WIP: Refs #35281 -- Unified and generalized request error handling.

django/conf/urls/__init__.py

@@ -1,9 +1,3 @@
 from django.urls import include
-from django.views import defaults
 
-__all__ = ["handler400", "handler403", "handler404", "handler500", "include"]
-
-handler400 = defaults.bad_request
-handler403 = defaults.permission_denied
-handler404 = defaults.page_not_found
-handler500 = defaults.server_error
+__all__ = ["include"]

django/core/checks/urls.py

@@ -131,7 +131,7 @@ def check_custom_error_handlers(app_configs, **kwargs):
     errors = []
     # All handlers take (request, exception) arguments except handler500
     # which takes (request).
-    for status_code, num_parameters in [(400, 2), (403, 2), (404, 2), (500, 1)]:
+    for status_code, num_parameters in [(400, 2), (403, 2), (404, 2), (500, 2)]:
         try:
             handler = resolver.resolve_error_handler(status_code)
         except (ImportError, ViewDoesNotExist) as e:

django/http/response.py

@@ -211,6 +211,23 @@ class HttpResponseBase:
     def get(self, header, alternate=None):
         return self.headers.get(header, alternate)
 
+    @classmethod
+    def response_class_by_status_code(cls, status_code):
+        return {
+            200: HttpResponse,
+            301: HttpResponsePermanentRedirect,
+            302: HttpResponseRedirect,
+            304: HttpResponseNotModified,
+            307: HttpResponseRedirect,
+            308: HttpResponsePermanentRedirect,
+            400: HttpResponseBadRequest,
+            403: HttpResponseForbidden,
+            404: HttpResponseNotFound,
+            405: HttpResponseNotAllowed,
+            410: HttpResponseGone,
+            500: HttpResponseServerError,
+        }.get(status_code, cls)
+
     def set_cookie(
         self,
         key,

django/urls/resolvers.py

@@ -10,6 +10,7 @@ import functools
 import inspect
 import re
 import string
+import warnings
 from importlib import import_module
 from pickle import PicklingError
 from urllib.parse import quote
@@ -21,6 +22,7 @@ from django.core.checks import Error, Warning
 from django.core.checks.urls import check_resolver
 from django.core.exceptions import ImproperlyConfigured
 from django.utils.datastructures import MultiValueDict
+from django.utils.deprecation import RemovedInDjango61Warning
 from django.utils.functional import cached_property
 from django.utils.http import RFC3986_SUBDELIMS, escape_leading_slashes
 from django.utils.regex_helper import _lazy_re_compile, normalize
@@ -728,15 +730,26 @@ class URLResolver:
             raise ImproperlyConfigured(msg.format(name=self.urlconf_name)) from e
         return patterns
 
-    def resolve_error_handler(self, view_type):
-        callback = getattr(self.urlconf_module, "handler%s" % view_type, None)
-        if not callback:
-            # No handler specified in file; use lazy import, since
-            # django.conf.urls imports this file.
-            from django.conf import urls
-
-            callback = getattr(urls, "handler%s" % view_type)
+    def resolve_error_handler(self, status_code):
+        # RemovedInDjango61Warning.
+        callback = getattr(self.urlconf_module, f"handler{status_code}", None)
+        if callback:
+            warnings.warn(
+                "handler<status> custom error handlers are deprecated, please "
+                "replace them by a generic `error_handler` view function.",
+                RemovedInDjango61Warning,
+            )
             return get_callable(callback)
+        error_view = getattr(self.urlconf_module, "error_handler", None)
+        if error_view:
+            error_view.status_code = status_code
+        else:
+            # No handler specified in file; use lazy import, since
+            # django.views.defaults imports this file.
+            from django.views.defaults import DefaultErrorView
+
+            error_view = DefaultErrorView.as_view(status_code=status_code)
+        return error_view
 
     def reverse(self, lookup_view, *args, **kwargs):
         return self._reverse_with_prefix(lookup_view, "", *args, **kwargs)

django/views/defaults.py

@@ -1,13 +1,17 @@
 from urllib.parse import quote
 
 from django.http import (
+    HttpResponse,
     HttpResponseBadRequest,
     HttpResponseForbidden,
     HttpResponseNotFound,
     HttpResponseServerError,
 )
 from django.template import Context, Engine, TemplateDoesNotExist, loader
+from django.utils.decorators import method_decorator
+from django.views.debug import DEBUG_ENGINE
 from django.views.decorators.csrf import requires_csrf_token
+from django.views.generic.base import ContextMixin, View
 
 ERROR_404_TEMPLATE_NAME = "404.html"
 ERROR_403_TEMPLATE_NAME = "403.html"
@@ -148,3 +152,63 @@ def permission_denied(request, exception, template_name=ERROR_403_TEMPLATE_NAME)
     return HttpResponseForbidden(
         template.render(request=request, context={"exception": str(exception)})
     )
+
+
+@method_decorator(requires_csrf_token, name="dispatch")
+class DefaultErrorView(ContextMixin, View):
+    status_code = None
+    context_by_status = {
+        400: {"title": "Bad Request (400)", "details": ""},
+        403: {"title": "403 Forbidden", "details": ""},
+        404: {
+            "title": "Not Found",
+            "details": "The requested resource was not found on this server.",
+        },
+        500: {"title": "Server Error (500)", "details": ""},
+    }
+
+    def setup(self, request, exception=None, **kwargs):
+        self.exception = exception
+        return super().setup(request, **kwargs)
+
+    def get(self, request, *args, **kwargs):
+        response_class = HttpResponse.response_class_by_status_code(self.status_code)
+        context = self.get_context_data(**kwargs)
+        try:
+            template = loader.get_template(self.get_template_name())
+            content = template.render(context, request)
+        except TemplateDoesNotExist:
+            template = DEBUG_ENGINE.from_string(ERROR_PAGE_TEMPLATE % context)
+            content = template.render(context=Context(context))
+        return response_class(content, status=self.status_code)
+
+    def post(self, *args, **kwargs):
+        return self.get(*args, **kwargs)
+
+    def get_template_name(self):
+        return f"{self.status_code}.html"
+
+    def get_context_data(self, **kwargs):
+        context = super().get_context_data(**kwargs)
+        context |= self.context_by_status.get(
+            self.status_code, {"title": f"Error ({self.status_code})", "details": ""}
+        )
+        context |= {
+            "request_path": quote(self.request.path),
+            "exception": self.exception_as_string(),
+        }
+        return context
+
+    def exception_as_string(self):
+        if self.status_code == 404:
+            # Try to get an "interesting" exception message, if any (and not the
+            # ugly Resolver404 dictionary)
+            try:
+                message = self.exception.args[0]
+            except (AttributeError, IndexError):
+                pass
+            else:
+                if isinstance(message, str):
+                    return message
+            return self.exception.__class__.__name__
+        return str(self.exception)

docs/internals/deprecation.txt

@@ -1179,9 +1179,8 @@ details on these changes.
   ``django.contrib.gis.utils`` will be removed.
 
 * ``django.conf.urls.defaults`` will be removed. The functions
-  ``include()``, ``patterns()``, and ``url()``, plus
-  :data:`~django.conf.urls.handler404` and :data:`~django.conf.urls.handler500`
-  are now available through ``django.conf.urls``.
+  ``include()``, ``patterns()``, and ``url()``, plus ``handler404` and
+  ``handler500`` are now available through ``django.conf.urls``.
 
 * The functions ``setup_environ()`` and ``execute_manager()`` will be removed
   from :mod:`django.core.management`. This also means that the old (pre-1.4)

docs/ref/urls.txt

@@ -187,6 +187,11 @@ By default, this is :func:`django.views.defaults.bad_request`. If you
 implement a custom view, be sure it accepts ``request`` and ``exception``
 arguments and returns an :class:`~django.http.HttpResponseBadRequest`.
 
+.. deprecated:: 5.2
+
+    The ``handler<code>`` handlers are deprecated and should be replaced by a
+    generic ``error_handler`` view function.
+
 ``handler403``
 ==============
 
@@ -200,6 +205,12 @@ By default, this is :func:`django.views.defaults.permission_denied`. If you
 implement a custom view, be sure it accepts ``request`` and ``exception``
 arguments and returns an :class:`~django.http.HttpResponseForbidden`.
 
+
+.. deprecated:: 5.2
+
+    The ``handler<code>`` handlers are deprecated and should be replaced by a
+    generic ``error_handler`` view function.
+
 ``handler404``
 ==============
 
@@ -212,6 +223,12 @@ By default, this is :func:`django.views.defaults.page_not_found`. If you
 implement a custom view, be sure it accepts ``request`` and ``exception``
 arguments and returns an :class:`~django.http.HttpResponseNotFound`.
 
+
+.. deprecated:: 5.2
+
+    The ``handler<code>`` handlers are deprecated and should be replaced by a
+    generic ``error_handler`` view function.
+
 ``handler500``
 ==============
 
@@ -224,3 +241,8 @@ have runtime errors in view code.
 By default, this is :func:`django.views.defaults.server_error`. If you
 implement a custom view, be sure it accepts a ``request`` argument and returns
 an :class:`~django.http.HttpResponseServerError`.
+
+.. deprecated:: 5.2
+
+    The ``handler<code>`` handlers are deprecated and should be replaced by a
+    generic ``error_handler`` view function.

docs/ref/views.txt

@@ -58,8 +58,61 @@ parameter will be transparently passed to the view.
 Error views
 ===========
 
-Django comes with a few views by default for handling HTTP errors. To override
-these with your own custom views, see :ref:`customizing-error-views`.
+When any uncaught exception is produced by a view of your site, Django is
+calling an error handling view, which is by default the following view.
+
+.. _default_error_view:
+
+The default error view
+----------------------
+
+.. class:: defaults.DefaultErrorView
+
+    .. versionadded:: 5.2 
+
+    The view is a class-based-view inheriting from
+    :class:`~django.views.generic.base.ContextMixin`
+    and class:`~django.views.generic.base.View`, so refer to theses classes for
+    common attributes and methods.
+
+    .. attribute:: status_code
+
+        The status code of the HTTP response to return.
+
+    .. attribute:: exception
+
+        The exception that produced the error leading to the call of this error
+        view.
+
+    .. method:: get_template_name()
+
+        Return by default a name on the pattern ``<status_code>.html``.
+
+    .. method:: exception_as_string()
+
+        Produce a string from the exception having triggered the error view.
+
+If you provide any template in your root template directory named after an error
+response code (``404.html``, ``500.html``, etc.), that template will be used to
+produce an error path. Otherwise, Django will produce a very simple page
+containing an error title and a standard message.
+
+The context used to render the error templates contains the following keys:
+
+    * ``title``: A short title for the error (like ``Not Found`` for a 404
+      error).
+    * ``details``: A short message explaining the error, possibley empty.
+    * ``request_path``: The original request path of the view producing the
+      error, quoted to prevent a content injection attack.
+    * ``exception``: The uncaught exception that triggered the error view, as a
+      string.
+
+which either produces a "Not
+Found" message or loads and renders the template ``404.html`` if you created it
+in your root template directory.
+
+To override this default view with your custom view, see
+:ref:`customizing-error-views`.
 
 .. _http_not_found_view:
 
@@ -68,6 +121,11 @@ The 404 (page not found) view
 
 .. function:: defaults.page_not_found(request, exception, template_name='404.html')
 
+.. deprecated:: 5.2
+
+    This view is deprecated as it has been replaced by the :ref:`default error
+    view <_default_error_view>`.
+
 When you raise :exc:`~django.http.Http404` from within a view, Django loads a
 special view devoted to handling 404 errors. By default, it's the view
 :func:`django.views.defaults.page_not_found`, which either produces a "Not
@@ -99,6 +157,11 @@ The 500 (server error) view
 
 .. function:: defaults.server_error(request, template_name='500.html')
 
+.. deprecated:: 5.2
+
+    This view is deprecated as it has been replaced by the :ref:`default error
+    view <_default_error_view>`.
+
 Similarly, Django executes special-case behavior in the case of runtime errors
 in view code. If a view results in an exception, Django will, by default, call
 the view ``django.views.defaults.server_error``, which either produces a
@@ -119,6 +182,11 @@ The 403 (HTTP Forbidden) view
 
 .. function:: defaults.permission_denied(request, exception, template_name='403.html')
 
+.. deprecated:: 5.2
+
+    This view is deprecated as it has been replaced by the :ref:`default error
+    view <_default_error_view>`.
+
 In the same vein as the 404 and 500 views, Django has a view to handle 403
 Forbidden errors. If a view results in a 403 exception then Django will, by
 default, call the view ``django.views.defaults.permission_denied``.
@@ -148,6 +216,11 @@ The 400 (bad request) view
 
 .. function:: defaults.bad_request(request, exception, template_name='400.html')
 
+.. deprecated:: 5.2
+
+    This view is deprecated as it has been replaced by the :ref:`default error
+    view <_default_error_view>`.
+
 When a :exc:`~django.core.exceptions.SuspiciousOperation` is raised in Django,
 it may be handled by a component of Django (for example resetting the session
 data). If not specifically handled, Django will consider the current request a

docs/topics/http/urls.txt

@@ -342,25 +342,28 @@ Error handling
 When Django can't find a match for the requested URL, or when an exception is
 raised, Django invokes an error-handling view.
 
-The views to use for these cases are specified by four variables. Their
-default values should suffice for most projects, but further customization is
-possible by overriding their default values.
+The default view Django uses for these cases is
+:class:`django.views.defaults.DefaultErrorView`. This view should suffice for
+most projects but further customization is possible by defining a custom view
+to handle errors, either by subclassing this view or by creating your own.
 
-See the documentation on :ref:`customizing error views
+See the documentation on :ref:`customizing error view
 <customizing-error-views>` for the full details.
 
-Such values can be set in your root URLconf. Setting these variables in any
-other URLconf will have no effect.
+.. versionchanged:: 5.2
+
+    In previous versions, the views to use for these cases are specified by four
+    variables.
 
     Values must be callables, or strings representing the full Python import path
     to the view that should be called to handle the error condition at hand.
 
     The variables are:
 
-* ``handler400`` -- See :data:`django.conf.urls.handler400`.
-* ``handler403`` -- See :data:`django.conf.urls.handler403`.
-* ``handler404`` -- See :data:`django.conf.urls.handler404`.
-* ``handler500`` -- See :data:`django.conf.urls.handler500`.
+    * ``handler400``
+    * ``handler403``
+    * ``handler404``
+    * ``handler500``
 
 .. _including-other-urlconfs:
 

docs/topics/http/views.txt

@@ -138,13 +138,26 @@ template.
 
 .. _customizing-error-views:
 
-Customizing error views
-=======================
+Customizing error view
+======================
 
-The default error views in Django should suffice for most web applications,
-but can easily be overridden if you need any custom behavior. Specify the
-handlers as seen below in your URLconf (setting them anywhere else will have no
-effect).
+The default error view in Django should suffice for most web applications, but
+but can easily be overridden if you need any custom behavior.
+
+The default error view can be overridden by setting a view in the
+``error_handler`` variable in your URLconf (setting it anywhere else will have
+no effect)::
+
+    error_handler = views.my_custom_error_view
+
+or if you have a class-based-view::
+
+    error_handler = views.MyCustomErrorView.as_view()
+
+.. versionchanged:: 5.2
+
+    On previous versions, there are multiple variables to define to override
+    particular views.
 
     The :func:`~django.views.defaults.page_not_found` view is overridden by
     :data:`~django.conf.urls.handler404`::

tests/check_framework/test_urls.py

@@ -8,8 +8,9 @@ from django.core.checks.urls import (
     check_url_settings,
     get_warning_for_invalid_pattern,
 )
-from django.test import SimpleTestCase
+from django.test import SimpleTestCase, ignore_warnings
 from django.test.utils import override_settings
+from django.utils.deprecation import RemovedInDjango61Warning
 
 
 class CheckUrlConfigTests(SimpleTestCase):
@@ -243,10 +244,11 @@ class CheckCustomErrorHandlersTests(SimpleTestCase):
     @override_settings(
         ROOT_URLCONF="check_framework.urls.bad_function_based_error_handlers",
     )
+    @ignore_warnings(category=RemovedInDjango61Warning)
     def test_bad_function_based_handlers(self):
         result = check_custom_error_handlers(None)
         self.assertEqual(len(result), 4)
-        for code, num_params, error in zip([400, 403, 404, 500], [2, 2, 2, 1], result):
+        for code, error in zip([400, 403, 404, 500], result):
             with self.subTest("handler{}".format(code)):
                 self.assertEqual(
                     error,
@@ -254,9 +256,7 @@ class CheckCustomErrorHandlersTests(SimpleTestCase):
                         "The custom handler{} view 'check_framework.urls."
                         "bad_function_based_error_handlers.bad_handler' "
                         "does not take the correct number of arguments "
-                        "(request{}).".format(
-                            code, ", exception" if num_params == 2 else ""
-                        ),
+                        "(request, exception).".format(code),
                         id="urls.E007",
                     ),
                 )
@@ -264,10 +264,11 @@ class CheckCustomErrorHandlersTests(SimpleTestCase):
     @override_settings(
         ROOT_URLCONF="check_framework.urls.bad_class_based_error_handlers",
     )
+    @ignore_warnings(category=RemovedInDjango61Warning)
     def test_bad_class_based_handlers(self):
         result = check_custom_error_handlers(None)
         self.assertEqual(len(result), 4)
-        for code, num_params, error in zip([400, 403, 404, 500], [2, 2, 2, 1], result):
+        for code, error in zip([400, 403, 404, 500], result):
             with self.subTest("handler%s" % code):
                 self.assertEqual(
                     error,
@@ -275,11 +276,7 @@ class CheckCustomErrorHandlersTests(SimpleTestCase):
                         "The custom handler%s view 'check_framework.urls."
                         "bad_class_based_error_handlers.HandlerView.as_view."
                         "<locals>.view' does not take the correct number of "
-                        "arguments (request%s)."
-                        % (
-                            code,
-                            ", exception" if num_params == 2 else "",
-                        ),
+                        "arguments (request, exception)." % code,
                         id="urls.E007",
                     ),
                 )
@@ -287,6 +284,7 @@ class CheckCustomErrorHandlersTests(SimpleTestCase):
     @override_settings(
         ROOT_URLCONF="check_framework.urls.bad_error_handlers_invalid_path"
     )
+    @ignore_warnings(category=RemovedInDjango61Warning)
     def test_bad_handlers_invalid_path(self):
         result = check_custom_error_handlers(None)
         paths = [
@@ -318,6 +316,7 @@ class CheckCustomErrorHandlersTests(SimpleTestCase):
     @override_settings(
         ROOT_URLCONF="check_framework.urls.good_function_based_error_handlers",
     )
+    @ignore_warnings(category=RemovedInDjango61Warning)
     def test_good_function_based_handlers(self):
         result = check_custom_error_handlers(None)
         self.assertEqual(result, [])
@@ -325,6 +324,7 @@ class CheckCustomErrorHandlersTests(SimpleTestCase):
     @override_settings(
         ROOT_URLCONF="check_framework.urls.good_class_based_error_handlers",
     )
+    @ignore_warnings(category=RemovedInDjango61Warning)
     def test_good_class_based_handlers(self):
         result = check_custom_error_handlers(None)
         self.assertEqual(result, [])

tests/csrf_tests/tests.py

@@ -22,7 +22,8 @@ from django.middleware.csrf import (
     get_token,
     rotate_token,
 )
-from django.test import SimpleTestCase, override_settings
+from django.test import SimpleTestCase, ignore_warnings, override_settings
+from django.utils.deprecation import RemovedInDjango61Warning
 from django.views.decorators.csrf import csrf_exempt, requires_csrf_token
 
 from .views import (
@@ -1477,6 +1478,7 @@ class CsrfViewMiddlewareUseSessionsTests(CsrfViewMiddlewareTestMixin, SimpleTest
 
 @override_settings(ROOT_URLCONF="csrf_tests.csrf_token_error_handler_urls", DEBUG=False)
 class CsrfInErrorHandlingViewsTests(CsrfFunctionTestMixin, SimpleTestCase):
+    @ignore_warnings(category=RemovedInDjango61Warning)
     def test_csrf_token_on_404_stays_constant(self):
         response = self.client.get("/does not exist/")
         # The error handler returns status code 599.

tests/handlers/tests_custom_error_handlers.py

@@ -1,7 +1,13 @@
 from django.core.exceptions import PermissionDenied
 from django.template.response import TemplateResponse
-from django.test import SimpleTestCase, modify_settings, override_settings
+from django.test import (
+    SimpleTestCase,
+    ignore_warnings,
+    modify_settings,
+    override_settings,
+)
 from django.urls import path
+from django.utils.deprecation import RemovedInDjango61Warning
 
 
 class MiddlewareAccessingContent:
@@ -38,6 +44,7 @@ handler403 = template_response_error_handler
     }
 )
 class CustomErrorHandlerTests(SimpleTestCase):
+    @ignore_warnings(category=RemovedInDjango61Warning)
     def test_handler_renders_template_response(self):
         """
         BaseHandler should render TemplateResponse if necessary.

tests/urlpatterns_reverse/tests.py

@@ -13,7 +13,13 @@ from django.contrib.auth.models import User
 from django.core.exceptions import ImproperlyConfigured, ViewDoesNotExist
 from django.http import HttpRequest, HttpResponsePermanentRedirect, HttpResponseRedirect
 from django.shortcuts import redirect
-from django.test import RequestFactory, SimpleTestCase, TestCase, override_settings
+from django.test import (
+    RequestFactory,
+    SimpleTestCase,
+    TestCase,
+    ignore_warnings,
+    override_settings,
+)
 from django.test.utils import override_script_prefix
 from django.urls import (
     NoReverseMatch,
@@ -32,6 +38,7 @@ from django.urls import (
     reverse_lazy,
 )
 from django.urls.resolvers import RegexPattern
+from django.utils.deprecation import RemovedInDjango61Warning
 
 from . import middleware, urlconf_outer, views
 from .utils import URLObject
@@ -1473,12 +1480,15 @@ class ErrorHandlerResolutionTests(SimpleTestCase):
         self.resolver = URLResolver(RegexPattern(r"^$"), urlconf)
         self.callable_resolver = URLResolver(RegexPattern(r"^$"), urlconf_callables)
 
+    @ignore_warnings(category=RemovedInDjango61Warning)
     def test_named_handlers(self):
         for code in [400, 403, 404, 500]:
             with self.subTest(code=code):
                 self.assertEqual(self.resolver.resolve_error_handler(code), empty_view)
 
+    @ignore_warnings(category=RemovedInDjango61Warning)
     def test_callable_handlers(self):
+        # After Django 6.1 removal, only test with 'error_handler' and one code.
         for code in [400, 403, 404, 500]:
             with self.subTest(code=code):
                 self.assertEqual(

tests/urlpatterns_reverse/urls_error_handlers_callables.py

@@ -4,7 +4,9 @@ from .views import empty_view
 
 urlpatterns = []
 
+# RemovedInDjango61Warning: the handler<...> variables can be removed
 handler400 = empty_view
 handler403 = empty_view
 handler404 = empty_view
 handler500 = empty_view
+error_handler = empty_view

tests/urlpatterns_reverse/urls_without_handlers.py

@@ -1,4 +1,4 @@
-# A URLconf that doesn't define any handlerXXX.
+# A URLconf that doesn't define any error handler view.
 from django.urls import path
 
 from .views import bad_view, empty_view