[restful-ws] Allow configuring default writer encoding for CloudEventsProvider

[cardil]

The CloudEventsProvider defaults to binary encoding. Only when there is an StructuredEncoding annotation present, this mode will be set. See the logic:

sdk-java/http/restful-ws/src/main/java/io/cloudevents/http/restful/ws/CloudEventsProvider.java

Lines 95 to 112 in 3614a4f

	Optional<String> structuredEncodingFormat = Arrays
	.stream(annotations)
	.filter(a -> a.annotationType().equals(StructuredEncoding.class))
	.map(a -> ((StructuredEncoding) a).value())
	.findFirst();
	if (structuredEncodingFormat.isPresent()) {
	writeStructured(
	event,
	structuredEncodingFormat.get(),
	new RestfulWSMessageWriter(httpHeaders, entityStream)
	);
	} else {
	writeBinary(
	event,
	new RestfulWSMessageWriter(httpHeaders, entityStream)
	);
	}

This makes the BinaryEncoding useless, confirmed by no usages in the code.

The default to the binary mode is unfortunate. Some implementations like Quarkus RESTEasy Reactive Server Sent Events (SSE) don't provide the annotations. This is problematic, as the binary mode doesn't make sense in SSE - the headers set by CloudEventsProvider are being dropped.

See the code:

https://github.com/quarkusio/quarkus/blob/247736226a8c8a55fa88a662eda05963803905eb/independent-projects/resteasy-reactive/server/runtime/src/main/java/org/jboss/resteasy/reactive/server/core/SseUtil.java#L141-L142

See repro: cardil/openshift-knative-showcase@15e0042
Related issue: quarkusio/quarkus#31559

The fact the Quarkus doesn't pass the method annotations, is probably a bug in Quarkus. But, I feel the CloudEvents SDK should allow setting the default mode. Then, the BinaryEncoding could have a meaning, of changing that default encoding per-method.

/kind bug

[pierDipi]

With @JemDay we were discussing configurations like this in the context of XML format writer but there is no concrete design or proposal yet.

[cardil]

How about we provide settings like interface, which people could define using Java's ServiceLoader. It may be something like:

interface Settings {
  default Encoding defaultEncoding() {
    return Encoding.BINARY;
  }
}

[cardil]

I created a Quarkus issue about this: quarkusio/quarkus#31587

[cardil]

As evidenced in cardil/openshift-knative-showcase#2 the fixing of quarkusio/quarkus#31587 (PR quarkusio/quarkus#32815) didn't help completely.