Span links improvements and bug fix

.gitlab-ci.yml

@@ -9,7 +9,7 @@ variables:
   INDEX_FILE: index.txt
   KUBERNETES_SERVICE_ACCOUNT_OVERWRITE: dd-trace-go
   FF_USE_LEGACY_KUBERNETES_EXECUTION_STRATEGY: "true"
-  BENCHMARK_TARGETS: "BenchmarkStartRequestSpan|BenchmarkHttpServeTrace|BenchmarkTracerAddSpans|BenchmarkStartSpan|BenchmarkSingleSpanRetention|BenchmarkOTelApiWithCustomTags|BenchmarkInjectW3C|BenchmarkExtractW3C|BenchmarkPartialFlushing|BenchmarkGraphQL|BenchmarkSampleWAFContext|BenchmarkCaptureStackTrace|BenchmarkSetTagString|BenchmarkSetTagStringPtr|BenchmarkSetTagMetric|BenchmarkSetTagStringer"
+  BENCHMARK_TARGETS: "BenchmarkStartRequestSpan|BenchmarkHttpServeTrace|BenchmarkTracerAddSpans|BenchmarkStartSpan|BenchmarkSingleSpanRetention|BenchmarkOTelApiWithCustomTags|BenchmarkInjectW3C|BenchmarkExtractW3C|BenchmarkPartialFlushing|BenchmarkGraphQL|BenchmarkSampleWAFContext|BenchmarkCaptureStackTrace|BenchmarkSetTagString|BenchmarkSetTagStringPtr|BenchmarkSetTagMetric|BenchmarkSetTagStringer|BenchmarkSerializeSpanLinksInMeta"
 
 include:
   - ".gitlab/benchmarks.yml"

ddtrace/ddtrace.go

@@ -103,25 +103,6 @@ type SpanContext interface {
 	ForeachBaggageItem(handler func(k, v string) bool)
 }
 
-// SpanLink represents a reference to a span that exists outside of the trace.
-//
-//go:generate msgp -unexported -marshal=false -o=span_link_msgp.go -tests=false
-
-type SpanLink struct {
-	// TraceID represents the low 64 bits of the linked span's trace id. This field is required.
-	TraceID uint64 `msg:"trace_id" json:"trace_id"`
-	// TraceIDHigh represents the high 64 bits of the linked span's trace id. This field is only set if the linked span's trace id is 128 bits.
-	TraceIDHigh uint64 `msg:"trace_id_high,omitempty" json:"trace_id_high"`
-	// SpanID represents the linked span's span id.
-	SpanID uint64 `msg:"span_id" json:"span_id"`
-	// Attributes is a mapping of keys to string values. These values are used to add additional context to the span link.
-	Attributes map[string]string `msg:"attributes,omitempty" json:"attributes"`
-	// Tracestate is the tracestate of the linked span. This field is optional.
-	Tracestate string `msg:"tracestate,omitempty" json:"tracestate"`
-	// Flags represents the W3C trace flags of the linked span. This field is optional.
-	Flags uint32 `msg:"flags,omitempty" json:"flags"`
-}
-
 // StartSpanOption is a configuration option that can be used with a Tracer's StartSpan method.
 type StartSpanOption func(cfg *StartSpanConfig)
 

ddtrace/span_link.go

@@ -0,0 +1,25 @@
+// Unless explicitly stated otherwise all files in this repository are licensed
+// under the Apache License Version 2.0.
+// This product includes software developed at Datadog (https://www.datadoghq.com/).
+// Copyright 2016 Datadog, Inc.
+
+package ddtrace
+
+// SpanLink represents a reference to a span that exists outside of the trace.
+//
+//go:generate msgp -unexported -marshal=false -o=span_link_msgp.go -tests=false
+
+type SpanLink struct {
+	// TraceID represents the low 64 bits of the linked span's trace id. This field is required.
+	TraceID uint64 `msg:"trace_id" json:"trace_id"`
+	// TraceIDHigh represents the high 64 bits of the linked span's trace id. This field is only set if the linked span's trace id is 128 bits.
+	TraceIDHigh uint64 `msg:"trace_id_high" json:"trace_id_high"`
+	// SpanID represents the linked span's span id.
+	SpanID uint64 `msg:"span_id" json:"span_id"`
+	// Attributes is a mapping of keys to string values. These values are used to add additional context to the span link.
+	Attributes map[string]string `msg:"attributes" json:"attributes"`
+	// Tracestate is the tracestate of the linked span. This field is optional.
+	Tracestate string `msg:"tracestate" json:"tracestate"`
+	// Flags represents the W3C trace flags of the linked span. This field is optional.
+	Flags uint32 `msg:"flags" json:"flags"`
+}

ddtrace/tracer/span.go

@@ -10,6 +10,7 @@ package tracer
 import (
 	"context"
 	"encoding/base64"
+	"encoding/json"
 	"fmt"
 	"os"
 	"reflect"
@@ -91,6 +92,13 @@ type span struct {
 	taskEnd func() // ends execution tracer (runtime/trace) task, if started
 }
 
+type SpanWithLinks interface {
+	ddtrace.Span
+
+	// AddSpanLink appends the given link to span's span links.
+	AddSpanLink(link ddtrace.SpanLink)
+}
+
 // Context yields the SpanContext for this Span. Note that the return
 // value of Context() is still valid after a call to Finish(). This is
 // called the span context and it is different from Go's context.
@@ -464,6 +472,27 @@ func (s *span) setMetric(key string, v float64) {
 	}
 }
 
+// AddSpanLink appends the given link to the span's span links.
+func (s *span) AddSpanLink(link ddtrace.SpanLink) {
+	s.SpanLinks = append(s.SpanLinks, link)
+}
+
+// serializeSpanLinksInMeta saves span links as a JSON string under `Span[meta][_dd.span_links]`.
+func (s *span) serializeSpanLinksInMeta() {
+	if len(s.SpanLinks) == 0 {
+		return
+	}
+	spanLinkBytes, err := json.Marshal(s.SpanLinks)
+	if err != nil {
+		log.Debug("Unable to marshal span links. Not adding span links to span meta.")
+		return
+	}
+	if s.Meta == nil {
+		s.Meta = make(map[string]string)
+	}
+	s.Meta["_dd.span_links"] = string(spanLinkBytes)
+}
+
 // Finish closes this Span (but not its children) providing the duration
 // of its part of the tracing session.
 func (s *span) Finish(opts ...ddtrace.FinishOption) {
@@ -514,6 +543,8 @@ func (s *span) Finish(opts ...ddtrace.FinishOption) {
 		}
 	}
 
+	s.serializeSpanLinksInMeta()
+
 	s.finish(t)
 	orchestrion.GLSPopValue(sharedinternal.ActiveSpanKey)
 }

ddtrace/tracer/span_test.go

@@ -6,8 +6,10 @@
 package tracer
 
 import (
+	"encoding/json"
 	"errors"
 	"fmt"
+	"gopkg.in/DataDog/dd-trace-go.v1/ddtrace"
 	"runtime"
 	"strings"
 	"sync"
@@ -1051,6 +1053,27 @@ func BenchmarkSetTagField(b *testing.B) {
 	}
 }
 
+func BenchmarkSerializeSpanLinksInMeta(b *testing.B) {
+	span := newBasicSpan("bench.span")
+
+	span.AddSpanLink(ddtrace.SpanLink{SpanID: 123, TraceID: 456})
+	span.AddSpanLink(ddtrace.SpanLink{SpanID: 789, TraceID: 101})
+
+	// Sample span pointer
+	attributes := map[string]string{
+		"link.kind": "span-pointer",
+		"ptr.dir":   "d",
+		"ptr.hash":  "eb29cb7d923f904f02bd8b3d85e228ed",
+		"ptr.kind":  "aws.s3.object",
+	}
+	span.AddSpanLink(ddtrace.SpanLink{TraceID: 0, SpanID: 0, Attributes: attributes})
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		span.serializeSpanLinksInMeta()
+	}
+}
+
 type boomError struct{}
 
 func (e *boomError) Error() string { return "boom" }
@@ -1092,3 +1115,43 @@ func testConcurrentSpanSetTag(t *testing.T) {
 	}
 	wg.Wait()
 }
+
+func TestSpanLinksInMeta(t *testing.T) {
+	t.Run("no_links", func(t *testing.T) {
+		tracer := newTracer()
+		defer tracer.Stop()
+
+		sp := tracer.StartSpan("test-no-links")
+		sp.Finish()
+
+		internalSpan := sp.(*span)
+		_, ok := internalSpan.Meta["_dd.span_links"]
+		assert.False(t, ok, "Expected no _dd.span_links in Meta.")
+	})
+
+	t.Run("with_links", func(t *testing.T) {
+		tracer := newTracer()
+		defer tracer.Stop()
+
+		sp, ok := tracer.StartSpan("test-with-links").(SpanWithLinks)
+		require.True(t, ok, "Span does not implement SpanWithLinks interface")
+
+		sp.AddSpanLink(ddtrace.SpanLink{SpanID: 123, TraceID: 456})
+		sp.AddSpanLink(ddtrace.SpanLink{SpanID: 789, TraceID: 012})
+		sp.Finish()
+
+		internalSpan := sp.(*span)
+		raw, ok := internalSpan.Meta["_dd.span_links"]
+		require.True(t, ok, "Expected _dd.span_links in Meta after adding links.")
+
+		var links []ddtrace.SpanLink
+		err := json.Unmarshal([]byte(raw), &links)
+		require.NoError(t, err, "Failed to unmarshal links JSON")
+		require.Len(t, links, 2, "Expected 2 links in _dd.span_links JSON")
+
+		assert.Equal(t, uint64(123), links[0].SpanID)
+		assert.Equal(t, uint64(456), links[0].TraceID)
+		assert.Equal(t, uint64(789), links[1].SpanID)
+		assert.Equal(t, uint64(012), links[1].TraceID)
+	})
+}