Autostart a redis instance in nix shell.

As a part of test environment, an unprivileged redis server is started on localhost:6379.
Redis connection pool detects when it is run in a development nix shell
and uses this port instead of a production unix socket. This way, redis
tests pass even on computers without redis installed.

selfprivacy_api/utils/redis_pool.py

@@ -3,6 +3,7 @@ Redis pool module for selfprivacy_api
 """
 import redis
 from selfprivacy_api.utils.singleton_metaclass import SingletonMetaclass
+from os import environ
 
 REDIS_SOCKET = "/run/redis-sp-api/redis.sock"
 
@@ -13,10 +14,18 @@ class RedisPool(metaclass=SingletonMetaclass):
     """
 
     def __init__(self):
-        self._pool = redis.ConnectionPool.from_url(
-            f"unix://{REDIS_SOCKET}",
-            decode_responses=True,
-        )
+        if "USE_REDIS_PORT" in environ.keys():
+            self._pool = redis.ConnectionPool(
+                host="127.0.0.1",
+                port=int(environ["USE_REDIS_PORT"]),
+                decode_responses=True,
+            )
+
+        else:
+            self._pool = redis.ConnectionPool.from_url(
+                f"unix://{REDIS_SOCKET}",
+                decode_responses=True,
+            )
         self._pubsub_connection = self.get_connection()
 
     def get_connection(self):

shell.nix

@@ -64,9 +64,14 @@ pkgs.mkShell {
   buildInputs = [
     sp-python
     pkgs.black
+    pkgs.redis
   ];
   shellHook = ''
     PYTHONPATH=${sp-python}/${sp-python.sitePackages}
+    # envs set with export and as attributes are treated differently.
+    # for example. printenv <Name> will not fetch the value of an attribute.
+    export USE_REDIS_PORT=6379
+    redis-server --port $USE_REDIS_PORT >/dev/null & 
     # maybe set more env-vars
   '';
 }