SWE-agent[bot] PR to fix: Messages framework incorrectly serializes/deserializes extra_tags when it's an empty string

[klieret]

This is a PR opened by AI tool SWE Agent to close #1 (Messages framework incorrectly serializes/deserializes extra_tags when it's an empty string).

Closes #1.

Thought process ('trajectory') of SWE-agent (click to expand)

🧑‍🚒 Response (0):
First, let's start by reproducing the issue described. We'll create a new Python script named reproduce_bug.py and write the provided code snippet into it to verify the behavior of the serialization and deserialization process.

create reproduce_bug.py

👀‍ Observation (0):

[File: /SWE-agent__django/reproduce_bug.py (1 lines total)]
1:

---

🧑‍🚒 Response (1):
Now let's paste in the example code from the issue to reproduce the bug.

edit 1:1
from django.conf import settings
settings.configure()  # Just to allow the following import
from django.contrib.messages.storage.base import Message
from django.contrib.messages.storage.cookie import MessageEncoder, MessageDecoder

original_message = Message(10, "Here is a message", extra_tags="")
encoded_message = MessageEncoder().encode(original_message)
decoded_message = MessageDecoder().decode(encoded_message)

print("Original extra_tags empty string:", original_message.extra_tags == "")
print("Decoded extra_tags is None:", decoded_message.extra_tags is None)
end_of_edit

👀‍ Observation (1):

[File: /SWE-agent__django/reproduce_bug.py (11 lines total)]
1:from django.conf import settings
2:settings.configure()  # Just to allow the following import
3:from django.contrib.messages.storage.base import Message
4:from django.contrib.messages.storage.cookie import MessageEncoder, MessageDecoder
5:
6:original_message = Message(10, "Here is a message", extra_tags="")
7:encoded_message = MessageEncoder().encode(original_message)
8:decoded_message = MessageDecoder().decode(encoded_message)
9:
10:print("Original extra_tags empty string:", original_message.extra_tags == "")
11:print("Decoded extra_tags is None:", decoded_message.extra_tags is None)
File updated. Please review the changes and make sure they are correct (correct indentation, no duplicate lines, etc). Edit the file again if necessary.

---

🧑‍🚒 Response (2):
Let's run the script to see if we can reproduce the issue as described, where extra_tags changes from an empty string to None after serialization and deserialization.

python reproduce_bug.py

👀‍ Observation (2):

Original extra_tags empty string: True
Decoded extra_tags is None: True

---

🧑‍🚒 Response (3):
We have successfully reproduced the issue where extra_tags changes from an empty string to None after serialization and deserialization. The next step is to locate and examine the code in the MessageEncoder and MessageDecoder classes to understand why this is happening and to make the necessary corrections.

Let's find the file containing the MessageEncoder and MessageDecoder classes. They are likely located in the django/contrib/messages/storage directory. We'll use the find_file command to locate the exact file.

find_file "cookie.py" django/contrib/messages/storage

👀‍ Observation (3):

Found 1 matches for "cookie.py" in /SWE-agent__django/django/contrib/messages/storage:
/SWE-agent__django/django/contrib/messages/storage/cookie.py

---

🧑‍🚒 Response (4):
Now that we've located the cookie.py file where the MessageEncoder and MessageDecoder are defined, let's open this file to inspect and modify the relevant code.

open django/contrib/messages/storage/cookie.py

👀‍ Observation (4):

[File: /SWE-agent__django/django/contrib/messages/storage/cookie.py (169 lines total)]
1:import binascii
2:import json
3:
4:from django.conf import settings
5:from django.contrib.messages.storage.base import BaseStorage, Message
6:from django.core import signing
7:from django.http import SimpleCookie
8:from django.utils.safestring import SafeData, mark_safe
9:
10:
11:class MessageEncoder(json.JSONEncoder):
12:    """
13:    Compactly serialize instances of the ``Message`` class as JSON.
14:    """
15:    message_key = '__json_message'
16:
17:    def default(self, obj):
18:        if isinstance(obj, Message):
19:            # Using 0/1 here instead of False/True to produce more compact json
20:            is_safedata = 1 if isinstance(obj.message, SafeData) else 0
21:            message = [self.message_key, is_safedata, obj.level, obj.message]
22:            if obj.extra_tags:
23:                message.append(obj.extra_tags)
24:            return message
25:        return super().default(obj)
26:
27:
28:class MessageDecoder(json.JSONDecoder):
29:    """
30:    Decode JSON that includes serialized ``Message`` instances.
31:    """
32:
33:    def process_messages(self, obj):
34:        if isinstance(obj, list) and obj:
35:            if obj[0] == MessageEncoder.message_key:
36:                if obj[1]:
37:                    obj[3] = mark_safe(obj[3])
38:                return Message(*obj[2:])
39:            return [self.process_messages(item) for item in obj]
40:        if isinstance(obj, dict):
41:            return {key: self.process_messages(value)
42:                    for key, value in obj.items()}
43:        return obj
44:
45:    def decode(self, s, **kwargs):
46:        decoded = super().decode(s, **kwargs)
47:        return self.process_messages(decoded)
48:
49:
50:class MessageSerializer:
51:    def dumps(self, obj):
52:        return json.dumps(
53:            obj,
54:            separators=(',', ':'),
55:            cls=MessageEncoder,
56:        ).encode('latin-1')
57:
58:    def loads(self, data):
59:        return json.loads(data.decode('latin-1'), cls=MessageDecoder)
60:
61:
62:class CookieStorage(BaseStorage):
63:    """
64:    Store messages in a cookie.
65:    """
66:    cookie_name = 'messages'
67:    # uwsgi's default configuration enforces a maximum size of 4kb for all the
68:    # HTTP headers. In order to leave some room for other cookies and headers,
69:    # restrict the session cookie to 1/2 of 4kb. See #18781.
70:    max_cookie_size = 2048
71:    not_finished = '__messagesnotfinished__'
72:    key_salt = 'django.contrib.messages'
73:
74:    def __init__(self, *args, **kwargs):
75:        super().__init__(*args, **kwargs)
76:        self.signer = signing.get_cookie_signer(salt=self.key_salt)
77:
78:    def _get(self, *args, **kwargs):
79:        """
80:        Retrieve a list of messages from the messages cookie. If the
81:        not_finished sentinel value is found at the end of the message list,
82:        remove it and return a result indicating that not all messages were
83:        retrieved by this storage.
84:        """
85:        data = self.request.COOKIES.get(self.cookie_name)
86:        messages = self._decode(data)
87:        all_retrieved = not (messages and messages[-1] == self.not_finished)
88:        if messages and not all_retrieved:
89:            # remove the sentinel value
90:            messages.pop()
91:        return messages, all_retrieved
92:
93:    def _update_cookie(self, encoded_data, response):
94:        """
95:        Either set the cookie with the encoded data if there is any data to
96:        store, or delete the cookie.
97:        """
98:        if encoded_data:
99:            response.set_cookie(
100:                self.cookie_name, encoded_data,
(69 more lines below)

---

🧑‍🚒 Response (5):
We need to adjust the serialization and deserialization logic in the MessageEncoder and MessageDecoder classes to handle the case where extra_tags is an empty string, ensuring it does not convert to None.

In the MessageEncoder class, the extra_tags is only appended to the message if it is truthy (line 22). We need to change this to explicitly check if extra_tags is not None.

Let's edit the MessageEncoder to include extra_tags even if it's an empty string.

edit 22:24
            if obj.extra_tags is not None:
                message.append(obj.extra_tags)
            return message
end_of_edit

👀‍ Observation (5):

[File: /SWE-agent__django/django/contrib/messages/storage/cookie.py (169 lines total)]
1:import binascii
2:import json
3:
4:from django.conf import settings
5:from django.contrib.messages.storage.base import BaseStorage, Message
6:from django.core import signing
7:from django.http import SimpleCookie
8:from django.utils.safestring import SafeData, mark_safe
9:
10:
11:class MessageEncoder(json.JSONEncoder):
12:    """
13:    Compactly serialize instances of the ``Message`` class as JSON.
14:    """
15:    message_key = '__json_message'
16:
17:    def default(self, obj):
18:        if isinstance(obj, Message):
19:            # Using 0/1 here instead of False/True to produce more compact json
20:            is_safedata = 1 if isinstance(obj.message, SafeData) else 0
21:            message = [self.message_key, is_safedata, obj.level, obj.message]
22:            if obj.extra_tags is not None:
23:                message.append(obj.extra_tags)
24:            return message
25:        return super().default(obj)
26:
27:
28:class MessageDecoder(json.JSONDecoder):
29:    """
30:    Decode JSON that includes serialized ``Message`` instances.
31:    """
32:
33:    def process_messages(self, obj):
34:        if isinstance(obj, list) and obj:
35:            if obj[0] == MessageEncoder.message_key:
36:                if obj[1]:
37:                    obj[3] = mark_safe(obj[3])
38:                return Message(*obj[2:])
39:            return [self.process_messages(item) for item in obj]
40:        if isinstance(obj, dict):
41:            return {key: self.process_messages(value)
42:                    for key, value in obj.items()}
43:        return obj
44:
45:    def decode(self, s, **kwargs):
46:        decoded = super().decode(s, **kwargs)
47:        return self.process_messages(decoded)
48:
49:
50:class MessageSerializer:
51:    def dumps(self, obj):
52:        return json.dumps(
53:            obj,
54:            separators=(',', ':'),
55:            cls=MessageEncoder,
56:        ).encode('latin-1')
57:
58:    def loads(self, data):
59:        return json.loads(data.decode('latin-1'), cls=MessageDecoder)
60:
61:
62:class CookieStorage(BaseStorage):
63:    """
64:    Store messages in a cookie.
65:    """
66:    cookie_name = 'messages'
67:    # uwsgi's default configuration enforces a maximum size of 4kb for all the
68:    # HTTP headers. In order to leave some room for other cookies and headers,
69:    # restrict the session cookie to 1/2 of 4kb. See #18781.
70:    max_cookie_size = 2048
71:    not_finished = '__messagesnotfinished__'
72:    key_salt = 'django.contrib.messages'
73:
74:    def __init__(self, *args, **kwargs):
75:        super().__init__(*args, **kwargs)
76:        self.signer = signing.get_cookie_signer(salt=self.key_salt)
77:
78:    def _get(self, *args, **kwargs):
79:        """
80:        Retrieve a list of messages from the messages cookie. If the
81:        not_finished sentinel value is found at the end of the message list,
82:        remove it and return a result indicating that not all messages were
83:        retrieved by this storage.
84:        """
85:        data = self.request.COOKIES.get(self.cookie_name)
86:        messages = self._decode(data)
87:        all_retrieved = not (messages and messages[-1] == self.not_finished)
88:        if messages and not all_retrieved:
89:            # remove the sentinel value
90:            messages.pop()
91:        return messages, all_retrieved
92:
93:    def _update_cookie(self, encoded_data, response):
94:        """
95:        Either set the cookie with the encoded data if there is any data to
96:        store, or delete the cookie.
97:        """
98:        if encoded_data:
99:            response.set_cookie(
100:                self.cookie_name, encoded_data,
(69 more lines below)
File updated. Please review the changes and make sure they are correct (correct indentation, no duplicate lines, etc). Edit the file again if necessary.

---

🧑‍🚒 Response (6):
The MessageEncoder class has been updated to correctly handle extra_tags when it's an empty string. Now, let's re-run the reproduce_bug.py script to verify that the issue has been resolved and that extra_tags remains an empty string after serialization and deserialization.

python reproduce_bug.py

👀‍ Observation (6):

Original extra_tags empty string: True
Decoded extra_tags is None: False

---

🧑‍🚒 Response (7):
The output confirms that the issue has been resolved: extra_tags remains an empty string after serialization and deserialization, as indicated by Decoded extra_tags is None: False.

Now that the fix is verified, we can clean up by removing the reproduce_bug.py script since it's no longer needed.

rm reproduce_bug.py

👀‍ Observation (7):

---

🧑‍🚒 Response (8):
The cleanup is complete. Now that we have fixed the issue and verified the solution, we should submit our changes to the code base. Let's submit the changes using the submit command.

submit

👀‍ Observation (8):

diff --git a/django/contrib/messages/storage/cookie.py b/django/contrib/messages/storage/cookie.py
index 1d390c7..e48d4ed 100644
--- a/django/contrib/messages/storage/cookie.py
+++ b/django/contrib/messages/storage/cookie.py
@@ -19,7 +19,7 @@ class MessageEncoder(json.JSONEncoder):
             # 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:
+            if obj.extra_tags is not None:
                 message.append(obj.extra_tags)
             return message
         return super().default(obj)