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Add retry decorator
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Lxstr committed Feb 11, 2024
1 parent 48adc49 commit e1f17fa
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Showing 2 changed files with 87 additions and 19 deletions.
61 changes: 61 additions & 0 deletions src/flask_session/_utils.py
Original file line number Diff line number Diff line change
@@ -0,0 +1,61 @@
"""
MIT License
Copyright (c) 2023 giuppep
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.
"""
import time
from functools import wraps
from typing import Any, Callable
from flask import current_app


def retry_query(
*, max_attempts: int = 3, delay: float = 0.3, backoff: int = 2
) -> Callable[..., Any]:
"""Decorator to retry a query when an OperationalError is raised.
Args:
max_attempts: Maximum number of attempts. Defaults to 3.
delay: Delay between attempts in seconds. Defaults to 0.3.
backoff: Backoff factor. Defaults to 2.
"""

def decorator(func: Callable[..., Any]) -> Callable[..., Any]:
@wraps(func)
def wrapper(*args: Any, **kwargs: Any) -> Any:
for attempt in range(max_attempts):
try:
return func(*args, **kwargs)
# TODO: use proper exception type
except Exception as e:
if attempt == max_attempts - 1:
raise e

sleep_time = delay * backoff**attempt
current_app.logger.exception(
f"Exception when querying database ({e})."
f"Retrying ({attempt + 1}/{max_attempts}) in {sleep_time:.2f}s."
)
time.sleep(sleep_time)

return wrapper

return decorator
45 changes: 26 additions & 19 deletions src/flask_session/sessions.py
Original file line number Diff line number Diff line change
Expand Up @@ -18,7 +18,7 @@
from itsdangerous import BadSignature, Signer, want_bytes
from sqlalchemy.exc import SQLAlchemyError
from werkzeug.datastructures import CallbackDict

from ._utils import retry_query
from .defaults import Defaults


Expand Down Expand Up @@ -219,17 +219,21 @@ def _cleanup_n_requests(self) -> None:

# METHODS TO BE IMPLEMENTED BY SUBCLASSES

@retry_query()
def _retrieve_session_data(self, store_id: str) -> Optional[dict]:
raise NotImplementedError()

@retry_query()
def _delete_session(self, store_id: str) -> None:
raise NotImplementedError()

@retry_query()
def _upsert_session(
self, session_lifetime: TimeDelta, session: ServerSideSession, store_id: str
) -> None:
raise NotImplementedError()

@retry_query()
def _delete_expired_sessions(self) -> None:
"""Delete expired sessions from the backend storage. Only required for non-TTL databases."""
pass
Expand Down Expand Up @@ -271,6 +275,7 @@ def __init__(
self.redis = redis
super().__init__(app, key_prefix, use_signer, permanent, sid_length)

@retry_query()
def _retrieve_session_data(self, store_id: str) -> Optional[dict]:
# Get the saved session (value) from the database
serialized_session_data = self.redis.get(store_id)
Expand All @@ -282,9 +287,11 @@ def _retrieve_session_data(self, store_id: str) -> Optional[dict]:
self.app.logger.error("Failed to unpickle session data", exc_info=True)
return None

@retry_query()
def _delete_session(self, store_id: str) -> None:
self.redis.delete(store_id)

@retry_query()
def _upsert_session(
self, session_lifetime: TimeDelta, session: ServerSideSession, store_id: str
) -> None:
Expand Down Expand Up @@ -315,7 +322,6 @@ class MemcachedSessionInterface(ServerSideSessionInterface):
.. versionadded:: 0.2
The `use_signer` parameter was added.
"""

serializer = pickle
Expand Down Expand Up @@ -363,6 +369,7 @@ def _get_memcache_timeout(self, timeout: int) -> int:
timeout += int(time.time())
return timeout

@retry_query()
def _retrieve_session_data(self, store_id: str) -> Optional[dict]:
# Get the saved session (item) from the database
serialized_session_data = self.client.get(store_id)
Expand All @@ -374,9 +381,11 @@ def _retrieve_session_data(self, store_id: str) -> Optional[dict]:
self.app.logger.error("Failed to unpickle session data", exc_info=True)
return None

@retry_query()
def _delete_session(self, store_id: str) -> None:
self.client.delete(store_id)

@retry_query()
def _upsert_session(
self, session_lifetime: TimeDelta, session: ServerSideSession, store_id: str
) -> None:
Expand Down Expand Up @@ -432,13 +441,16 @@ def __init__(
self.cache = FileSystemCache(cache_dir, threshold=threshold, mode=mode)
super().__init__(app, key_prefix, use_signer, permanent, sid_length)

@retry_query()
def _retrieve_session_data(self, store_id: str) -> Optional[dict]:
# Get the saved session (item) from the database
return self.cache.get(store_id)

@retry_query()
def _delete_session(self, store_id: str) -> None:
self.cache.delete(store_id)

@retry_query()
def _upsert_session(
self, session_lifetime: TimeDelta, session: ServerSideSession, store_id: str
) -> None:
Expand Down Expand Up @@ -502,6 +514,7 @@ def __init__(

super().__init__(app, key_prefix, use_signer, permanent, sid_length)

@retry_query()
def _retrieve_session_data(self, store_id: str) -> Optional[dict]:
# Get the saved session (document) from the database
document = self.store.find_one({"id": store_id})
Expand All @@ -514,12 +527,14 @@ def _retrieve_session_data(self, store_id: str) -> Optional[dict]:
self.app.logger.error("Failed to unpickle session data", exc_info=True)
return None

@retry_query()
def _delete_session(self, store_id: str) -> None:
if self.use_deprecated_method:
self.store.remove({"id": store_id})
else:
self.store.delete_one({"id": store_id})

@retry_query()
def _upsert_session(
self, session_lifetime: TimeDelta, session: ServerSideSession, store_id: str
) -> None:
Expand Down Expand Up @@ -645,19 +660,18 @@ def __repr__(self):

self.sql_session_model = Session

@retry_query()
def _delete_expired_sessions(self) -> None:
try:
self.db.session.query(self.sql_session_model).filter(
self.sql_session_model.expiry <= datetime.utcnow()
).delete(synchronize_session=False)
self.db.session.commit()
except SQLAlchemyError as e:
self.app.logger.exception(
e, "Failed to delete expired sessions. Retrying...", exc_info=True
)
except SQLAlchemyError:
self.db.session.rollback()
raise

@retry_query()
def _retrieve_session_data(self, store_id: str) -> Optional[dict]:
# Get the saved session (record) from the database
record = self.sql_session_model.query.filter_by(session_id=store_id).first()
Expand All @@ -667,10 +681,7 @@ def _retrieve_session_data(self, store_id: str) -> Optional[dict]:
try:
self.db.session.delete(record)
self.db.session.commit()
except SQLAlchemyError as e:
self.app.logger.exception(
e, "Failed to retrieve sessions. Retrying...", exc_info=True
)
except SQLAlchemyError:
self.db.session.rollback()
raise
record = None
Expand All @@ -681,22 +692,21 @@ def _retrieve_session_data(self, store_id: str) -> Optional[dict]:
session_data = self.serializer.loads(serialized_session_data)
return session_data
except pickle.UnpicklingError as e:
self.app.logger.error(
self.app.logger.exception(
e, "Failed to unpickle session data", exc_info=True
)
return None

@retry_query()
def _delete_session(self, store_id: str) -> None:
try:
self.sql_session_model.query.filter_by(session_id=store_id).delete()
self.db.session.commit()
except SQLAlchemyError as e:
self.app.logger.exception(
e, "Failed to delete session. Retrying...", exc_info=True
)
except SQLAlchemyError:
self.db.session.rollback()
raise

@retry_query()
def _upsert_session(
self, session_lifetime: TimeDelta, session: ServerSideSession, store_id: str
) -> None:
Expand All @@ -719,9 +729,6 @@ def _upsert_session(
)
self.db.session.add(record)
self.db.session.commit()
except SQLAlchemyError as e:
self.app.logger.exception(
e, "Failed to upsert session. Retrying...", exc_info=True
)
except SQLAlchemyError:
self.db.session.rollback()
raise

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