spreadsheet: add validation for sheet name length

spreadsheet/sheet.go

@@ -105,6 +105,7 @@ func (s Sheet) SetName(name string) {
 // Validate validates the sheet, returning an error if it is found to be invalid.
 func (s Sheet) Validate() error {
 
+	// check for re-used row numbers
 	usedRows := map[uint32]struct{}{}
 	for _, r := range s.x.SheetData.Row {
 		if r.RAttr != nil {
@@ -113,6 +114,7 @@ func (s Sheet) Validate() error {
 			}
 			usedRows[*r.RAttr] = struct{}{}
 		}
+		// or re-used column labels within a row
 		usedCells := map[string]struct{}{}
 		for _, c := range r.C {
 			if c.RAttr == nil {
@@ -125,6 +127,10 @@ func (s Sheet) Validate() error {
 			usedCells[*c.RAttr] = struct{}{}
 		}
 	}
+
+	if len(s.Name()) > 31 {
+		return fmt.Errorf("sheet name '%s' has %d characters, max length is 31", s.Name(), len(s.Name()))
+	}
 	if err := s.cts.Validate(); err != nil {
 		return err
 	}

spreadsheet/sheet_test.go

@@ -119,5 +119,16 @@ func TestAutoFilter(t *testing.T) {
 	if sheet.X().AutoFilter != nil {
 		t.Errorf("autofilter should have been nil after clear")
 	}
-
+}
+
+func TestSheetNameLength(t *testing.T) {
+	wb := spreadsheet.New()
+	sheet := wb.AddSheet()
+	if err := sheet.Validate(); err != nil {
+		t.Errorf("expected no validaton error on new sheet, got %s:", err)
+	}
+	sheet.SetName("01234567890123456789012345678901")
+	if err := sheet.Validate(); err == nil {
+		t.Errorf("expected validation error with sheet name too long")
+	}
 }