Maintain support for legacy Django versions

Author: adamantike

instrumentation/opentelemetry-instrumentation-django/src/opentelemetry/instrumentation/django/middleware.py

@@ -16,6 +16,7 @@
 from time import time
 from typing import Callable
 
+from django import VERSION as django_version
 from django.http import HttpRequest, HttpResponse
 
 from opentelemetry.context import attach, detach
@@ -42,6 +43,32 @@
 except ImportError:
     from django.urls import Resolver404, resolve
 
+DJANGO_2_0 = django_version >= (2, 0)
+
+if DJANGO_2_0:
+    # Since Django 2.0, only `settings.MIDDLEWARE` is supported, so new-style
+    # middlewares can be used.
+    class MiddlewareMixin:
+        def __init__(self, get_response):
+            self.get_response = get_response
+
+        def __call__(self, request):
+            self.process_request(request)
+            response = self.get_response(request)
+            return self.process_response(request, response)
+
+
+else:
+    # Django versions 1.x can use `settings.MIDDLEWARE_CLASSES` and expect
+    # old-style middlewares, which are created by inheriting from
+    # `deprecation.MiddlewareMixin` since its creation in Django 1.10 and 1.11,
+    # or from `object` for older versions.
+    try:
+        from django.utils.deprecation import MiddlewareMixin
+    except ImportError:
+        MiddlewareMixin = object
+
+
 _logger = getLogger(__name__)
 _attributes_by_preference = [
     [
@@ -65,7 +92,7 @@
 ]
 
 
-class _DjangoMiddleware:
+class _DjangoMiddleware(MiddlewareMixin):
     """Django Middleware for OpenTelemetry"""
 
     _environ_activation_key = (
@@ -84,9 +111,6 @@ class _DjangoMiddleware:
         [Span, HttpRequest, HttpResponse], None
     ] = None
 
-    def __init__(self, get_response):
-        self.get_response = get_response
-
     @staticmethod
     def _get_span_name(request):
         try:
@@ -109,11 +133,6 @@ def _get_span_name(request):
         except Resolver404:
             return "HTTP {}".format(request.method)
 
-    def __call__(self, request):
-        self.process_request(request)
-        response = self.get_response(request)
-        return self.process_response(request, response)
-
     def process_request(self, request):
         # request.META is a dictionary containing all available HTTP headers
         # Read more about request.META here: