Serve custom 404 page only on subdomain and cname requests

Author: humitos

readthedocs/core/views/__init__.py

@@ -131,6 +131,24 @@ def server_error_404(request, exception=None, template_name='404.html'):  # pyli
         else:
             return response
 
+    # Try to serve custom 404 pages if it's a subdomain/cname
+    if request.subdomain or request.cname:
+        return server_error_404_subdomain(request, template_name)
+
+    # Return the default 404 page generated by Read the Docs
+    r = render(request, template_name)
+    r.status_code = 404
+    return r
+
+
+def server_error_404_subdomain(request, template_name='404.html'):
+    """
+    Handler for 404 pages on subdomains.
+
+    Check if the project associated has a custom ``404.html`` on it's project's
+    root (default version) and serve it. Otherwise, fallback to the default
+    ``template_name`` rendered by Django.
+    """
     project, path = project_and_path_from_request(request, request.get_full_path())
     version_slug = project.get_default_version()
     version = project.versions.get(slug=version_slug)