From 1ff2e71e7d43c652f505b0680f8550ef0c863233 Mon Sep 17 00:00:00 2001
From: Damien Mathieu <42@dmathieu.com>
Date: Mon, 15 Apr 2024 16:33:25 +0200
Subject: [PATCH] Add span flags to OTLP exported data (#5194)

* add trace flags to OTLP export

* add changelog entry

* add span flags to links too

* rely on the parent span context for span flags

* test BuildSpanFlags, not with an actual span

* Update exporters/otlp/otlptrace/internal/tracetransform/span.go

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

---------

Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>
Co-authored-by: Chester Cheung <cheung.zhy.csu@gmail.com>
---
 CHANGELOG.md                                  |  1 +
 .../otlptrace/internal/tracetransform/span.go | 13 ++++++++++
 .../internal/tracetransform/span_test.go      | 26 +++++++++++++++++++
 3 files changed, 40 insertions(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 0611a13cecc..d42a24eb9a3 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -11,6 +11,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 ### Added
 
 - Add `Recorder` in `go.opentelemetry.io/otel/log/logtest` to facilitate testing the log bridge implementations. (#5134)
+- Add span flags to OTLP spans and links exported by `go.opentelemetry.io/otel/exporters/otlp/otlptrace`. (#5194)
 
 ### Changed
 
diff --git a/exporters/otlp/otlptrace/internal/tracetransform/span.go b/exporters/otlp/otlptrace/internal/tracetransform/span.go
index e03bf46a5ad..c3c69c5a0d6 100644
--- a/exporters/otlp/otlptrace/internal/tracetransform/span.go
+++ b/exporters/otlp/otlptrace/internal/tracetransform/span.go
@@ -110,6 +110,7 @@ func span(sd tracesdk.ReadOnlySpan) *tracepb.Span {
 	if psid := sd.Parent().SpanID(); psid.IsValid() {
 		s.ParentSpanId = psid[:]
 	}
+	s.Flags = buildSpanFlags(sd.Parent())
 
 	return s
 }
@@ -146,16 +147,28 @@ func links(links []tracesdk.Link) []*tracepb.Span_Link {
 		tid := otLink.SpanContext.TraceID()
 		sid := otLink.SpanContext.SpanID()
 
+		flags := buildSpanFlags(otLink.SpanContext)
+
 		sl = append(sl, &tracepb.Span_Link{
 			TraceId:                tid[:],
 			SpanId:                 sid[:],
 			Attributes:             KeyValues(otLink.Attributes),
 			DroppedAttributesCount: uint32(otLink.DroppedAttributeCount),
+			Flags:                  flags,
 		})
 	}
 	return sl
 }
 
+func buildSpanFlags(sc trace.SpanContext) uint32 {
+	flags := tracepb.SpanFlags_SPAN_FLAGS_CONTEXT_HAS_IS_REMOTE_MASK
+	if sc.IsRemote() {
+		flags |= tracepb.SpanFlags_SPAN_FLAGS_CONTEXT_IS_REMOTE_MASK
+	}
+
+	return uint32(flags)
+}
+
 // spanEvents transforms span Events to an OTLP span events.
 func spanEvents(es []tracesdk.Event) []*tracepb.Span_Event {
 	if len(es) == 0 {
diff --git a/exporters/otlp/otlptrace/internal/tracetransform/span_test.go b/exporters/otlp/otlptrace/internal/tracetransform/span_test.go
index f22ebab7b77..ef2a87ca66a 100644
--- a/exporters/otlp/otlptrace/internal/tracetransform/span_test.go
+++ b/exporters/otlp/otlptrace/internal/tracetransform/span_test.go
@@ -122,6 +122,7 @@ func TestLinks(t *testing.T) {
 		TraceId:                []uint8{0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0},
 		SpanId:                 []uint8{0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0},
 		DroppedAttributesCount: 3,
+		Flags:                  0x100,
 	}
 	assert.Equal(t, expected, got[0])
 
@@ -166,6 +167,30 @@ func TestStatus(t *testing.T) {
 	}
 }
 
+func TestBuildSpanFlags(t *testing.T) {
+	for _, tt := range []struct {
+		name        string
+		spanContext trace.SpanContext
+		wantFlags   uint32
+	}{
+		{
+			name:      "with an empty span context",
+			wantFlags: 0x100,
+		},
+		{
+			name: "with a remote span context",
+			spanContext: trace.NewSpanContext(trace.SpanContextConfig{
+				Remote: true,
+			}),
+			wantFlags: 0x300,
+		},
+	} {
+		t.Run(tt.name, func(t *testing.T) {
+			assert.Equal(t, tt.wantFlags, buildSpanFlags(tt.spanContext))
+		})
+	}
+}
+
 func TestNilSpan(t *testing.T) {
 	assert.Nil(t, span(nil))
 }
@@ -270,6 +295,7 @@ func TestSpanData(t *testing.T) {
 		SpanId:                 []byte{0xFF, 0xFE, 0xFD, 0xFC, 0xFB, 0xFA, 0xF9, 0xF8},
 		ParentSpanId:           []byte{0xEF, 0xEE, 0xED, 0xEC, 0xEB, 0xEA, 0xE9, 0xE8},
 		TraceState:             "key1=val1,key2=val2",
+		Flags:                  0x300,
 		Name:                   spanData.Name,
 		Kind:                   tracepb.Span_SPAN_KIND_SERVER,
 		StartTimeUnixNano:      uint64(startTime.UnixNano()),