fix: add robust date parsing in schedule_fn

src/firebase_functions/scheduler_fn.py

@@ -15,6 +15,7 @@
 
 import dataclasses as _dataclasses
 import datetime as _dt
+from datetime import timezone as _timezone
 import functools as _functools
 import typing as _typing
 
@@ -101,12 +102,27 @@ def on_schedule_wrapped(request: _Request) -> _Response:
             schedule_time: _dt.datetime
             schedule_time_str = request.headers.get("X-CloudScheduler-ScheduleTime")
             if schedule_time_str is None:
-                schedule_time = _dt.datetime.utcnow()
+                schedule_time = _dt.datetime.now(_timezone.utc)
             else:
-                schedule_time = _dt.datetime.strptime(
-                    schedule_time_str,
-                    "%Y-%m-%dT%H:%M:%S%z",
-                )
+                try:
+                    # Try to parse with the stdlib which supports fractional
+                    # seconds and offsets in Python 3.11+ via fromisoformat.
+                    # Normalize RFC3339 'Z' to '+00:00' for fromisoformat.
+                    iso_str = schedule_time_str
+                    if iso_str.endswith("Z"):
+                        iso_str = iso_str[:-1] + "+00:00"
+                    schedule_time = _dt.datetime.fromisoformat(iso_str)
+                except ValueError:
+                    # Fallback to strict parsing without fractional seconds
+                    try:
+                        schedule_time = _dt.datetime.strptime(
+                            schedule_time_str,
+                            "%Y-%m-%dT%H:%M:%S%z",
+                        )
+                    except ValueError as e:
+                        # If all parsing fails, log and use current UTC time
+                        _logging.exception(e)
+                        schedule_time = _dt.datetime.now(_timezone.utc)
             event = ScheduledEvent(
                 job_name=request.headers.get("X-CloudScheduler-JobName"),
                 schedule_time=schedule_time,