refresh_utils.py

"""
Copyright 2021 Google LLC

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

 https://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
"""

from __future__ importannotations

importasyncio
importcopy
importdatetime
importlogging
importrandom
fromtypingimportAny, Callable

importaiohttp
fromgoogle.auth.credentialsimportCredentials
fromgoogle.auth.credentialsimportScoped
importgoogle.auth.transport.requests

logger=logging.getLogger(name=__name__)

# _refresh_buffer is the amount of time before a refresh's result expires
# that a new refresh operation begins.
_refresh_buffer: int=4*60# 4 minutes


def_seconds_until_refresh(
expiration: datetime.datetime,
) ->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): The expiration time of the certificate.

 Returns:
 int: Time in seconds to wait before performing next refresh.
 """

duration=int(
 (expiration-datetime.datetime.now(datetime.timezone.utc)).total_seconds()
 )

# if certificate duration is less than 1 hour
ifduration<3600:
# something is wrong with certificate, refresh now
ifduration<_refresh_buffer:
return0
# otherwise wait until 4 minutes before expiration for next refresh
returnduration-_refresh_buffer

returnduration//2


asyncdef_is_valid(task: asyncio.Task) ->bool:
try:
metadata=awaittask
# only valid if now is before the cert expires
ifdatetime.datetime.now(datetime.timezone.utc) <metadata.expiration:
returnTrue
exceptException:
# supress any errors from task
logger.debug("Current instance metadata is invalid.")
returnFalse


def_downscope_credentials(
credentials: Credentials,
scopes: list[str] = ["https://www.googleapis.com/auth/sqlservice.login"],
) ->Credentials:
"""Generate a down-scoped credential.

 Args:
 credentials (google.auth.credentials.Credentials):
 Credentials object used to generate down-scoped credentials.
 scopes (list[str]): List of Google scopes to
 include in down-scoped credentials object.

 Returns:
 google.auth.credentials.Credentials: Down-scoped credentials object.
 """
# credentials sourced from a service account or metadata are children of
# Scoped class and are capable of being re-scoped
ifisinstance(credentials, Scoped):
scoped_creds=credentials.with_scopes(scopes=scopes)
# authenticated user credentials can not be re-scoped
else:
# create shallow copy to not overwrite scopes on default credentials
scoped_creds=copy.copy(credentials)
# overwrite '_scopes' to down-scope user credentials
# Cloud SDK reference: https://github.com/google-cloud-sdk-unofficial/google-cloud-sdk/blob/93920ccb6d2cce0fe6d1ce841e9e33410551d66b/lib/googlecloudsdk/command_lib/sql/generate_login_token_util.py#L116
scoped_creds._scopes=scopes
# down-scoped credentials require refresh, are invalid after being re-scoped
request=google.auth.transport.requests.Request()
scoped_creds.refresh(request)
returnscoped_creds


def_exponential_backoff(attempt: int) ->float:
"""Calculates a duration to backoff in milliseconds based on the attempt i.

 The formula is:

 base * multi^(attempt + 1 + random)

 With base = 200ms and multi = 1.618, and random = [0.0, 1.0),
 the backoff values would fall between the following low and high ends:

 Attempt Low (ms) High (ms)

 0 324 524
 1 524 847
 2 847 1371
 3 1371 2218
 4 2218 3588

 The theoretical worst case scenario would have a client wait 8.5s in total
 for an API request to complete (with the first four attempts failing, and
 the fifth succeeding).
 """
base=200
multi=1.618
exp=attempt+1+random.random()
returnbase*pow(multi, exp)


asyncdefretry_50x(
request_coro: Callable, *args: Any, **kwargs: Any
) ->aiohttp.ClientResponse:
"""Retry any 50x HTTP response up to X number of times."""
max_retries=5
foriinrange(max_retries):
resp=awaitrequest_coro(*args, **kwargs)
# backoff for any 50X errors
ifresp.status>=500andi<max_retries:
# calculate backoff time
backoff=_exponential_backoff(i)
awaitasyncio.sleep(backoff/1000)
else:
break
returnresp