Return type definition of Kafka.structured seems incorrect

Describe the Bug

The types for return values from Kafka.structured(cloudEventInstance) seem to be incorrect. The returned object has the following structure if viewed using logs or a debugger:

{
  key: 'fubar',
  value: '{"id":"ef233aa0-00a0-4b5a-9886-f8ff7566ef50","time":"2022-04-14T20:26:32.291Z","type":"foo","source":"bar","specversion":"1.0","partitionkey":"fubar","data":{"hello":"world}}',
  headers: { 'content-type': 'application/cloudevents+json; charset=utf-8' },
  body: '{"id":"ef233aa0-00a0-4b5a-9886-f8ff7566ef50","time":"2022-04-14T20:26:32.291Z","type":"foo","source":"bar","specversion":"1.0","partitionkey":"fubar","data":{"hello":"world}}',
  timestamp: '1649967992291'
}

However, the types come from CE.Message<string>. This results in the following intellisense structure being suggested:

{
  body: unknown,
  headers: CE.Headers
}

It seems as though the headers key is correct, but the body is incorrect, and other keys are missing.

Steps to Reproduce

1. Create a CloudEvent, e.g new ce.CloudEvent({ type: 'foo', source: 'bar', data: { hello: 'world' }, partitionkey: 'foobar' }
2. Pass it to, e.g Kafka.structured(theEvent)
3. Attempt to access the timestamp, value, or key. These are not known properties on the return value.
4. Try to use the body and you find it is incorrectly typed as unknown

Expected Behavior

I would have expected the types to reflect the Object in the Describe the bug section, e.g:

{
  key: string|undefined
  value: string,
  headers: CE.Headers,
  body: string,
  timestamp: string
}

Is this an invalid assumption to make? Passing the result of Kafka.structured(cloudEventInstance) object to a Kafka client such as KafkaJS requires casting the object to access the necessary properties to satisfy the TS compiler. It seems like this casting should be unnecessary.

Additional context

I’m using version 6.0.1 of the cloudevents module. The image below might help provide some context.

[lance]

@FelixHarvey @evanshortiss thank you for your detailed descriptions of the issues you are seeing with the SDK - and I would welcome any contributions you have towards improvement. The interfaces are a bit clumsy.

The Binding interface is what is causing all of this trouble, I think. https://github.com/cloudevents/sdk-javascript/blob/d9ee0e05d1b38c84314d3e0535b17c25470d95a5/src/message/index.ts#L25-L30

I want this to be generic so that various protocols such as HTTP and Kafka, which have differing implementations can all behave similarly when serializing and deserializing CloudEvent messages. The Serializer and Deserializer interfaces that Binding exposes are meant to be the generic API. https://github.com/cloudevents/sdk-javascript/blob/d9ee0e05d1b38c84314d3e0535b17c25470d95a5/src/message/index.ts#L63-L79

However, the result is what you are seeing now. There is some amount of type casting that is inevitable. If you have ideas or suggestions to improve this situation, I’d be more than happy to talk about them.

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