Replaced Error with a warning in case parsing of VT_SPAN_CONTEXT fails

go/vt/vtgate/plugin_mysql_server.go

@@ -147,20 +147,25 @@ func startSpanTestable(ctx context.Context, query, label string,
 	newSpanFromString func(context.Context, string, string) (trace.Span, context.Context, error)) (trace.Span, context.Context, error) {
 	_, comments := sqlparser.SplitMarginComments(query)
 	match := r.FindStringSubmatch(comments.Leading)
+	span, ctx := getSpan(ctx, match, newSpan, label, newSpanFromString)
+
+	trace.AnnotateSQL(span, query)
+
+	return span, ctx, nil
+}
+
+func getSpan(ctx context.Context, match []string, newSpan func(context.Context, string) (trace.Span, context.Context), label string, newSpanFromString func(context.Context, string, string) (trace.Span, context.Context, error)) (trace.Span, context.Context) {
 	var span trace.Span
-	if len(match) == 0 {
-		span, ctx = newSpan(ctx, label)
-	} else {
+	if len(match) != 0 {
 		var err error
 		span, ctx, err = newSpanFromString(ctx, match[1], label)
-		if err != nil {
-			return nil, nil, err
+		if err == nil {
+			return span, ctx
 		}
+		log.Warningf("Unable to parse VT_SPAN_CONTEXT: %s", err.Error())
 	}
-
-	trace.AnnotateSQL(span, query)
-
-	return span, ctx, nil
+	span, ctx = newSpan(ctx, label)
+	return span, ctx
 }
 
 func startSpan(ctx context.Context, query, label string) (trace.Span, context.Context, error) {

go/vt/vtgate/plugin_mysql_server_test.go

@@ -17,6 +17,7 @@ limitations under the License.
 package vtgate
 
 import (
+	"fmt"
 	"io/ioutil"
 	"os"
 	"path"
@@ -170,6 +171,12 @@ func newFromStringFail(t *testing.T) func(ctx context.Context, parentSpan string
 	}
 }
 
+func newFromStringError(t *testing.T) func(ctx context.Context, parentSpan string, label string) (trace.Span, context.Context, error) {
+	return func(ctx context.Context, parentSpan string, label string) (trace.Span, context.Context, error) {
+		return trace.NoopSpan{}, context.Background(), fmt.Errorf("")
+	}
+}
+
 func newFromStringExpect(t *testing.T, expected string) func(ctx context.Context, parentSpan string, label string) (trace.Span, context.Context, error) {
 	return func(ctx context.Context, parentSpan string, label string) (trace.Span, context.Context, error) {
 		assert.Equal(t, expected, parentSpan)
@@ -206,6 +213,18 @@ func TestSpanContextPassedInEvenAroundOtherComments(t *testing.T) {
 	assert.NoError(t, err)
 }
 
+func TestSpanContextNotParsable(t *testing.T) {
+	hasRun := false
+	_, _, err := startSpanTestable(context.Background(), "/*VT_SPAN_CONTEXT=123*/SQL QUERY", "someLabel",
+		func(c context.Context, s string) (trace.Span, context.Context) {
+			hasRun = true
+			return trace.NoopSpan{}, context.Background()
+		},
+		newFromStringError(t))
+	assert.NoError(t, err)
+	assert.True(t, hasRun, "Should have continued execution despite failure to parse VT_SPAN_CONTEXT")
+}
+
 func newTestAuthServerStatic() *mysql.AuthServerStatic {
 	jsonConfig := "{\"user1\":{\"Password\":\"password1\", \"UserData\":\"userData1\", \"SourceHost\":\"localhost\"}}"
 	return mysql.NewAuthServerStatic("", jsonConfig, 0)