add aurweb.models.session.Session ORM database object

+ Added aurweb.util module.
    - Added make_random_string function.
+ Added aurweb.db.make_random_value function.
    - Takes a model and a column and introspects them to figure out the
      proper column length to create a random string for; then creates
      a unique string for that column.
Signed-off-by: Kevin Morris <kevr@0cost.org>

aurweb/db.py

 import math
 
 import aurweb.config
+import aurweb.util
 
-engine = None  # See get_engine
+# See get_engine.
+engine = None
 
 # ORM Session class.
 Session = None
@@ -10,6 +12,44 @@ Session = None
 # Global ORM Session object.
 session = None
 
+# Global introspected object memo.
+introspected = dict()
+
+
+def make_random_value(table: str, column: str):
+    """ Generate a unique, random value for a string column in a table.
+
+    This can be used to generate for example, session IDs that
+    align with the properties of the database column with regards
+    to size.
+
+    Internally, we use SQLAlchemy introspection to look at column
+    to decide which length to use for random string generation.
+
+    :return: A unique string that is not in the database
+    """
+    global introspected
+
+    # Make sure column is converted to a string for memo interaction.
+    scolumn = str(column)
+
+    # If the target column is not yet introspected, store its introspection
+    # object into our global `introspected` memo.
+    if scolumn not in introspected:
+        from sqlalchemy import inspect
+        target_column = scolumn.split('.')[-1]
+        col = list(filter(lambda c: c.name == target_column,
+                          inspect(table).columns))[0]
+        introspected[scolumn] = col
+
+    col = introspected.get(scolumn)
+    length = col.type.length
+
+    string = aurweb.util.make_random_string(length)
+    while session.query(table).filter(column == string).first():
+        string = aurweb.util.make_random_string(length)
+    return string
+
 
 def query(model, *args, **kwargs):
     return session.query(model).filter(*args, **kwargs)

aurweb/models/session.py

+from sqlalchemy import Column, Integer
+from sqlalchemy.orm import backref, mapper, relationship
+
+from aurweb.db import make_random_value
+from aurweb.models.user import User
+from aurweb.schema import Sessions
+
+
+class Session:
+    UsersID = Column(Integer, nullable=True)
+
+    def __init__(self, **kwargs):
+        self.UsersID = kwargs.get("UsersID")
+        self.SessionID = kwargs.get("SessionID")
+        self.LastUpdateTS = kwargs.get("LastUpdateTS")
+
+
+mapper(Session, Sessions, primary_key=[Sessions.c.SessionID], properties={
+    "User": relationship(User, backref=backref("session",
+                                               uselist=False))
+})
+
+
+def generate_unique_sid():
+    return make_random_value(Session, Session.SessionID)

aurweb/util.py

+import random
+import string
+
+
+def make_random_string(length):
+    return ''.join(random.choices(string.ascii_lowercase +
+                                  string.digits, k=length))

test/test_session.py

+""" Test our Session model. """
+from datetime import datetime
+from unittest import mock
+
+import pytest
+
+from aurweb.models.account_type import AccountType
+from aurweb.models.session import generate_unique_sid
+from aurweb.testing import setup_test_db
+from aurweb.testing.models import make_session, make_user
+
+user, _session = None, None
+
+
+@pytest.fixture(autouse=True)
+def setup():
+    from aurweb.db import session
+
+    global user, _session
+
+    setup_test_db("Users", "Sessions")
+
+    account_type = session.query(AccountType).filter(
+        AccountType.AccountType == "User").first()
+    user = make_user(Username="test", Email="test@example.org",
+                     ResetKey="testReset", Passwd="testPassword",
+                     AccountType=account_type)
+    _session = make_session(UsersID=user.ID, SessionID="testSession",
+                            LastUpdateTS=datetime.utcnow())
+
+
+def test_session():
+    assert _session.SessionID == "testSession"
+    assert _session.UsersID == user.ID
+
+
+def test_session_user_association():
+    # Make sure that the Session user attribute is correct.
+    assert _session.User == user
+
+
+def test_generate_unique_sid():
+    # Mock up aurweb.models.session.generate_sid by returning
+    # sids[i % 2] from 0 .. n. This will swap between each sid
+    # between each call.
+    sids = ["testSession", "realSession"]
+    i = 0
+
+    def mock_generate_sid(length):
+        nonlocal i
+        sid = sids[i % 2]
+        i += 1
+        return sid
+
+    with mock.patch("aurweb.util.make_random_string", mock_generate_sid):
+        assert generate_unique_sid() == "realSession"