feat(client): check server version

If the client sends a X-Deis-Version header to the server, a django
middleware class will validate and ensure that the versions are the
same. If they are not, the request is rejected, and a HttpResponse
object is returned with the client and server versions displayed.

Author: Matthew Fisher

api/middleware.py

@@ -0,0 +1,25 @@
+import json
+
+from django.http import HttpResponse
+
+from deis import __version__
+
+
+class VersionMiddleware:
+
+    def process_request(self, request):
+        # server and client version must match "x.y"
+        server_version = __version__.rsplit('.', 1)[0]
+        try:
+            if request.META['HTTP_X_DEIS_VERSION'] != server_version:
+                message = {
+                    'error': 'Client and server versions do not match.\n' +
+                    'Client version: {}\n'.format(server_version) +
+                    'Server version: {}'.format(request.META['HTTP_X_DEIS_VERSION'])
+                }
+                return HttpResponse(
+                    json.dumps(message),
+                    content_type='application/json'
+                )
+        except KeyError:
+            pass

deis/settings.py

@@ -108,6 +108,7 @@
     'django.middleware.csrf.CsrfViewMiddleware',
     'django.contrib.auth.middleware.AuthenticationMiddleware',
     'django.contrib.messages.middleware.MessageMiddleware',
+    'api.middleware.VersionMiddleware',
     # Uncomment the next line for simple clickjacking protection:
     # 'django.middleware.clickjacking.XFrameOptionsMiddleware',
 )