add a post-processing script to make our ICS files RFC 5545 compliant

fkr · fkr · commit 5a4b56bf6493 · 2025-12-21T22:31:43.000+01:00
Apparently there is a minor bug in yaml2ics (or somewhere lower), that
causes our ICS files to not be RFC 5545 compliant in regards to the
RRULE. Until this is fixed in yaml2ics, a post-processing script on
our side can mitigate that.

Signed-off-by: Felix Kronlage-Dammers &lt;fkr@hazardous.org&gt;
diff --git a/.github/workflows/test-yaml.yml b/.github/workflows/test-yaml.yml
@@ -27,5 +27,8 @@ jobs:
       run: |
         mkdir ./calendar
         yaml2ics main.yml > ./calendar/scs.ics
+        python fix_ics_rrule.py ./calendar/scs.ics
         yaml2ics openops.yml > ./calendar/openops.ics
+        python fix_ics_rrule.py ./calendar/openops.ics
         yaml2ics sig_standard_cert.yml > ./calendar/sig_standard_cert.ics
+        python fix_ics_rrule.py ./calendar/sig_standard_cert.ics
diff --git a/.github/workflows/yaml2ics.yml b/.github/workflows/yaml2ics.yml
@@ -28,8 +28,11 @@ jobs:
       run: |
         mkdir ./calendar
         yaml2ics main.yml > ./calendar/scs.ics
+        python fix_ics_rrule.py ./calendar/scs.ics
         yaml2ics openops.yml > ./calendar/openops.ics
+        python fix_ics_rrule.py ./calendar/openops.ics
         yaml2ics sig_standard_cert.yml > ./calendar/sig_standard_cert.ics
+        python fix_ics_rrule.py ./calendar/sig_standard_cert.ics
     - name: Deploy
       uses: peaceiris/actions-gh-pages@v3
       with:
diff --git a/fix_ics_rrule.py b/fix_ics_rrule.py
@@ -0,0 +1,266 @@
+#!/usr/bin/env python3
+"""
+Fix RRULE UNTIL values in ICS files to be RFC 5545 compliant.
+
+According to RFC 5545 Section 3.3.10:
+"If the DTSTART property is specified as a date with UTC time or a date 
+with local time and time zone reference, then the UNTIL rule part MUST 
+be specified as a date with UTC time."
+
+This script ensures that RRULE UNTIL values include the 'Z' suffix when
+DTSTART uses a TZID parameter.
+
+Usage:
+    python fix_ics_rrule.py input.ics [output.ics]
+    
+If output.ics is not specified, it will overwrite the input file.
+"""
+
+import re
+import sys
+from datetime import datetime
+from pathlib import Path
+
+
+def extract_timezone_from_dtstart(dtstart_line):
+    """
+    Extract timezone information from a DTSTART line.
+    
+    Handles various formats including:
+    - DTSTART;TZID=Europe/Berlin:20250221T090500
+    - DTSTART;TZID=/ics.py/2020.1/Europe/Berlin:20250221T090500
+    
+    Returns:
+        tuple: (timezone_name, is_utc) where is_utc indicates if DTSTART is already in UTC
+    """
+    # Check if DTSTART is in UTC format (ends with Z)
+    if dtstart_line.endswith('Z'):
+        return None, True
+    
+    # Check if DTSTART has no timezone (floating time)
+    if 'TZID=' not in dtstart_line:
+        return None, False
+    
+    # Extract TZID value
+    tzid_match = re.search(r'TZID=([^:;]+)', dtstart_line)
+    if not tzid_match:
+        return None, False
+    
+    tzid = tzid_match.group(1)
+    
+    # Handle /ics.py/version/Timezone/Name format
+    # Extract the actual timezone (last two path components for standard timezones)
+    if '/' in tzid:
+        parts = tzid.split('/')
+        # Filter out empty parts and 'ics.py' and version numbers
+        clean_parts = [p for p in parts if p and p != 'ics.py' and not re.match(r'^\d{4}\.\d+$', p)]
+        
+        # Reconstruct timezone name (usually last 1-2 components)
+        if len(clean_parts) >= 2:
+            # Most timezones are Continent/City format
+            tzid = '/'.join(clean_parts[-2:])
+        elif len(clean_parts) == 1:
+            tzid = clean_parts[0]
+    
+    return tzid, False
+
+
+def convert_local_to_utc(datetime_str, timezone_name):
+    """
+    Convert a local datetime string to UTC.
+    
+    Args:
+        datetime_str: String in format YYYYMMDDTHHMMSS
+        timezone_name: IANA timezone name (e.g., 'Europe/Berlin')
+    
+    Returns:
+        String in format YYYYMMDDTHHMMSSZ (UTC)
+    """
+    try:
+        import pytz
+        
+        # Parse the datetime string
+        dt = datetime.strptime(datetime_str, '%Y%m%dT%H%M%S')
+        
+        # Get timezone
+        tz = pytz.timezone(timezone_name)
+        
+        # Localize to the timezone (handles DST properly)
+        dt_local = tz.localize(dt)
+        
+        # Convert to UTC
+        dt_utc = dt_local.astimezone(pytz.UTC)
+        
+        # Format back to string with Z suffix
+        return dt_utc.strftime('%Y%m%dT%H%M%SZ')
+    
+    except Exception as e:
+        print(f"Warning: Could not convert {datetime_str} in timezone {timezone_name} to UTC: {e}", 
+              file=sys.stderr)
+        print(f"         Appending 'Z' without conversion (may be incorrect!)", file=sys.stderr)
+        # Fallback: just append Z (not ideal but maintains format)
+        return datetime_str + 'Z'
+
+
+def fix_until_in_rrule(rrule_line, timezone_name, dtstart_is_utc):
+    """
+    Fix UNTIL values in an RRULE line to be RFC 5545 compliant.
+    
+    Args:
+        rrule_line: The RRULE line to fix
+        timezone_name: The timezone of the associated DTSTART
+        dtstart_is_utc: Whether DTSTART is already in UTC
+    
+    Returns:
+        Fixed RRULE line
+    """
+    # If DTSTART is not timezone-aware (floating time), no fix needed
+    if timezone_name is None and not dtstart_is_utc:
+        return rrule_line
+    
+    # Check if RRULE has an UNTIL value
+    if 'UNTIL=' not in rrule_line:
+        return rrule_line
+    
+    # Check if UNTIL already has a Z suffix (already in UTC)
+    if re.search(r'UNTIL=\d{8}T\d{6}Z', rrule_line):
+        return rrule_line
+    
+    # Check if UNTIL is a date-only value (no time component)
+    # Date-only values don't need the Z suffix according to RFC 5545
+    if re.search(r'UNTIL=\d{8}(?:[;\s]|$)', rrule_line):
+        return rrule_line
+    
+    # Find UNTIL datetime value without Z
+    until_match = re.search(r'UNTIL=(\d{8}T\d{6})(?=[;\s]|$)', rrule_line)
+    if not until_match:
+        return rrule_line
+    
+    until_value = until_match.group(1)
+    
+    # Convert to UTC if we have timezone information
+    if timezone_name:
+        until_utc = convert_local_to_utc(until_value, timezone_name)
+    else:
+        # DTSTART is in UTC, so assume UNTIL is too
+        until_utc = until_value + 'Z'
+    
+    # Replace the UNTIL value
+    fixed_line = rrule_line.replace(f'UNTIL={until_value}', f'UNTIL={until_utc}')
+    
+    return fixed_line
+
+
+def fix_ics_file(input_path, output_path=None):
+    """
+    Fix RRULE UNTIL values in an ICS file.
+    
+    Args:
+        input_path: Path to input ICS file
+        output_path: Path to output ICS file (optional, defaults to input_path)
+    
+    Returns:
+        Number of RRULE lines that were fixed
+    """
+    if output_path is None:
+        output_path = input_path
+    
+    input_path = Path(input_path)
+    output_path = Path(output_path)
+    
+    if not input_path.exists():
+        raise FileNotFoundError(f"Input file not found: {input_path}")
+    
+    with open(input_path, 'r', encoding='utf-8') as f:
+        content = f.read()
+    
+    lines = content.split('\n')
+    result = []
+    fixes_count = 0
+    
+    # Track state as we parse the file
+    current_timezone = None
+    current_dtstart_is_utc = False
+    in_vevent = False
+    
+    for line in lines:
+        # Track when we're in a VEVENT
+        if line.strip() == 'BEGIN:VEVENT':
+            in_vevent = True
+            current_timezone = None
+            current_dtstart_is_utc = False
+        elif line.strip() == 'END:VEVENT':
+            in_vevent = False
+            current_timezone = None
+            current_dtstart_is_utc = False
+        
+        # Extract timezone from DTSTART
+        if in_vevent and line.startswith('DTSTART'):
+            current_timezone, current_dtstart_is_utc = extract_timezone_from_dtstart(line)
+            result.append(line)
+        
+        # Fix RRULE if needed
+        elif in_vevent and line.startswith('RRULE:'):
+            original_line = line
+            fixed_line = fix_until_in_rrule(line, current_timezone, current_dtstart_is_utc)
+            
+            if fixed_line != original_line:
+                fixes_count += 1
+                print(f"Fixed RRULE:", file=sys.stderr)
+                print(f"  Before: {original_line}", file=sys.stderr)
+                print(f"  After:  {fixed_line}", file=sys.stderr)
+            
+            result.append(fixed_line)
+        
+        else:
+            result.append(line)
+    
+    # Write output
+    fixed_content = '\n'.join(result)
+    
+    with open(output_path, 'w', encoding='utf-8') as f:
+        f.write(fixed_content)
+    
+    return fixes_count
+
+
+def main():
+    """Main entry point for the script."""
+    if len(sys.argv) < 2:
+        print("Usage: python fix_ics_rrule.py input.ics [output.ics]", file=sys.stderr)
+        print("\nIf output.ics is not specified, the input file will be modified in place.", 
+              file=sys.stderr)
+        sys.exit(1)
+    
+    input_file = sys.argv[1]
+    output_file = sys.argv[2] if len(sys.argv) > 2 else None
+    
+    try:
+        # Check if pytz is available
+        try:
+            import pytz
+        except ImportError:
+            print("Warning: pytz module not found. Timezone conversions may be incorrect.", 
+                  file=sys.stderr)
+            print("Install with: pip install pytz", file=sys.stderr)
+            print("", file=sys.stderr)
+        
+        fixes_count = fix_ics_file(input_file, output_file)
+        
+        if output_file:
+            print(f"\nFixed {fixes_count} RRULE(s) in {input_file}", file=sys.stderr)
+            print(f"Output written to: {output_file}", file=sys.stderr)
+        else:
+            print(f"\nFixed {fixes_count} RRULE(s) in {input_file}", file=sys.stderr)
+            print(f"File modified in place.", file=sys.stderr)
+        
+        if fixes_count == 0:
+            print("No RRULE fixes were needed - file is already compliant!", file=sys.stderr)
+    
+    except Exception as e:
+        print(f"Error: {e}", file=sys.stderr)
+        sys.exit(1)
+
+
+if __name__ == '__main__':
+    main()
