During the handshake the heartbeat duration the server wants is stored in the connection so that clients can retrieve and use it for error detection

include/connection.h

@@ -153,6 +153,15 @@ public:
         return _implementation.channels();
     }
 
+    /**
+    *  Retrieve the heartbeat delay used by this connection
+    *  @return uint16_t
+    */
+    uint16_t heartbeat() const
+    {
+        return _implementation.heartbeat();
+    }
+
     /**
      *  Some classes have access to private properties
      */

include/connectionimpl.h

@@ -93,6 +93,12 @@ protected:
      */
     std::queue<OutBuffer> _queue;
 
+    /**
+    *  Heartbeat delay
+    *  @var uint16_t
+    */
+    uint16_t _heartbeat = 0;
+
     /**
      *  Helper method to send the close frame
      *  Return value tells if the connection is still valid
@@ -342,6 +348,23 @@ public:
         return _channels.size();
     }
 
+    /**
+     *  Heartbeat delay
+     *  @return uint16_t
+    */
+    uint16_t heartbeat() const
+    {
+        return _heartbeat;
+    }
+
+    /**
+     *  Set the heartbeat delay
+    */
+    void setHeartbeat(uint16_t heartbeat)
+    {
+        _heartbeat = heartbeat;
+    }
+
     /**
      *  The actual connection is a friend and can construct this class
      */

src/connectiontuneframe.h

@@ -137,6 +137,9 @@ public:
         // theoretically it is possible that the connection object gets destructed between sending the messages
         Monitor monitor(connection);
         
+        // store the heartbeat the server wants 
+        connection->setHeartbeat(heartbeat());
+
         // send it back
         connection->send(ConnectionTuneOKFrame(channelMax(), frameMax(), heartbeat()));