trace: Add Span.AddLink method

CHANGELOG.md

@@ -10,6 +10,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 
 ### Added
 
+- Add `AddLink` method to the `Span` interface in `go.opentelemetry.io/otel/trace`. (#5032)
 - Add `WithProxy` option in `go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetrichttp`. (#4906)
 - Add `WithProxy` option in `go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlptracehttp`. (#4906)
 - The `Enabled` method is added to the `Logger` interface in `go.opentelemetry.io/otel/log`.

bridge/opentracing/internal/mock.go

@@ -176,6 +176,11 @@
 	Attributes []attribute.KeyValue
 }
 
+type MockLink struct {
+	SpanContext trace.SpanContext
+	Attributes  []attribute.KeyValue
+}
+
 type MockSpan struct {
 	embedded.Span
 
@@ -190,6 +195,7 @@
 	EndTime      time.Time
 	ParentSpanID trace.SpanID
 	Events       []MockEvent
+	Links        []MockLink
 }
 
 var (
@@ -286,6 +292,13 @@
 	})
 }
 
+func (s *MockSpan) AddLink(link trace.Link) {
+	s.Links = append(s.Links, MockLink{
+		SpanContext: link.SpanContext,
+		Attributes:  link.Attributes,
+	})
+}
+
 func (s *MockSpan) OverrideTracer(tracer trace.Tracer) {
 	s.officialTracer = tracer
 }

internal/global/trace.go

@@ -182,6 +182,9 @@
 // AddEvent does nothing.
 func (nonRecordingSpan) AddEvent(string, ...trace.EventOption) {}
 
+// AddLink does nothing.
+func (nonRecordingSpan) AddLink(trace.Link) {}
+
 // SetName does nothing.
 func (nonRecordingSpan) SetName(string) {}
 

sdk/trace/span.go

@@ -629,7 +629,7 @@
 	return s.tracer.provider.resource
 }
 
-func (s *recordingSpan) addLink(link trace.Link) {
+func (s *recordingSpan) AddLink(link trace.Link) {
 	if !s.IsRecording() || !link.SpanContext.IsValid() {
 		return
 	}
@@ -803,6 +803,9 @@
 // AddEvent does nothing.
 func (nonRecordingSpan) AddEvent(string, ...trace.EventOption) {}
 
+// AddLink does nothing.
+func (nonRecordingSpan) AddLink(trace.Link) {}
+
 // SetName does nothing.
 func (nonRecordingSpan) SetName(string) {}
 

sdk/trace/trace_test.go

@@ -1976,3 +1976,81 @@ func TestEmptyRecordingSpanAttributes(t *testing.T) {
 func TestEmptyRecordingSpanDroppedAttributes(t *testing.T) {
 	assert.Equal(t, 0, (&recordingSpan{}).DroppedAttributes())
 }
+
+func TestAddLinkWithInvalidSpanContext(t *testing.T) {
+	te := NewTestExporter()
+	sl := NewSpanLimits()
+	tp := NewTracerProvider(
+		WithSpanLimits(sl),
+		WithSyncer(te),
+		WithResource(resource.Empty()),
+	)
+	span := startSpan(tp, "AddSpanWithInvalidSpanContext")
+	inValidContext := trace.NewSpanContext(trace.SpanContextConfig{
+		TraceID: trace.TraceID([16]byte{}),
+		SpanID:  [8]byte{},
+	})
+	attrs := []attribute.KeyValue{{Key: "k", Value: attribute.StringValue("v")}}
+	span.AddLink(trace.Link{
+		SpanContext: inValidContext,
+		Attributes:  attrs,
+	})
+
+	want := &snapshot{
+		name: "span0",
+		spanContext: trace.NewSpanContext(trace.SpanContextConfig{
+			TraceID:    tid,
+			TraceFlags: 0x1,
+		}),
+		parent:               sc.WithRemote(true),
+		links:                nil,
+		spanKind:             trace.SpanKindInternal,
+		instrumentationScope: instrumentation.Scope{Name: "AddSpanWithInvalidSpanContext"},
+	}
+	got, err := endSpan(te, span)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if diff := cmpDiff(got, want); diff != "" {
+		t.Errorf("AddLinkWithInvalidSpanContext: -got +want %s", diff)
+	}
+}
+
+func TestAddLink(t *testing.T) {
+	te := NewTestExporter()
+	sl := NewSpanLimits()
+	tp := NewTracerProvider(
+		WithSpanLimits(sl),
+		WithSyncer(te),
+		WithResource(resource.Empty()),
+	)
+	attrs := []attribute.KeyValue{{Key: "k", Value: attribute.StringValue("v")}}
+	span := startSpan(tp, "AddSpan")
+
+	link := trace.Link{SpanContext: sc, Attributes: attrs}
+	span.AddLink(link)
+
+	want := &snapshot{
+		name: "span0",
+		spanContext: trace.NewSpanContext(trace.SpanContextConfig{
+			TraceID:    tid,
+			TraceFlags: 0x1,
+		}),
+		parent: sc.WithRemote(true),
+		links: []Link{
+			{
+				SpanContext: sc,
+				Attributes:  attrs,
+			},
+		},
+		spanKind:             trace.SpanKindInternal,
+		instrumentationScope: instrumentation.Scope{Name: "AddSpan"},
+	}
+	got, err := endSpan(te, span)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if diff := cmpDiff(got, want); diff != "" {
+		t.Errorf("AddLink: -got +want %s", diff)
+	}
+}

sdk/trace/tracer.go

@@ -138,7 +138,7 @@ func (tr *tracer) newRecordingSpan(psc, sc trace.SpanContext, name string, sr Sa
 	}
 
 	for _, l := range config.Links() {
-		s.addLink(l)
+		s.AddLink(l)
 	}
 
 	s.SetAttributes(sr.Attributes...)

trace/noop.go

@@ -75,6 +75,9 @@
 // AddEvent does nothing.
 func (noopSpan) AddEvent(string, ...EventOption) {}
 
+// AddLink does nothing.
+func (noopSpan) AddLink(Link) {}
+
 // SetName does nothing.
 func (noopSpan) SetName(string) {}
 

trace/noop/noop.go

@@ -100,6 +100,9 @@ func (Span) RecordError(error, ...trace.EventOption) {}
 // AddEvent does nothing.
 func (Span) AddEvent(string, ...trace.EventOption) {}
 
+// AddLink does nothing.
+func (Span) AddLink(trace.Link) {}
+
 // SetName does nothing.
 func (Span) SetName(string) {}
 

trace/trace.go

@@ -350,6 +350,12 @@ type Span interface {
 	// AddEvent adds an event with the provided name and options.
 	AddEvent(name string, options ...EventOption)
 
+	// AddLink adds a link.
+	// Adding links at span creation using WithLinks is preferred to calling AddLink
+	// later, for contexts that are available during span creation, because head
+	// sampling decisions can only consider information present during span creation.
+	AddLink(link Link)
+
 	// IsRecording returns the recording state of the Span. It will return
 	// true if the Span is active and events can be recorded.
 	IsRecording() bool