A few internet references report that etags for the same underlying

resource but with different representation (xml, json ...) should have
different etags.

That is currently not the case. Added code to allow incorporation of
representation info into the etag. By default the representation is
"json", but future patches can pass the representation down and modify
flow to match requested representation.

Author: rouilj

roundup/rest.py

@@ -118,7 +118,8 @@ def format_object(self, *args, **kwargs):
         return result
     return format_object
 
-def calculate_etag (node, key, classname="Missing", id="0"):
+def calculate_etag (node, key, classname="Missing", id="0",
+                    repr_format="json"):
     '''given a hyperdb node generate a hashed representation of it to be
     used as an etag.
 
@@ -142,13 +143,15 @@ def calculate_etag (node, key, classname="Missing", id="0"):
     '''
 
     items = node.items(protected=True) # include every item
-    etag = hmac.new(bs2b(key),bs2b(repr(sorted(items)))).hexdigest()
+    etag = hmac.new(bs2b(key),bs2b(repr_format + 
+                                   repr(sorted(items)))).hexdigest()
     logger.debug("object=%s%s; tag=%s; repr=%s", classname, id,
                  etag, repr(node.items(protected=True)))
     # Quotes are part of ETag spec, normal headers don't have quotes
     return '"%s"' % etag
 
-def check_etag (node, key, etags, classname="Missing", id="0"):
+def check_etag (node, key, etags, classname="Missing", id="0",
+                repr_format="json"):
     '''Take a list of etags and compare to the etag for the given node.
 
     Iterate over all supplied etags,
@@ -159,7 +162,8 @@ def check_etag (node, key, etags, classname="Missing", id="0"):
     '''
     have_etag_match=False
 
-    node_etag = calculate_etag(node, key, classname, id)
+    node_etag = calculate_etag(node, key, classname, id,
+                               repr_format=repr_format)
 
     for etag in etags:
         if etag is not None:
@@ -508,13 +512,13 @@ def patch_data(self, op, old_val, new_val):
 
         return result
 
-    def raise_if_no_etag(self, class_name, item_id, input):
+    def raise_if_no_etag(self, class_name, item_id, input, repr_format="json"):
         class_obj = self.db.getclass(class_name)
         if not check_etag(class_obj.getnode(item_id),
                 self.db.config.WEB_SECRET_KEY,
                 obtain_etags(self.client.request.headers, input),
                 class_name,
-                item_id):
+                          item_id, repr_format=repr_format):
             raise PreconditionFailed(
                 "If-Match is missing or does not match."
                 " Retrieve asset and retry modification if valid.")
@@ -789,7 +793,7 @@ def get_element(self, class_name, item_id, input):
 
         node = class_obj.getnode(itemid)
         etag = calculate_etag(node, self.db.config.WEB_SECRET_KEY,
-                              class_name, itemid)
+                              class_name, itemid, repr_format="json")
         props = None
         protected=False
         verbose=1
@@ -871,7 +875,7 @@ def get_attribute(self, class_name, item_id, attr_name, input):
         class_obj = self.db.getclass(class_name)
         node = class_obj.getnode(item_id)
         etag = calculate_etag(node, self.db.config.WEB_SECRET_KEY,
-                              class_name, item_id)
+                              class_name, item_id,  repr_format="json")
         data = node.__getattr__(attr_name)
         result = {
             'id': item_id,

test/rest_common.py

@@ -655,22 +655,22 @@ def dummyClosure(adate=None, translator=None):
             items = node.items(protected=True) # include every item
             print(repr(sorted(items)))
             print(etag)
-            self.assertEqual(etag, '"f2901b2653b813eeb277c0dc84c03ba3"')
+            self.assertEqual(etag, '"0433784660a141e8262835171e70fd2f"')
 
             # modify key and verify we have a different etag
             etag = calculate_etag(node, self.db.config['WEB_SECRET_KEY'] + "a")
             items = node.items(protected=True) # include every item
             print(repr(sorted(items)))
             print(etag)
-            self.assertNotEqual(etag, '"f2901b2653b813eeb277c0dc84c03ba3"')
+            self.assertNotEqual(etag, '"0433784660a141e8262835171e70fd2f"')
 
             # change data and verify we have a different etag
             node.username="Paul"
             etag = calculate_etag(node, self.db.config['WEB_SECRET_KEY'])
             items = node.items(protected=True) # include every item
             print(repr(sorted(items)))
             print(etag)
-            self.assertEqual(etag, '"98f8052193220afdb649c6caaaa80e40"')
+            self.assertEqual(etag, '"8abeacd284d58655c620d60389e29d4d"')
         finally:
             date.Date = originalDate