tracer: add span kind

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

tracer/noop.go

@@ -13,6 +13,7 @@ func (t *noopTracer) Start(ctx context.Context, name string, opts ...SpanOption)
 		name:   name,
 		ctx:    ctx,
 		tracer: t,
+		opts:   NewSpanOptions(opts...),
 	}
 	if span.ctx == nil {
 		span.ctx = context.Background()
@@ -64,6 +65,10 @@ func (s *noopSpan) AddLabels(labels ...interface{}) {
 	s.opts.Labels = append(s.opts.Labels, labels...)
 }
 
+func (s *noopSpan) Kind() SpanKind {
+	return s.opts.Kind
+}
+
 // NewTracer returns new memory tracer
 func NewTracer(opts ...Option) Tracer {
 	return &noopTracer{

tracer/options.go

@@ -6,9 +6,58 @@ import (
 	"go.unistack.org/micro/v3/logger"
 )
 
+type SpanKind int
+
+const (
+	// SpanKindUnspecified is an unspecified SpanKind and is not a valid
+	// SpanKind. SpanKindUnspecified should be replaced with SpanKindInternal
+	// if it is received.
+	SpanKindUnspecified SpanKind = 0
+	// SpanKindInternal is a SpanKind for a Span that represents an internal
+	// operation within an application.
+	SpanKindInternal SpanKind = 1
+	// SpanKindServer is a SpanKind for a Span that represents the operation
+	// of handling a request from a client.
+	SpanKindServer SpanKind = 2
+	// SpanKindClient is a SpanKind for a Span that represents the operation
+	// of client making a request to a server.
+	SpanKindClient SpanKind = 3
+	// SpanKindProducer is a SpanKind for a Span that represents the operation
+	// of a producer sending a message to a message broker. Unlike
+	// SpanKindClient and SpanKindServer, there is often no direct
+	// relationship between this kind of Span and a SpanKindConsumer kind. A
+	// SpanKindProducer Span will end once the message is accepted by the
+	// message broker which might not overlap with the processing of that
+	// message.
+	SpanKindProducer SpanKind = 4
+	// SpanKindConsumer is a SpanKind for a Span that represents the operation
+	// of a consumer receiving a message from a message broker. Like
+	// SpanKindProducer Spans, there is often no direct relationship between
+	// this Span and the Span that produced the message.
+	SpanKindConsumer SpanKind = 5
+)
+
+func (sk SpanKind) String() string {
+	switch sk {
+	case SpanKindInternal:
+		return "internal"
+	case SpanKindServer:
+		return "server"
+	case SpanKindClient:
+		return "client"
+	case SpanKindProducer:
+		return "producer"
+	case SpanKindConsumer:
+		return "consumer"
+	default:
+		return "unspecified"
+	}
+}
+
 // SpanOptions contains span option
 type SpanOptions struct {
 	Labels []interface{}
+	Kind   SpanKind
 }
 
 // SpanOption func signature
@@ -20,20 +69,26 @@ type EventOptions struct{}
 // EventOption func signature
 type EventOption func(o *EventOptions)
 
-func SpanLabels(labels ...interface{}) SpanOption {
+func WithSpanLabels(labels ...interface{}) SpanOption {
 	return func(o *SpanOptions) {
 		o.Labels = labels
 	}
 }
 
+func WithSpanKind(k SpanKind) SpanOption {
+	return func(o *SpanOptions) {
+		o.Kind = k
+	}
+}
+
 // Options struct
 type Options struct {
+	// Context used to store custome tracer options
+	Context context.Context
 	// Logger used for logging
 	Logger logger.Logger
 	// Name of the tracer
 	Name string
-	// Context used to store custome tracer options
-	Context context.Context
 }
 
 // Option func signature
@@ -46,6 +101,17 @@ func Logger(l logger.Logger) Option {
 	}
 }
 
+// NewSpanOptions returns default SpanOptions
+func NewSpanOptions(opts ...SpanOption) SpanOptions {
+	options := SpanOptions{
+		Kind: SpanKindInternal,
+	}
+	for _, o := range opts {
+		o(&options)
+	}
+	return options
+}
+
 // NewOptions returns default options
 func NewOptions(opts ...Option) Options {
 	options := Options{

tracer/tracer.go

@@ -33,4 +33,6 @@ type Span interface {
 	SetLabels(labels ...interface{})
 	// AddLabels append the span labels
 	AddLabels(labels ...interface{})
+	// Kind returns span kind
+	Kind() SpanKind
 }