XLSX generation: Remove invalid unicode characters

src/pretix/helpers/safe_openpyxl.py

@@ -24,8 +24,7 @@ from inspect import isgenerator
 
 from openpyxl import Workbook
 from openpyxl.cell.cell import (
-    ILLEGAL_CHARACTERS_RE, KNOWN_TYPES, TIME_TYPES, TYPE_FORMULA, TYPE_STRING,
-    Cell,
+    KNOWN_TYPES, TIME_TYPES, TYPE_FORMULA, TYPE_STRING, Cell,
 )
 from openpyxl.compat import NUMERIC_TYPES
 from openpyxl.utils import column_index_from_string
@@ -49,6 +48,12 @@ There are mainly two problems this solves:
 - It removes characters considered invalid by Excel to avoid exporter crashes.
 """
 
+ILLEGAL_CHARACTERS_RE = re.compile(
+    # From the XML specification
+    # Char ::= #x9 | #xA | #xD | [#x20-#xD7FF] | [#xE000-#xFFFD] | [#x10000-#x10FFFF]
+    r'[^\u0020-\uD7FF\u0009\u000A\u000D\uE000-\uFFFD\U00010000-\U0010FFFF]'
+)
+
 
 def remove_invalid_excel_chars(val):
     if isinstance(val, Cell):

src/tests/helpers/test_safe_openpyxl.py

@@ -24,11 +24,13 @@ from openpyxl.cell.cell import TYPE_STRING
 from pretix.helpers.safe_openpyxl import SafeWorkbook
 
 
-def test_nullbyte_removed():
+def test_invalid_byte_removed():
     wb = SafeWorkbook()
     ws = wb.create_sheet()
     ws.append(["foo\u0000bar"])
     assert ws.cell(1, 1).value == "foobar"
+    ws.append(["foo\uffffbaz"])
+    assert ws.cell(2, 1).value == "foobaz"
 
 
 def test_no_formulas():