[1.5.x] Fixed #19387 -- Preserved SafeData status in contrib.messages

Thanks Anton Baklanov for the report and the patch.
Backport of e277301c2 from master.

django/contrib/messages/storage/cookie.py

@@ -4,6 +4,7 @@ from django.conf import settings
 from django.contrib.messages.storage.base import BaseStorage, Message
 from django.http import SimpleCookie
 from django.utils.crypto import salted_hmac, constant_time_compare
+from django.utils.safestring import SafeData, mark_safe
 from django.utils import six
 
 
@@ -15,7 +16,9 @@ class MessageEncoder(json.JSONEncoder):
 
     def default(self, obj):
         if isinstance(obj, Message):
-            message = [self.message_key, obj.level, obj.message]
+            # Using 0/1 here instead of False/True to produce more compact json
+            is_safedata = 1 if isinstance(obj.message, SafeData) else 0
+            message = [self.message_key, is_safedata, obj.level, obj.message]
             if obj.extra_tags:
                 message.append(obj.extra_tags)
             return message
@@ -30,7 +33,9 @@ class MessageDecoder(json.JSONDecoder):
     def process_messages(self, obj):
         if isinstance(obj, list) and obj:
             if obj[0] == MessageEncoder.message_key:
-                return Message(*obj[1:])
+                if obj[1]:
+                    obj[3] = mark_safe(obj[3])
+                return Message(*obj[2:])
             return [self.process_messages(item) for item in obj]
         if isinstance(obj, dict):
             return dict([(key, self.process_messages(value))

django/contrib/messages/tests/cookie.py

@@ -6,6 +6,7 @@ from django.contrib.messages.storage.cookie import (CookieStorage,
     MessageEncoder, MessageDecoder)
 from django.contrib.messages.storage.base import Message
 from django.test.utils import override_settings
+from django.utils.safestring import SafeData, mark_safe
 
 
 def set_cookie_data(storage, messages, invalid=False, encode_empty=False):
@@ -132,3 +133,21 @@ class CookieTest(BaseTest):
         value = encoder.encode(messages)
         decoded_messages = json.loads(value, cls=MessageDecoder)
         self.assertEqual(messages, decoded_messages)
+
+    def test_safedata(self):
+        """
+        Tests that a message containing SafeData is keeping its safe status when
+        retrieved from the message storage.
+        """
+        def encode_decode(data):
+            message = Message(constants.DEBUG, data)
+            encoded = storage._encode(message)
+            decoded = storage._decode(encoded)
+            return decoded.message
+
+        storage = self.get_storage()
+
+        self.assertIsInstance(
+            encode_decode(mark_safe("<b>Hello Django!</b>")), SafeData)
+        self.assertNotIsInstance(
+            encode_decode("<b>Hello Django!</b>"), SafeData)

django/contrib/messages/tests/session.py

@@ -1,5 +1,8 @@
+from django.contrib.messages import constants
 from django.contrib.messages.tests.base import BaseTest
+from django.contrib.messages.storage.base import Message
 from django.contrib.messages.storage.session import SessionStorage
+from django.utils.safestring import SafeData, mark_safe
 
 
 def set_session_data(storage, messages):
@@ -36,3 +39,14 @@ class SessionTest(BaseTest):
         set_session_data(storage, example_messages)
         # Test that the message actually contains what we expect.
         self.assertEqual(list(storage), example_messages)
+
+    def test_safedata(self):
+        """
+        Tests that a message containing SafeData is keeping its safe status when
+        retrieved from the message storage.
+        """
+        storage = self.get_storage()
+
+        message = Message(constants.DEBUG, mark_safe("<b>Hello Django!</b>"))
+        set_session_data(storage, [message])
+        self.assertIsInstance(list(storage)[0].message, SafeData)