message_info_service.py

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#!/usr/bin/env python

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""" The node provided by this file exposes a helper service used by
the C++ rosserial_server. The service allows the C++ driver to look
up message definitions and hash strings which would not have been
known to it at compile time, allowing it to fully advertise topics
originating from microcontrollers.

This allows rosserial_server to be distributed in binary form. """

import rospy
from rosserial_msgs.srv import RequestMessageInfo
from rosserial_python import load_message


class MessageInfoService(object):
  """  """
  def __init__(self):
    rospy.init_node("message_info_service")
    rospy.loginfo("rosserial message_info_service node")
    self.service = rospy.Service("message_info", RequestMessageInfo, self._cb)
    self.cache = {}
  
  def _cb(self, req):
    package_message = tuple(req.type.split("/"))
    if not self.cache.has_key(package_message):
      rospy.loginfo("Loading module to return info on %s/%s." % package_message)
      msg = load_message(*package_message)
      self.cache[package_message] = (msg._md5sum, msg._full_text)
    else:
      rospy.loginfo("Returning info from cache on %s/%s." % package_message)

    return self.cache[package_message]

  def spin(self):
    rospy.spin()

if __name__=="__main__":
  MessageInfoService().spin()