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https://github.com/opennti/nti.webhooks

Python/Zope3 server-side webhooks implementation
https://github.com/opennti/nti.webhooks

Last synced: 9 months ago
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Python/Zope3 server-side webhooks implementation

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README 

          
==============

 nti.webhooks

==============



.. image:: https://github.com/NextThought/nti.webhooks/workflows/tests/badge.svg

   :target: https://github.com/NextThought/nti.webhooks/actions?query=workflow%3Atests



.. image:: https://coveralls.io/repos/github/NextThought/nti.webhooks/badge.svg?branch=master

   :target: https://coveralls.io/github/NextThought/nti.webhooks?branch=master



.. image:: https://readthedocs.org/projects/ntiwebhooks/badge/?version=latest

   :target: https://ntiwebhooks.readthedocs.io/en/latest/?badge=latest

   :alt: Documentation Status



This package provides the infrastructure and delivery mechanisms for a

server to support webhook delivery. For complete details and the

changelog, see the `documentation

`_.



.. sphinx-include-begin-prelude



Webhooks

========



Webhooks are HTTPS requests from one party --- the source --- to

another party, the destination. These requests are one-way: the source

sends the request to the destination, and aside from conforming that

the request was received, takes no further action (the request's

response from the destination is irrelevant). These requests are sent

from the source to let the destination know that something has

happened: a new entity (or resource, in the REST sense) has been

created, an old one updated or deleted, etc. Such requests typically

carry a payload in the body providing information about the action

(usually the representation of the affected resource). Destinations

are identified via complete URL; destinations may expect to be

informed of events affecting one, several, or all possible types of

entities handled by the source.



This Package

============



This package is installed in a source server and manages

the registration and sending of webhooks. The registrations may be

either static, or they may be dynamic, as in the case of `REST Hooks

`_, where individual "subscriptions" may be

started and stopped.



This package is intended to integrate with highly event-driven

applications using `zope.event `_,

that define their resources using `zope.interface

`_, manage event delivery,

resource adaptation, and dependency injection using `zope.component

`_, and (optionally) implement a

hierarchy of component registries using `zope.site

`_ and `nti.site

`_. Data persistence is provided

through `persistent objects `_,

typically with `ZODB `_.



Data Model (Subscription Combinations)

--------------------------------------



One of the motivating examples of this package is integration with

`Zapier `_ and more generally the notion of `REST

Hooks `_.



In this model, a configuration on a *server* (origin) that sends data

to a *target* URL when events occur is called a *subscription.*

Subscriptions are meant to include:



#. An event name (or names) the subscription includes;

#. A parent user or account relationship;

#. A target URL; and

#. Active vs inactive state.



Subscription lookup must be performant, so the user and event name

information for subscriptions should be fast to find.



Here, event names are defined to "use the noun.verb dot syntax, IE:

contact.create or lead.delete)." Using ``zope.event`` and

``zope.component,`` this translates to the pair of object type or

interface, and event type or interface. For example,

``(IContentContainer, IObjectAddedEvent).``



Zapier generates a unique target URL for each event name, so to get

created (added), modified, and deleted resources for a single type of

object there will be three different target URLs and thus three

different subscriptions. In general, there's an *N* x *M* expansion of

object types and event types to target URLs or subscriptions.



This package implements this model directly. (You can of course use

umbrella interfaces applied to multiple object or event types to send

related events to a single subscription.) Aggregating data views of

"all webhook deliveries for a type of object" or "all webhook

deliveries for a type of event" for presentation purposes could

be written, but isn't particularly natural given how its set up now.



An important outcome of this model is that there's no need for any

given HTTP request to explicitly include something that identifies the

type of event; the default dialect (see below) assume that the URL

includes everything the receiver needs for that and doesn't do

anything like add an X-NTI-EventType header or add something to the

JSON body. It can be a URL parameter or a whole different URL, doesn't

matter.



.. sphinx-include-after-prelude



Out Of Scope

============



Certain concerns are out of scope for this package (but other packages

built upon this package my provide them). These include, but are not

limited to:



- Providing a user interface for managing subscriptions.

- Providing an HTTPS API for managing subscriptions. This package

  provides the underlying data storage, but accepting parameters, etc,

  and marshaling them into the correct Python calls, is not a concern

  here.

- Providing a user interface or HTTPS API for viewing webhook audit

  logs.

- Enabling webhooks to fire only for specific objects. This package

  deals with scopes (sites) and kinds of objects, not individual instances.



In Scope/Features

=================



Certain concerns are very much in scope for this package, and this

package should provide a complete, easy to use solution that addresses

these concerns. Where necessary, if a concern cannot be addressed

directly by this package, extension points (interfaces and

``zope.component`` utilities) may be defined. These include, but are

not limited to:



- Resource Representation



  The on-the-wire form of the resources is built using

  `nti.externalization `_.



  To allow customization of the external forms, a named externalizer

  is used; nti.externalization will fall back to the default

  externalizer if no externalizer of the given name is available. The

  default externalizer is named "webhook-delivery", but dialects may

  use something different.



- Alternate Webhook Dialects



  Webhooks are a general protocol and mostly interoperable. But to

  support cases where particular destinations have specific

  requirements, "dialects" are used. There is a default dialect and

  then there may be specializations of it. Each webhook subscription

  may have associated with it the name of a dialect to use. These

  dialects are found in the component registry. For example, a dialect

  may choose to use a different externalizer name such as

  "zapier-webhook-delivery".



- Transactional



  Webhooks should not be delivered if the ultimate creation or

  persistence of a resource failed. To this end, webhook delivery in

  this package is integrated with the `transaction

  `_ package.



  Resources are externalized during a late phase of the transaction

  commit process; the details about the delivery are recorded and

  persisted, and only after the transaction is successfully committed

  does the HTTP request get made.



- Concurrency



  Webhook delivery and record keeping should be lightweight, and

  all actual network IO should proceed in a non-blocking fashion. This

  means that this package will spawn threads (or greenlets, using

  `gevent `_.



- Error Handling/Failure Retry



  A limited amount of retry logic is provided by this package, but

  that does not extend to process boundaries. If the process hosting

  this package is killed while a delivery is pending, no automatic

  provision is made to resume delivery attempts in any other process.



  The API is present to allow that to be implemented, though.



- Auditing/Delivery History



  For each subscription, delivery attempts, status, and responses are

  stored in a ring-buffer like structure. This can be inspected to see

  if deliveries succeeded, failed, or never completed.



- Access Control on Deliveries



  Each subscription is associated with an ``IPrincipal`` that owns it.

  A request is only delivered to a subscription if the ``IPrincipal``

  that owns the subscription can access the entity, as determined by

  `zope.security `_.



- Access Control on Subscriptions



  While not enforced by this package, the above owner relationship

  will be used to provide role managers that grant read and read/write

  access to remove subscriptions only to the owner of the

  subscription.



  TODO: Make sure client packages can extend that to provide for admin

  access. So long as we don't DENY it should be fine.



- Hierarchy of Subscriptions



  Subscriptions are made within a particular Zope site (the closest

  enclosing site to a resource when a resource is subscribed to, or

  the currently active site otherwise). These sites may have parents.



  TODO: Work out the details of that.



  When an event is received that might result in webhook delivery,

  active subscriptions are checked for in the currently active site,

  as well as in the sites up the hierarchy of the resource itself. All

  applicable subscribers will get a delivery.



  For example, if the president of the company (an administrator)

  subscribes to "new user created" events at the global (root, base or

  "/") level, and a department head subscribes to "new user created"

  for their department ("/NOAA"), while a local office manager

  subscribes to events for their office ("/NOAA/NWS/OUN"), then

  creating a new user in the OKC office may send three deliveries, one

  to the manager, one to the secretary, and one to the president.



  .. note:: If there are identical subscribed URLs with differing permission

            requirements, then if access is granted for *any

            subscription*, the payload will be delivered.



  .. note:: While looking up both the resource and active site tree

            might seem complex, following both hierarchies is

            necessary in the event of operations that span multiple

            child sites. This is probably most common with bulk

            operations, but a simple example would be the president

            logging in to the root site, searching for and deleting

            all employees named "Bill." If one was in the OKC office

            and one was in the OUN office, the managers of both

            locations should get delivery.



- Converting From Object Events to Webhook Events



  TODO: Write me.



  This package needs to have a clear way to have client packages

  specify what events should produce webhook deliveries. The exact

  mechanism is TBD. Possibly clients are expected to use

  ```` ZCML directives to apply marker interfaces? Or

  they might register a subscriber provided by this package for their

  own existing interfaces?



  We want this process, and the process of finding all active

  subscriptions, to be fast. I'm imagining something like view lookup,

  keeping active subscriptions in the various component registries?

  That doesn't work non-persistently.