DoContext wraps the http client.Do.

EnableJaeger set jaeger as global tracer.

Get wraps the http.Get.

NewClientSpan must return an finish function.

NewServerSpanFromMap must return an finish function.

NewServerSpanFromMap must return an finish function.

Post wraps the http.Post.

WithPost returns option for post exec func.

WithPostCheck set span tag/logs if cFunc returns error.

WithPre returns option for pre exec func.

DefaultClient is same as http.DefaultClient.