Fixed #30451 -- Added ASGI handler and coroutine-safety.

This adds an ASGI handler, asgi.py file for the default project layout,
a few async utilities and adds async-safety to many parts of Django.

django/conf/project_template/project_name/asgi.py-tpl

@@ -0,0 +1,16 @@
+"""
+ASGI config for {{ project_name }} project.
+
+It exposes the ASGI callable as a module-level variable named ``application``.
+
+For more information on this file, see
+https://docs.djangoproject.com/en/{{ docs_version }}/howto/deployment/asgi/
+"""
+
+import os
+
+from django.core.asgi import get_asgi_application
+
+os.environ.setdefault('DJANGO_SETTINGS_MODULE', '{{ project_name }}.settings')
+
+application = get_asgi_application()

django/contrib/staticfiles/handlers.py

@@ -4,25 +4,20 @@
 from django.conf import settings
 from django.contrib.staticfiles import utils
 from django.contrib.staticfiles.views import serve
+from django.core.handlers.asgi import ASGIHandler
 from django.core.handlers.exception import response_for_exception
 from django.core.handlers.wsgi import WSGIHandler, get_path_info
 from django.http import Http404
 
 
-class StaticFilesHandler(WSGIHandler):
+class StaticFilesHandlerMixin:
     """
-    WSGI middleware that intercepts calls to the static files directory, as
-    defined by the STATIC_URL setting, and serves those files.
+    Common methods used by WSGI and ASGI handlers.
     """
     # May be used to differentiate between handler types (e.g. in a
     # request_finished signal)
     handles_files = True
 
-    def __init__(self, application):
-        self.application = application
-        self.base_url = urlparse(self.get_base_url())
-        super().__init__()
-
     def load_middleware(self):
         # Middleware are already loaded for self.application; no need to reload
         # them for self.
@@ -57,7 +52,37 @@ def get_response(self, request):
         except Http404 as e:
             return response_for_exception(request, e)
 
+
+class StaticFilesHandler(StaticFilesHandlerMixin, WSGIHandler):
+    """
+    WSGI middleware that intercepts calls to the static files directory, as
+    defined by the STATIC_URL setting, and serves those files.
+    """
+    def __init__(self, application):
+        self.application = application
+        self.base_url = urlparse(self.get_base_url())
+        super().__init__()
+
     def __call__(self, environ, start_response):
         if not self._should_handle(get_path_info(environ)):
             return self.application(environ, start_response)
         return super().__call__(environ, start_response)
+
+
+class ASGIStaticFilesHandler(StaticFilesHandlerMixin, ASGIHandler):
+    """
+    ASGI application which wraps another and intercepts requests for static
+    files, passing them off to Django's static file serving.
+    """
+    def __init__(self, application):
+        self.application = application
+        self.base_url = urlparse(self.get_base_url())
+
+    async def __call__(self, scope, receive, send):
+        # Only even look at HTTP requests
+        if scope['type'] == 'http' and self._should_handle(scope['path']):
+            # Serve static content
+            # (the one thing super() doesn't do is __call__, apparently)
+            return await super().__call__(scope, receive, send)
+        # Hand off to the main app
+        return await self.application(scope, receive, send)

django/core/asgi.py

@@ -0,0 +1,13 @@
+import django
+from django.core.handlers.asgi import ASGIHandler
+
+
+def get_asgi_application():
+    """
+    The public interface to Django's ASGI support. Return an ASGI 3 callable.
+
+    Avoids making django.core.handlers.ASGIHandler a public API, in case the
+    internal implementation changes or moves in the future.
+    """
+    django.setup(set_prefix=False)
+    return ASGIHandler()

django/core/exceptions.py

@@ -63,6 +63,11 @@ class RequestDataTooBig(SuspiciousOperation):
     pass
 
 
+class RequestAborted(Exception):
+    """The request was closed before it was completed, or timed out."""
+    pass
+
+
 class PermissionDenied(Exception):
     """The user did not have permission to do that"""
     pass
@@ -181,3 +186,8 @@ def __repr__(self):
 class EmptyResultSet(Exception):
     """A database query predicate is impossible."""
     pass
+
+
+class SynchronousOnlyOperation(Exception):
+    """The user tried to call a sync-only function from an async context."""
+    pass