Keeps track of the number of connected clients (#448)

Keeps track of the number of connected clients in the GridConnect TCP hub.
Conversation is in #447.

* Adds an accessor to fetch the number of connected stations.

* fix whitespace

* Keeps track of the number of connected clients
in the GridConnect TCP hub.

* fix whitespace

* Fix typo

src/openlcb/SimpleStack.hxx

@@ -383,8 +383,15 @@ public:
     {
         /// @TODO (balazs.racz) make this more efficient by rendering to string
         /// only once for all connections.
-        /// @TODO (balazs.racz) do not leak this.
-        new GcTcpHub(can_hub(), port);
+        gcHubServer_.reset(new GcTcpHub(can_hub(), port));
+    }
+
+    /// Retrieve the instance of the GridConnect Hub server, which was started
+    /// with start_tcp_hub_server().
+    /// @return the TCP hub server, or nullptr if no server was ever started.
+    GcTcpHub *get_tcp_hub_server()
+    {
+        return gcHubServer_.get();
     }
 
     /// Connects to a CAN hub using TCP with the gridconnect protocol.
@@ -473,6 +480,9 @@ private:
     /// the CAN interface to function. Will be called exactly once by the
     /// constructor of the base class.
     std::unique_ptr<PhysicalIf> create_if(const openlcb::NodeID node_id);
+
+    /// Holds the ownership of the TCP hub server (if one was created).
+    std::unique_ptr<GcTcpHub> gcHubServer_;
 };
 
 class SimpleTcpStackBase : public SimpleStackBase

src/utils/GcTcpHub.cxx

@@ -38,17 +38,30 @@
 #include "nmranet_config.h"
 #include "utils/GridConnectHub.hxx"
 
-void GcTcpHub::OnNewConnection(int fd)
+void GcTcpHub::on_new_connection(int fd)
 {
     const bool use_select =
         (config_gridconnect_tcp_use_select() == CONSTANT_TRUE);
-    create_gc_port_for_can_hub(canHub_, fd, nullptr, use_select);
+    {
+        AtomicHolder h(this);
+        numClients_++;
+    }
+    create_gc_port_for_can_hub(canHub_, fd, this, use_select);
+}
+
+void GcTcpHub::notify()
+{
+    AtomicHolder h(this);
+    if (numClients_)
+    {
+        numClients_--;
+    }
 }
 
 GcTcpHub::GcTcpHub(CanHubFlow *can_hub, int port)
     : canHub_(can_hub)
-    , tcpListener_(port, std::bind(&GcTcpHub::OnNewConnection, this,
-                                   std::placeholders::_1))
+    , tcpListener_(port,
+          std::bind(&GcTcpHub::on_new_connection, this, std::placeholders::_1))
 {
 }
 

src/utils/GcTcpHub.cxxtest

@@ -64,6 +64,7 @@ protected:
             fprintf(stderr, "waiting for exiting.\r");
             usleep(100000);
         }
+        EXPECT_EQ(0U, tcpHub_.get_num_clients());
     }
 
     struct Client
@@ -154,6 +155,7 @@ protected:
 
 TEST_F(GcTcpHubTest, CreateDestroy)
 {
+    EXPECT_EQ(0u, tcpHub_.get_num_clients());
 }
 
 TEST_F(GcTcpHubTest, TwoClientsPingPong)
@@ -165,6 +167,9 @@ TEST_F(GcTcpHubTest, TwoClientsPingPong)
     writeline(b.fd_, ":S001N01;");
     EXPECT_EQ(":S001N01;", readline(a.fd_, ';'));
     EXPECT_EQ(3U, can_hub0.size());
+
+    EXPECT_EQ(2u, tcpHub_.get_num_clients());
+
     // Test writing outwards.
     send_packet(":S002N0102;");
     EXPECT_EQ(":S002N0102;", readline(a.fd_, ';'));
@@ -177,13 +182,15 @@ TEST_F(GcTcpHubTest, ClientCloseExpect)
     unsigned can_hub_size = can_hub0.size();
     LOG(INFO, "can hub: %p ", &can_hub0);
     EXPECT_EQ(1U, can_hub_size);
+    EXPECT_EQ(0U, tcpHub_.get_num_clients());
     {
         Client a;
         Client b;
         expect_packet(":S001N01;");
         writeline(b.fd_, ":S001N01;");
         EXPECT_EQ(":S001N01;", readline(a.fd_, ';'));
         EXPECT_EQ(can_hub_size + 2, can_hub0.size());
+        EXPECT_EQ(2U, tcpHub_.get_num_clients());
         wait();
     }
     // Test writing outwards.

src/utils/GcTcpHub.hxx

@@ -43,7 +43,7 @@ class ExecutorBase;
  * format. Any new incoming connection will be wired into the same virtual CAN
  * hub. All packets will be forwarded to every participant, without
  * loopback. */
-class GcTcpHub
+class GcTcpHub : private Notifiable, private Atomic
 {
 public:
     /// Constructor.
@@ -60,16 +60,28 @@ public:
         return tcpListener_.is_started();
     }
 
+    /// @return currently connected client count.
+    unsigned get_num_clients()
+    {
+        return numClients_;
+    }
+
 private:
     /// Callback when a new connection arrives.
     ///
     /// @param fd filedes of the freshly established incoming connection.
     ///
-    void OnNewConnection(int fd);
+    void on_new_connection(int fd);
+
+    /// Error callback from the gridconnect socket. This is invoked when a
+    /// client disconnects.
+    void notify() override;
 
     /// @param can_hub Which CAN-hub should we attach the TCP gridconnect hub
     /// onto.
     CanHubFlow *canHub_;
+    /// How many clients are connected right now.
+    unsigned numClients_ {0};
     /// Helper object representing the listening on the socket.
     SocketListener tcpListener_;
 };