[opentracing] start time is evaluated in options

opentracing/tracer.go

@@ -29,7 +29,6 @@ func (t *Tracer) StartSpan(operationName string, options ...ot.StartSpanOption)
 
 func (t *Tracer) startSpanWithOptions(operationName string, options ot.StartSpanOptions) ot.Span {
 	if options.StartTime.IsZero() {
-		// TODO: we should set this value
 		options.StartTime = time.Now().UTC()
 	}
 
@@ -57,6 +56,8 @@ func (t *Tracer) startSpanWithOptions(operationName string, options ot.StartSpan
 		span = t.impl.NewChildSpan(operationName, parent.Span)
 	}
 
+	// create an OpenTracing compatible Span; the SpanContext has a
+	// back-reference that is used for parent-child hierarchy
 	otSpan := &Span{
 		Span: span,
 		context: SpanContext{
@@ -66,9 +67,11 @@ func (t *Tracer) startSpanWithOptions(operationName string, options ot.StartSpan
 			sampled:  span.Sampled,
 		},
 	}
-
 	otSpan.context.span = otSpan
 
+	// set start time
+	otSpan.Span.Start = options.StartTime.UnixNano()
+
 	if parent != nil {
 		// propagate baggage items
 		if l := len(parent.context.baggage); l > 0 {

opentracing/tracer_test.go

@@ -2,6 +2,7 @@ package opentracing
 
 import (
 	"testing"
+	"time"
 
 	opentracing "github.com/opentracing/opentracing-go"
 	"github.com/stretchr/testify/assert"
@@ -89,3 +90,16 @@ func TestTracerSpanTags(t *testing.T) {
 
 	assert.Equal("value", span.Span.Meta["key"])
 }
+
+func TestTracerSpanStartTime(t *testing.T) {
+	assert := assert.New(t)
+
+	config := NewConfiguration()
+	tracer, _, _ := NewTracer(config)
+
+	startTime := time.Now().Add(-10 * time.Second)
+	span, ok := tracer.StartSpan("web.request", opentracing.StartTime(startTime)).(*Span)
+	assert.True(ok)
+
+	assert.Equal(startTime.UnixNano(), span.Span.Start)
+}