Opentracing support

vendor/github.com/openzipkin/zipkin-go-opentracing/propagation.go

@@ -0,0 +1,68 @@
+package zipkintracer
+
+import (
+	opentracing "github.com/opentracing/opentracing-go"
+
+	"github.com/openzipkin/zipkin-go-opentracing/flag"
+	"github.com/openzipkin/zipkin-go-opentracing/types"
+)
+
+type accessorPropagator struct {
+	tracer *tracerImpl
+}
+
+// DelegatingCarrier is a flexible carrier interface which can be implemented
+// by types which have a means of storing the trace metadata and already know
+// how to serialize themselves (for example, protocol buffers).
+type DelegatingCarrier interface {
+	SetState(traceID types.TraceID, spanID uint64, parentSpanID *uint64, sampled bool, flags flag.Flags)
+	State() (traceID types.TraceID, spanID uint64, parentSpanID *uint64, sampled bool, flags flag.Flags)
+	SetBaggageItem(key, value string)
+	GetBaggage(func(key, value string))
+}
+
+func (p *accessorPropagator) Inject(
+	spanContext opentracing.SpanContext,
+	carrier interface{},
+) error {
+	dc, ok := carrier.(DelegatingCarrier)
+	if !ok || dc == nil {
+		return opentracing.ErrInvalidCarrier
+	}
+	sc, ok := spanContext.(SpanContext)
+	if !ok {
+		return opentracing.ErrInvalidSpanContext
+	}
+	dc.SetState(sc.TraceID, sc.SpanID, sc.ParentSpanID, sc.Sampled, sc.Flags)
+	for k, v := range sc.Baggage {
+		dc.SetBaggageItem(k, v)
+	}
+	return nil
+}
+
+func (p *accessorPropagator) Extract(
+	carrier interface{},
+) (opentracing.SpanContext, error) {
+	dc, ok := carrier.(DelegatingCarrier)
+	if !ok || dc == nil {
+		return nil, opentracing.ErrInvalidCarrier
+	}
+
+	traceID, spanID, parentSpanID, sampled, flags := dc.State()
+	sc := SpanContext{
+		TraceID:      traceID,
+		SpanID:       spanID,
+		Sampled:      sampled,
+		Baggage:      nil,
+		ParentSpanID: parentSpanID,
+		Flags:        flags,
+	}
+	dc.GetBaggage(func(k, v string) {
+		if sc.Baggage == nil {
+			sc.Baggage = map[string]string{}
+		}
+		sc.Baggage[k] = v
+	})
+
+	return sc, nil
+}