Make sure we can sync on an empty remote collection.

XXX: Kinto/kinto#433 (comment)
Related bug in Kinto/kinto#433.

kinto_signer/tests/test_updater.py

@@ -59,16 +59,18 @@ def test_collection_records_asks_storage_for_last_modified_records(self):
             filters=[Filter('last_modified', 1234, COMPARISON.GT)])
 
     def test_get_remote_last_modified(self):
-        headers = {'ETag': '"1234"'}
+        headers = {'ETag': '"1234"', 'Total-Records': '10'}
         self.remote.session.request.return_value = (None, headers)
-        self.updater.get_remote_last_modified()
+        collection_timestamp, count = self.updater.get_remote_last_modified()
         self.remote.session.request.assert_called_with(
             'get', '/buckets/buck/collections/coll/records')
+        assert collection_timestamp == 1234
+        assert count == 10
 
     def test_update_remote(self):
         records = [{'id': idx, 'foo': 'bar %s' % idx} for idx in range(1, 3)]
         self.updater.get_remote_last_modified = mock.MagicMock(
-            return_value=1234)
+            return_value=(1234, 2))
         self.updater.get_collection_records = mock.MagicMock(
             return_value=records)
 
@@ -83,6 +85,17 @@ def test_update_remote(self):
         batch.__enter__().patch_collection.assert_called_with(
             data={'signature': 'signature'})
 
+    def test_update_remote_on_empty_remote(self):
+        records = [{'id': idx, 'foo': 'bar %s' % idx} for idx in range(1, 3)]
+        self.updater.get_remote_last_modified = mock.MagicMock(
+            return_value=(1234, 0))
+        self.updater.get_collection_records = mock.MagicMock(
+            return_value=records)
+
+        self.updater.update_remote("hash", "signature")
+
+        self.updater.get_collection_records.assert_called_with(None)
+
     def test_sign_and_update_remote(self):
         records = [{'id': idx, 'foo': 'bar %s' % idx}
                    for idx in range(1, 3)]

kinto_signer/updater.py

@@ -46,11 +46,17 @@ def get_collection_records(self, last_modified=None):
     def get_remote_last_modified(self):
         endpoint = self.remote._get_endpoint('records')
         # XXX Replace with a HEAD request.
+
         _, headers = self.remote.session.request('get', endpoint)
-        return int(headers['ETag'].strip('"'))
+        collection_timestamp = int(headers['ETag'].strip('"'))
+        records_count = int(headers['Total-Records'])
+
+        return collection_timestamp, records_count
 
     def update_remote(self, new_hash, signature):
-        last_modified = self.get_remote_last_modified()
+        last_modified, records_count = self.get_remote_last_modified()
+        if records_count == 0:
+            last_modified = None
         new_records = self.get_collection_records(last_modified)
 
         # Update the remote collection.