How to execute subscriber callback on some condition?

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Hi all,

I am working on a small project in Python and ROS Indigo. To implement a small functionality, I have created a node in which the node has a subscriber (queue size 10) and corresponding callback method. The callback method makes a call to a web-api in turn.

The web-api looses network connection to the server for a brief period and therefore the data is not pushed to the web-api. My understanding is ROS makes a queue for executing callback methods. Because then, I would hold the callback execution as long as there is no established connection to the web-api and execute callback once the connection is back. If the subscribed data would get accumulated, I wont loose them when eventually the callback would get execute.

Please suggest how to achieve this. Thanks

class Message():
    def __init__(self):

        # Create a subscriber for our custom message.
        rospy.Subscriber("message_topic", String, self.callback, queue_size=10)

        # Create the client
        self.wc = WebClient(self.user_name)

    def callback(self, data):
        try:
            # condition to check connection here does not help, still loose messages if no connection
            # if self.wc.connect():
            self.wc.api_call('send_msg', text=data.data)
        except Exception as e:
            print "Problem in connection : ",e
            rospy.sleep(2.0)
            self.make_connection()

# Main function.
if __name__ == '__main__':
    # Initialize the node and name it.
    rospy.init_node('web_message')
    try:
        msg = Message()
     except rospy.ROSInterruptException: pass