Add comments in DebugToolbarMiddleware.

Reorder process_response slightly to ensure instrumentation is
deactivated for streaming responses.

Author: aaugustin

debug_toolbar/middleware.py

@@ -39,27 +39,35 @@ class DebugToolbarMiddleware(object):
     debug_toolbars = {}
 
     def process_request(self, request):
+        # Decide whether the toolbar is active for this request.
         func_path = dt_settings.CONFIG['SHOW_TOOLBAR_CALLBACK']
         # Replace this with import_by_path in Django >= 1.6.
         mod_path, func_name = func_path.rsplit('.', 1)
         show_toolbar = getattr(import_module(mod_path), func_name)
         if not show_toolbar(request):
             return
-        response = None
+
         toolbar = DebugToolbar(request)
+        self.__class__.debug_toolbars[threading.current_thread().ident] = toolbar
+
+        # Activate instrumentation ie. monkey-patch.
         for panel in toolbar.enabled_panels:
             panel.enable_instrumentation()
+
+        # Run process_request methods of panels like Django middleware.
+        response = None
         for panel in toolbar.enabled_panels:
             response = panel.process_request(request)
             if response:
                 break
-        self.__class__.debug_toolbars[threading.current_thread().ident] = toolbar
         return response
 
     def process_view(self, request, view_func, view_args, view_kwargs):
         toolbar = self.__class__.debug_toolbars.get(threading.current_thread().ident)
         if not toolbar:
             return
+
+        # Run process_view methods of panels like Django middleware.
         response = None
         for panel in toolbar.enabled_panels:
             response = panel.process_view(request, view_func, view_args, view_kwargs)
@@ -69,26 +77,42 @@ def process_view(self, request, view_func, view_args, view_kwargs):
 
     def process_response(self, request, response):
         toolbar = self.__class__.debug_toolbars.pop(threading.current_thread().ident, None)
-        if not toolbar or getattr(response, 'streaming', False):
+        if not toolbar:
             return response
+
+        # Run process_response methods of panels like Django middleware.
         for panel in reversed(toolbar.enabled_panels):
             new_response = panel.process_response(request, response)
             if new_response:
                 response = new_response
+
+        # Deactivate instrumentation ie. monkey-unpatch. This must run
+        # regardless of the response. Keep 'return' clauses below.
+        # (NB: Django's model for middleware doesn't guarantee anything.)
         for panel in reversed(toolbar.enabled_panels):
             panel.disable_instrumentation()
+
+        # Check for responses where the toolbar can't be inserted.
+        content_encoding = response.get('Content-Encoding', '')
+        content_type = response.get('Content-Type', '').split(';')[0]
+        if any((getattr(response, 'streaming', False),
+                'gzip' in content_encoding,
+                content_type not in _HTML_TYPES)):
+            return response
+
+        # Collapse the toolbar by default if SHOW_COLLAPSED is set.
         if toolbar.config['SHOW_COLLAPSED'] and 'djdt' not in request.COOKIES:
             response.set_cookie('djdt', 'hide', 864000)
-        if ('gzip' not in response.get('Content-Encoding', '') and
-                response.get('Content-Type', '').split(';')[0] in _HTML_TYPES):
-            content = force_text(response.content, encoding=settings.DEFAULT_CHARSET)
-            try:
-                insert_at = content.lower().rindex(dt_settings.CONFIG['INSERT_BEFORE'].lower())
-            except ValueError:
-                pass
-            else:
-                toolbar_content = toolbar.render_toolbar()
-                response.content = content[:insert_at] + toolbar_content + content[insert_at:]
+
+        # Insert the toolbar in the response.
+        content = force_text(response.content, encoding=settings.DEFAULT_CHARSET)
+        try:
+            insert_at = content.lower().rindex(dt_settings.CONFIG['INSERT_BEFORE'].lower())
+        except ValueError:
+            pass
+        else:
+            toolbar_content = toolbar.render_toolbar()
+            response.content = content[:insert_at] + toolbar_content + content[insert_at:]
             if response.get('Content-Length', None):
                 response['Content-Length'] = len(response.content)
         return response