Hijack cached parameters for dynamic parameter updates without dynamic_reconfigure

test-parameter-callback.cpp

#include <ros/ros.h>
#include <ros/xmlrpc_manager.h>

const std::string PARAMETER {"test_parameter"};

namespace ros {
std::set<std::string> g_subscribed_params;
namespace param {
void paramUpdateCallback(XmlRpc::XmlRpcValue& params, XmlRpc::XmlRpcValue& result);
}
}


void paramUpdate(XmlRpc::XmlRpcValue& params, XmlRpc::XmlRpcValue& result){
   ROS_INFO_STREAM("paramUpdate called: " << static_cast<std::string>(params[1]));
   if(static_cast<std::string>(params[1]) == PARAMETER)
      ROS_INFO_STREAM(PARAMETER << ": updated to new value " << static_cast<std::string>(params[2]));

   ros::param::paramUpdateCallback(params, result);
}

int main(int argc, char** argv){
   ros::init(argc, argv, "parameter_subscriber");
   ros::NodeHandle nh{};

   std::string param{};

   nh.getParamCached(PARAMETER, param);
   ros::XMLRPCManager::instance()->bind("paramUpdate", paramUpdate);

   ros::Rate r(1);
   while(ros::ok()){
      ROS_INFO_STREAM(PARAMETER << ": '" << param << "' / subscribed_params: " << ros::g_subscribed_params.size());
      nh.getParamCached(PARAMETER, param);
      ros::spinOnce();
      r.sleep();
   }

   return 0;
}

Unfortunately, I could not get it to work yet, because apparently the subscription for the parameter fails to set up.

https://github.com/v4hn/subscribe_ros_param

for the full repository