From 0a9b2e0d8ccc009e3119c34f4d68a6e33442df05 Mon Sep 17 00:00:00 2001
From: Anthony Mirabella <a9@aneurysm9.com>
Date: Tue, 5 May 2020 14:20:09 -0400
Subject: [PATCH] left-pad 64-bit B3 trace IDs (#698)

---
 api/trace/b3_propagator.go                    | 13 +++++++---
 .../testtrace/b3_propagator_data_test.go      | 25 +++++++++++++++++++
 2 files changed, 35 insertions(+), 3 deletions(-)

diff --git a/api/trace/b3_propagator.go b/api/trace/b3_propagator.go
index fe78f8727..269daa643 100644
--- a/api/trace/b3_propagator.go
+++ b/api/trace/b3_propagator.go
@@ -31,7 +31,7 @@ const (
 	B3ParentSpanIDHeader = "X-B3-ParentSpanId"
 )
 
-// B3 propagator serializes core.SpanContext to/from B3 Headers.
+// B3 propagator serializes SpanContext to/from B3 Headers.
 // This propagator supports both version of B3 headers,
 //  1. Single Header :
 //    X-B3: {TraceId}-{SpanId}-{SamplingState}-{ParentSpanId}
@@ -87,8 +87,15 @@ func (b3 B3) Extract(ctx context.Context, supplier propagation.HTTPSupplier) con
 	return ContextWithRemoteSpanContext(ctx, sc)
 }
 
+func fixB3TID(in string) string {
+	if len(in) == 16 {
+		in = strings.Repeat("0", 16) + in
+	}
+	return in
+}
+
 func (b3 B3) extract(supplier propagation.HTTPSupplier) SpanContext {
-	tid, err := IDFromHex(supplier.Get(B3TraceIDHeader))
+	tid, err := IDFromHex(fixB3TID(supplier.Get(B3TraceIDHeader)))
 	if err != nil {
 		return EmptySpanContext()
 	}
@@ -139,7 +146,7 @@ func (b3 B3) extractSingleHeader(supplier propagation.HTTPSupplier) SpanContext
 	}
 
 	var err error
-	sc.TraceID, err = IDFromHex(parts[0])
+	sc.TraceID, err = IDFromHex(fixB3TID(parts[0]))
 	if err != nil {
 		return EmptySpanContext()
 	}
diff --git a/api/trace/testtrace/b3_propagator_data_test.go b/api/trace/testtrace/b3_propagator_data_test.go
index 6cb4a092c..432ce4995 100644
--- a/api/trace/testtrace/b3_propagator_data_test.go
+++ b/api/trace/testtrace/b3_propagator_data_test.go
@@ -24,6 +24,10 @@ type extractTest struct {
 	wantSc  trace.SpanContext
 }
 
+var (
+	traceID64bitPadded = mustTraceIDFromHex("0000000000000000a3ce929d0e0e4736")
+)
+
 var extractMultipleHeaders = []extractTest{
 	{
 		name: "sampling state defer",
@@ -125,6 +129,17 @@ var extractMultipleHeaders = []extractTest{
 		},
 		wantSc: trace.EmptySpanContext(),
 	},
+	{
+		name: "left-padding 64-bit traceID",
+		headers: map[string]string{
+			trace.B3TraceIDHeader: "a3ce929d0e0e4736",
+			trace.B3SpanIDHeader:  "00f067aa0ba902b7",
+		},
+		wantSc: trace.SpanContext{
+			TraceID: traceID64bitPadded,
+			SpanID:  spanID,
+		},
+	},
 }
 
 var extractSingleHeader = []extractTest{
@@ -188,6 +203,16 @@ var extractSingleHeader = []extractTest{
 		},
 		wantSc: trace.EmptySpanContext(),
 	},
+	{
+		name: "left-padding 64-bit traceID",
+		headers: map[string]string{
+			trace.B3SingleHeader: "a3ce929d0e0e4736-00f067aa0ba902b7",
+		},
+		wantSc: trace.SpanContext{
+			TraceID: traceID64bitPadded,
+			SpanID:  spanID,
+		},
+	},
 }
 
 var extractInvalidB3MultipleHeaders = []extractTest{