get_cached_content fails with 'SafeString object has no attribute append' error

[jenda1]

get_cached_content() expects the cached_items is a list. It is... often. But sometimes it is a SafeString and then the line

django-wiki/src/wiki/models/article.py

Line 258 in e5d6b97

cached_items.append(cache_content_key)

fails because string does not have append method.

It looks that the cache content is set outside the get_cached_content method sometimes, but I do not know where...

There is the exception:

  File "/tmp/venv/lib/python3.8/site-packages/django/core/handlers/exception.py", line 34, in inner
    response = get_response(request)
  File "/tmp/venv/lib/python3.8/site-packages/django/core/handlers/base.py", line 145, in _get_response
    response = self.process_exception_by_middleware(e, request)
  File "/tmp/venv/lib/python3.8/site-packages/django/core/handlers/base.py", line 143, in _get_response
    response = response.render()
  File "/tmp/venv/lib/python3.8/site-packages/django/template/response.py", line 105, in render
    self.content = self.rendered_content
  File "/tmp/venv/lib/python3.8/site-packages/django/template/response.py", line 83, in rendered_content
    return template.render(context, self._request)
  File "/tmp/venv/lib/python3.8/site-packages/django/template/backends/django.py", line 61, in render
    return self.template.render(context)
  File "/tmp/venv/lib/python3.8/site-packages/django/template/base.py", line 171, in render
    return self._render(context)
  File "/tmp/venv/lib/python3.8/site-packages/django/test/utils.py", line 95, in instrumented_test_render
    return self.nodelist.render(context)
  File "/tmp/venv/lib/python3.8/site-packages/django/template/base.py", line 936, in render
    bit = node.render_annotated(context)
  File "/tmp/venv/lib/python3.8/site-packages/django/template/base.py", line 903, in render_annotated
    return self.render(context)
  File "/tmp/venv/lib/python3.8/site-packages/django/template/loader_tags.py", line 150, in render
    return compiled_parent._render(context)
  File "/tmp/venv/lib/python3.8/site-packages/django/test/utils.py", line 95, in instrumented_test_render
    return self.nodelist.render(context)
  File "/tmp/venv/lib/python3.8/site-packages/django/template/base.py", line 936, in render
    bit = node.render_annotated(context)
  File "/tmp/venv/lib/python3.8/site-packages/django/template/base.py", line 903, in render_annotated
    return self.render(context)
  File "/tmp/venv/lib/python3.8/site-packages/django/template/loader_tags.py", line 150, in render
    return compiled_parent._render(context)
  File "/tmp/venv/lib/python3.8/site-packages/django/test/utils.py", line 95, in instrumented_test_render
    return self.nodelist.render(context)
  File "/tmp/venv/lib/python3.8/site-packages/django/template/base.py", line 936, in render
    bit = node.render_annotated(context)
  File "/tmp/venv/lib/python3.8/site-packages/django/template/base.py", line 903, in render_annotated
    return self.render(context)
  File "/tmp/venv/lib/python3.8/site-packages/django/template/loader_tags.py", line 150, in render
    return compiled_parent._render(context)
  File "/tmp/venv/lib/python3.8/site-packages/django/test/utils.py", line 95, in instrumented_test_render
    return self.nodelist.render(context)
  File "/tmp/venv/lib/python3.8/site-packages/django/template/base.py", line 936, in render
    bit = node.render_annotated(context)
  File "/tmp/venv/lib/python3.8/site-packages/django/template/base.py", line 903, in render_annotated
    return self.render(context)
  File "/tmp/venv/lib/python3.8/site-packages/classytags/core.py", line 151, in render
    return self.render_tag(context, **kwargs)
  File "/tmp/venv/lib/python3.8/site-packages/sekizai/templatetags/sekizai_tags.py", line 87, in render_tag
    rendered_contents = nodelist.render(context)
  File "/tmp/venv/lib/python3.8/site-packages/django/template/base.py", line 936, in render
    bit = node.render_annotated(context)
  File "/tmp/venv/lib/python3.8/site-packages/django/template/base.py", line 903, in render_annotated
    return self.render(context)
  File "/tmp/venv/lib/python3.8/site-packages/django/template/loader_tags.py", line 62, in render
    result = block.nodelist.render(context)
  File "/tmp/venv/lib/python3.8/site-packages/django/template/base.py", line 936, in render
    bit = node.render_annotated(context)
  File "/tmp/venv/lib/python3.8/site-packages/django/template/base.py", line 903, in render_annotated
    return self.render(context)
  File "/tmp/venv/lib/python3.8/site-packages/django/template/loader_tags.py", line 62, in render
    result = block.nodelist.render(context)
  File "/tmp/venv/lib/python3.8/site-packages/django/template/base.py", line 936, in render
    bit = node.render_annotated(context)
  File "/tmp/venv/lib/python3.8/site-packages/django/template/base.py", line 903, in render_annotated
    return self.render(context)
  File "/tmp/venv/lib/python3.8/site-packages/django/template/loader_tags.py", line 62, in render
    result = block.nodelist.render(context)
  File "/tmp/venv/lib/python3.8/site-packages/django/template/base.py", line 936, in render
    bit = node.render_annotated(context)
  File "/tmp/venv/lib/python3.8/site-packages/django/template/base.py", line 903, in render_annotated
    return self.render(context)
  File "/tmp/venv/lib/python3.8/site-packages/django/template/library.py", line 214, in render
    _dict = self.func(*resolved_args, **resolved_kwargs)
  File "/tmp/venv/lib/python3.8/site-packages/wiki/templatetags/wiki_tags.py", line 53, in wiki_render
    content = article.get_cached_content(user=context.get("user"))
  File "/tmp/venv/lib/python3.8/site-packages/wiki/models/article.py", line 258, in get_cached_content
    cached_items.append(cache_content_key)
AttributeError: 'SafeString' object has no attribute 'append'

[benjaoming]

Thanks for reporting @jenda1 - seems like an issue that could perhaps be addressed with a test case and a fix.

[Steckelfisch]

me too:

Traceback:

File "/home/braas/projects/django_wiki/ve-djang-wiki/lib/python3.8/site-packages/django/core/handlers/exception.py" in inner
  34.             response = get_response(request)

......

File "/home/braas/projects/django_wiki/ve-djang-wiki/lib/python3.8/site-packages/django/template/library.py" in render
  214.         _dict = self.func(*resolved_args, **resolved_kwargs)

File "/home/braas/projects/django_wiki/django-wiki/src/wiki/templatetags/wiki_tags.py" in wiki_render
  53.         content = article.get_cached_content(user=context.get("user"))

File "/home/braas/projects/django_wiki/django-wiki/src/wiki/models/article.py" in get_cached_content
  262.         cached_items.append(cache_content_key)

Exception Type: AttributeError at /
Exception Value: 'SafeText' object has no attribute 'append'

[jenda1]

If there is agreement, I'll remove the "per-article-user" caching schema. It simplify the code, speed up the wiki, and fix this issue. I'll revert to "per-article" caching.

TLDR; the "per-article-user" caching schema was added in 8cc19e5 by me. The idea was to allow the creation of a plugin that renders the page differently for each user. But I have not created such plugin, I came up with an easier way to achieve what I needed. AFIK there is no plugin that uses the functionality.
The "per-article-user" is useless now, it causes problems and it is a bit expensive because cache entry can not be used for another user.

[Steckelfisch]

If there is agreement, I'll remove the "per-article-user" caching schema. It simplify the code, speed up the wiki, and fix this issue. I'll revert to "per-article" caching.

I agree.
Fyi: for me the problem appeared when i upgraded my codebase to the latest development version

[iburadempa]

I use cached sessions with LocMemCache and found the problem to be reproducible. I also couldn't find a cause in the django-wiki code. My guess would be that the cache pollution is related to sessions. But anyway, 1e4b2fd solves the problem and calls for a bugfix release!

[Steckelfisch]

I confirm #1072 solves the problem

[benjaoming]

#1080 may fix the exception but it will produce wrong cache results because the user session isn't taken into account.

[Steckelfisch]

in models/Article.py, near line 260
The first view of an Article shows correctly.
Then, for each Article entry, two entries are stored.
The second view of the same Article throws the exeption

cache_key = self.get_cache_key() # value: wikiarticle85nl-nl
cache_content_key = self.get_cache_content_key(user) # value: wikiarticle85nl-nl
. . . . .
cache.set(cache_key, cached_items, settings.CACHE_TIMEOUT)
cache.set(cache_content_key, cached_content, settings.CACHE_TIMEOUT)

I think the first cache entry will be overwritten with the second one.

[Steckelfisch]

ah. Found it.

the user key is sluggified, and that removes the ':'. AnonymousUser has an empty lastname, so the resulting cache_content_key
is equal to the cache_key.
models/article.py, line 235:
key_raw = "{key}:{user}".format()
should be:
key_raw = "{key}-{user}".format()

then, everything woks correctly.

@jenda1 "It looks that the cache content is set outside the get_cached_content method sometimes, but I do not know where..."
you where almost right :-)

[Steckelfisch]

I wil update test_cache test in test_models. Then I will fix the issue and submit a pull request.

[mesenev]

My main page gives me 500 because of this. Any workaround for 0.7?

[benjaoming]

This issue is back and is confirmed with test cases added recently.