Add support for AddLink to the OpenCensus bridge (#5116)

* add support for AddLink to the OpenCensus bridge

* Update CHANGELOG.md

Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>

---------

Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>

CHANGELOG.md

@@ -23,6 +23,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
   At which point, users will be required to migrage their code, and this package will be deprecated then removed. (#5085)
 - Add support for `Summary` metrics in the `go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetrichttp` and `go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetricgrpc` exporters. (#5100)
 - Add `otel.scope.name` and `otel.scope.version` tags to spans exported by `go.opentelemetry.io/otel/exporters/zipkin`. (#5108)
+- Add support for `AddLink` to `go.opentelemetry.io/otel/bridge/opencensus`. (#5116)
 
 ### Changed
 

bridge/opencensus/doc.go

@@ -37,8 +37,6 @@
 //
 // There are known limitations to the trace bridge:
 //
-//   - The AddLink method for OpenCensus Spans is ignored, and an error is sent
-//     to the OpenTelemetry ErrorHandler.
 //   - The NewContext method of the OpenCensus Tracer cannot embed an OpenCensus
 //     Span in a context unless that Span was created by that Tracer.
 //   - Conversion of custom OpenCensus Samplers to OpenTelemetry is not

bridge/opencensus/internal/oc2otel/attributes.go

@@ -20,6 +20,17 @@ func Attributes(attr []octrace.Attribute) []attribute.KeyValue {
 	return otelAttr
 }
 
+func AttributesFromMap(attr map[string]interface{}) []attribute.KeyValue {
+	otelAttr := make([]attribute.KeyValue, 0, len(attr))
+	for k, v := range attr {
+		otelAttr = append(otelAttr, attribute.KeyValue{
+			Key:   attribute.Key(k),
+			Value: AttributeValue(v),
+		})
+	}
+	return otelAttr
+}
+
 func AttributeValue(ocval interface{}) attribute.Value {
 	switch v := ocval.(type) {
 	case bool:

bridge/opencensus/internal/oc2otel/attributes_test.go

@@ -37,6 +37,29 @@ func TestAttributes(t *testing.T) {
 	}
 }
 
+func TestAttributesFromMap(t *testing.T) {
+	in := map[string]interface{}{
+		"bool":    true,
+		"int64":   int64(49),
+		"float64": float64(1.618),
+		"key":     "val",
+	}
+
+	want := []attribute.KeyValue{
+		attribute.Bool("bool", true),
+		attribute.Int64("int64", 49),
+		attribute.Float64("float64", 1.618),
+		attribute.String("key", "val"),
+	}
+	got := AttributesFromMap(in)
+
+	gotAttributeSet := attribute.NewSet(got...)
+	wantAttributeSet := attribute.NewSet(want...)
+	if !gotAttributeSet.Equals(&wantAttributeSet) {
+		t.Errorf("Attributes conversion want %v, got %v", wantAttributeSet.Encoded(attribute.DefaultEncoder()), gotAttributeSet.Encoded(attribute.DefaultEncoder()))
+	}
+}
+
 func TestAttributeValueUnknown(t *testing.T) {
 	got := AttributeValue([]byte{})
 	if got != attribute.StringValue("unknown") {

bridge/opencensus/internal/span.go

@@ -110,8 +110,20 @@ func (s *Span) AddMessageReceiveEvent(messageID, uncompressedByteSize, compresse
 }
 
 // AddLink adds a link to this span.
+// This drops the OpenCensus LinkType because there is no such concept in OpenTelemetry.
 func (s *Span) AddLink(l octrace.Link) {
-	Handle(fmt.Errorf("ignoring OpenCensus link %+v for span %q because OpenTelemetry doesn't support setting links after creation", l, s.String()))
+	s.otelSpan.AddLink(trace.Link{
+		SpanContext: trace.NewSpanContext(trace.SpanContextConfig{
+			TraceID: trace.TraceID(l.TraceID),
+			SpanID:  trace.SpanID(l.SpanID),
+			// We don't know if this was sampled or not.
+			// Mark it as sampled, since sampled means
+			// "the caller may have recorded trace data":
+			// https://www.w3.org/TR/trace-context/#sampled-flag
+			TraceFlags: trace.FlagsSampled,
+		}),
+		Attributes: oc2otel.AttributesFromMap(l.Attributes),
+	})
 }
 
 // String prints a string representation of this span.

bridge/opencensus/internal/span_test.go

@@ -28,6 +28,7 @@ type span struct {
 	attrs     []attribute.KeyValue
 	eName     string
 	eOpts     []trace.EventOption
+	links     []trace.Link
 }
 
 func (s *span) IsRecording() bool                         { return s.recording }
@@ -37,6 +38,7 @@ func (s *span) SetName(n string)                          { s.name = n }
 func (s *span) SetStatus(c codes.Code, d string)          { s.sCode, s.sMsg = c, d }
 func (s *span) SetAttributes(a ...attribute.KeyValue)     { s.attrs = a }
 func (s *span) AddEvent(n string, o ...trace.EventOption) { s.eName, s.eOpts = n, o }
+func (s *span) AddLink(l trace.Link)                      { s.links = append(s.links, l) }
 
 func TestSpanIsRecordingEvents(t *testing.T) {
 	s := &span{recording: true}
@@ -230,16 +232,51 @@ func TestSpanAddMessageReceiveEvent(t *testing.T) {
 }
 
 func TestSpanAddLinkFails(t *testing.T) {
-	h, restore := withHandler()
-	defer restore()
-
 	// OpenCensus does not try to set links if not recording.
 	s := &span{recording: true}
 	ocS := internal.NewSpan(s)
 	ocS.AddLink(octrace.Link{})
+	ocS.AddLink(octrace.Link{
+		TraceID: octrace.TraceID([16]byte{1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}),
+		SpanID:  octrace.SpanID([8]byte{2, 0, 0, 0, 0, 0, 0, 0}),
+		Attributes: map[string]interface{}{
+			"foo":    "bar",
+			"number": int64(3),
+		},
+	})
 
-	if h.err == nil {
-		t.Error("span.AddLink failed to raise an error")
+	wantLinks := []trace.Link{
+		{
+			SpanContext: trace.NewSpanContext(trace.SpanContextConfig{
+				TraceFlags: trace.FlagsSampled,
+			}),
+		},
+		{
+			SpanContext: trace.NewSpanContext(trace.SpanContextConfig{
+				TraceID:    trace.TraceID([]byte{1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}),
+				SpanID:     trace.SpanID([]byte{2, 0, 0, 0, 0, 0, 0, 0}),
+				TraceFlags: trace.FlagsSampled,
+			}),
+			Attributes: []attribute.KeyValue{
+				attribute.String("foo", "bar"),
+				attribute.Int64("number", 3),
+			},
+		},
+	}
+
+	if len(s.links) != len(wantLinks) {
+		t.Fatalf("got wrong number of links; want %v, got %v", len(wantLinks), len(s.links))
+	}
+
+	for i, l := range s.links {
+		if !l.SpanContext.Equal(wantLinks[i].SpanContext) {
+			t.Errorf("link[%v] has the wrong span context; want %+v, got %+v", i, wantLinks[i].SpanContext, l.SpanContext)
+		}
+		gotAttributeSet := attribute.NewSet(l.Attributes...)
+		wantAttributeSet := attribute.NewSet(wantLinks[i].Attributes...)
+		if !gotAttributeSet.Equals(&wantAttributeSet) {
+			t.Errorf("link[%v] has the wrong attributes; want %v, got %v", i, wantAttributeSet.Encoded(attribute.DefaultEncoder()), gotAttributeSet.Encoded(attribute.DefaultEncoder()))
+		}
 	}
 }