Use sync/async pattern for middleware since Django 3.1

CHANGES.rst

@@ -18,6 +18,7 @@ Unreleased
 - Made ``bulk_update_with_history()`` return the number of model rows updated (gh-1206)
 - Fixed ``HistoryRequestMiddleware`` not cleaning up after itself (i.e. deleting
   ``HistoricalRecords.context.request``) under some circumstances (gh-1188)
+- Made ``HistoryRequestMiddleware`` async-capable (gh-1209)
 
 3.3.0 (2023-03-08)
 ------------------

simple_history/middleware.py

@@ -1,23 +1,40 @@
+from contextlib import contextmanager
+
+from asgiref.sync import iscoroutinefunction
+from django.utils.decorators import sync_and_async_middleware
+
 from .models import HistoricalRecords
 
 
-class HistoryRequestMiddleware:
+@contextmanager
+def _context_manager(request):
+    HistoricalRecords.context.request = request
+
+    try:
+        yield None
+    finally:
+        del HistoricalRecords.context.request
+
+
+@sync_and_async_middleware
+def HistoryRequestMiddleware(get_response):
     """Expose request to HistoricalRecords.
 
     This middleware sets request as a local context/thread variable, making it
     available to the model-level utilities to allow tracking of the authenticated user
     making a change.
     """
 
-    def __init__(self, get_response):
-        self.get_response = get_response
-
-    def __call__(self, request):
-        HistoricalRecords.context.request = request
-        try:
-            response = self.get_response(request)
-        except Exception as e:
-            raise e
-        finally:
-            del HistoricalRecords.context.request
-        return response
+    if iscoroutinefunction(get_response):
+
+        async def middleware(request):
+            with _context_manager(request):
+                return await get_response(request)
+
+    else:
+
+        def middleware(request):
+            with _context_manager(request):
+                return get_response(request)
+
+    return middleware