From 0462924d538179978007d967821fb241431d4423 Mon Sep 17 00:00:00 2001
From: Munir Abdinur <munir.abdinur@datadoghq.com>
Date: Thu, 8 Aug 2024 11:16:28 -0400
Subject: [PATCH] chore(w3c): ensure last parent id is never set to 16 zeros
 (#2808)

---
 ddtrace/tracer/textmap.go      |  8 ++------
 ddtrace/tracer/textmap_test.go | 10 ++++++++--
 2 files changed, 10 insertions(+), 8 deletions(-)

diff --git a/ddtrace/tracer/textmap.go b/ddtrace/tracer/textmap.go
index cd9b7860f8..1fee0ba689 100644
--- a/ddtrace/tracer/textmap.go
+++ b/ddtrace/tracer/textmap.go
@@ -507,7 +507,7 @@ func getDatadogPropagator(cp *chainedPropagator) *propagator {
 // if the reparenting ID is not set on the context, the span ID from datadog headers is used.
 func overrideDatadogParentID(ctx, w3cCtx, ddCtx *spanContext) {
 	ctx.spanID = w3cCtx.spanID
-	if w3cCtx.reparentID != "" && w3cCtx.reparentID != "0000000000000000" {
+	if w3cCtx.reparentID != "" {
 		ctx.reparentID = w3cCtx.reparentID
 	} else if ddCtx != nil {
 		// NIT: could be done without using fmt.Sprintf? Is it worth it?
@@ -967,7 +967,7 @@ func composeTracestate(ctx *spanContext, priority int, oldState string) string {
 	if !ctx.isRemote {
 		b.WriteString(";p:")
 		b.WriteString(spanIDHexEncoded(ctx.SpanID(), 16))
-	} else if ctx.reparentID != "" && ctx.reparentID != "0000000000000000" {
+	} else if ctx.reparentID != "" {
 		b.WriteString(";p:")
 		b.WriteString(ctx.reparentID)
 	}
@@ -1202,10 +1202,6 @@ func parseTracestate(ctx *spanContext, header string) {
 				setPropagatingTag(ctx, "_dd.p."+keySuffix, val)
 			}
 		}
-		// if dd list-member is present and last parent is not set, set it to zeros
-		if ctx.reparentID == "" {
-			ctx.reparentID = "0000000000000000"
-		}
 	}
 }
 
diff --git a/ddtrace/tracer/textmap_test.go b/ddtrace/tracer/textmap_test.go
index 6147821fcf..9575ac226d 100644
--- a/ddtrace/tracer/textmap_test.go
+++ b/ddtrace/tracer/textmap_test.go
@@ -1756,7 +1756,7 @@ func TestEnvVars(t *testing.T) {
 					},
 					out:        []uint64{8687463697196027922, 1311768467284833366},
 					priority:   1,
-					lastParent: "0000000000000000",
+					lastParent: "",
 				},
 			}
 			for i, tc := range tests {
@@ -1839,7 +1839,13 @@ func TestEnvVars(t *testing.T) {
 					if tc.priority != 0 {
 						sctx.setSamplingPriority(int(tc.priority), samplernames.Unknown)
 					}
-					assert.Equal(s.(*span).Meta["_dd.parent_id"], tc.lastParent)
+
+					if tc.lastParent == "" {
+						assert.Empty(s.(*span).Meta["_dd.parent_id"])
+					} else {
+						assert.Equal(s.(*span).Meta["_dd.parent_id"], tc.lastParent)
+					}
+
 					assert.Equal(true, sctx.updated)
 
 					headers := TextMapCarrier(map[string]string{})