Adds support for additional kwargs in middlewares (Solves issue #82)

README.md

@@ -233,6 +233,61 @@ delete_old_tasks.send(max_task_age=86400)
   </dd>
 </dl>
 
+#### Providing custom kwargs to middleware classes
+
+Some middleware classes require extra arguments (ie: rate limiter backend in `dramatiq.middleware.GroupCallbacks`).
+
+Given the above scenario, you need to setup your middleware class in your django `settings.py`:
+
+```python
+DRAMATIQ_BROKER = {
+    ...
+    "MIDDLEWARE": [
+        ...
+        "dramatiq.middleware.GroupCallbacks",
+        ...
+    ]
+    ...
+}
+```
+
+Now we need to extend the default `DjangoDramatiqConfig` class to specify the custom args for
+`dramatiq.middleware.GroupCallbacks`.
+
+
+You can create your own django app or add this class to some `app.py` module:
+
+```python
+from django_dramatiq.apps import DjangoDramatiqConfig
+
+
+class CustomDjangoDramatiqConfig(DjangoDramatiqConfig):
+
+    @classmethod
+    def middleware_groupcallbacks_kwargs(cls):
+        return {"rate_limiter_backend": cls.get_rate_limiter_backend()}
+
+
+CustomDjangoDramatiqConfig.initialize()
+```
+
+Notice the naming convention, if you need to provide arguments to `dramatiq.middleware.GroupCallbacks`
+you will need to add a `@classmethod` with the name `middleware_<middleware_name>_kwargs`,
+where `<middleware_name>` is the class name of the middleware in lowercase.
+
+In this class method, you need to return a `dict` of kwargs for your middleware.
+
+The final step is setup this new custom *dramatiq* app config instead of the default one in your `settings.py`:
+
+
+```python
+INSTALLED_APPS = [
+    ...
+    "yourapp.apps.CustomDjangoDramatiqConfig",
+    ...
+]
+```
+
 
 ### Usage with [django-configurations]
 

django_dramatiq/apps.py

@@ -29,16 +29,15 @@
     ]
 }
 
-RATE_LIMITER_BACKEND = None
-
 
 class DjangoDramatiqConfig(AppConfig):
     name = "django_dramatiq"
     verbose_name = "Django Dramatiq"
 
+    RATE_LIMITER_BACKEND = None
+
     @classmethod
     def initialize(cls):
-        global RATE_LIMITER_BACKEND
 
         dramatiq.set_encoder(cls.select_encoder())
 
@@ -62,27 +61,38 @@ def initialize(cls):
             )
             rate_limiter_backend_class = import_string(rate_limiter_backend_path)
             rate_limiter_backend_options = rate_limiter_backend_settings.get("BACKEND_OPTIONS", {})
-            RATE_LIMITER_BACKEND = rate_limiter_backend_class(**rate_limiter_backend_options)
+            cls.RATE_LIMITER_BACKEND = rate_limiter_backend_class(**rate_limiter_backend_options)
 
         broker_settings = cls.broker_settings()
         broker_path = broker_settings["BROKER"]
         broker_class = import_string(broker_path)
         broker_options = broker_settings.get("OPTIONS", {})
-        middleware = [load_middleware(path) for path in broker_settings.get("MIDDLEWARE", [])]
+        middleware = [
+            load_middleware(path, **cls.get_middleware_kwargs(path))
+            for path in broker_settings.get("MIDDLEWARE", [])
+        ]
 
         if result_backend is not None:
             middleware.append(results_middleware)
 
         broker = broker_class(middleware=middleware, **broker_options)
         dramatiq.set_broker(broker)
 
-    @property
-    def rate_limiter_backend(self):
-        global RATE_LIMITER_BACKEND
-        if RATE_LIMITER_BACKEND is None:
+    @classmethod
+    def get_rate_limiter_backend(cls):
+        if cls.RATE_LIMITER_BACKEND is None:
             raise RuntimeError("The rate limiter backend has not been configured.")
 
-        return RATE_LIMITER_BACKEND
+        return cls.RATE_LIMITER_BACKEND
+
+    @classmethod
+    def get_middleware_kwargs(cls, path):
+        if isinstance(path, str):
+            middleware_path = path.rsplit('.', 1)[1].lower()
+            middleware_kwargs_method = "middleware_{}_kwargs".format(middleware_path)
+            if hasattr(cls, middleware_kwargs_method):
+                return getattr(cls, middleware_kwargs_method)()
+        return {}
 
     @classmethod
     def broker_settings(cls):
@@ -104,6 +114,3 @@ def tasks_database(cls):
     def select_encoder(cls):
         encoder = getattr(settings, "DRAMATIQ_ENCODER", DEFAULT_ENCODER)
         return import_string(encoder)()
-
-
-DjangoDramatiqConfig.initialize()

django_dramatiq/utils.py

@@ -1,7 +1,7 @@
 from django.utils.module_loading import import_string
 
 
-def load_middleware(path_or_obj):
+def load_middleware(path_or_obj, **kwargs):
     if isinstance(path_or_obj, str):
-        return import_string(path_or_obj)()
+        return import_string(path_or_obj)(**kwargs)
     return path_or_obj