From c0329fac3b8e794643e40c0151893f88b18c6076 Mon Sep 17 00:00:00 2001
From: Alan Novitskiy <anovitskiy@shipt.com>
Date: Wed, 25 Mar 2020 14:00:44 -0700
Subject: [PATCH] update http propagation to handle SpanID as a 16-character
 hexadecimal encoding of an 8-byte array

---
 propagation/http.go      | 16 +++++++---------
 propagation/http_test.go | 16 +++++++++++-----
 2 files changed, 18 insertions(+), 14 deletions(-)

diff --git a/propagation/http.go b/propagation/http.go
index 1797d37..317f5f5 100644
--- a/propagation/http.go
+++ b/propagation/http.go
@@ -17,7 +17,6 @@
 package propagation // import "contrib.go.opencensus.io/exporter/stackdriver/propagation"
 
 import (
-	"encoding/binary"
 	"encoding/hex"
 	"fmt"
 	"net/http"
@@ -56,23 +55,23 @@ func (f *HTTPFormat) SpanContextFromRequest(req *http.Request) (sc trace.SpanCon
 	}
 	tid, h := h[:slash], h[slash+1:]
 
-	buf, err := hex.DecodeString(tid)
+	tidBuf, err := hex.DecodeString(tid)
 	if err != nil {
 		return trace.SpanContext{}, false
 	}
-	copy(sc.TraceID[:], buf)
+	copy(sc.TraceID[:], tidBuf)
 
 	// Parse the span id field.
-	spanstr := h
+	sid := h
 	semicolon := strings.Index(h, `;`)
 	if semicolon != -1 {
-		spanstr, h = h[:semicolon], h[semicolon+1:]
+		sid, h = h[:semicolon], h[semicolon+1:]
 	}
-	sid, err := strconv.ParseUint(spanstr, 10, 64)
+	sidBuf, err := hex.DecodeString(sid)
 	if err != nil {
 		return trace.SpanContext{}, false
 	}
-	binary.BigEndian.PutUint64(sc.SpanID[:], sid)
+	copy(sc.SpanID[:], sidBuf)
 
 	// Parse the options field, options field is optional.
 	if !strings.HasPrefix(h, "o=") {
@@ -88,7 +87,6 @@ func (f *HTTPFormat) SpanContextFromRequest(req *http.Request) (sc trace.SpanCon
 
 // SpanContextToRequest modifies the given request to include a Stackdriver Trace header.
 func (f *HTTPFormat) SpanContextToRequest(sc trace.SpanContext, req *http.Request) {
-	sid := binary.BigEndian.Uint64(sc.SpanID[:])
-	header := fmt.Sprintf("%s/%d;o=%d", hex.EncodeToString(sc.TraceID[:]), sid, int64(sc.TraceOptions))
+	header := fmt.Sprintf("%s/%s;o=%d", hex.EncodeToString(sc.TraceID[:]), hex.EncodeToString(sc.SpanID[:]), int64(sc.TraceOptions))
 	req.Header.Set(httpHeader, header)
 }
diff --git a/propagation/http_test.go b/propagation/http_test.go
index 9ad93b7..f8d0aa1 100644
--- a/propagation/http_test.go
+++ b/propagation/http_test.go
@@ -15,6 +15,7 @@
 package propagation
 
 import (
+	"encoding/hex"
 	"net/http"
 	"reflect"
 	"testing"
@@ -24,15 +25,20 @@ import (
 
 func TestHTTPFormat(t *testing.T) {
 	format := &HTTPFormat{}
-	traceID := [16]byte{16, 84, 69, 170, 120, 67, 188, 139, 242, 6, 177, 32, 0, 16, 0, 0}
-	spanID1 := [8]byte{255, 0, 0, 0, 0, 0, 0, 123}
-	spanID2 := [8]byte{0, 0, 0, 0, 0, 0, 0, 123}
+	var traceID [16]byte
+	var spanID1, spanID2 [8]byte
+	traceBuf, _ := hex.DecodeString("105445aa7843bc8bf206b12000100000")
+	spanBuf1, _ := hex.DecodeString("1234567890abcdef")
+	spanBuf2, _ := hex.DecodeString("1234567812345678")
+	copy(traceID[:], traceBuf)
+	copy(spanID1[:], spanBuf1)
+	copy(spanID2[:], spanBuf2)
 	tests := []struct {
 		incoming        string
 		wantSpanContext trace.SpanContext
 	}{
 		{
-			incoming: "105445aa7843bc8bf206b12000100000/18374686479671623803;o=1",
+			incoming: "105445aa7843bc8bf206b12000100000/1234567890abcdef;o=1",
 			wantSpanContext: trace.SpanContext{
 				TraceID:      traceID,
 				SpanID:       spanID1,
@@ -40,7 +46,7 @@ func TestHTTPFormat(t *testing.T) {
 			},
 		},
 		{
-			incoming: "105445aa7843bc8bf206b12000100000/123;o=0",
+			incoming: "105445aa7843bc8bf206b12000100000/1234567812345678;o=0",
 			wantSpanContext: trace.SpanContext{
 				TraceID:      traceID,
 				SpanID:       spanID2,