Span links improvements and bug fix

ddtrace/ddtrace.go

@@ -79,6 +79,9 @@ type Span interface {
 	// item should propagate to all descendant spans, both in- and cross-process.
 	SetBaggageItem(key, val string)
 
+	// AddSpanLinks appends the given links to the span's span links.
+	AddSpanLinks(spanLinks ...SpanLink)
+
 	// Finish finishes the current span with the given options. Finish calls should be idempotent.
 	Finish(opts ...FinishOption)
 
@@ -103,25 +106,6 @@ 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/internal/globaltracer.go

@@ -80,6 +80,9 @@ func (NoopSpan) BaggageItem(_ string) string { return "" }
 // SetBaggageItem implements ddtrace.Span.
 func (NoopSpan) SetBaggageItem(_, _ string) {}
 
+// AddSpanLinks implements ddtrace.Span.
+func (s NoopSpan) AddSpanLinks(_ ...ddtrace.SpanLink) {}
+
 // Finish implements ddtrace.Span.
 func (NoopSpan) Finish(_ ...ddtrace.FinishOption) {}
 

ddtrace/mocktracer/mockspan.go

@@ -188,6 +188,11 @@ func (s *mockspan) SetBaggageItem(key, val string) {
 	return
 }
 
+// AddSpanLinks appends the given links to the span's span links.
+func (s *mockspan) AddSpanLinks(spanLinks ...ddtrace.SpanLink) {
+	s.links = append(s.links, spanLinks...)
+}
+
 // Finish finishes the current span with the given options.
 func (s *mockspan) Finish(opts ...ddtrace.FinishOption) {
 	var cfg ddtrace.FinishConfig

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/civisibility_tslv.go

@@ -200,6 +200,15 @@ func (e *ciVisibilityEvent) SetBaggageItem(key, val string) {
 	e.span.SetBaggageItem(key, val)
 }
 
+// AddSpanLinks appends the given links to the span's span links.
+//
+// Parameters:
+//
+// spanLinks - list of span links to append.
+func (e *ciVisibilityEvent) AddSpanLinks(spanLinks ...ddtrace.SpanLink) {
+	e.span.SpanLinks = append(e.span.SpanLinks, spanLinks...)
+}
+
 // Finish completes the event's span with optional finish options.
 //
 // Parameters:

ddtrace/tracer/span.go

@@ -10,6 +10,7 @@ package tracer
 import (
 	"context"
 	"encoding/base64"
+	"encoding/json"
 	"fmt"
 	"os"
 	"reflect"
@@ -464,6 +465,26 @@ func (s *span) setMetric(key string, v float64) {
 	}
 }
 
+// AddSpanLinks appends the given links to the span's span links.
+func (s *span) AddSpanLinks(spanLinks ...ddtrace.SpanLink) {
+	s.SpanLinks = append(s.SpanLinks, spanLinks...)
+}
+
+// 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 {
+		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 +535,8 @@ func (s *span) Finish(opts ...ddtrace.FinishOption) {
 		}
 	}
 
+	s.serializeSpanLinksInMeta()
+
 	s.finish(t)
 	orchestrion.GLSPopValue(sharedinternal.ActiveSpanKey)
 }

ddtrace/tracer/tracer.go

@@ -573,7 +573,7 @@ func (t *tracer) StartSpan(operationName string, options ...ddtrace.StartSpanOpt
 		noDebugStack: t.config.noDebugStack,
 	}
 
-	span.SpanLinks = append(span.SpanLinks, opts.SpanLinks...)
+	span.AddSpanLinks(opts.SpanLinks...)
 
 	if t.config.hostname != "" {
 		span.setMeta(keyHostname, t.config.hostname)