Add max error length

CHANGES.rst

@@ -6,7 +6,10 @@ Changelog
 
 Minor changes:
 
-- ...
+- Calendar.from_ical no longer throws long errors
+  Ref: #473
+  Fixes: #472
+  [jacadzaca]
 
 Breaking changes:
 

src/icalendar/cal.py

@@ -390,14 +390,22 @@ def from_ical(cls, st, multiple=False):
         if multiple:
             return comps
         if len(comps) > 1:
-            raise ValueError(f'Found multiple components where '
-                             f'only one is allowed: {st!r}')
+            raise ValueError(cls._format_error(
+                'Found multiple components where only one is allowed', st))
         if len(comps) < 1:
-            raise ValueError(f'Found no components where '
-                             f'exactly one is required: '
-                             f'{st!r}')
+            raise ValueError(cls._format_error(
+                'Found no components where exactly one is required', st))
         return comps[0]
 
+    def _format_error(error_description, bad_input, elipsis='[...]'):
+        # there's three character more in the error, ie. ' ' x2 and a ':'
+        max_error_length = 100 - 3
+        if len(error_description) + len(bad_input) + len(elipsis) > max_error_length:
+            truncate_to = max_error_length - len(error_description) - len(elipsis)
+            return f'{error_description}: {bad_input[:truncate_to]} {elipsis}'
+        else:
+            return f'{error_description}: {bad_input}'
+
     def content_line(self, name, value, sorted=True):
         """Returns property as content line.
         """

src/icalendar/tests/calendars/big_bad_calendar.ics

@@ -0,0 +1,41 @@
+BEGIN:VCALENDAR
+BEGIN:VEVENT
+END:VEVENT
+BEGIN:VEVENT
+END:VEVENT
+BEGIN:VEVENT
+END:VEVENT
+BEGIN:VEVENT
+END:VEVENT
+BEGIN:VEVENT
+END:VEVENT
+BEGIN:VEVENT
+END:VEVENT
+BEGIN:VEVENT
+END:VEVENT
+BEGIN:VEVENT
+END:VEVENT
+BEGIN:VEVENT
+END:VEVENT
+BEGIN:VEVENT
+END:VEVENT
+BEGIN:VEVENT
+END:VEVENT
+BEGIN:VEVENT
+END:VEVENT
+BEGIN:VEVENT
+END:VEVENT
+BEGIN:VEVENT
+END:VEVENT
+BEGIN:VEVENT
+END:VEVENT
+BEGIN:VEVENT
+END:VEVENT
+BEGIN:VEVENT
+END:VEVENT
+BEGIN:VEVENT
+END:VEVENT
+BEGIN:VEVENT
+END:VEVENT
+BEGIN:VEVENT
+END:VEVENT

src/icalendar/tests/calendars/small_bad_calendar.ics

@@ -0,0 +1,3 @@
+BEGIN:VCALENDAR
+BEGIN:VEVENT
+END:VEVENT

src/icalendar/tests/test_components_break_on_bad_ics.py

@@ -26,3 +26,14 @@ def test_rdate_dosent_become_none_on_invalid_input_issue_464(events):
     assert events.issue_464_invalid_rdate.is_broken
     assert ('RDATE', 'Expected period format, got: 199709T180000Z/PT5H30M') in events.issue_464_invalid_rdate.errors
     assert not b'RDATE:None' in events.issue_464_invalid_rdate.to_ical()
+
+@pytest.mark.parametrize('calendar_name', [
+    'big_bad_calendar',
+    'small_bad_calendar',
+    'multiple_calendar_components',
+])
+def test_error_message_doesnt_get_too_big(calendars, calendar_name):
+    with pytest.raises(ValueError) as exception:
+        calendars[calendar_name]
+    assert len(str(exception).split(': ')[1]) <= 100
+