preparing for extracted span links PR

ddtrace/ddtrace.go

@@ -33,6 +33,18 @@ type SpanContextW3C interface {
 	TraceID128Bytes() [16]byte
 }
 
+// SpanContextWithLinks represents a SpanContext with additional methods for
+// access to the SpanLinks on the span context, if present.
+type SpanContextWithLinks interface {
+	SpanContext
+
+	// SpanLinks returns the span links on the SpanContext.
+	SpanLinks() []SpanLink
+
+	// Setlinks takes in a slice of SpanLinks and sets them to the SpanContext.
+	SetLinks(links []SpanLink)
+}
+
 // Tracer specifies an implementation of the Datadog tracer which allows starting
 // and propagating spans. The official implementation if exposed as functions
 // within the "tracer" package.

ddtrace/tracer/spancontext.go

@@ -111,6 +111,8 @@ type spanContext struct {
 	baggage    map[string]string
 	hasBaggage uint32 // atomic int for quick checking presence of baggage. 0 indicates no baggage, otherwise baggage exists.
 	origin     string // e.g. "synthetics"
+
+	spanLinks []ddtrace.SpanLink // links to related spans in separate|external|disconnected traces
 }
 
 // newSpanContext creates a new SpanContext to serve as context for the given
@@ -166,6 +168,8 @@ func (c *spanContext) SpanID() uint64 { return c.spanID }
 // TraceID implements ddtrace.SpanContext.
 func (c *spanContext) TraceID() uint64 { return c.traceID.Lower() }
 
+func (c *spanContext) TraceIDUpper() uint64 { return c.traceID.Upper() }
+
 // TraceID128 implements ddtrace.SpanContextW3C.
 func (c *spanContext) TraceID128() string {
 	if c == nil {
@@ -179,6 +183,14 @@ func (c *spanContext) TraceID128Bytes() [16]byte {
 	return c.traceID
 }
 
+func (c *spanContext) SpanLinks() []ddtrace.SpanLink {
+	return c.spanLinks
+}
+
+func (c *spanContext) SetLinks(links []ddtrace.SpanLink) {
+	c.spanLinks = links
+}
+
 // ForeachBaggageItem implements ddtrace.SpanContext.
 func (c *spanContext) ForeachBaggageItem(handler func(k, v string) bool) {
 	if atomic.LoadUint32(&c.hasBaggage) == 0 {