Auto-creation of black-box sources

0-Description.md

1. This is very high-level and half baked.
2. This is intended to suggest one way that black-box sources could be auto-created in specific circumstances from a declaration of interest in events.
3. This assumes a model somewhat similar to Broker and Trigger (called Broker and Rules here) with the following additions:
   1. The Rule has a filter expression which matches more than event types. I've used CEL here.
   2. There is a process which propagates "upstream" (i.e. from consumer to origin) the set of filters currently listening.
4. We use an annotation, eventing.knative.dev/filter, as a way to copy filters from the Rules upstream through the components towards the event origin. Using an annotation allows non-filtering entities (such as Channel or Subscription) to propagate their filters upstream, even though they don't perform any filtering of their own.
5. This assumes that the user has also made github-enabled secrets available to the default service account, and that the githubsource CR defaults to using the default service account. (This means a one-time setup to enable GitHub, and then githubsources will be auto-generated as rules requesting them are called for.

Read in order:

• rules.yaml
• router.yaml
• githubsource.yaml

1-rules.yaml

# This is the rule where I listen for GitHub events for a repo or organization.
apiVersion: eventing.knative.dev/v1alpha1
kind: Rule
metadata:
  name: knative-sockpuppet
  annotations:  # Filled in by propagation agent, not written by user.
    eventing.knative.dev/filter: |
      ['type = "" && source.startsWith("https://github.com/knative/eventing/")']
spec:
  filter:
    expression: 'type = "github.pull_request.create" && source.startsWith("https://github.com/knative/eventing/")'
  target:
    ref:
      apiVersion: serving.knative.dev/v1alpha1
      kind: Service
      name: sockpuppet

2-router.yaml

# Internal implementation of the ingress filtering function for the broker
apiVersion: internal.eventing.knative.dev/v1alpha1
kind: BrokerRouter
metadata:
  name: default
  annotations:
    eventing.knative.dev/filter: \  # List of all downstream Rule filters, copied from annotations on downstreams and merged.
      ['....',
       'type = "github.pull_request.create" && source.startsWith("https://github.com/knative/eventing/")',
       '....',
      ]
spec:
  ....
  filter: |  # Auto-filled by the filter propagator from the eventing.knative.dev/filter annotation using '||' of conditions.
    ....
    ("github.pull_request.create" && source.startsWith("https://github.com/knative/eventing/"))
    ....

3-githubsource.yaml

# GitHub CRD has annotations that indicate that you can create a CR to fulfil
# type = github.* and source ~= https://github.com/([^/]+)
apiVersion: apiextensions.k8s.io/v1beta1
kind: CustemResourceDefinition
metadata:
  name: githubsources.sources.knative.dev
  labels:
    eventing.knative.dev/source: "true"
  annotations:
    eventing.knative.dev/sourceFulfilment: |  # I hate naming
      type_prefix: "github"  # If type prefix matches this regex
      type_property_list: "spec.eventTypes"  # Put type into this field
      source_prefix: "https://github.com/([^/]+)"  # If source prefix matches this regex
      source_property: "spec.ownerAndRepository"  # Put source into this field
spec:
  ...