protobuf. Create a
-                // fresh copy for each decrypt attempt.
-                memcpy(bytes, p->encrypted.bytes, rawSize);
-                // Try to decrypt the packet if we can
-                crypto->decrypt(p->from, p->id, rawSize, bytes);
-
-                // printBytes("plaintext", bytes, p->encrypted.size);
-
-                // Take those raw bytes and convert them back into a well structured protobuf we can understand
-                meshtastic_Data decodedtmp;
-                memset(&decodedtmp, 0, sizeof(decodedtmp));
-                if (!pb_decode_from_bytes(bytes, rawSize, &meshtastic_Data_msg, &decodedtmp)) {
-                    LOG_DEBUG("Invalid protobufs in received mesh packet id=0x%08x (bad psk?)", p->id);
-                } else if (decodedtmp.portnum == meshtastic_PortNum_UNKNOWN_APP) {
-                    LOG_DEBUG("Invalid portnum (bad psk?)");
-#if !(MESHTASTIC_EXCLUDE_PKI)
-                } else if (!owner.is_licensed && isToUs(p) && decodedtmp.portnum == meshtastic_PortNum_TEXT_MESSAGE_APP) {
-                    LOG_WARN("Rejecting legacy DM");
-                    return DecodeState::DECODE_FAILURE;
-#endif
-                } else {
-                    p->decoded = decodedtmp;
-                    p->which_payload_variant = meshtastic_MeshPacket_decoded_tag; // change type to decoded
-                    decrypted = true;
+                decrypted = attemptAESDecrypt(p, rawSize);
+                if (decrypted) {
+                    LOG_DEBUG("Packet decrypted using channel %d", chIndex);
+                    break;
+                }
+
+                // We have a sticky problem here in a specific case.
+                // If we're routing packets between presets over UDP
+                // The channel hash may be bogus.
+                // So we probably need to try to decrypt with every channel
+                // even if the hash doesn't match, to see if any of them work.
+                // If we find one that works, we can just re-write the hash
+            } else if (p->transport_mechanism == meshtastic_MeshPacket_TransportMechanism_TRANSPORT_UNICAST_UDP) {
+                // On Portduino, we allow UDP packets to bypass the channel hash check, since the hash may not be
+                // correct for packets coming over UDP from the meshswitch daemon.
+                // This allows us to support routing between presets over UDP even if the channel hashes don't match.
+                channels.setCrypto(chIndex);
+                decrypted = attemptAESDecrypt(p, rawSize);
+                if (decrypted) {
+                    LOG_DEBUG("Packet decrypted using channel %d with UDP bypass", chIndex);
                     break;
                 }
             }

src/mesh/udp/UdpUnicastConnector.h

@@ -0,0 +1,149 @@
+#pragma once
+#ifdef ARCH_PORTDUINO
+// Native unicast-UDP connector for meshtasticd. Forwards every outbound MeshPacket to a single
+// configured peer (the meshswitch routing daemon) and injects packets received back from it,
+// routing on the cleartext header exactly like the multicast handler. This is a meshtasticd-only
+// (Linux) feature, so it uses plain POSIX sockets directly rather than the portduino AsyncUDP
+// library.
+//
+// meshtasticd is the client here: it connect()s one UDP socket to the peer, send()s outbound
+// packets, and recv()s the daemon's replies on that same socket (the daemon always answers the
+// source endpoint it last heard from, so no well-known listen port is required).
+
+#include "configuration.h"
+#include "main.h"
+#include "mesh/Router.h"
+#include "mesh/mesh-pb-constants.h"
+
+#include <atomic>
+#include <cstdlib>
+#include <string>
+#include <thread>
+
+#include <arpa/inet.h>
+#include <netinet/in.h>
+#include <sys/socket.h>
+#include <unistd.h>
+
+#define UDP_UNICAST_DEFAULT_PORT 4403 // matches the daemon's default listen port
+
+class UdpUnicastConnector final
+{
+  public:
+    UdpUnicastConnector() = default;
+    ~UdpUnicastConnector() { stop(); }
+
+    // peer is "host" or "host:port" (IPv4 literal). Returns true once connected.
+    bool start(const std::string &peer)
+    {
+        if (isRunning)
+            return true;
+
+        std::string host = peer;
+        uint16_t port = UDP_UNICAST_DEFAULT_PORT;
+        auto colon = peer.rfind(':');
+        if (colon != std::string::npos) {
+            host = peer.substr(0, colon);
+            port = (uint16_t)atoi(peer.substr(colon + 1).c_str());
+        }
+
+        sockaddr_in addr = {};
+        addr.sin_family = AF_INET;
+        addr.sin_port = htons(port);
+        if (inet_pton(AF_INET, host.c_str(), &addr.sin_addr) != 1) {
+            LOG_ERROR("UDP unicast: bad peer address '%s'", peer.c_str());
+            return false;
+        }
+
+        fd = socket(AF_INET, SOCK_DGRAM, 0);
+        if (fd < 0) {
+            LOG_ERROR("UDP unicast: socket() failed");
+            return false;
+        }
+        // connect() pins the destination for send() and filters recv() to datagrams from the peer.
+        if (::connect(fd, reinterpret_cast<sockaddr *>(&addr), sizeof(addr)) < 0) {
+            LOG_ERROR("UDP unicast: connect() to %s:%u failed", host.c_str(), port);
+            ::close(fd);
+            fd = -1;
+            return false;
+        }
+
+        isRunning = true;
+        rxThread = std::thread([this]() { receiveLoop(); });
+        LOG_INFO("UDP unicast connector to %s:%u started", host.c_str(), port);
+        return true;
+    }
+
+    void stop()
+    {
+        if (!isRunning)
+            return;
+        isRunning = false;
+        if (fd >= 0)
+            ::shutdown(fd, SHUT_RDWR); // unblock the recv() in the rx thread
+        if (rxThread.joinable())
+            rxThread.join();
+        if (fd >= 0) {
+            ::close(fd);
+            fd = -1;
+        }
+    }
+
+    // Called from Router::send for every outbound packet.
+    void onSend(const meshtastic_MeshPacket *mp)
+    {
+        if (!isRunning || fd < 0 || !mp)
+            return;
+        // Never reflect a packet that arrived over UDP straight back out over UDP. The daemon's
+        // (from,id) dedup is the backstop if this ever slips through.
+        if (mp->transport_mechanism == meshtastic_MeshPacket_TransportMechanism_TRANSPORT_UNICAST_UDP)
+            return;
+
+        uint8_t buffer[meshtastic_MeshPacket_size];
+        size_t len = pb_encode_to_bytes(buffer, sizeof(buffer), &meshtastic_MeshPacket_msg, mp);
+        if (len == 0)
+            return;
+#ifdef MSG_NOSIGNAL
+        constexpr int kSendFlags = MSG_NOSIGNAL;
+#else
+        constexpr int kSendFlags = 0;
+#endif
+        if (::send(fd, buffer, len, kSendFlags) < 0)
+            LOG_DEBUG("UDP unicast: send() failed for packet id=%u", mp->id);
+    }
+
+  private:
+    void receiveLoop()
+    {
+        uint8_t buf[meshtastic_MeshPacket_size];
+        while (isRunning) {
+            ssize_t n = ::recv(fd, buf, sizeof(buf), 0);
+            if (n <= 0) {
+                if (!isRunning)
+                    break;
+                continue; // transient error or shutdown in progress
+            }
+            meshtastic_MeshPacket mp = meshtastic_MeshPacket_init_zero;
+            if (!pb_decode_from_bytes(buf, (size_t)n, &meshtastic_MeshPacket_msg, &mp))
+                continue;
+            if (mp.which_payload_variant != meshtastic_MeshPacket_encrypted_tag)
+                continue;
+            // Drop packets with spoofed local origin — same guard as the multicast handler.
+            if (isFromUs(&mp)) {
+                LOG_WARN("UDP unicast packet with spoofed local from=0x%x, dropping", mp.from);
+                continue;
+            }
+            mp.transport_mechanism = meshtastic_MeshPacket_TransportMechanism_TRANSPORT_UNICAST_UDP;
+            UniquePacketPoolPacket p = packetPool.allocUniqueCopy(mp);
+            p->rx_snr = 0;
+            p->rx_rssi = 0;
+            if (router)
+                router->enqueueReceivedMessage(p.release());
+        }
+    }
+
+    int fd = -1;
+    std::atomic<bool> isRunning{false};
+    std::thread rxThread;
+};
+#endif // ARCH_PORTDUINO

src/platform/portduino/PortduinoGlue.cpp

@@ -1171,6 +1171,7 @@ bool loadConfig(const char *configPath)
                     TCPPort = (portduino_config.api_port);
                 }
             }
+            portduino_config.udp_unicast_peer = (yamlConfig["General"]["UDPUnicastPeer"]).as<std::string>("");
             portduino_config.mac_address = (yamlConfig["General"]["MACAddress"]).as<std::string>("");
             if (portduino_config.mac_address != "") {
                 portduino_config.mac_address_explicit = true;

src/platform/portduino/PortduinoGlue.h

@@ -230,6 +230,7 @@ extern struct portduino_config_struct {
     bool mac_address_explicit = false;
     std::string mac_address_source = "";
     int api_port = -1;
+    std::string udp_unicast_peer = ""; // meshswitch routing daemon peer, "host" or "host:port"; empty = disabled
     std::string config_directory = "";
     std::string available_directory = "/etc/meshtasticd/available.d/";
     int maxtophone = 100;
@@ -641,6 +642,8 @@ extern struct portduino_config_struct {
             out << YAML::Key << "ConfigDirectory" << YAML::Value << config_directory;
         if (api_port != -1)
             out << YAML::Key << "TCPPort" << YAML::Value << api_port;
+        if (udp_unicast_peer != "")
+            out << YAML::Key << "UDPUnicastPeer" << YAML::Value << udp_unicast_peer;
         if (mac_address_explicit)
             out << YAML::Key << "MACAddress" << YAML::Value << mac_address;
         if (mac_address_source != "")