Fix bug with parsing labels from baggage

Previously we would still try set profiler labels even if incoming
baggage had no k6 metadata. This skips setting profiler labels with no
k6 metadata.

x/k6/baggage.go

@@ -114,12 +114,11 @@ func getBaggageLabelsFromContext(ctx context.Context) *pyroscope.LabelSet {
 		return nil
 	}
 
-	labels := baggageToLabels(b)
-	return &labels
+	return baggageToLabels(b)
 }
 
 // baggageToLabels converts request baggage to a LabelSet.
-func baggageToLabels(b baggage.Baggage) pyroscope.LabelSet {
+func baggageToLabels(b baggage.Baggage) *pyroscope.LabelSet {
 	labelPairs := make([]string, 0, len(b.Members())*2)
 	for _, m := range b.Members() {
 		if !strings.HasPrefix(m.Key(), "k6.") {
@@ -134,5 +133,10 @@ func baggageToLabels(b baggage.Baggage) pyroscope.LabelSet {
 		labelPairs = append(labelPairs, key, m.Value())
 	}
 
-	return pyroscope.Labels(labelPairs...)
+	if len(labelPairs) == 0 {
+		return nil
+	}
+
+	labels := pyroscope.Labels(labelPairs...)
+	return &labels
 }

x/k6/baggage_test.go

@@ -131,6 +131,41 @@ func Test_getBaggageLabels(t *testing.T) {
 	})
 }
 
+func Test_baggageToLabels(t *testing.T) {
+	t.Run("with_k6_baggage", func(t *testing.T) {
+		b := testMustNewBaggage(t,
+			"k6.test_run_id", "123",
+			"not_k6.some_other_key", "value",
+		)
+
+		labelSet := baggageToLabels(b)
+		require.NotNil(t, labelSet)
+
+		gotLabels := testPprofLabelsToMap(t, *labelSet)
+		expectedLabels := map[string]string{
+			"k6_test_run_id": "123",
+		}
+
+		require.Equal(t, expectedLabels, gotLabels)
+	})
+
+	t.Run("with_empty_baggage", func(t *testing.T) {
+		b := testMustNewBaggage(t)
+
+		labelSet := baggageToLabels(b)
+		require.Nil(t, labelSet)
+	})
+
+	t.Run("with_no_k6_baggage", func(t *testing.T) {
+		b := testMustNewBaggage(t,
+			"not_k6.some_other_key", "value",
+		)
+
+		labelSet := baggageToLabels(b)
+		require.Nil(t, labelSet)
+	})
+}
+
 func testAddBaggageToRequest(t *testing.T, req *http.Request, kvPairs ...string) *http.Request {
 	t.Helper()
 
@@ -157,6 +192,24 @@ func testAddBaggageToRequest(t *testing.T, req *http.Request, kvPairs ...string)
 	return req
 }
 
+func testMustNewBaggage(t *testing.T, kvPairs ...string) baggage.Baggage {
+	t.Helper()
+
+	require.Equal(t, 0, len(kvPairs)%2, "kvPairs must be a multiple of 2")
+
+	members := make([]baggage.Member, 0, len(kvPairs)/2)
+	for i := 0; i < len(kvPairs); i += 2 {
+		key := kvPairs[i]
+		value := kvPairs[i+1]
+		members = append(members, testMustNewMember(t, key, value))
+	}
+
+	b, err := baggage.New(members...)
+	require.NoError(t, err)
+
+	return b
+}
+
 func testMustNewMember(t *testing.T, key string, value string) baggage.Member {
 	t.Helper()