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fix: remove default argument now from _seconds_until_refresh #356

Merged
merged 2 commits into from
Jul 25, 2024
Merged

fix: remove default argument now from _seconds_until_refresh #356

merged 2 commits into from
Jul 25, 2024

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jackwotherspoon
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@jackwotherspoon jackwotherspoon commented Jul 24, 2024 •
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_seconds_until_refresh which is used for background refresh strategy
(lazy refresh is unaffected!) should not have now as a default argument
due to Python only evaluating default arguments once at function definition.

Python's default arguments are evaluated only once when the function
is defined, not each time the function is called. (source)

Problematic code:

alloydb-python-connector/google/cloud/alloydb/connector/refresh_utils.py

Lines 29 to 53 in 14d6b1c

def _seconds_until_refresh(
expiration: datetime, now: datetime = datetime.now(timezone.utc)
) -> int:
"""
Calculates the duration to wait before starting the next refresh.
Usually the duration will be half of the time until certificate
expiration.
Args:
expiration (datetime.datetime): Time of certificate expiration.
now (datetime.datetime): Current time (UTC)
Returns:
int: Time in seconds to wait before performing next refresh.
"""
duration = int((expiration - now).total_seconds())
# if certificate duration is less than 1 hour
if duration < 3600:
# something is wrong with certificate, refresh now
if duration < _refresh_buffer:
return 0
# otherwise wait until 4 minutes before expiration for next refresh
return duration - _refresh_buffer
return duration // 2

Having now as a default argument means it is set once and then never
adjusted. So in subsequent calls to _seconds_until_refresh the duration
will just continue to grow larger and larger as it evaluates agains the same now

The result of this means that duration // 2 block is always being hit and
will continue to grow. It could grow to be greater than 3600 and lead to errors.

@jackwotherspoon jackwotherspoon self-assigned this Jul 24, 2024
@jackwotherspoon jackwotherspoon requested a review from a team as a code owner July 24, 2024 20:24
@jackwotherspoon jackwotherspoon changed the title chore: explicitly pass in now fix: remove default argument now from _seconds_until_refresh Jul 25, 2024
@enocom enocom self-requested a review July 25, 2024 01:51
@enocom
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enocom commented Jul 25, 2024

Probably should add a note that this only affects clients using the default refresh strategy and not lazy refresh.

@jackwotherspoon
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Probably should add a note that this only affects clients using the default refresh strategy and not lazy refresh.

good call, added a note to PR description

@jackwotherspoon jackwotherspoon merged commit 27f31cd into main Jul 25, 2024
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@jackwotherspoon jackwotherspoon deleted the update-now branch July 25, 2024 12:21
@release-please release-please bot mentioned this pull request Jul 24, 2024
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@enocom
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enocom commented Jul 25, 2024

Fixes #357

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@nancynh nancynh nancynh approved these changes

@enocom enocom enocom approved these changes

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@jackwotherspoon @enocom @nancynh