PubSub subscription `dataAsPayload` flag that sends only the `data/data_base64` value of the data attribute to the application

/area runtime

This feature applies only to the HTTP application protocol. This is not a usability issue with the gRPC API spec.

In some cases, the application may not need the full CloudEvent payload sent to the HTTP application. This is particularly the case with raw events, where receiving the CloudEvent wrapper is unexpected/confusing. This also avoids some performance hit in Base64 encoding/decoding when sending binary data (e.g. Avro/Protobuf). It is important to propagate the telemetry trace IDs through the call flow, but those are added to the header of the request to the app.

Here is what the configuration for raw events could look like:

apiVersion: dapr.io/v1alpha1
kind: Subscription
metadata:
  name: products
spec:
  pubsubname: pubsub
  topic: inventory
  route: products
  dataAsPayload: true

Note: dataAsPayload is not defined as a metadata attribute because it could apply per route in the case of PubSub Routing:

apiVersion: dapr.io/v2alpha1
kind: Subscription
metadata:
  name: mysubscriptions
spec:
  pubsubname: pubsub
  topic: inventory
  dataAsPayload: false   # (maybe) if specified, acts as the default for the routes
  routes:
    rules:
      - match: "event.type == 'widget'"
        path: widgets
        dataAsPayload: true    # overrides the default
      - match: "event.type == 'gadget'"
        path: gadgets
    default: products
    defaultDataAsPayload: true

Site note: In hindsight, default should have been a nested structure:

    default:
      path: products
      dataAsPayload: true

I don't think the CRD can be changed now. 🤷

From an SDK perspective (C# shown) the handler's method signature would look like this for dataAsPayload: false

public IActionResult Widget([FromBody] CloudEvent<Widget> widgetEvent)

Or like this with dataAsPayload: true

public IActionResult Widget([FromBody] Widget widget)

Release Note

RELEASE NOTE: Subscriptions can optionally send only the data of a CloudEvent to the application