#33458: Messages framework incorrectly serializes/deserializes extra_tags when
it's
an empty string
--------------------------------------------+------------------------
Reporter: Tim McCurrach | Owner: nobody
Type: Bug | Status: new
Component: contrib.messages | Version: 4.0
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
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When a message is serialised and then deserialised with any of the built
in storage backends, then `extra_tags==""` is converted to
`extra_tags==None`. This is because `MessageEncoder` checks for the
truthyness of `extra_tags` rather than checking it is not `None`.
=== To replicate this bug ===
{{{
>>> 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)
>>> original_message.extra_tags == ""
True
>>> decoded_message.extra_tags is None
True
}}}
=== Effect of the bug in application behaviour ===
This error occurred in the wild with a template tag similar to the
following:
{{{
{% if x not in message.extra_tags %}
}}}
When the message was displayed as part of a redirect, it had been
serialised and deserialized which meant that extra_tags was `None` instead
of the empty string. This caused an error.
It's important to note that this bug affects all of the standard API
(`messages.debug`, `messages.info` etc. all have a default value of
`extra_tags` equal to `""`).
--
Ticket URL: <https://code.djangoproject.com/ticket/33458>
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