RecursionError on deepcopy of Request

[mlegner]

I noticed that calling deepcopy on a Request object causes infinite recursion with a RecursionError.

Minimal working example:

import copy
from django.conf import settings
from django.http.request import HttpRequest
from rest_framework.request import Request

settings.configure()
request = Request(HttpRequest())
copy.deepcopy(request)

This produces the following output:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "~/.asdf/installs/python/3.10.5/lib/python3.10/copy.py", line 172, in deepcopy
    y = _reconstruct(x, memo, *rv)
  File "~/.asdf/installs/python/3.10.5/lib/python3.10/copy.py", line 272, in _reconstruct
    if hasattr(y, '__setstate__'):
  File "~/python_playground/.venv/lib/python3.10/site-packages/rest_framework/request.py", line 426, in __getattr__
    return getattr(self._request, attr)
  File "~/python_playground/.venv/lib/python3.10/site-packages/rest_framework/request.py", line 426, in __getattr__
    return getattr(self._request, attr)
  File "~/python_playground/.venv/lib/python3.10/site-packages/rest_framework/request.py", line 426, in __getattr__
    return getattr(self._request, attr)
  [Previous line repeated 993 more times]
RecursionError: maximum recursion depth exceeded

The problem seems to be the custom __getattr__ function defined in rest_framework/request.py#L410-L418:

    def __getattr__(self, attr):
        """
        If an attribute does not exist on this instance, then we also attempt
        to proxy it to the underlying HttpRequest object.
        """
        try:
            return getattr(self._request, attr)
        except AttributeError:
            return self.__getattribute__(attr)

For some reason, there is a Request instance without _request attribute, so that the self._request in this function causes another call to __getattr__. A possible fix that works for me (and is otherwise equal to the current implementation) is the following:

-            return getattr(self._request, attr)
+            _request = self.__getattribute__("_request")
+            return getattr(_request, attr)

I would be happy to convert this to an issue and/or create a PR with this change.

My program versions:

• Python: 3.10.5
• Django: 4.1.2
• rest_framework: 3.14.0

[tomchristie]

Okay - I don't quite understand that, but must be something to do with the implementation details of deepcopy.

(Ie. at some point we've got a new Request instance, but ._request is not yet populated.)

I guess a test case and a fix would probably be okay here. What's the use-case for deepcopy on the request instance?

[mlegner]

Thanks for the quick feedback, @tomchristie!

Okay - I don't quite understand that, but must be something to do with the implementation details of deepcopy.

(Ie. at some point we've got a new Request instance, but ._request is not yet populated.)

Yes, that's what I found in my debugging session. But I also didn't quite get to the root cause there.

What's the use-case for deepcopy on the request instance?

This is in the context of drf-spectacular, where Requests are attached to Serializers for schema generation (see tfranzel/drf-spectacular#792); when calling get_fields and one of the fields is a serializer with a Request attached, this issue is triggered.

This does not happen with the default behavior of drf-spectacular, but I hit this with a custom AutoSchema in one of my projects.

I guess a test case and a fix would probably be okay here.

Should I create a PR for this?

[tomchristie]

Should I create a PR for this?

Sure thing, yup.

[tomchristie]

---> #8684