Move v1 checksums to image and track v2 separately

digest/checksums.py

@@ -75,6 +75,14 @@ def simple_checksum_handler(json_data):
     return h, fn
 
 
+def content_checksum_handler():
+    h = hashlib.sha256()
+
+    def fn(buf):
+        h.update(buf)
+    return h, fn
+
+
 def compute_simple(fp, json_data):
     data = json_data + '\n'
     return 'sha256:{0}'.format(sha256_file(fp, data))