rosbridge watcher

rosbridge_watcher.py

#!/usr/bin/env python3

import rospy
import urllib.request
import urllib.error
import socket
import os

# This is not a param to avoid param injection
# or unexpected programm killed because of a simple rosparam set with a wrong value
ROSBRIDGE_BIN_PATH = '/opt/ros/melodic/lib/rosbridge_server/rosbridge_websocket'

class RosbridgeWatcher():
	"""
	Watch the health of the rosbridge and restart it if not available.
	"""

	def __init__(self):
		self.rosbridge_uri = rospy.get_param('rosbridge_uri', 'http://localhost:9090')
		self.watch_period = rospy.get_param('watch_period', 1.0)
		self.grace_period = rospy.get_param('grace_period', 60.0)
		self.timeout = rospy.get_param('timeout', 10)

		self.watch_timer = rospy.Timer(rospy.Duration(self.watch_period), self.watch)

		self.last_kill = rospy.Time()

		rospy.get_rostime()


	def watch(self, req):
		"""
		Try to connect to websocket bridge to check if bridge is OK
		"""
		# Check if in gace period
		last_kill_sec = (rospy.get_rostime() - self.last_kill).to_sec()
		if last_kill_sec < self.grace_period:
			rospy.logdebug('Grace period.')
			return

		# Try to do a simple http request, we don't care about the result
		# We just want to know if it fails because of timeout or not
		try:
			urllib.request.urlopen(self.rosbridge_uri, timeout=self.timeout)
		except socket.timeout as e:
				self.restart_rosbridge()
		except urllib.error.URLError as e:
			if isinstance(e.reason, socket.timeout):
				self.restart_rosbridge()


	def restart_rosbridge(self):
		rospy.logwarn('Rosbridge not responding, need to restart it!')
		self.last_kill = rospy.get_rostime()
		# Using rosnode.kill_nodes doens't work, so use linux signals..
		os.system('pkill -QUIT -f ' + ROSBRIDGE_BIN_PATH)


if __name__ == "__main__":
	rospy.init_node('rosbridge_watcher', log_level=rospy.INFO)
	rosbridge_watcher = RosbridgeWatcher()
	rospy.spin()

See RobotWebTools/rosbridge_suite#403