ValueError when parsing RTDB timestamps without microseconds in db_fn.py

[jniebur]

The firebase-functions library crashes when handling Real-Time Database (RTDB) events with timestamps that don't include microseconds. The _db_endpoint_handler function in db_fn.py at line 114 attempts to parse timestamps using a strict format string '%Y-%m-%dT%H:%M:%S.%f%z' that requires microseconds, but Firebase sometimes sends timestamps in the format '2025-10-30T21:15:51Z' without the .%f component.

Similar to this issue.

Reproducibility: intermittent

To Reproduce

1. Set up a Firebase Function using on_value_written decorator for Real-Time Database
2. Trigger a write event to the RTDB
3. The function crashes when Firebase sends a timestamp without microseconds

Error Message

ValueError: time data '2025-10-30T21:15:51Z' does not match format '%Y-%m-%dT%H:%M:%S.%f%z'

Full Stack Trace

Exception on / [POST]
  Traceback (most recent call last):
    File "/layers/google.python.pip/pip/lib/python3.11/site-packages/flask/app.py", line 1511, in wsgi_app
      response = self.full_dispatch_request()
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    File "/layers/google.python.pip/pip/lib/python3.11/site-packages/flask/app.py", line 919, in full_dispatch_request
      rv = self.handle_user_exception(e)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    File "/layers/google.python.pip/pip/lib/python3.11/site-packages/flask/app.py", line 917, in full_dispatch_request
      rv = self.dispatch_request()
           ^^^^^^^^^^^^^^^^^^^^^^^
    File "/layers/google.python.pip/pip/lib/python3.11/site-packages/flask/app.py", line 902, in dispatch_request
      return self.ensure_sync(self.view_functions[rule.endpoint])(**view_args)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    File "/layers/google.python.pip/pip/lib/python3.11/site-packages/functions_framework/execution_id.py", line 157, in wrapper
      result = view_function(*args, **kwargs)
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    File "/layers/google.python.pip/pip/lib/python3.11/site-packages/functions_framework/__init__.py", line 188, in view_func
      function(event)
    File "/layers/google.python.pip/pip/lib/python3.11/site-packages/firebase_functions/db_fn.py", line 154, in on_value_written_wrapped
      return _db_endpoint_handler(
             ^^^^^^^^^^^^^^^^^^^^^
    File "/layers/google.python.pip/pip/lib/python3.11/site-packages/firebase_functions/db_fn.py", line 114, in _db_endpoint_handler
      time=_dt.datetime.strptime(
           ^^^^^^^^^^^^^^^^^^^^^^
    File "/layers/google.python.runtime/python/lib/python3.11/_strptime.py", line 567, in _strptime_datetime
      tt, fraction, gmtoff_fraction = _strptime(data_string, format)
                                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    File "/layers/google.python.runtime/python/lib/python3.11/_strptime.py", line 349, in _strptime
      raise ValueError("time data %r does not match format %r" %
  ValueError: time data '2025-10-30T21:15:51Z' does not match format '%Y-%m-%dT%H:%M:%S.%f%z'

Environment

• Python version: 3.11
• firebase-functions version: 0.4.3
• Deployment: Google Cloud Functions (2nd gen)
• Trigger type: Real-Time Database (on_value_written)
• Runtime: python311

Additional Context

The problematic code in db_fn.py:114 uses a single strict format string that requires microseconds. The timestamp '2025-10-30T21:15:51Z' is a valid ISO 8601 timestamp but doesn't match the expected format '%Y-%m-%dT%H:%M:%S.%f%z'.

[CorieW]

Hi @jniebur. Thanks for opening this issue. We've receieved it and will investigate as soon as possible.