Invalid base64-encoded string: number of data characters (217) cannot be 1 more than a multiple of 4

Question

I am learning Django and creating a to-do app using the framework. While setting up the Django rest framework API, I got an unusual error. I've been using Django for quite a while, but have never come across this error before. I don't know why this error is getting thrown.

The error occurred the very first time when I executed the command manage.py runserver and navigated to users.

The error is as below:

Invalid base64-encoded string: number of data characters (217) cannot be 1 more than a multiple of 4
Request Method: GET
Request URL:    http://127.0.0.1:8001/users/
Django Version: 3.1
Exception Type: Error
Exception Value:    
Invalid base64-encoded string: number of data characters (217) cannot be 1 more than a multiple of 4
Exception Location: /usr/local/Cellar/[email protected]/3.8.5/Frameworks/Python.framework/Versions/3.8/lib/python3.8/base64.py, line 87, in b64decode
Python Executable:  /Users/yogendrakumar/PycharmProjects/todo_app/bin/python
Python Version: 3.8.5
Python Path:    
['/Users/yogendrakumar/PycharmProjects/todo_app',
 '/usr/local/Cellar/[email protected]/3.8.5/Frameworks/Python.framework/Versions/3.8/lib/python38.zip',
 '/usr/local/Cellar/[email protected]/3.8.5/Frameworks/Python.framework/Versions/3.8/lib/python3.8',
 '/usr/local/Cellar/[email protected]/3.8.5/Frameworks/Python.framework/Versions/3.8/lib/python3.8/lib-dynload',
 '/Users/yogendrakumar/PycharmProjects/todo_app/lib/python3.8/site-packages']
Server time:    Sat, 29 Aug 2020 12:25:01 +0530

views.py:

from django.contrib.auth.models import User, Group
from rest_framework import viewsets
from rest_framework import permissions
from todo.serializers import UserSerializer, GroupSerializer


class UserViewSet(viewsets.ModelViewSet):
    """
    API endpoint that allows users to be viewed or edited.
    """
    queryset = User.objects.all().order_by('-date_joined')
    serializer_class = UserSerializer
    permission_classes = [permissions.IsAuthenticated]


class GroupViewSet(viewsets.ModelViewSet):
    """
    API endpoint that allows groups to be viewed or edited.
    """
    queryset = Group.objects.all()
    serializer_class = GroupSerializer
    permission_classes = [permissions.IsAuthenticated]

Below is the stack trace/traceback:

Environment:


Request Method: GET
Request URL: http://127.0.0.1:8001/users/

Django Version: 3.1
Python Version: 3.8.5
Installed Applications:
['django.contrib.admin',
 'django.contrib.auth',
 'django.contrib.contenttypes',
 'django.contrib.sessions',
 'django.contrib.messages',
 'django.contrib.staticfiles',
 'rest_framework',
 'todo']
Installed Middleware:
['django.middleware.security.SecurityMiddleware',
 'django.contrib.sessions.middleware.SessionMiddleware',
 'django.middleware.common.CommonMiddleware',
 'django.middleware.csrf.CsrfViewMiddleware',
 'django.contrib.auth.middleware.AuthenticationMiddleware',
 'django.contrib.messages.middleware.MessageMiddleware',
 'django.middleware.clickjacking.XFrameOptionsMiddleware']



Traceback (most recent call last):
  File "/Users/yogendrakumar/PycharmProjects/todo_app/lib/python3.8/site-packages/django/contrib/sessions/backends/base.py", line 215, in _get_session
    return self._session_cache

During handling of the above exception ('SessionStore' object has no attribute '_session_cache'), another exception occurred:
  File "/Users/yogendrakumar/PycharmProjects/todo_app/lib/python3.8/site-packages/django/contrib/sessions/backends/base.py", line 118, in decode
    return signing.loads(session_data, salt=self.key_salt, serializer=self.serializer)
  File "/Users/yogendrakumar/PycharmProjects/todo_app/lib/python3.8/site-packages/django/core/signing.py", line 135, in loads
    base64d = TimestampSigner(key, salt=salt).unsign(s, max_age=max_age).encode()
  File "/Users/yogendrakumar/PycharmProjects/todo_app/lib/python3.8/site-packages/django/core/signing.py", line 201, in unsign
    result = super().unsign(value)
  File "/Users/yogendrakumar/PycharmProjects/todo_app/lib/python3.8/site-packages/django/core/signing.py", line 184, in unsign
    raise BadSignature('Signature "%s" does not match' % sig)

During handling of the above exception (Signature "xnqTuv_ylPs2HNImqZUFHZYYDRY5IfETbWXc5_4zbB8" does not match), another exception occurred:
  File "/Users/yogendrakumar/PycharmProjects/todo_app/lib/python3.8/site-packages/django/core/handlers/exception.py", line 47, in inner
    response = get_response(request)
  File "/Users/yogendrakumar/PycharmProjects/todo_app/lib/python3.8/site-packages/django/core/handlers/base.py", line 179, in _get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "/Users/yogendrakumar/PycharmProjects/todo_app/lib/python3.8/site-packages/django/views/decorators/csrf.py", line 54, in wrapped_view
    return view_func(*args, **kwargs)
  File "/Users/yogendrakumar/PycharmProjects/todo_app/lib/python3.8/site-packages/rest_framework/viewsets.py", line 114, in view
    return self.dispatch(request, *args, **kwargs)
  File "/Users/yogendrakumar/PycharmProjects/todo_app/lib/python3.8/site-packages/rest_framework/views.py", line 505, in dispatch
    response = self.handle_exception(exc)
  File "/Users/yogendrakumar/PycharmProjects/todo_app/lib/python3.8/site-packages/rest_framework/views.py", line 465, in handle_exception
    self.raise_uncaught_exception(exc)
  File "/Users/yogendrakumar/PycharmProjects/todo_app/lib/python3.8/site-packages/rest_framework/views.py", line 476, in raise_uncaught_exception
    raise exc
  File "/Users/yogendrakumar/PycharmProjects/todo_app/lib/python3.8/site-packages/rest_framework/views.py", line 493, in dispatch
    self.initial(request, *args, **kwargs)
  File "/Users/yogendrakumar/PycharmProjects/todo_app/lib/python3.8/site-packages/rest_framework/views.py", line 410, in initial
    self.perform_authentication(request)
  File "/Users/yogendrakumar/PycharmProjects/todo_app/lib/python3.8/site-packages/rest_framework/views.py", line 324, in perform_authentication
    request.user
  File "/Users/yogendrakumar/PycharmProjects/todo_app/lib/python3.8/site-packages/rest_framework/request.py", line 220, in user
    self._authenticate()
  File "/Users/yogendrakumar/PycharmProjects/todo_app/lib/python3.8/site-packages/rest_framework/request.py", line 373, in _authenticate
    user_auth_tuple = authenticator.authenticate(self)
  File "/Users/yogendrakumar/PycharmProjects/todo_app/lib/python3.8/site-packages/rest_framework/authentication.py", line 123, in authenticate
    if not user or not user.is_active:
  File "/Users/yogendrakumar/PycharmProjects/todo_app/lib/python3.8/site-packages/django/utils/functional.py", line 240, in inner
    self._setup()
  File "/Users/yogendrakumar/PycharmProjects/todo_app/lib/python3.8/site-packages/django/utils/functional.py", line 376, in _setup
    self._wrapped = self._setupfunc()
  File "/Users/yogendrakumar/PycharmProjects/todo_app/lib/python3.8/site-packages/django/contrib/auth/middleware.py", line 23, in <lambda>
    request.user = SimpleLazyObject(lambda: get_user(request))
  File "/Users/yogendrakumar/PycharmProjects/todo_app/lib/python3.8/site-packages/django/contrib/auth/middleware.py", line 11, in get_user
    request._cached_user = auth.get_user(request)
  File "/Users/yogendrakumar/PycharmProjects/todo_app/lib/python3.8/site-packages/django/contrib/auth/__init__.py", line 174, in get_user
    user_id = _get_user_session_key(request)
  File "/Users/yogendrakumar/PycharmProjects/todo_app/lib/python3.8/site-packages/django/contrib/auth/__init__.py", line 58, in _get_user_session_key
    return get_user_model()._meta.pk.to_python(request.session[SESSION_KEY])
  File "/Users/yogendrakumar/PycharmProjects/todo_app/lib/python3.8/site-packages/django/contrib/sessions/backends/base.py", line 65, in __getitem__
    return self._session[key]
  File "/Users/yogendrakumar/PycharmProjects/todo_app/lib/python3.8/site-packages/django/contrib/sessions/backends/base.py", line 220, in _get_session
    self._session_cache = self.load()
  File "/Users/yogendrakumar/PycharmProjects/todo_app/lib/python3.8/site-packages/django/contrib/sessions/backends/db.py", line 44, in load
    return self.decode(s.session_data) if s else {}
  File "/Users/yogendrakumar/PycharmProjects/todo_app/lib/python3.8/site-packages/django/contrib/sessions/backends/base.py", line 122, in decode
    return self._legacy_decode(session_data)
  File "/Users/yogendrakumar/PycharmProjects/todo_app/lib/python3.8/site-packages/django/contrib/sessions/backends/base.py", line 126, in _legacy_decode
    encoded_data = base64.b64decode(session_data.encode('ascii'))
  File "/usr/local/Cellar/[email protected]/3.8.5/Frameworks/Python.framework/Versions/3.8/lib/python3.8/base64.py", line 87, in b64decode
    return binascii.a2b_base64(s)

Exception Type: Error at /users/
Exception Value: Invalid base64-encoded string: number of data characters (217) cannot be 1 more than a multiple of 4

serializers.py:

from django.contrib.auth.models import User, Group
from rest_framework import serializers


class UserSerializer(serializers.HyperlinkedModelSerializer):
    class Meta:
        model = User
        fields = ['url', 'username', 'email', 'groups']


class GroupSerializer(serializers.HyperlinkedModelSerializer):
    class Meta:
        model = Group
        fields = ['url', 'name']

Answer 1

The reason this error crops up because you're on a wrong version of Django. If you haven't changed anything with the version of Django, then the issue most probably is that you've forgotten to activate your correct virtual environment.