views: no cache for badge view

* (closes #54).

invenio_formatter/config.py

@@ -15,3 +15,6 @@
 
 FORMATTER_BADGES_TITLE_MAPPING = {}
 """Mapping of titles."""
+
+FORMATTER_BADGES_MAX_CACHE_AGE = 0
+"""The maximum amount of time a badge will be considered fresh."""

invenio_formatter/views.py

@@ -10,7 +10,11 @@
 
 from __future__ import absolute_import, print_function
 
-from flask import Blueprint, Response, current_app
+import hashlib
+from datetime import datetime as dt
+from datetime import timedelta
+
+from flask import Blueprint, Response, current_app, request
 
 
 def create_badge_blueprint(allowed_types):
@@ -39,11 +43,25 @@ def badge(title, value, ext='svg'):
         elif ext == 'png':
             generator = generate_badge_png
             mimetype = 'image/png'
-        return Response(
-            generator(
-                current_app.config['FORMATTER_BADGES_TITLE_MAPPING'].get(
-                    title, title),
-                value),
-            mimetype=mimetype)
+
+        badge_title_mapping = \
+            current_app.config['FORMATTER_BADGES_TITLE_MAPPING'].get(
+                title, title)
+        response = Response(generator(badge_title_mapping, value),
+                            mimetype=mimetype)
+        # Generate Etag from badge title and value.
+        hashable_badge = "{0}.{1}".format(badge_title_mapping,
+                                          value).encode('utf-8')
+        response.set_etag(hashlib.sha1(hashable_badge).hexdigest())
+        # Add headers to prevent caching.
+        response.headers["Pragma"] = "no-cache"
+        response.cache_control.no_cache = True
+        response.cache_control.max_age = \
+            current_app.config['FORMATTER_BADGES_MAX_CACHE_AGE']
+        response.last_modified = dt.utcnow()
+        extra = timedelta(
+            seconds=current_app.config['FORMATTER_BADGES_MAX_CACHE_AGE'])
+        response.expires = response.last_modified + extra
+        return response.make_conditional(request)
 
     return blueprint

tests/test_views.py

@@ -61,3 +61,27 @@ def test_views_badge_png(app):
         with app.test_client() as client:
             response = client.get('/badge/DOI/value.png')
             assert b'\x89PNG\r\n' in response.data
+
+
+def test_views_badge_etag(app):
+    """Test Etag for badges."""
+    with app.app_context():
+        with app.test_client() as client:
+            response = client.get('/badge/DOI/value.png')
+            response = client.get(
+                '/badge/DOI/value.png',
+                headers={'If-None-Match': response.headers['ETag']})
+            assert response.status_code == 304
+
+
+def test_views_badge_no_cache_headers(app):
+    """Test Etag for badges."""
+    with app.app_context():
+        with app.test_client() as client:
+            response = client.get('/badge/DOI/value.png')
+            assert response.headers['Pragma'] == 'no-cache'
+            cache_control_values = ['no-cache', 'max-age']
+            assert set(cache_control_values).issubset(response.cache_control)
+            assert response.last_modified
+            assert response.expires
+            assert response.get_etag()[0]