Do not always return 412 errors when request header `If-None-Match: *…

…`` is sent on ``POST /collection`` (fixes #673)

cliquet/resource/__init__.py

@@ -276,17 +276,19 @@ def collection_post(self):
             Add custom behaviour by overriding
             :meth:`cliquet.resource.UserResource.process_record`
         """
-        self._raise_412_if_modified()
+        existing = None
         new_record = self.request.validated['data']
-
-        # Since ``id`` does not belong to schema, it can only be found in body.
         try:
             id_field = self.model.id_field
+            # Since ``id`` does not belong to schema, look up in body.
             new_record[id_field] = _id = self.request.json['data'][id_field]
             self._raise_400_if_invalid_id(_id)
-        except (KeyError, ValueError):
+            existing = self._get_record_or_404(_id)
+        except (HTTPNotFound, KeyError, ValueError):
             pass
 
+        self._raise_412_if_modified(record=existing)
+
         new_record = self.process_record(new_record)
         try:
             unique_fields = self.mapping.get_option('unique_fields')
@@ -753,7 +755,7 @@ def _raise_412_if_modified(self, record=None):
 
         if_match = decode_header(if_match) if if_match else None
 
-        if if_none_match and decode_header(if_none_match) == '*':
+        if record and if_none_match and decode_header(if_none_match) == '*':
             modified_since = -1  # Always raise.
         elif if_match:
             try:

cliquet/tests/resource/test_preconditions.py

@@ -129,6 +129,7 @@ def test_412_on_single_record_has_last_modified_timestamp(self):
         self.assertIsNotNone(error.headers.get('Last-Modified'))
 
     def test_create_returns_412_if_changed_meanwhile(self):
+        self.resource.request.validated = {'data': {'field': 'new'}}
         self.assertRaises(httpexceptions.HTTPPreconditionFailed,
                           self.resource.collection_post)
 
@@ -159,16 +160,39 @@ def test_put_returns_412_if_deleted_meanwhile(self):
         self.assertRaises(httpexceptions.HTTPPreconditionFailed,
                           self.resource.put)
 
-    def test_if_none_match_star_fails_if_record_exists(self):
+    def test_put_if_none_match_star_fails_if_record_exists(self):
         self.resource.request.headers.pop('If-Match')
         self.resource.request.headers['If-None-Match'] = '*'
         self.resource.record_id = self.stored['id']
         self.assertRaises(httpexceptions.HTTPPreconditionFailed,
                           self.resource.put)
+
+    def test_put_if_none_match_star_succeeds_if_record_does_not_exist(self):
+        self.resource.request.headers.pop('If-Match')
+        self.resource.request.headers['If-None-Match'] = '*'
         self.resource.request.validated = {'data': {'field': 'new'}}
         self.resource.record_id = self.resource.model.id_generator()
         self.resource.put()  # not raising.
 
+    def test_post_if_none_match_star_fails_if_record_exists(self):
+        self.resource.request.headers.pop('If-Match')
+        self.resource.request.headers['If-None-Match'] = '*'
+        self.resource.request.json = self.resource.request.validated = {
+            'data': {
+                'id': self.stored['id'],
+                'field': 'new'}}
+        self.assertRaises(httpexceptions.HTTPPreconditionFailed,
+                          self.resource.collection_post)
+
+    def test_post_if_none_match_star_succeeds_if_record_does_not_exist(self):
+        self.resource.request.headers.pop('If-Match')
+        self.resource.request.headers['If-None-Match'] = '*'
+        self.resource.request.validated = {
+            'data': {
+                'id': self.resource.model.id_generator(),
+                'field': 'new'}}
+        self.resource.collection_post()  # not raising.
+
     def test_patch_returns_412_if_changed_meanwhile(self):
         self.resource.record_id = self.stored['id']
         self.assertRaises(httpexceptions.HTTPPreconditionFailed,