GODRIVER-1962 unwrap errors in WithTransaction (mongodb#634)

Author: iwysiu

mongo/errors.go

@@ -127,16 +127,21 @@ func unwrap(err error) error {
 	return u.Unwrap()
 }
 
-// IsNetworkError returns true if err is a network error
-func IsNetworkError(err error) bool {
+// errorHasLabel returns true if err contains the specified label
+func errorHasLabel(err error, label string) bool {
 	for ; err != nil; err = unwrap(err) {
 		if e, ok := err.(ServerError); ok {
-			return e.HasErrorLabel("NetworkError")
+			return e.HasErrorLabel(label)
 		}
 	}
 	return false
 }
 
+// IsNetworkError returns true if err is a network error
+func IsNetworkError(err error) bool {
+	return errorHasLabel(err, "NetworkError")
+}
+
 // MongocryptError represents an libmongocrypt error during client-side encryption.
 type MongocryptError struct {
 	Code    int32

mongo/session.go

@@ -193,10 +193,8 @@ func (s *sessionImpl) WithTransaction(ctx context.Context, fn func(sessCtx Sessi
 			default:
 			}
 
-			if cerr, ok := err.(CommandError); ok {
-				if cerr.HasErrorLabel(driver.TransientTransactionError) {
-					continue
-				}
+			if errorHasLabel(err, driver.TransientTransactionError) {
+				continue
 			}
 			return res, err
 		}

mongo/with_transactions_test.go

@@ -35,6 +35,18 @@ var (
 	withTxnFailedEvents    []*event.CommandFailedEvent
 )
 
+type wrappedError struct {
+	err error
+}
+
+func (we wrappedError) Error() string {
+	return we.err.Error()
+}
+
+func (we wrappedError) Unwrap() error {
+	return we.err
+}
+
 func TestConvenientTransactions(t *testing.T) {
 	client := setupConvenientTransactions(t)
 	db := client.Database("TestConvenientTransactions")
@@ -381,6 +393,30 @@ func TestConvenientTransactions(t *testing.T) {
 		// Assert that transaction is canceled within 500ms and not 2 seconds.
 		assert.Soon(t, callback, 500*time.Millisecond)
 	})
+	t.Run("wrapped transient transaction error retried", func(t *testing.T) {
+		sess, err := client.StartSession()
+		assert.Nil(t, err, "StartSession error: %v", err)
+		defer sess.EndSession(context.Background())
+
+		// returnError tracks whether or not the callback is being retried
+		returnError := true
+		res, err := sess.WithTransaction(context.Background(), func(sessCtx SessionContext) (interface{}, error) {
+			if returnError {
+				returnError = false
+				return nil, wrappedError{
+					CommandError{
+						Name:   "test Error",
+						Labels: []string{driver.TransientTransactionError},
+					},
+				}
+			}
+			return false, nil
+		})
+		assert.Nil(t, err, "WithTransaction error: %v", err)
+		resBool, ok := res.(bool)
+		assert.True(t, ok, "expected result type %T, got %T", false, res)
+		assert.False(t, resBool, "expected result false, got %v", resBool)
+	})
 }
 
 func setupConvenientTransactions(t *testing.T, extraClientOpts ...*options.ClientOptions) *Client {