Node service not publishing to topic

edit

I have a problem with a simple node I wrote when it fails to publish any messages to a topic.

I'm using the following version of ROS:

SUMMARY
========

PARAMETERS
 * /rosdistro: melodic
 * /rosversion: 1.14.1

My subscriber node looks like this:

#include <ros/ros.h>
#include <geometry_msgs/Twist.h>
#include <stdlib.h>
#include <iomanip>

void poseMessageReceived(const geometry_msgs::Twist& msg) {
        ROS_INFO_STREAM("Received velocity cmd:" << std::setprecision(4) << std::fixed
                << " SUB linear==" << msg.linear.x
                << " SUB angular==" << msg.linear.z);
}

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

    ROS_INFO_STREAM("Subscribed to: subpose_node/cmd_vel");

    ros::Subscriber sub = nh.subscribe("subpose_node/cmd_vel", 1000, &poseMessageReceived);
    ros::spin();
}

There is nothing magical in the subscriber code.

My publisher node is a service node and it looks like this -- please ignore Foo.h srv for now:

#include <stdlib.h>
#include <iomanip>
#include <ros/ros.h>
#include <geometry_msgs/Twist.h>
#include <svcsrv/Foo.h>

bool PubTwist(
  svcsrv::Foo::Request &req,
  svcsrv::Foo::Response &resp
) {
    ROS_INFO_STREAM("Received message: " << "linearX==" << req.linear.x << " linearZ" << req.linear.z);

    resp.linear.x = req.linear.x;
    resp.linear.z = req.linear.z;

    return true;
}

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

    // register service with the master
    ros::ServiceServer server = nh.advertiseService("pub_twist", &PubTwist);

    ROS_INFO("Ready to receive and send messages!");

    ros::Publisher pub = nh.advertise<geometry_msgs::Twist>("subpose_node/cmd_vel", 1000);
    geometry_msgs::Twist msg;
    msg.linear.x = 0.0;
    msg.linear.z = 0.0;
    pub.publish(msg);

    ros::spin();
    return 0;
}

The service client is also very simple:

#include <cstdlib>
#include <ros/ros.h>
#include <svcsrv/Foo.h>
int main(int argc, char **argv)
{
  ros::init(argc, argv, "send_twist_message");

  ros::NodeHandle n;
  ros::ServiceClient client = n.serviceClient<svcsrv::Foo>("pub_twist");

  svcsrv::Foo::Request req;
  svcsrv::Foo::Response resp;

  req.linear.x = 3.0;
  req.linear.z = 4.0;

  if (client.call(req, resp))
  {
    ROS_INFO_STREAM("Received pub_twist response: " << "linearX==" << resp.linear.x << " linearZ==" << resp.linear.z);
  }
  else
  {
    ROS_ERROR("Failed to call service pub_twist");
    return 1;
  }

  return 0;
}

When I run rosnode info it displays that the node should be able to publish to subpose_node/cmd_vel:

Connections:
 * topic: /rosout
    * to: /rosout
    * direction: outbound
    * transport: TCPROS
 * topic: /subpose_node/cmd_vel
    * to: /rostopic_15809_1534959147174
    * direction: outbound
    * transport: TCPROS
 * topic: /subpose_node/cmd_vel
    * to: /subscribe_to_twist
    * direction: outbound
    * transport: TCPROS

However subscriber NEVER receives any message. Any idea what I'm missing out here?

What's puzzling is that if I replace the service node code with the following code in works perfectly fine:

#include <stdlib.h>
#include <iomanip>
#include <ros/ros.h>
#include <geometry_msgs/Twist.h>
#include <std_srvs/Empty.h>

bool toggle_pub = false;
bool togglePub(
  std_srvs::Empty::Request &req,
  std_srvs::Empty::Response &resp
) {
    toggle_pub = !toggle_pub;
    ROS_INFO_STREAM("Toggled send of a message:"
            << toggle_pub);
    return true;
}

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

    // register service with the master
    ros::ServiceServer server = nh.advertiseService("toggle_pubsvc", &togglePub);

    // publisher
    ros::Publisher pub = nh.advertise<geometry_msgs::Twist>("subpose_node/cmd_vel", 1000);
    ros::Rate rate(2);

    while(ros ...