Why I got error "msg does not have header"?

edit

Hi,

I try to make a custom message with header to get the timestamp because my aim is to receive data from two topics and generate a graph. After some reading, I found that I need to synchronise the topics and take both topics into a single callback. So I use rostopic delay to check the header of my rostopic. I can get the header from the first custom but no this message.

This is the error:

[ERROR] [1560803887.275108]: msg does not have header

Here are my custom message:

Header header
float32[] distance

Here is my publisher that use the custom message:

#!/usr/bin/env python
import rospy
from std_msgs.msg import Int32
def distanceTrav():
   pub = rospy.Publisher('distanceTurtleTravelled', Int32, queue_size=1000)
   rospy.init_node('distanceTurtle', anonymous=True)
   rate = rospy.Rate(1) # 1hz
   dist = 1
   while not rospy.is_shutdown():
      rospy.loginfo(dist)
      pub.publish(dist)
      rate.sleep()
      dist = dist+1
if __name__ == '__main__':
   try:
      distanceTrav()
   except rospy.ROSInterruptException:
      pass

Here is my CMakelist:

cmake_minimum_required(VERSION 2.8.3) 
project(walabot)
find_package(catkin REQUIRED COMPONENTS
  roscpp
  rospy
  std_msgs
  geometry_msgs
  message_generation
)

add_message_files(
  FILES
  signal.msg
  distanceTravelled.msg
)

generate_messages(
  DEPENDENCIES
  std_msgs
)

catkin_package(
  LIBRARIES walabot
  CATKIN_DEPENDS roscpp rospy std_msgs message_runtime
)

include_directories(
  ${catkin_INCLUDE_DIRS}
)