Fixed #25598 -- Added SCRIPT_NAME prefix to STATIC_URL and MEDIA_URL set to relative paths.

Thanks Florian Apolloner for reviews.

Co-authored-by: Joel Dunham <Joel.Dunham@technicalsafetybc.ca>

5 files changed, 99 insertions, 2 deletions

diff --git a/django/conf/__init__.py b/django/conf/__init__.py
index b32e56184d..ec7efadf46 100644
--- a/django/conf/__init__.py
+++ b/django/conf/__init__.py
@@ -15,7 +15,8 @@ from pathlib import Path
 
 import django
 from django.conf import global_settings
-from django.core.exceptions import ImproperlyConfigured
+from django.core.exceptions import ImproperlyConfigured, ValidationError
+from django.core.validators import URLValidator
 from django.utils.deprecation import RemovedInDjango40Warning
 from django.utils.functional import LazyObject, empty
 
@@ -109,6 +110,26 @@ class LazySettings(LazyObject):
             setattr(holder, name, value)
         self._wrapped = holder
 
+    @staticmethod
+    def _add_script_prefix(value):
+        """
+        Add SCRIPT_NAME prefix to relative paths.
+
+        Useful when the app is being served at a subpath and manually prefixing
+        subpath to STATIC_URL and MEDIA_URL in settings is inconvenient.
+        """
+        # Don't apply prefix to valid URLs.
+        try:
+            URLValidator()(value)
+            return value
+        except (ValidationError, AttributeError):
+            pass
+        # Don't apply prefix to absolute paths.
+        if value.startswith('/'):
+            return value
+        from django.urls import get_script_prefix
+        return '%s%s' % (get_script_prefix(), value)
+
     @property
     def configured(self):
         """Return True if the settings have already been configured."""
@@ -128,6 +149,14 @@ class LazySettings(LazyObject):
             )
         return self.__getattr__('PASSWORD_RESET_TIMEOUT_DAYS')
 
+    @property
+    def STATIC_URL(self):
+        return self._add_script_prefix(self.__getattr__('STATIC_URL'))
+
+    @property
+    def MEDIA_URL(self):
+        return self._add_script_prefix(self.__getattr__('MEDIA_URL'))
+
 
 class Settings:
     def __init__(self, settings_module):
diff --git a/docs/ref/settings.txt b/docs/ref/settings.txt
index 00538ccbf7..4405d152b2 100644
--- a/docs/ref/settings.txt
+++ b/docs/ref/settings.txt
@@ -1989,6 +1989,13 @@ Example: ``"http://media.example.com/"``
     :setting:`MEDIA_URL` and :setting:`STATIC_URL` must have different
     values. See :setting:`MEDIA_ROOT` for more details.
 
+.. note::
+
+    If :setting:`MEDIA_URL` is a relative path, then it will be prefixed by the
+    server-provided value of ``SCRIPT_NAME`` (or ``/`` if not set). This makes
+    it easier to serve a Django application in a subpath without adding an
+    extra configuration to the settings.
+
 .. setting:: MIDDLEWARE
 
 ``MIDDLEWARE``
@@ -3306,6 +3313,13 @@ You may need to :ref:`configure these files to be served in development
 <serving-static-files-in-development>` and will definitely need to do so
 :doc:`in production </howto/static-files/deployment>`.
 
+.. note::
+
+    If :setting:`STATIC_URL` is a relative path, then it will be prefixed by
+    the server-provided value of ``SCRIPT_NAME`` (or ``/`` if not set). This
+    makes it easier to serve a Django application in a subpath without adding
+    an extra configuration to the settings.
+
 .. setting:: STATICFILES_DIRS
 
 ``STATICFILES_DIRS``
diff --git a/docs/releases/3.1.txt b/docs/releases/3.1.txt
index 3a9381626b..da954bab56 100644
--- a/docs/releases/3.1.txt
+++ b/docs/releases/3.1.txt
@@ -233,6 +233,11 @@ Miscellaneous
 * The compatibility imports of ``Context``, ``ContextPopException``, and
   ``RequestContext`` in ``django.template.base`` are removed.
 
+* The :setting:`STATIC_URL` and :setting:`MEDIA_URL` settings set to relative
+  paths are now prefixed by the server-provided value of ``SCRIPT_NAME`` (or
+  ``/`` if not set). This change should not affect settings set to valid URLs
+  or absolute paths.
+
 .. _deprecated-features-3.1:
 
 Features deprecated in 3.1
diff --git a/tests/file_storage/tests.py b/tests/file_storage/tests.py
index 1c4176014c..1f7fd94b5a 100644
--- a/tests/file_storage/tests.py
+++ b/tests/file_storage/tests.py
@@ -521,7 +521,7 @@ class FileStorageTests(SimpleTestCase):
         defaults_storage = self.storage_class()
         settings = {
             'MEDIA_ROOT': 'overridden_media_root',
-            'MEDIA_URL': 'overridden_media_url/',
+            'MEDIA_URL': '/overridden_media_url/',
             'FILE_UPLOAD_PERMISSIONS': 0o333,
             'FILE_UPLOAD_DIRECTORY_PERMISSIONS': 0o333,
         }
diff --git a/tests/settings_tests/tests.py b/tests/settings_tests/tests.py
index d663f6e819..55ca0de524 100644
--- a/tests/settings_tests/tests.py
+++ b/tests/settings_tests/tests.py
@@ -12,6 +12,7 @@ from django.test import (
     override_settings, signals,
 )
 from django.test.utils import requires_tz_support
+from django.urls import clear_script_prefix, set_script_prefix
 
 
 @modify_settings(ITEMS={
@@ -567,3 +568,51 @@ class OverrideSettingsIsolationOnExceptionTests(SimpleTestCase):
         signals.setting_changed.disconnect(self.receiver)
         # This call shouldn't raise any errors.
         decorated_function()
+
+
+class MediaURLStaticURLPrefixTest(SimpleTestCase):
+    def set_script_name(self, val):
+        clear_script_prefix()
+        if val is not None:
+            set_script_prefix(val)
+
+    def test_not_prefixed(self):
+        # Don't add SCRIPT_NAME prefix to valid URLs, absolute paths or None.
+        tests = (
+            '/path/',
+            'http://myhost.com/path/',
+            None,
+        )
+        for setting in ('MEDIA_URL', 'STATIC_URL'):
+            for path in tests:
+                new_settings = {setting: path}
+                with self.settings(**new_settings):
+                    for script_name in ['/somesubpath', '/somesubpath/', '/', '', None]:
+                        with self.subTest(script_name=script_name, **new_settings):
+                            try:
+                                self.set_script_name(script_name)
+                                self.assertEqual(getattr(settings, setting), path)
+                            finally:
+                                clear_script_prefix()
+
+    def test_add_script_name_prefix(self):
+        tests = (
+            # Relative paths.
+            ('/somesubpath', 'path/', '/somesubpath/path/'),
+            ('/somesubpath/', 'path/', '/somesubpath/path/'),
+            ('/', 'path/', '/path/'),
+            # Invalid URLs.
+            ('/somesubpath/', 'htp://myhost.com/path/', '/somesubpath/htp://myhost.com/path/'),
+            # Blank settings.
+            ('/somesubpath/', '', '/somesubpath/'),
+        )
+        for setting in ('MEDIA_URL', 'STATIC_URL'):
+            for script_name, path, expected_path in tests:
+                new_settings = {setting: path}
+                with self.settings(**new_settings):
+                    with self.subTest(script_name=script_name, **new_settings):
+                        try:
+                            self.set_script_name(script_name)
+                            self.assertEqual(getattr(settings, setting), expected_path)
+                        finally:
+                            clear_script_prefix()