Allow programmatic configuration of unicast relays.

include/gz/transport/Discovery.hh

@@ -740,6 +740,42 @@ namespace gz
         }
       }
 
+      /// \brief Register a new relay address.
+      /// \param[in] _ip New IP address.
+      public: void AddRelayAddress(const std::string &_ip)
+      {
+        std::lock_guard<std::mutex> lock(this->mutex);
+        // Sanity check: Make sure that this IP address is not already saved.
+        for (auto const &addr : this->relayAddrs)
+        {
+          if (addr.sin_addr.s_addr == inet_addr(_ip.c_str()))
+            return;
+        }
+
+        sockaddr_in addr;
+        memset(&addr, 0, sizeof(addr));
+        addr.sin_family = AF_INET;
+        addr.sin_addr.s_addr = inet_addr(_ip.c_str());
+        addr.sin_port = htons(static_cast<u_short>(this->port));
+
+        this->relayAddrs.push_back(addr);
+      }
+
+      // \brief Gets this instance's relay addresses.
+      // \return The list of relay addresses.
+      public: std::vector<std::string> RelayAddresses() const
+      {
+        std::vector<std::string> result;
+
+        std::lock_guard<std::mutex> lock(this->mutex);
+
+        for (auto const &addr : this->relayAddrs) {
+          result.push_back(inet_ntoa(addr.sin_addr));
+        }
+
+        return result;
+      }
+
       /// \brief Broadcast periodic heartbeats.
       private: void UpdateHeartbeat()
       {
@@ -1254,6 +1290,8 @@ namespace gz
         if (_msg.SerializeToArray(buffer + sizeof(msgSize), msgSize))
         {
           // Send the discovery message to the unicast relays.
+          std::lock_guard<std::mutex> lock(this->mutex);
+
           for (const auto &sockAddr : this->relayAddrs)
           {
             errno = 0;
@@ -1420,26 +1458,6 @@ namespace gz
         return true;
       }
 
-      /// \brief Register a new relay address.
-      /// \param[in] _ip New IP address.
-      private: void AddRelayAddress(const std::string &_ip)
-      {
-        // Sanity check: Make sure that this IP address is not already saved.
-        for (auto const &addr : this->relayAddrs)
-        {
-          if (addr.sin_addr.s_addr == inet_addr(_ip.c_str()))
-            return;
-        }
-
-        sockaddr_in addr;
-        memset(&addr, 0, sizeof(addr));
-        addr.sin_family = AF_INET;
-        addr.sin_addr.s_addr = inet_addr(_ip.c_str());
-        addr.sin_port = htons(static_cast<u_short>(this->port));
-
-        this->relayAddrs.push_back(addr);
-      }
-
       /// \brief Default activity interval value (ms.).
       /// \sa ActivityInterval.
       /// \sa SetActivityInterval.

include/gz/transport/Node.hh

@@ -762,6 +762,19 @@ namespace gz
       public: std::optional<TopicStatistics> TopicStats(
                   const std::string &_topic) const;
 
+      /// \brief Adds a unicast relay IP. All nodes in this process will send
+      /// UDP unicast traffic to the address to connect networks when UDP
+      /// multicast traffic is not forwarded.
+      /// It's also possible to use the environment variable GZ_RELAY to add
+      /// relays.
+      /// \param[in] _relayAddress IPv4 address of the relay to add.
+      public: void AddGlobalRelay(const std::string& _relayAddress);
+
+      /// \brief Gets the relay addresses configured for all nodes in this
+      /// process.
+      /// \return The relay addresses.
+      public: std::vector<std::string> GlobalRelays() const;
+
       /// \brief Get a pointer to the shared node (singleton shared by all the
       /// nodes).
       /// \return The pointer to the shared node.

include/gz/transport/NodeShared.hh

@@ -284,6 +284,19 @@ namespace gz
       public: std::optional<TopicStatistics> TopicStats(
                   const std::string &_topic) const;
 
+      /// \brief Adds a unicast relay IP. All nodes in this process will send
+      /// UDP unicast traffic to the address to connect networks when UDP
+      /// multicast traffic is not forwarded.
+      /// It's also possible to use the environment variable GZ_RELAY to add
+      /// relays.
+      /// \param[in] _relayAddress IPv4 address of the relay to add.
+      public: void AddGlobalRelay(const std::string& _relayAddress);
+
+      /// \brief Gets the relay addresses configured for all nodes in this
+      /// process.
+      /// \return The relay addresses.
+      public: std::vector<std::string> GlobalRelays() const;
+
       /// \brief Constructor.
       protected: NodeShared();
 

src/Node.cc

@@ -1139,3 +1139,13 @@ bool Node::RequestRaw(const std::string &_topic,
   bool executed = this->Request(_topic, *req, _timeout, *res, _result);
   return executed && res->SerializeToString(&_response);
 }
+
+/////////////////////////////////////////////////
+void Node::AddGlobalRelay(const std::string& _relayAddress) {
+  Shared()->AddGlobalRelay(_relayAddress);
+}
+
+/////////////////////////////////////////////////
+std::vector<std::string> Node::GlobalRelays() const {
+  return Shared()->GlobalRelays();
+}

src/NodeShared.cc

@@ -23,6 +23,7 @@
 #include <iostream>
 #include <map>
 #include <mutex>
+#include <set>
 #include <shared_mutex>  //NOLINT
 #include <string>
 #include <thread>
@@ -1941,3 +1942,22 @@ int NodeSharedPrivate::NonNegativeEnvVar(const std::string &_envVar,
   }
   return numVal;
 }
+
+void NodeShared::AddGlobalRelay(const std::string& _relayAddress) {
+  dataPtr->msgDiscovery->AddRelayAddress(_relayAddress);
+  dataPtr->srvDiscovery->AddRelayAddress(_relayAddress);
+}
+
+std::vector<std::string> NodeShared::GlobalRelays() const {
+  // Merge relays from message and service discovery. They should be identical
+  // since they're typically build from the same sources.
+  //
+  // This is confusing - do we want to add different handling here?
+  auto msgRelays = dataPtr->msgDiscovery->RelayAddresses();
+  std::set<std::string> msgRelaySet(msgRelays.cbegin(), msgRelays.cend());
+  auto srvRelays = dataPtr->srvDiscovery->RelayAddresses();
+  std::set<std::string> srvRelaySet(srvRelays.cbegin(), srvRelays.cend());
+  srvRelaySet.merge(msgRelaySet);
+
+  return std::vector<std::string>(srvRelaySet.cbegin(), srvRelaySet.cend());
+}

src/Node_TEST.cc

@@ -2341,6 +2341,31 @@ TEST(NodeTest, statistics)
   EXPECT_EQ(std::nullopt, node.TopicStats("/test"));
 }
 
+//////////////////////////////////////////////////
+/// \brief Test adding and querying relays
+TEST(NodeTest, relay) {
+  transport::Node node;
+
+  // Make sure the relay we're about to add hasn't already been configured.
+  const std::vector<std::string> relaysBeforeAdd = node.GlobalRelays();
+  {
+    auto relaysBeforeIt = std::find_if(
+        relaysBeforeAdd.cbegin(), relaysBeforeAdd.cend(),
+        [](const std::string &relay) { return relay == "127.0.0.123"; });
+    ASSERT_EQ(relaysBeforeIt, relaysBeforeAdd.cend());
+  }
+  node.AddGlobalRelay("127.0.0.123");
+
+  const std::vector<std::string> relaysAfterAdd = node.GlobalRelays();
+  {
+    EXPECT_EQ(relaysAfterAdd.size(), relaysBeforeAdd.size() + 1);
+    auto relayIt = std::find_if(
+        relaysAfterAdd.cbegin(), relaysAfterAdd.cend(),
+        [](const std::string &relay) { return relay == "127.0.0.123"; });
+    EXPECT_NE(relayIt, relaysAfterAdd.cend());
+  }
+}
+
 //////////////////////////////////////////////////
 int main(int argc, char **argv)
 {