Avro format implementation

[sunng87]

This patch is to provide an Avro format implementation for the CloudEvent 1.0.

Fixes #115

TODO items:

• unit tests
• extension fields?
• data

[tompoch]

What is the relation of this to the content mode as defined in the Kafka Protocol Binding? Do I read correctly that this PR corresponds to the structured mode, but not to the binary?

[tompoch]

I would expect some reference to the schema-registry maintaining the avro schemas. Am I missing something?

[sunng87]

This patch is to implement Avro as a cloudevent serialization format. It doesn't cover kafka binding for now. Perhaps we can provide that integration in future.

[pierDipi]

Awesome @sunng87!

I left some comments/questions/suggestions.

[pierDipi]

Can we inject AvroCloudEventData directly?

Suggested change

	public AvroCloudEventDataWrapper(Map<String, Object> data) {
	avroCloudEventData = new AvroCloudEventData();
	avroCloudEventData.setValue(data);
	}
	public AvroCloudEventDataWrapper(AvroCloudEventData avroCloudEventData) {
	this.avroCloudEventData = Objects.requireNonNull(avroCloudEventData);
	}

[sunng87]

The reason I'm using a map here is I tried to avoid exposing generated data type in a public api. The AvroCloudEventData contains some Avro serialization logic.

[pierDipi]

OK, sounds good!

Can we add only the Objects.requireNonNull check?

Suggested change

	public AvroCloudEventDataWrapper(Map<String, Object> data) {
	avroCloudEventData = new AvroCloudEventData();
	avroCloudEventData.setValue(data);
	}
	public AvroCloudEventDataWrapper(Map<String, Object> data) {
	avroCloudEventData = new AvroCloudEventData();
	avroCloudEventData.setValue(Objects.requireNonNull(data));
	}

[pierDipi]

Can we add more test cases?

• Using a CloudEvent v0.3 (CloudEventBuilder.v03())
• passing null as avroCloudEventData to AvroCloudEventDataWrapper (we can create a new class AvroCloudEventDataWrapperTest for this
• Testing all data types specified in the union type for data field (null included): https://github.com/cloudevents/sdk-java/pull/407/files#diff-09cbc79dec7471fa039c796a1fdfc9f13013cb7e9636e23bc32687378f59cb2aR23-R60

[sunng87]

Ok. I will do it in next few commits.

[pkgonan]

@sunng87 @pierDipi Hi. Any changes of this pr?

[sunng87]

hi @pkgonan I'm no longer working on this. Feel free to fork and continue this work