Adding to existing subscriptions via Web API

MikeTTMikeTT Prestwick
Hello, I am trying to figure out how to have multiple subscriptions via the web API, for example a subscription to the Controller Execution State, and another subscription to a RAPID persistent variable.

I am able to successfully subscribe to either one of these individually using the POST method, my question is how do I then go about adding the second subscription. The documentation states:

"Client can add new subscribable resource to existing subscription-group using PUT method."

As I understand it, this means I should be using the PUT method, but when I attempt to use it with the same syntax as my previous POST, I get a 405 Method not allowed error. I can also see in the documentation that I am supposed to be supplying a "Group ID" parameter, but I don't know what this is or how to obtain it.

Any help would be appreciated.




Best Answer

Answers

  • dnilssondnilsson Gothenburg admin
    edited October 26
    Here's an example code doing that for python3.


    import sys, argparse
    import xml.etree.ElementTree as ET
    from ws4py.client.threadedclient import WebSocketClient
    import requests
    from requests.auth import HTTPDigestAuth


    def print_event(evt):
        root = ET.fromstring(evt)        
        if root.findall(".//{0}li[@class='pnl-ctrlstate-ev']".format(namespace)):
            print ("\tController State : " + root.find(".//{0}li[@class='pnl-ctrlstate-ev']/{0}span".format(namespace)).text)
        if root.findall(".//{0}li[@class='pnl-opmode-ev']".format(namespace)):
            print ("\tOperation Mode : " + root.find(".//{0}li[@class='pnl-opmode-ev']/{0}span".format(namespace)).text)
        if root.findall(".//{0}li[@class='pnl-speedratio-ev']".format(namespace)):
            print ("\tSpeed Ratio : " + root.find(".//{0}li[@class='pnl-speedratio-ev']/{0}span".format(namespace)).text)



    # This class encapsulates the Web Socket Callbacks functions.
    class RobWebSocketClient(WebSocketClient):
        def opened(self):
            print ("Web Sockect connection established")

        def closed(self, code, reason=None):
            print ("Closed down", code, reason)

        def received_message(self, event_xml):        
            if event_xml.is_text:            
                print ("Events : ")
                print_event(event_xml.data.decode("utf-8"))
            else:
                print ("Received Illegal Event " + str(event_xml))
            
        
    # The main RobotWare Panel class
    class RWPanel:

        def __init__(self, host, username, password):
            self.host = host
            self.username = username
            self.password = password
            self.digest_auth = HTTPDigestAuth(self.username,self.password)
            self.subscription_url = 'http://{0}/subscription'.format(self.host)
            self.session = requests.Session()
            
        
        def subscribe(self):       
            # Create a payload to subscribe on RobotWare Panel Resources with high priority     
            payload = {'resources':['1','2','3'],
                '1':'/rw/panel/speedratio',
                '1-p':'1',
                '2':'/rw/panel/ctrlstate',
                '2-p':'1',
                '3':'/rw/panel/opmode',
                '3-p':'1'}        

            resp = self.session.post(self.subscription_url , auth=self.digest_auth, data=payload)
            print ("Initial Events : ")
            print_event(resp.text)           
            if resp.status_code == 201:
                self.location = resp.headers['Location']
                self.cookie = '-http-session-={0}; ABBCX={1}'.format(resp.cookies['-http-session-'], resp.cookies['ABBCX'])
                return True
            else:
               print ('Error subscribing ' + str(resp.status_code))
               return False             

        def start_recv_events(self):
            self.header = [('Cookie',self.cookie)]
            self.ws = RobWebSocketClient(self.location, 
                                         protocols=['robapi2_subscription'], 
                                         headers=self.header)
            self.ws.connect()
            self.ws.run_forever()

        def close(self):
            self.ws.close()  


    def enable_http_debug():
        import logging
        import httplib2 as httplib
        httplib.debuglevel = 1
        logging.basicConfig() # Initialize logging
        logging.getLogger().setLevel(logging.DEBUG)
        requests_log = logging.getLogger("requests.packages.urllib3")
        requests_log.setLevel(logging.DEBUG)
        requests_log.propagate = True

    def main(argv):
        try:
          parser = argparse.ArgumentParser()
          parser.add_argument("-host",help="The host to connect. Defaults to localhost on port 80", default='localhost:80')
          parser.add_argument("-user",help="The login user name. Defaults to default user name", default='Default User')
          parser.add_argument("-passcode",help="The login password. Defaults to default password", default='robotics')  
          parser.add_argument("-debug",help="Enable HTTP level debugging.", action='store_true')  
          args = parser.parse_args()       
          
          if args.debug:
            enable_http_debug()
         
          rwpanel = RWPanel(args.host, args.user, args.passcode)
          if rwpanel.subscribe():
            rwpanel.start_recv_events()
        except KeyboardInterrupt:
          rwpanel.close()


    if __name__ == "__main__":
        main(sys.argv[1:])

  • MikeTTMikeTT Prestwick
    edited October 26
    Hi dnilsson, thanks for taking the time to reply,

    I'm not that familiar with python so please correct me if I'm wrong but it looks like you are initially subscribing to 3 different resources via HTTP POST inside your subscribe function. I can basically do this with my C# code too, the bit I am stuck on is adding another subscription after the first set was already done.

    So, in your example, how would you now subscribe to a 4th resource without losing the subscription to the first 3? Do you need to do a whole new POST request which has all 4 resources in the payload?

    I was hoping there would be some way of using the PUT method (with just the 4th resource in the payload) to simply get an updated location which would work for all 4 via the websocket. Is this not possible?

    EDIT: I guess it's not such a big deal if I need to subscribe to all 4 resources at once in one big POST request, but then how do I deal with the 3 initial subscriptions, do I need to use the DELETE method to unsubscribe first?
  • MikeTTMikeTT Prestwick
    Okay, thanks for that, I think I have a better understanding of it now, I will give it a try and let you know how I get on!
  • MikeTTMikeTT Prestwick
    Hi Daniel, just confirming that I tried what you suggested and got it working, thanks for the help!
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