Add _catalog endpoint as specified by V2 API

Fixes #391

endpoints/v2/v2util.py

@@ -0,0 +1,19 @@
+from flask import request
+from app import get_app_url
+
+_MAX_RESULTS_PER_PAGE = 100
+
+def add_pagination(query, url):
+  """ Adds optional pagination to the given query by looking for the Docker V2 pagination request
+      args. """
+  limit = request.args.get('n', None)
+  page = request.args.get('page', 1)
+
+  if limit is None:
+    return None, query
+
+  limit = max(limit, _MAX_RESULTS_PER_PAGE)
+  url = get_app_url() + url
+  query = query.paginate(page, limit)
+  link = url + '?n=%s&last=%s; rel="next"' % (limit, page + 1)
+  return link, query