Converting timestamp and duration to the number type to follow Zipkin span types

[dsborets]

In order to follow a Zipkin Span specification, I'm proposing to change string type to number for timestamp and duration.

[justindsmith]

Thanks @dsborets!

Just to be sure, did you validate this change against a zipkin endpoint to make sure the data is received and handled correctly in zipkin? Just want to make sure there are no breaking change, otherwise looks good.

[mayurkale22]

LGTM, please address @justindsmith's comment.

[dsborets]

Hi @justindsmith . Sure, I tested it and found that Zipkin accepting any spans disregards of timestamp and duration fields type (string or number). So we should be safe. I found this issue when we started to use Zipkin-to-Datadog proxy. And that proxy following Zipkin specification accepting only number type (simply by unmarshalling json to Go structure). Initially I thought it's a proxy's problem, but finally realized type discrepancy in opencensus exporter. Probably nobody used opencensus with any servers with more strict type casting than standard Zipkin server

[justindsmith]

Thanks for the clarification @dsborets. Looks good to me!

[dsborets]

Thank you 👍