DynamoDB: Add table_exists parameter and extend documentation (#237)

Author: Lxstr

CONTRIBUTING.rst

@@ -16,7 +16,7 @@ Install dependencies
 
 .. code-block:: bash
 
-    $ pip install -r requirements/dev.in
+    $ pip install -r requirements/dev.txt
     $ pip install -r requirements/docs.in
 
 Install the package in editable mode
@@ -44,7 +44,7 @@ or
 
     $ sphinx-build -b html docs docs/_build
 
-Run the tests together or individually
+Run the tests together or individually, requires the docker containers to be up and running (see below)
 
 .. code-block:: bash
     

CONTRIBUTORS.md

@@ -1,5 +1,6 @@
 ## Contributors
 
+-   [MauriceBrg](https://github.com/MauriceBrg)
 -   [giuppep](https://github.com/giuppep)
 -   [eiriklid](https://github.com/eiriklid)
 -   [necat1](https://github.com/necat1)

docs/config_reference.rst

@@ -18,6 +18,7 @@ These are specific to Flask-Session.
    - **cachelib**: CacheLibSessionInterface
    - **mongodb**: MongoDBSessionInterface
    - **sqlalchemy**: SqlAlchemySessionInterface
+   - **dynamodb**: DynamoDBSessionInterface
 
 .. py:data:: SESSION_PERMANENT
 
@@ -215,6 +216,12 @@ Dynamodb
       
       Default: ``'Sessions'``
 
+.. py:data:: SESSION_DYNAMODB_TABLE_EXISTS
+
+      By default it will create a new table with the TTL setting activated unless you set this parameter to ``True``, then it assumes that the table already exists.
+      
+      Default: ``False``
+
 .. deprecated:: 0.7.0
 
    ``SESSION_FILE_DIR``, ``SESSION_FILE_THRESHOLD``, ``SESSION_FILE_MODE``. Use ``SESSION_CACHELIB`` instead.

docs/config_serialization.rst

@@ -14,7 +14,7 @@ The msgspec library has speed and memory advantages over other libraries. Howeve
 If you encounter a TypeError such as: "Encoding objects of type <type> is unsupported", you may be attempting to serialize an unsupported type. In this case, you can either convert the object to a supported type or use a different serializer.
 
 Casting to a supported type:
-~~~~~~~~~~~~~~~~~~~~~~~~~~~
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 .. code-block:: python
 

src/flask_session/__init__.py

@@ -106,6 +106,9 @@ def _get_interface(self, app):
         SESSION_DYNAMODB_TABLE = config.get(
             "SESSION_DYNAMODB_TABLE", Defaults.SESSION_DYNAMODB_TABLE
         )
+        SESSION_DYNAMODB_TABLE_EXISTS = config.get(
+            "SESSION_DYNAMODB_TABLE_EXISTS", Defaults.SESSION_DYNAMODB_TABLE_EXISTS
+        )
 
         # PostgreSQL settings
         SESSION_POSTGRESQL = config.get(
@@ -191,6 +194,7 @@ def _get_interface(self, app):
                 **common_params,
                 client=SESSION_DYNAMODB,
                 table_name=SESSION_DYNAMODB_TABLE,
+                table_exists=SESSION_DYNAMODB_TABLE_EXISTS,
             )
 
         elif SESSION_TYPE == "postgresql":

src/flask_session/defaults.py

@@ -43,8 +43,9 @@ class Defaults:
     # DynamoDB settings
     SESSION_DYNAMODB = None
     SESSION_DYNAMODB_TABLE = "Sessions"
+    SESSION_DYNAMODB_TABLE_EXISTS = False
 
     # PostgreSQL settings
     SESSION_POSTGRESQL = None
     SESSION_POSTGRESQL_TABLE = "flask_sessions"
-    SESSION_POSTGRESQL_SCHEMA = "public"
+    SESSION_POSTGRESQL_SCHEMA = "public"

src/flask_session/dynamodb/dynamodb.py

@@ -1,13 +1,15 @@
+"""Provides a Session Interface to DynamoDB"""
+
 import warnings
 from datetime import datetime
 from datetime import timedelta as TimeDelta
 from decimal import Decimal
 from typing import Optional
 
 import boto3
-from mypy_boto3_dynamodb.service_resource import DynamoDBServiceResource
 from flask import Flask
 from itsdangerous import want_bytes
+from mypy_boto3_dynamodb.service_resource import DynamoDBServiceResource
 
 from ..base import ServerSideSession, ServerSideSessionInterface
 from ..defaults import Defaults
@@ -20,12 +22,41 @@ class DynamoDBSession(ServerSideSession):
 class DynamoDBSessionInterface(ServerSideSessionInterface):
     """A Session interface that uses dynamodb as backend. (`boto3` required)
 
-    :param client: A ``DynamoDBServiceResource`` instance.
+    By default (``table_exists=False``) it will create a DynamoDB table with this configuration:
+
+    - Table Name: Value of ``table_name``, by default ``Sessions``
+    - Key Schema: Simple Primary Key ``id`` of type string
+    - Billing Mode: Pay per Request
+    - Time to Live enabled, attribute name: ``expiration``
+    - The following permissions are required:
+        - ``dynamodb:CreateTable``
+        - ``dynamodb:DescribeTable``
+        - ``dynamodb:UpdateTimeToLive``
+        - ``dynamodb:GetItem``
+        - ``dynamodb:UpdateItem``
+        - ``dynamodb:DeleteItem``
+
+    If you set ``table_exists`` to True, you're responsible for creating a table with this config:
+
+    - Table Name: Value of ``table_name``, by default ``Sessions``
+    - Key Schema: Simple Primary Key ``id`` of type string
+    - Time to Live enabled, attribute name: ``expiration``
+    - The following permissions are required under these circumstances:
+        - ``dynamodb:GetItem``
+        - ``dynamodb:UpdateItem``
+        - ``dynamodb:DeleteItem``
+
+    :param client: A ``DynamoDBServiceResource`` instance, i.e. the result
+                of ``boto3.resource("dynamodb", ...)``.
     :param key_prefix: A prefix that is added to all DynamoDB store keys.
     :param use_signer: Whether to sign the session id cookie or not.
     :param permanent: Whether to use permanent session or not.
     :param sid_length: The length of the generated session id in bytes.
     :param table_name: DynamoDB table name to store the session.
+    :param table_exists: The table already exists, don't try to create it (default=False).
+
+    .. versionadded:: 0.9
+        The `table_exists` parameter was added.
 
     .. versionadded:: 0.6
         The `sid_length` parameter was added.
@@ -46,8 +77,11 @@ def __init__(
         sid_length: int = Defaults.SESSION_ID_LENGTH,
         serialization_format: str = Defaults.SESSION_SERIALIZATION_FORMAT,
         table_name: str = Defaults.SESSION_DYNAMODB_TABLE,
+        table_exists: Optional[bool] = Defaults.SESSION_DYNAMODB_TABLE_EXISTS,
     ):
 
+        # NOTE: The name client is a bit misleading as we're using the resource API of boto3 as opposed to the service API
+        #       which would be instantiated as boto3.client.
         if client is None:
             warnings.warn(
                 "No valid DynamoDBServiceResource instance provided, attempting to create a new instance on localhost:8000.",
@@ -62,44 +96,58 @@ def __init__(
                 aws_secret_access_key="dummy",
             )
 
+        self.client = client
+        self.table_name = table_name
+
+        if not table_exists:
+            self._create_table()
+
+        self.store = client.Table(table_name)
+        super().__init__(
+            app,
+            key_prefix,
+            use_signer,
+            permanent,
+            sid_length,
+            serialization_format,
+        )
+
+    def _create_table(self):
         try:
-            client.create_table(
+            self.client.create_table(
                 AttributeDefinitions=[
                     {"AttributeName": "id", "AttributeType": "S"},
                 ],
-                TableName=table_name,
+                TableName=self.table_name,
                 KeySchema=[
                     {"AttributeName": "id", "KeyType": "HASH"},
                 ],
                 BillingMode="PAY_PER_REQUEST",
             )
-            client.meta.client.get_waiter("table_exists").wait(TableName=table_name)
-            client.meta.client.update_time_to_live(
+            self.client.meta.client.get_waiter("table_exists").wait(
+                TableName=self.table_name
+            )
+            self.client.meta.client.update_time_to_live(
                 TableName=self.table_name,
                 TimeToLiveSpecification={
                     "Enabled": True,
                     "AttributeName": "expiration",
                 },
             )
-        except (AttributeError, client.meta.client.exceptions.ResourceInUseException):
+        except (
+            AttributeError,
+            self.client.meta.client.exceptions.ResourceInUseException,
+        ):
             # TTL already exists, or table already exists
             pass
 
-        self.client = client
-        self.store = client.Table(table_name)
-        super().__init__(
-            app,
-            key_prefix,
-            use_signer,
-            permanent,
-            sid_length,
-            serialization_format,
-        )
-
     def _retrieve_session_data(self, store_id: str) -> Optional[dict]:
         # Get the saved session (document) from the database
         document = self.store.get_item(Key={"id": store_id}).get("Item")
-        if document:
+        session_is_not_expired = Decimal(datetime.utcnow().timestamp()) <= document.get(
+            "expiration"
+        )
+        if document and session_is_not_expired:
             serialized_session_data = want_bytes(document.get("val").value)
             return self.serializer.loads(serialized_session_data)
         return None

tests/test_dynamodb.py

@@ -2,6 +2,7 @@
 
 import boto3
 import flask
+import pytest
 from flask_session.defaults import Defaults
 from flask_session.dynamodb import DynamoDBSession
 
@@ -52,3 +53,43 @@ def test_dynamodb_default(self, app_utils):
             with app.test_request_context():
                 assert isinstance(flask.session, DynamoDBSession)
                 app_utils.test_session(app)
+
+    def test_dynamodb_with_existing_table(self, app_utils):
+        """
+        Setting the SESSION_DYNAMODB_TABLE_EXISTS to True for an
+        existing table shouldn't change anything.
+        """
+
+        with self.setup_dynamodb():
+            app = app_utils.create_app(
+                {
+                    "SESSION_TYPE": "dynamodb",
+                    "SESSION_DYNAMODB": self.client,
+                    "SESSION_DYNAMODB_TABLE_EXISTS": True,
+                }
+            )
+
+            with app.test_request_context():
+                assert isinstance(flask.session, DynamoDBSession)
+                app_utils.test_session(app)
+
+    def test_dynamodb_with_existing_table_fails_if_table_doesnt_exist(self, app_utils):
+        """Accessing a non-existent table should result in problems."""
+
+        app = app_utils.create_app(
+            {
+                "SESSION_TYPE": "dynamodb",
+                "SESSION_DYNAMODB": boto3.resource(
+                    "dynamodb",
+                    endpoint_url="http://localhost:8000",
+                    region_name="us-west-2",
+                    aws_access_key_id="dummy",
+                    aws_secret_access_key="dummy",
+                ),
+                "SESSION_DYNAMODB_TABLE": "non-existent-123",
+                "SESSION_DYNAMODB_TABLE_EXISTS": True,
+            }
+        )
+        with app.test_request_context(), pytest.raises(AssertionError):
+            assert isinstance(flask.session, DynamoDBSession)
+            app_utils.test_session(app)