Add support for Distributed Tracing extension

[cardil]

Is your feature request related to a problem? Please describe.
A Distributed Tracing Extension is part of the specification. Javascript SDK should support it.

Describe the solution you would like to see
An implementation of Distributed Tracing should be implemented in similar way as it is done for Go and Java SDK's.

[cardil]

/cc @piecioshka

[lance]

@cardil good catch!

A Distributed Tracing Extension is part of the specification. Javascript SDK should support it.

To be clear, expectations for the SDKs do not require that this be implemented. https://github.com/cloudevents/spec/blob/master/SDK.md#technical-requirements

But I agree - it would be good.

[github-actions]

This issue is stale because it has been open 30 days with no activity.

[lance]

@cardil I've been thinking about this, and I wonder how you see this in practical usage. In the spec, the example given is,

CURL -X POST example/webhook.json \
-H 'ce-id: 1' \
-H 'ce-specversion: 1.x-wip' \
-H 'ce-type: example' \
-H 'ce-source: http://localhost' \
-H 'ce-traceparent:  00-0af7651916cd43dd8448eb211c80319c-b9c7c989f97918e1-01' \
-H 'traceparent:  00-4bf92f3577b34da6a3ce929d0e0e4736-00f067aa0ba902b7-01' \
-H 'tracestate: rojo=00-4bf92f3577b34da6a3ce929d0e0e4736-00f067aa0ba902b7-01,congo=lZWRzIHRoNhcm5hbCBwbGVhc3VyZS4`

Receiving an event message like this in the SDK would result in a CloudEvent that had the extension traceparent. For example assuming those headers above,

const event = HTTP.toEvent(headers, body);
console.log(event.traceparent); // 00-0af7651916cd43dd8448eb211c80319c-b9c7c989f97918e1-01

Producing an event, that includes this information is similarly straightforward.

const event = new CloudEvent({ source: '/example', type: 'tracer', traceparent: '00-0af7651916cd43dd8448eb211c80319c-b9c7c989f97918e1-01' });
const message = HTTP.binary(event);
console.log(message.headers); // should include a 'ce-traceparent: 00-0af7651916cd43dd8448eb211c80319c-b9c7c989f97918e1-01' header

Looking at the spec, I'm not sure there is anything else for us to support. Is there some specific behavior that you had in mind?

[lance]

If what we have already is sufficient to consider the Distributed Tracing extension supported, we should add this to the README.md and maybe provide an example.

[cardil]

Awesome. I think we can easily resolve this issue with just writing those examples above in documentation.

[cardil]

I assume tracestate is also supported, just as traceparent?

[cardil]

I think if both of those are supported, we should write those in documentation as examples, and maybe also add a unit test to make sure this behavior will be kept.

[lance]

I assume tracestate is also supported, just as traceparent?

Yes - it behaves just as any extension. A ce-<extname>: <extvalue> header will get created when creating new events, and a ce-<extname> header will result in that <extname> being a property of the event.

[cardil]

@lance Looking at Golang implementation it seems like more than just passing those extensions should be done:

https://github.com/cloudevents/sdk-go/blob/8ff3fbc/v2/client/client_observed.go#L48-L57