Dynamic Webhook Subscriptions

In addition to static webhook subscriptions defined in ZCML, this package supports dynamic webhook subscriptions created, activated, inactivated, and removed through code at runtime. Such subscriptions, and their delivery history, are typically persistent in the ZODB sense of the word.

Subscriptions are managed via an implementation of nti.webhooks.interfaces.IWebhookSubscriptionManager. We’ve already seen (in Configured Global, Transient Webhook Subscriptions) how there is a global, non-persistent subscription manager installed by default. This document explores issues around persistent, local subscription managers.


Persistent subscription managers, and their subscriptions and in turn delivery histories, should:

This second requirement is met by having the subscription manager be a zope.container.interfaces.IContainer of IWebhookSubscription objects, which in turn are containers of IWebhookDeliveryAttempt objects.

The first requirement is somewhat harder. This package offers a high-level API to help with it, integrated with nti.site. In this API, persistent webhook subscription managers are stored in the site manager using nti.site.localutility.install_utility() with a name in the etc namespace.


This page has sub-pages for specific topics.


To begin, we will provide a persistent site hierarchy with traversable paths. Following the example from the main documentation, we’ll create a department named “NWS” and office named “OUN”, plus some people in each one. The department and office will be sites, with a site manager.

First define the classes. These are stored in a module named employees.

from persistent import Persistent
from zope.container.contained import Contained
from zope.site.folder import Folder
from zope.site import LocalSiteManager
from zope.annotation.interfaces import IAttributeAnnotatable
from zope.interface import implementer

class Employees(Folder):
    def __init__(self):
        self['employees'] = Folder()

class Department(Employees):

class Office(Employees):

class Employee(Contained, Persistent):
    COUNTER = 0

    def __init__(self):
        self.__counter__ = self.COUNTER
        Employee.COUNTER += 1

    def __repr__(self):
        return "<Employee %s %d>" % (

class ExternalizableEmployee(Employee):
    def toExternalObject(self, **kwargs):
        return self.__name__

from zope.testing import cleanup
cleanup.addCleanUp(lambda: setattr(Employee, 'COUNTER', 0))
>>> from employees import Department, Office, ExternalizableEmployee as Employee

Now we’ll create a database and store our hierarchy.


The nti.webhooks.testing.ZODBFixture establishes a global, unnamed, utility for the ZODB.interfaces.IDatabase that it opens. This is what things like zope.app.appsetup do as well; your application needs to arrange for that utility to be available.

The nti.site.runner.run_job_in_site() function also has this requirement.

Begin with some common imports and set up the required packages and fixture.

>>> import transaction
>>> from nti.webhooks.testing import ZODBFixture
>>> from nti.webhooks.testing import DoctestTransaction
>>> from nti.webhooks.testing import mock_delivery_to
>>> from nti.site.hostpolicy import install_main_application_and_sites
>>> from nti.site.testing import print_tree
>>> from zope.traversing import api as ztapi
>>> from zope.configuration import xmlconfig
>>> mock_delivery_to('https://example.com/some/path', method='POST', status=200)
>>> mock_delivery_to('https://example.com/another/path', method='POST', status=404)
>>> conf_context = xmlconfig.string("""
... <configure
...     xmlns="http://namespaces.zope.org/zope"
...     xmlns:webhooks="http://nextthought.com/ntp/webhooks"
...     >
...   <include package="nti.webhooks" />
...   <include package="nti.webhooks" file="subscribers_promiscuous.zcml" />
...   <include package="nti.site" />
...   <include package="zope.traversing" />
... </configure>
... """)

Next, start a transaction and get a database connection, and add our objects. We can show that we have a traversable path to the lowest level object; we’ll use this path to refer to that object in the future (we don’t keep a reference to the actual object because we’ll be opening and closing multiple transactions).

>>> tx = DoctestTransaction()
>>> conn = tx.begin()
>>> root_folder, main_folder = install_main_application_and_sites(
...        conn,
...        root_alias=None, main_name='NOAA', main_alias=None)
>>> department = main_folder['NWS'] = Department()
>>> office = department['OUN'] = Office()
>>> department_bob = department['employees']['Bob'] = Employee()
>>> office_bob = office['employees']['Bob'] = Employee()
>>> print_tree(root_folder, depth=0, details=())
<ISite,IRootFolder>: <zope.site.folder.Folder object...>
     <ISite,IMainApplicationFolder>: NOAA
         <ISite>: NWS
             <ISite>: OUN
                     Bob => <Employee Bob 1>
                 Bob => <Employee Bob 0>
>>> office_bob_path = ztapi.getPath(office_bob)
>>> print(office_bob_path)
>>> tx.finish()

High-level API

The high-level API lets us create subscriptions based on a resource, frequently one we’ve traversed to.

nti.webhooks.api.subscribe_to_resource(resource, to, for_=None, when=<InterfaceClass zope.interface.interfaces.IObjectEvent>, dialect_id=None, owner_id=None, permission_id=None)[source]

Produce and return a persistent IWebhookSubscription based on the resource.

Only the resource and to arguments are mandatory. The other arguments are optional, and are the same as the attributes in that interface.


The resource to subscribe to. Passing a resource does two things. First, the resources is used to find the closest enclosing ISite that is persistent. A IWebhookSubscriptionManager utility will be installed in this site if one does not already exist, and the subscription will be created there.

Second, if for_ is not given, then the interfaces provided by the resource will be used for for_. This doesn’t actually subscribe just to events on that exact object, but to events for objects with the same set of interfaces.

>>> from nti.webhooks.api import subscribe_to_resource
>>> conn = tx.begin()
>>> office_bob = ztapi.traverse(conn.root()['Application'], office_bob_path)
>>> subscription = subscribe_to_resource(office_bob, 'https://example.com/some/path')
>>> subscription
<...PersistentSubscription at 0x... to='https://example.com/some/path' for=employees.ExternalizableEmployee when=IObjectEvent>

What Just Happened

Several things happened here. The next sections will detail them.

A Subscription Manager Was Created

First, by getting the path to the subscription, we can see that a subscription manager containing the subscription was created at the closest enclosing site manager. We can also traverse this path to get back to the subscription, and its manager:

>>> path = ztapi.getPath(subscription)
>>> print(path)
>>> ztapi.traverse(root_folder, path) is subscription
>>> ztapi.traverse(root_folder, '/NOAA/NWS/OUN/++etc++site/default/WebhookSubscriptionManager')
<....PersistentWebhookSubscriptionManager object at 0x...>

The for Was Inferred

The API automatically deduced the value to use for for, in this case the same thing that office_bob provides:

>>> from zope.interface import providedBy
>>> subscription.for_
<implementedBy employees.ExternalizableEmployee>
>>> subscription.for_.__name__
>>> providedBy(office_bob)
<implementedBy employees.ExternalizableEmployee>
>>> providedBy(office_bob).inherit
<class 'employees.ExternalizableEmployee'>

This is a complex value; because of how pickling works, it will stay in sync with exactly what that class actually provides.

>>> list(providedBy(office_bob).flattened())
[<InterfaceClass ...IContained>, <InterfaceClass ...ILocation>, <InterfaceClass ...IPersistent>, <InterfaceClass ...Interface>]
>>> import pickle
>>> pickle.loads(pickle.dumps(subscription.for_)) is providedBy(office_bob)

For instructions on customizing how this is inferred, see Customizing For.

The when Was Guessed


The value for when, IObjectEvent, may not be what you want. This may change in the future. See Configuration for more information.


This may change in the future. While it might be nice to have a single subscription that is when any of a group of events fires, the Zapier API prefers to have one subscription per event type. (TODO: Confirm this.) If that’s the case, then there might be a higher-level concept to group related subscriptions together.

The Subscription is Active

Even though the office that contains this subscription is not the current site, we can still find this subscription and confirm that it is active.

>>> def subscriptions_for_bob(conn):
...     from nti.webhooks.subscribers import find_active_subscriptions_for
...     from zope.lifecycleevent import ObjectModifiedEvent
...     office_bob = ztapi.traverse(conn.root()['Application'], office_bob_path)
...     event = ObjectModifiedEvent(office_bob)
...     return find_active_subscriptions_for(event.object, event)
>>> from zope.component import getSiteManager
>>> getSiteManager() is office.getSiteManager()
>>> len(subscriptions_for_bob(conn))
>>> subscriptions_for_bob(conn)[0] is subscription
>>> tx.finish()

Relation To Static Subscriptions

A static subscription registered globally is also found:

>>> conf_context = xmlconfig.string("""
... <configure
...     xmlns="http://namespaces.zope.org/zope"
...     xmlns:webhooks="http://nextthought.com/ntp/webhooks"
...     >
...   <include package="zope.component" />
...   <include package="zope.container" />
...   <include package="nti.webhooks" />
...   <webhooks:staticSubscription
...             to="https://example.com/another/path"
...             for="employees.Employee"
...             when="zope.lifecycleevent.interfaces.IObjectModifiedEvent" />
... </configure>
... """)
>>> conn = tx.begin()
>>> subscriptions = subscriptions_for_bob(conn)
>>> len(subscriptions)
>>> subscriptions
[<...Subscription at 0x... to='https://example.com/another/path' for=Employee when=IObjectModifiedEvent>, <...PersistentSubscription at 0x... to='https://example.com/some/path' ... when=IObjectEvent>]
>>> tx.finish()

Delivery to Static and Dynamic Subscriptions

Now we can attempt delivery to these subscriptions. They will have a delivery attempt recorded, and in the case of the persistent subscription, it will be persistent itself.

First, we define a helper function that will trigger and wait for the deliveries. We also ensure that the deliveries happen in a deterministic order.

>>> from nti.webhooks.testing import begin_synchronous_delivery
>>> begin_synchronous_delivery()
>>> def trigger_delivery():
...    from zope import lifecycleevent, component
...    from nti.webhooks.interfaces import IWebhookDeliveryManager
...    conn = tx.begin()
...    office_bob = ztapi.traverse(conn.root()['Application'], office_bob_path)
...    lifecycleevent.modified(office_bob)
...    tx.finish()
...    component.getUtility(IWebhookDeliveryManager).waitForPendingDeliveries()

Next, we deliver the events, and then fetch the updated subscriptions.

>>> trigger_delivery()
>>> conn = tx.begin()
>>> subscriptions = subscriptions_for_bob(conn)
>>> subscriptions
[<...Subscription at 0x... to='https://example.com/another/path' for=Employee when=IObjectModifiedEvent>, <...PersistentSubscription at 0x... to='https://example.com/some/path' ... when=IObjectEvent>]
>>> global_subscription = subscriptions[0]
>>> persistent_subscription = subscriptions[1]

Our attempt at persistent delivery was successful.

>>> attempt = persistent_subscription.pop()
>>> print(attempt.status)
>>> attempt.response.status_code
>>> print(attempt.request.url)
>>> print(attempt.request.method)
>>> import pprint
>>> pprint.pprint({str(k): str(v) for k, v in attempt.request.headers.items()})
{'Accept': '*/*',
 'Accept-Encoding': 'gzip, deflate',
 'Connection': 'keep-alive',
 'Content-Length': '5',
 'Content-Type': 'application/json',
 'User-Agent': 'nti.webhooks...'}
>>> print(attempt.request.body)
>>> tx.finish()

Because of the way the mock HTTP responses were set up, the static/global subscription delivery failed.

>>> attempt = global_subscription.pop()
>>> print(attempt.status)
>>> print(attempt.message)
404 Not Found
>>> attempt.response.status_code
>>> print(attempt.request.url)
>>> print(attempt.request.method)
>>> import pprint
>>> pprint.pprint({str(k): str(v) for k, v in attempt.request.headers.items()})
{'Accept': '*/*',
 'Accept-Encoding': 'gzip, deflate',
 'Connection': 'keep-alive',
 'Content-Length': '5',
 'Content-Type': 'application/json',
 'User-Agent': 'nti.webhooks...'}
>>> print(attempt.request.body)
>>> len(attempt.internal_info.exception_history)