Function Scheduler failing due to incorrect timestamp format

[BennetVellaExient]

File "/layers/google.python.pip/pip/lib/python3.12/site-packages/firebase_functions/scheduler_fn.py", line 102, in on_schedule_wrapped
    schedule_time = _dt.datetime.strptime(
                    ^^^^^^^^^^^^^^^^^^^^^^
  File "/layers/google.python.runtime/python/lib/python3.12/_strptime.py", line 653, in _strptime_datetime
    tt, fraction, gmtoff_fraction = _strptime(data_string, format)
                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/layers/google.python.runtime/python/lib/python3.12/_strptime.py", line 432, in _strptime
    raise ValueError("time data %r does not match format %r" %
ValueError: time data '2025-10-17T16:50:00.510855-07:00' does not match format '%Y-%m-%dT%H:%M:%S%z'"

This started happening over the weekend with no changes / alterations to our workers. From the internal logic it appears to be sourced at:

    def on_schedule_decorator(func: _C):

        @_functools.wraps(func)
        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()
            else:
                schedule_time = _dt.datetime.strptime(
                    schedule_time_str,
                    "%Y-%m-%dT%H:%M:%S%z",
                )

So I'm suspecting that the following request.headers.get("X-CloudScheduler-ScheduleTime") has changed? Upgrading the sdk version is likely to be a major endeavour, what's the simplest solution here?

[BennetVellaExient]

def on_schedule_wrapped(request: _Request) -> _Response:
    schedule_time_str = request.headers.get("X-CloudScheduler-ScheduleTime")

    if schedule_time_str is None:
        schedule_time = _dt.utcnow()
    else:
        try:
            # Supports the expected RFC 3339 format and ISO 8601 as well
            schedule_time = dateutil_parser.isoparse(schedule_time_str)
        except ValueError as e:
            print(f"Failed to parse RFC 3339 timestamp: {e}")
            schedule_time = _dt.utcnow()

Something like the above might be what we would want, since the incoming datetime still satisfies the documented definition, but the current implementation does not.

Reference:
https://cloud.google.com/scheduler/docs/reference/rpc/google.cloud.scheduler.v1#appenginehttptarget

[CorieW]

Hi @BennetVellaExient! Thanks for raising this. It's been received and we will provide updates when available.

[BennetVellaExient]

fix-cloudscheduler-scheduletime.patch

Content:

diff --git a/src/firebase_functions/scheduler_fn.py b/src/firebase_functions/scheduler_fn.py
index 1979f67..8fee83d 100644
--- a/src/firebase_functions/scheduler_fn.py
+++ b/src/firebase_functions/scheduler_fn.py
@@ -103,10 +103,16 @@ def on_schedule(**kwargs) -> _typing.Callable[[_C], _Response]:
             if schedule_time_str is None:
                 schedule_time = _dt.datetime.utcnow()
             else:
-                schedule_time = _dt.datetime.strptime(
-                    schedule_time_str,
-                    "%Y-%m-%dT%H:%M:%S%z",
-                )
+                try:
+                    # Robust RFC 3339 parsing
+                    schedule_time = dateutil_parser.isoparse(schedule_time_str)
+                except ValueError as e:
+                    print(f"Failed to parse RFC 3339 timestamp: {e}")
+                    schedule_time = _dt.utcnow()
+                        schedule_time = _dt.datetime.strptime(
+                            schedule_time_str,
+                            "%Y-%m-%dT%H:%M:%S%z",
+                        )
             event = ScheduledEvent(
                 job_name=request.headers.get("X-CloudScheduler-JobName"),
                 schedule_time=schedule_time,

Maybe this is of use.