Do not always override operation name when tracing endpoints

[embs]

I'd like the operation name not to get overwritten in a server span when it's already set by the client who is calling the endpoint -- which is the case when using same span for client/server, like here: microservices-demo/user#53

I guess this behavior could be achieved by modifying

kit/tracing/opentracing/endpoint.go

Line 25 in 0d313fb

serverSpan.SetOperationName(operationName)

Maybe we could add some conditional logic to set operation name only if the span isn't being shared between client/server? (I'm afraid this could be Zipkin-specific though)

Does that make sense? I would gladly try fixing up a PR if it does.

[basvanbeek]

it is Zipkin specific and Zipkin standard behavior. Also worth mentioning is the fact that Zipkin is moving away from client / server shared spans with V2.

[yurishkuro]

it is illegal to start a span via OpenTracing API without an operation name. Also it is generally a bad idea trusting the client to name your server endpoint, the server is the authority.

btw, Jaeger (http://github.com/uber/jaeger), recently accepted to CNCF, does not mix client/server spans, if you want to try it out.

[embs]

Thank you for your kind suggestions and explanations.

I'll try moving towards using single-host spans, then.