fix(django): Await async middleware process_* hooks

When an async Django middleware defines an `async def` hook such as
`process_view` or `process_exception`, the SDK wrapped it in a synchronous
function. That hid the coroutine from Django's `iscoroutinefunction` check in
`BaseHandler.load_middleware`, so Django wrapped the hook in `SyncToAsync` and
called it synchronously. The underlying coroutine was then never awaited, and
the request failed with:

```
ValueError: The view ... didn't return an HttpResponse object.
            It returned an unawaited coroutine instead.
```

`_get_wrapped_method` in the Django middleware integration now produces an
`async def` wrapper when the wrapped middleware hook is a coroutine function,
instead of always producing a synchronous wrapper.

Author: Romain Fliedel

sentry_sdk/integrations/django/middleware.py

@@ -32,8 +32,9 @@
 
 if not DJANGO_SUPPORTS_ASYNC_MIDDLEWARE:
     _asgi_middleware_mixin_factory = lambda _: object
+    iscoroutinefunction = lambda _: False
 else:
-    from .asgi import _asgi_middleware_mixin_factory
+    from .asgi import _asgi_middleware_mixin_factory, iscoroutinefunction
 
 
 def patch_django_middlewares() -> None:
@@ -104,15 +105,39 @@ def _check_middleware_span(
 
     def _get_wrapped_method(old_method: "F") -> "F":
         with capture_internal_exceptions():
+            # Middleware hooks (e.g. `process_view`, `process_exception`) may be
+            # `async def` when the middleware is async. A synchronous wrapper
+            # would hide the coroutine from Django's `iscoroutinefunction` check,
+            # causing Django to call the hook synchronously and never await the
+            # returned coroutine. Wrap async hooks with an async wrapper so the
+            # wrapped method continues to report as a coroutine function.
+            if iscoroutinefunction is not None and iscoroutinefunction(old_method):
 
-            def sentry_wrapped_method(*args: "Any", **kwargs: "Any") -> "Any":
-                middleware_span = _check_middleware_span(old_method)
+                async def async_sentry_wrapped_method(
+                    *args: "Any", **kwargs: "Any"
+                ) -> "Any":
+                    middleware_span = _check_middleware_span(old_method)
 
-                if middleware_span is None:
-                    return old_method(*args, **kwargs)
+                    if middleware_span is None:
+                        return await old_method(*args, **kwargs)
 
-                with middleware_span:
-                    return old_method(*args, **kwargs)
+                    with middleware_span:
+                        return await old_method(*args, **kwargs)
+
+                sentry_wrapped_method = async_sentry_wrapped_method
+
+            else:
+
+                def sync_sentry_wrapped_method(*args: "Any", **kwargs: "Any") -> "Any":
+                    middleware_span = _check_middleware_span(old_method)
+
+                    if middleware_span is None:
+                        return old_method(*args, **kwargs)
+
+                    with middleware_span:
+                        return old_method(*args, **kwargs)
+
+                sentry_wrapped_method = sync_sentry_wrapped_method
 
             try:
                 # fails for __call__ of function on Python 2 (see py2.7-django-1.11)

tests/integrations/django/asgi/test_asgi.py

@@ -1049,3 +1049,50 @@ async def test_transaction_http_method_custom(
         (event1, event2) = events
         assert event1["request"]["method"] == "OPTIONS"
         assert event2["request"]["method"] == "HEAD"
+
+
+@pytest.mark.asyncio
+@pytest.mark.skipif(
+    django.VERSION < (3, 1),
+    reason="async views/middleware introduced in Django 3.1",
+)
+async def test_async_middleware_process_view_is_awaited(
+    sentry_init, settings, make_asgi_application
+):
+    """Regression test for async ``process_view`` being coerced to sync."""
+    sentry_init(integrations=[DjangoIntegration()])
+
+    settings.MIDDLEWARE = [
+        "tests.integrations.django.myapp.middleware.AsyncProcessViewMiddleware"
+    ]
+    application = make_asgi_application()
+
+    comm = HttpCommunicator(application, "GET", "/simple_async_view")
+    response = await comm.get_response()
+    await comm.wait()
+
+    assert response["status"] == 200
+
+
+@pytest.mark.asyncio
+@pytest.mark.skipif(
+    django.VERSION < (3, 1),
+    reason="async views/middleware introduced in Django 3.1",
+)
+async def test_async_middleware_process_exception_is_awaited(
+    sentry_init, settings, make_asgi_application
+):
+    """Regression test for async ``process_exception`` being coerced to sync."""
+    sentry_init(integrations=[DjangoIntegration()])
+
+    settings.MIDDLEWARE = [
+        "tests.integrations.django.myapp.middleware.AsyncProcessExceptionMiddleware"
+    ]
+    application = make_asgi_application()
+
+    comm = HttpCommunicator(application, "GET", "/view-exc")
+    response = await comm.get_response()
+    await comm.wait()
+
+    assert response["status"] == 200
+    assert response["body"] == b"handled by async process_exception"

tests/integrations/django/myapp/middleware.py

@@ -3,6 +3,7 @@
 if django.VERSION >= (3, 1):
     import asyncio
 
+    from asgiref.sync import iscoroutinefunction, markcoroutinefunction
     from django.utils.decorators import sync_and_async_middleware
 
     @sync_and_async_middleware
@@ -21,6 +22,53 @@ def middleware(request):
 
         return middleware
 
+    class AsyncProcessViewMiddleware:
+        """A correctly-written async-only middleware exposing an async ``process_view``.
+        see: https://docs.djangoproject.com/en/5.2/topics/http/middleware/#asynchronous-support
+
+        This is the supported way to write async middleware per the Django docs:
+        declare ``async_capable`` and mark the instance as a coroutine when the
+        inner ``get_response`` is async.
+        """
+
+        async_capable = True
+        sync_capable = False
+
+        def __init__(self, get_response):
+            self.get_response = get_response
+            if iscoroutinefunction(self.get_response):
+                markcoroutinefunction(self)
+
+        async def __call__(self, request):
+            return await self.get_response(request)
+
+        async def process_view(self, request, view_func, view_args, view_kwargs):
+            return None
+
+    class AsyncProcessExceptionMiddleware:
+        """Async-only middleware exposing an async ``process_exception`` hook.
+
+        The view raises, so Django invokes ``process_exception``. If the async
+        ``process_exception`` is awaited correctly, it returns an ``HttpResponse``
+        that short-circuits the error and the request succeeds with status 200.
+        """
+
+        async_capable = True
+        sync_capable = False
+
+        def __init__(self, get_response):
+            self.get_response = get_response
+            if iscoroutinefunction(self.get_response):
+                markcoroutinefunction(self)
+
+        async def __call__(self, request):
+            return await self.get_response(request)
+
+        async def process_exception(self, request, exception):
+            from django.http import HttpResponse
+
+            return HttpResponse("handled by async process_exception", status=200)
+
 
 def custom_urlconf_middleware(get_response):
     def middleware(request):