FastAPI: add redis integration

This includes the addition of the python-fakeredis package,
used for stubbing python-redis when a user does not have a
configured cache.

Signed-off-by: Kevin Morris <kevr@0cost.org>

aurweb/redis.py

@@ -0,0 +1,57 @@
+import logging
+
+import fakeredis
+
+from redis import ConnectionPool, Redis
+
+import aurweb.config
+
+logger = logging.getLogger(__name__)
+pool = None
+
+
+class FakeConnectionPool:
+    """ A fake ConnectionPool class which holds an internal reference
+    to a fakeredis handle.
+
+    We normally deal with Redis by keeping its ConnectionPool globally
+    referenced so we can persist connection state through different calls
+    to redis_connection(), and since FakeRedis does not offer a ConnectionPool,
+    we craft one up here to hang onto the same handle instance as long as the
+    same instance is alive; this allows us to use a similar flow from the
+    redis_connection() user's perspective.
+    """
+
+    def __init__(self):
+        self.handle = fakeredis.FakeStrictRedis()
+
+    def disconnect(self):
+        pass
+
+
+def redis_connection():  # pragma: no cover
+    global pool
+
+    disabled = aurweb.config.get("options", "cache") != "redis"
+
+    # If we haven't initialized redis yet, construct a pool.
+    if disabled:
+        logger.debug("Initializing fake Redis instance.")
+        if pool is None:
+            pool = FakeConnectionPool()
+        return pool.handle
+    else:
+        logger.debug("Initializing real Redis instance.")
+        if pool is None:
+            redis_addr = aurweb.config.get("options", "redis_address")
+            pool = ConnectionPool.from_url(redis_addr)
+
+    # Create a connection to the pool.
+    return Redis(connection_pool=pool)
+
+
+def kill_redis():
+    global pool
+    if pool:
+        pool.disconnect()
+        pool = None