topic Re: Validation callback in python in NSO Developer Hub Discussions

Validation callback in python

frjansso — Fri, 01 Mar 2019 11:56:58 GMT

Python code demonstrating a validation callback.

# -*- mode: python; python-indent: 4 -*-
import ncs
from ncs.dp import Daemon
from ncs.maapi import Maapi
from _ncs.dp import register_valpoint_cb, register_trans_validate_cb, trans_set_fd




class Validation(object):
    def __init__(self, log):
        self.log = log
        self.daemon = Daemon("foo-validation-daemon", log=log)
        self.maapi = Maapi()


        register_trans_validate_cb(self.daemon.ctx(), self)
        register_valpoint_cb(self.daemon.ctx(),
                             'the-validation-callpoint-name',
                             self)
        self.daemon.start()


    def cb_validate(self, tctx, kp, newval):
        self.log.info('validate called')
        # return ncs.CONFD_ERR to fail the validation otherwise
        # ncs.CONFD_OK
        return ncs.CONFD_OK


    def cb_init(self, tctx):
        self.maapi.attach(tctx)
        trans_set_fd(tctx, self.daemon._wsock)


    def cb_stop(self, tctx):
        self.maapi.detach(tctx)




# ---------------------------------------------
# COMPONENT THREAD THAT WILL BE STARTED BY NCS.
# ---------------------------------------------
class Main(ncs.application.Application):
    def setup(self):
        # The application class sets up logging for us. It is accessible
        # through 'self.log' and is a ncs.log.Log instance.
        self.log.info('Main RUNNING')


        self.v = Validation(self.log)


        # If we registered any callback(s) above, the Application class
        # took care of creating a daemon (related to the service/action point).


        # When this setup method is finished, all registrations are
        # considered done and the application is 'started'.


    def teardown(self):
        # When the application is finished (which would happen if NCS went
        # down, packages were reloaded or some error occurred) this teardown
        # method will be called.


        self.log.info('Main FINISHED')

Re: Validation callback in python

rogaglia — Sun, 06 Aug 2017 21:52:27 GMT

Hi Fredrik,

Great example as I had this question this week.

One point that you may want to add is a description in the cb_validate() method where you clarify that there is where validation happens and which are the accepted outputs (other than CONFD_OK, I believe it is CONFD_ERR).

Finally, I was wondering what is the format for "newval" when the callback is applied to a list instead of a leaf. The values of the keys? are they comma separated?

Roque

Re: Validation callback in python

frjansso — Mon, 07 Aug 2017 05:14:15 GMT

Not sure what newval actually does, it's always 'undefined' in my tests.

If you have a list, cb_validation is called once for each list entry.

Re: Validation callback in python

Jan Lindblad — Mon, 07 Aug 2017 11:08:38 GMT

newval is supposed to hold the new value of the leaf, if the validation point is placed on a leaf. Did you try that, and if so, did you find the mechanism is broken?

Re: Validation callback in python

rogaglia — Mon, 07 Aug 2017 11:18:02 GMT

Hi Jan,

Personally, that was my understanding and why I was asking how tailf:validate works on lists.

Roque

Re: Validation callback in python

Jan Lindblad — Mon, 07 Aug 2017 11:28:02 GMT

For a validation point placed on a list (or container, type empty leaf, ...) , newval will be undefined. You will need to read the value(s) you want using MAAGIC/MAAPI etc.

Re: Validation callback in python

frjansso — Mon, 07 Aug 2017 14:27:55 GMT

Makes sense now, I never tried to att the validation point to a single leaf.

Re: Validation callback in python

mareis — Fri, 16 Feb 2018 00:15:33 GMT

Hi Fredrik,

I'm looking for a way to return a message to the user when validation fails.

Returning ncs.CONFD_ERR I get:

admin@ncs(config-device-IOS-0)# description srt

admin@ncs(config-device-IOS-0)# commit

Aborted: application error

Which is not very user friendly.

By raising an exception I can customize a message to the user. For instance:

admin@ncs(config-device-IOS-0)# description 123

admin@ncs(config-device-IOS-0)# commit

Aborted: 'services loopback device IOS-0 description': Python cb_validate error. This is not a good description

Is that the proper way to do it or is there a better option?

Thanks

Marcelo

Re: Validation callback in python

Jan Lindblad — Fri, 16 Feb 2018 09:17:00 GMT

You have a python validation callback defined? Or an error message register_error_cb(...) formatter callback? Not entirely clear. Basically you can use error_seterr(...)

Re: Validation callback in python

mareis — Fri, 16 Feb 2018 14:28:23 GMT

Hi Jan,

I have a validation callback defined, similar to the example above. It seems I can't call error_seterr from cb_validate as it expects an _ncs.UserInfo object, which I don't have within cb_validate. Would I need a register_error_cb for that?

Thanks

Marcelo

Re: Validation callback in python

mohamkh7 — Thu, 31 Jan 2019 06:24:06 GMT

Hi,

As per the example of above, New Daemon(Independent Thread) is registered to handle tailf:validation.

Can we attach the validation callback to existing Service(Service uses Daemon internally)

Or this is the only way exists ?

Regards

Zahid

Re: Validation callback in python

frjansso — Fri, 08 Feb 2019 17:59:36 GMT

You mean to tie the validation callback to a service class? I'm actually not sure... but I guess the question is why? 🙂

Re: Validation callback in python

frjansso — Fri, 08 Feb 2019 18:00:09 GMT

You mean to tie the validation callback to a service class? I'm actually not sure... but I guess my question is why? 🙂