step4.go

// The ext package provides a set of standardized tags available for use.
import "github.com/opentracing/opentracing-go/ext"

func homeHandler(w http.ResponseWriter, r *http.Request) {
// ...
// We record any errors now.
    _, err := http.Get("http://localhost:8080/service")
    if err != nil {
        ext.Error.Set(span, true) // Tag the span as errored
        span.LogEventWithPayload("GET service error", err) // Log the error
    }
// ...
}