From 4620b9527669bdb1f9a122f4c279508c72d97ca3 Mon Sep 17 00:00:00 2001
From: Manuel Raynaud <manu@raynaud.io>
Date: Tue, 4 Jan 2022 12:07:15 +0100
Subject: [PATCH] =?UTF-8?q?=E2=9C=A8(back)=20override=20channel=5Fredis=20?=
 =?UTF-8?q?channel=20layer?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

The channel layer provided by channel_redis use msgpack to serialize and
deserialize messages. We have a problem when a video is serialized. It
is impossible then to deserialize it because in the urls the resolution
can be used as key and those keys are integer. Msgpack is unable to
deserialize this kind of key. As suggested in the issue[1] open on
channel_redis git repository we implement our own serialize and
deserialize methods.
1: https://github.com/django/channels_redis/issues/287
---
 src/backend/marsha/settings.py                |  2 +-
 src/backend/marsha/websocket/layers.py        | 36 +++++++++++++++++++
 .../marsha/websocket/tests/test_layers.py     | 31 ++++++++++++++++
 3 files changed, 68 insertions(+), 1 deletion(-)
 create mode 100644 src/backend/marsha/websocket/layers.py
 create mode 100644 src/backend/marsha/websocket/tests/test_layers.py

diff --git a/src/backend/marsha/settings.py b/src/backend/marsha/settings.py
index 97655bbd74..df24cf01df 100644
--- a/src/backend/marsha/settings.py
+++ b/src/backend/marsha/settings.py
@@ -171,7 +171,7 @@ class Base(Configuration):
     # }
     CHANNEL_LAYERS = {
         "default": {
-            "BACKEND": "channels_redis.core.RedisChannelLayer",
+            "BACKEND": "marsha.websocket.layers.JsonRedisChannelLayer",
             "CONFIG": {
                 "hosts": values.ListValue(
                     [("redis", 6379)], environ_name="REDIS_HOST", environ_prefix=None
diff --git a/src/backend/marsha/websocket/layers.py b/src/backend/marsha/websocket/layers.py
new file mode 100644
index 0000000000..855886ef66
--- /dev/null
+++ b/src/backend/marsha/websocket/layers.py
@@ -0,0 +1,36 @@
+"""Layers used by django channels"""
+import json
+import random
+
+from django.core.serializers.json import DjangoJSONEncoder
+
+from channels_redis.core import RedisChannelLayer
+
+
+class JsonRedisChannelLayer(RedisChannelLayer):
+    """Use json to serialize and deserialize messages."""
+
+    def serialize(self, message):
+        """
+        Serializes message in json.
+        """
+        value = bytes(json.dumps(message, cls=DjangoJSONEncoder), encoding="utf-8")
+        if self.crypter:
+            value = self.crypter.encrypt(value)
+
+        # As we use an sorted set to expire messages we need to guarantee uniqueness,
+        # with 12 bytes.
+        random_prefix = random.getrandbits(8 * 12).to_bytes(12, "big")
+        return random_prefix + value
+
+    def deserialize(self, message):
+        """
+        Deserializes from a byte string.
+        """
+        # Removes the random prefix
+        message = message[12:]
+        message = message.decode("utf-8")
+
+        if self.crypter:
+            message = self.crypter.decrypt(message, self.expiry + 10)
+        return json.loads(message)
diff --git a/src/backend/marsha/websocket/tests/test_layers.py b/src/backend/marsha/websocket/tests/test_layers.py
new file mode 100644
index 0000000000..0373793081
--- /dev/null
+++ b/src/backend/marsha/websocket/tests/test_layers.py
@@ -0,0 +1,31 @@
+"""Test marsha layers use by django channels."""
+from django.test import TestCase
+
+from marsha.websocket.layers import JsonRedisChannelLayer
+
+
+class JsonRedisChannelLayerTest(TestCase):
+    """Test serialize and deserialize."""
+
+    def test_serialize_message(self):
+        """
+        Test default serialization method
+        """
+        message = {"a": True, "b": None, "c": {"d": []}}
+        channel_layer = JsonRedisChannelLayer()
+        serialized = channel_layer.serialize(message)
+        self.assertIsInstance(serialized, bytes)
+        self.assertEqual(serialized[12:], b'{"a": true, "b": null, "c": {"d": []}}')
+
+    def test_deserialize_message(self):
+        """
+        Test default deserialization method
+        """
+        message = (
+            b'[\x85\xf8\xdeY\xe5\xa3}is\x0f3{"a": true, "b": null, "c": {"d": []}}'
+        )
+        channel_layer = JsonRedisChannelLayer()
+        deserialized = channel_layer.deserialize(message)
+
+        self.assertIsInstance(deserialized, dict)
+        self.assertEqual(deserialized, {"a": True, "b": None, "c": {"d": []}})