remove pickle usage in redis-backed cache helper

shared/helpers/cache.py

@@ -1,8 +1,8 @@
 import asyncio
 import base64
 import hashlib
+import json
 import logging
-import pickle
 from functools import wraps
 from typing import Any, Callable, Hashable, List, Optional
 
@@ -86,8 +86,6 @@ def set(self, key: str, ttl: int, value: Any):
 
 
 class RedisBackend(BaseBackend):
-    current_protocol = pickle.DEFAULT_PROTOCOL
-
     def __init__(self, redis_connection: Redis):
         self.redis_connection = redis_connection
 
@@ -100,16 +98,18 @@ def get(self, key: str) -> Any:
         if serialized_value is None:
             return NO_VALUE
         try:
-            return pickle.loads(serialized_value)
+            return json.loads(serialized_value)
         except ValueError:
             return NO_VALUE
 
     def set(self, key: str, ttl: int, value: Any):
-        serialized_value = pickle.dumps(value, self.current_protocol)
         try:
+            serialized_value = json.dumps(value)
             self.redis_connection.setex(key, ttl, serialized_value)
         except RedisError:
             log.warning("Unable to set cache on redis", exc_info=True)
+        except TypeError:
+            log.exception("Attempted to cache a type that is not JSON-serializable")
 
 
 class LogMapping(dict):

tests/unit/helpers/test_cache.py

@@ -1,3 +1,5 @@
+import unittest
+
 import pytest
 from redis.exceptions import TimeoutError
 
@@ -67,28 +69,30 @@ def setex(self, key, expire, value):
         raise TimeoutError()
 
 
-class TestRedisBackend(object):
+class TestRedisBackend(unittest.TestCase):
     def test_simple_redis_call(self):
         redis_backend = RedisBackend(FakeRedis())
         assert redis_backend.get("normal_key") == NO_VALUE
-        redis_backend.set("normal_key", 120, {"value_1": set("ascdefgh"), 1: [1, 3]})
+        value_1 = list(set("ascdefgh"))
+        redis_backend.set("normal_key", 120, {"value_1": value_1, "1": [1, 3]})
         assert redis_backend.get("normal_key") == {
-            "value_1": set("ascdefgh"),
-            1: [1, 3],
+            "value_1": value_1,
+            "1": [1, 3],
         }
 
-    def test_simple_redis_call_invalid_pickle_version(self):
-        redis_instance = FakeRedis()
-        # PICKLE HERE WILL BE SET TO VERSION 9 (\x09 in the second byte of the value)
-        # IF THIS STOPS FAILING WITH ValueError, CHANGE THE SECOND BYTE TO SOMETHING HIGHER
-        redis_instance.setex("key", 120, b"\x80\x09X\x05\x00\x00\x00valueq\x00.")
-        redis_backend = RedisBackend(redis_instance)
-        assert redis_backend.get("key") == NO_VALUE
-
     def test_simple_redis_call_exception(self):
         redis_backend = RedisBackend(FakeRedisWithIssues())
         assert redis_backend.get("normal_key") == NO_VALUE
-        redis_backend.set("normal_key", 120, {"value_1": set("ascdefgh"), 1: [1, 3]})
+        redis_backend.set(
+            "normal_key", 120, {"value_1": list(set("ascdefgh")), "1": [1, 3]}
+        )
+        assert redis_backend.get("normal_key") == NO_VALUE
+
+    def test_simple_redis_call_not_json_serializable(self):
+        redis_backend = RedisBackend(FakeRedis())
+
+        unserializable = set("abcdefg")
+        redis_backend.set("normal_key", 120, unserializable)
         assert redis_backend.get("normal_key") == NO_VALUE