We are currently solving the following issue within our repository. Here is the issue text:
--- BEGIN ISSUE ---
Per collection caching using dot separator
Per collection caching can be configured in settings using `_` as separator:

```ini
kinto.bid_cid_record_cache_expires_seconds = 60
```
Since `_` is valid character in both bucket and collection ids, this could be confusing. I propose that we change it to `.`

--- END ISSUE ---

Below are some code segments, each from a relevant file. One or more of these files may contain bugs.
--- BEGIN FILES ---
Path: `kinto/views/records.py`
Content:
```
1 from pyramid.security import Authenticated
2 from pyramid.settings import asbool
3 
4 from kinto.core import resource, utils
5 from kinto.core.errors import raise_invalid
6 from kinto.views import object_exists_or_404
7 from kinto.schema_validation import (validate_from_bucket_schema_or_400, validate_schema,
8                                      ValidationError, RefResolutionError)
9 
10 
11 _parent_path = '/buckets/{{bucket_id}}/collections/{{collection_id}}'
12 
13 
14 @resource.register(name='record',
15                    collection_path=_parent_path + '/records',
16                    record_path=_parent_path + '/records/{{id}}')
17 class Record(resource.ShareableResource):
18 
19     schema_field = 'schema'
20 
21     def __init__(self, request, **kwargs):
22         # Before all, first check that the parent collection exists.
23         # Check if already fetched before (in batch).
24         collections = request.bound_data.setdefault('collections', {})
25         collection_uri = self.get_parent_id(request)
26         if collection_uri not in collections:
27             # Unknown yet, fetch from storage.
28             bucket_uri = utils.instance_uri(request, 'bucket', id=self.bucket_id)
29             collection = object_exists_or_404(request,
30                                               collection_id='collection',
31                                               parent_id=bucket_uri,
32                                               object_id=self.collection_id)
33             collections[collection_uri] = collection
34         self._collection = collections[collection_uri]
35 
36         super().__init__(request, **kwargs)
37 
38     def get_parent_id(self, request):
39         self.bucket_id = request.matchdict['bucket_id']
40         self.collection_id = request.matchdict['collection_id']
41         return utils.instance_uri(request, 'collection',
42                                   bucket_id=self.bucket_id,
43                                   id=self.collection_id)
44 
45     def process_record(self, new, old=None):
46         """Validate records against collection or bucket schema, if any."""
47         new = super().process_record(new, old)
48 
49         # Is schema validation enabled?
50         settings = self.request.registry.settings
51         schema_validation = 'experimental_collection_schema_validation'
52         if not asbool(settings.get(schema_validation)):
53             return new
54 
55         # Remove internal and auto-assigned fields from schemas and record.
56         internal_fields = (self.model.id_field,
57                            self.model.modified_field,
58                            self.schema_field,
59                            self.model.permissions_field)
60 
61         # The schema defined on the collection will be validated first.
62         if 'schema' in self._collection:
63             schema = self._collection['schema']
64 
65             try:
66                 validate_schema(new, schema, ignore_fields=internal_fields)
67             except ValidationError as e:
68                 raise_invalid(self.request, name=e.field, description=e.message)
69             except RefResolutionError as e:
70                 raise_invalid(self.request, name='schema', description=str(e))
71 
72             # Assign the schema version to the record.
73             schema_timestamp = self._collection[self.model.modified_field]
74             new[self.schema_field] = schema_timestamp
75 
76         # Validate also from the record:schema field defined on the bucket.
77         validate_from_bucket_schema_or_400(new, resource_name="record", request=self.request,
78                                            ignore_fields=internal_fields)
79 
80         return new
81 
82     def collection_get(self):
83         result = super().collection_get()
84         self._handle_cache_expires(self.request.response)
85         return result
86 
87     def get(self):
88         result = super().get()
89         self._handle_cache_expires(self.request.response)
90         return result
91 
92     def _handle_cache_expires(self, response):
93         """If the parent collection defines a ``cache_expires`` attribute,
94         then cache-control response headers are sent.
95 
96         .. note::
97 
98             Those headers are also sent if the
99             ``kinto.record_cache_expires_seconds`` setting is defined.
100         """
101         is_anonymous = Authenticated not in self.request.effective_principals
102         if not is_anonymous:
103             return
104 
105         cache_expires = self._collection.get('cache_expires')
106         if cache_expires is None:
107             by_bucket = '{}_record_cache_expires_seconds'.format(self.bucket_id)
108             by_collection = '{}_{}_record_cache_expires_seconds'.format(
109                 self.bucket_id, self.collection_id)
110             settings = self.request.registry.settings
111             cache_expires = settings.get(by_collection,
112                                          settings.get(by_bucket))
113 
114         if cache_expires is not None:
115             response.cache_expires(seconds=int(cache_expires))
116
```
--- END FILES ---

Please first localize the bug based on the issue statement, and then generate a patch according to the `git diff` format fenced by three backticks.

Here is an example:

```diff
diff --git a/examples/server_async.py b/examples/server_async.py
--- a/examples/server_async.py
+++ b/examples/server_async.py
@@ -313,4 +313,4 @@
 
 
 if __name__ == "__main__":
-    asyncio.run(run_async_server("."), debug=True)
+    asyncio.run(run_async_server(), debug=True)
diff --git a/examples/server_sync.py b/examples/server_sync.py
--- a/examples/server_sync.py
+++ b/examples/server_sync.py
@@ -313,5 +313,5 @@
 
 
 if __name__ == "__main__":
-    server = run_sync_server(".")
+    server = run_sync_server()
     server.shutdown()

```

diff --git a/kinto/views/records.py b/kinto/views/records.py
--- a/kinto/views/records.py
+++ b/kinto/views/records.py
@@ -104,12 +104,16 @@
 
         cache_expires = self._collection.get('cache_expires')
         if cache_expires is None:
-            by_bucket = '{}_record_cache_expires_seconds'.format(self.bucket_id)
-            by_collection = '{}_{}_record_cache_expires_seconds'.format(
+            by_collection = '{}.{}.record_cache_expires_seconds'.format(
                 self.bucket_id, self.collection_id)
+            by_bucket = '{}.record_cache_expires_seconds'.format(self.bucket_id)
+            by_collection_legacy = '{}_{}_record_cache_expires_seconds'.format(
+                self.bucket_id, self.collection_id)
+            by_bucket_legacy = '{}_record_cache_expires_seconds'.format(self.bucket_id)
             settings = self.request.registry.settings
-            cache_expires = settings.get(by_collection,
-                                         settings.get(by_bucket))
-
+            for s in (by_collection, by_bucket, by_collection_legacy, by_bucket_legacy):
+                cache_expires = settings.get(s)
+                if cache_expires is not None:
+                    break
         if cache_expires is not None:
             response.cache_expires(seconds=int(cache_expires))

{"golden_diff": "diff --git a/kinto/views/records.py b/kinto/views/records.py\n--- a/kinto/views/records.py\n+++ b/kinto/views/records.py\n@@ -104,12 +104,16 @@\n \n         cache_expires = self._collection.get('cache_expires')\n         if cache_expires is None:\n-            by_bucket = '{}_record_cache_expires_seconds'.format(self.bucket_id)\n-            by_collection = '{}_{}_record_cache_expires_seconds'.format(\n+            by_collection = '{}.{}.record_cache_expires_seconds'.format(\n                 self.bucket_id, self.collection_id)\n+            by_bucket = '{}.record_cache_expires_seconds'.format(self.bucket_id)\n+            by_collection_legacy = '{}_{}_record_cache_expires_seconds'.format(\n+                self.bucket_id, self.collection_id)\n+            by_bucket_legacy = '{}_record_cache_expires_seconds'.format(self.bucket_id)\n             settings = self.request.registry.settings\n-            cache_expires = settings.get(by_collection,\n-                                         settings.get(by_bucket))\n-\n+            for s in (by_collection, by_bucket, by_collection_legacy, by_bucket_legacy):\n+                cache_expires = settings.get(s)\n+                if cache_expires is not None:\n+                    break\n         if cache_expires is not None:\n             response.cache_expires(seconds=int(cache_expires))\n", "issue": "Per collection caching using dot separator\nPer collection caching can be configured in settings using `_` as separator:\r\n\r\n```ini\r\nkinto.bid_cid_record_cache_expires_seconds = 60\r\n```\r\nSince `_` is valid character in both bucket and collection ids, this could be confusing. I propose that we change it to `.`\n", "before_files": [{"content": "from pyramid.security import Authenticated\nfrom pyramid.settings import asbool\n\nfrom kinto.core import resource, utils\nfrom kinto.core.errors import raise_invalid\nfrom kinto.views import object_exists_or_404\nfrom kinto.schema_validation import (validate_from_bucket_schema_or_400, validate_schema,\n                                     ValidationError, RefResolutionError)\n\n\n_parent_path = '/buckets/{{bucket_id}}/collections/{{collection_id}}'\n\n\n@resource.register(name='record',\n                   collection_path=_parent_path + '/records',\n                   record_path=_parent_path + '/records/{{id}}')\nclass Record(resource.ShareableResource):\n\n    schema_field = 'schema'\n\n    def __init__(self, request, **kwargs):\n        # Before all, first check that the parent collection exists.\n        # Check if already fetched before (in batch).\n        collections = request.bound_data.setdefault('collections', {})\n        collection_uri = self.get_parent_id(request)\n        if collection_uri not in collections:\n            # Unknown yet, fetch from storage.\n            bucket_uri = utils.instance_uri(request, 'bucket', id=self.bucket_id)\n            collection = object_exists_or_404(request,\n                                              collection_id='collection',\n                                              parent_id=bucket_uri,\n                                              object_id=self.collection_id)\n            collections[collection_uri] = collection\n        self._collection = collections[collection_uri]\n\n        super().__init__(request, **kwargs)\n\n    def get_parent_id(self, request):\n        self.bucket_id = request.matchdict['bucket_id']\n        self.collection_id = request.matchdict['collection_id']\n        return utils.instance_uri(request, 'collection',\n                                  bucket_id=self.bucket_id,\n                                  id=self.collection_id)\n\n    def process_record(self, new, old=None):\n        \"\"\"Validate records against collection or bucket schema, if any.\"\"\"\n        new = super().process_record(new, old)\n\n        # Is schema validation enabled?\n        settings = self.request.registry.settings\n        schema_validation = 'experimental_collection_schema_validation'\n        if not asbool(settings.get(schema_validation)):\n            return new\n\n        # Remove internal and auto-assigned fields from schemas and record.\n        internal_fields = (self.model.id_field,\n                           self.model.modified_field,\n                           self.schema_field,\n                           self.model.permissions_field)\n\n        # The schema defined on the collection will be validated first.\n        if 'schema' in self._collection:\n            schema = self._collection['schema']\n\n            try:\n                validate_schema(new, schema, ignore_fields=internal_fields)\n            except ValidationError as e:\n                raise_invalid(self.request, name=e.field, description=e.message)\n            except RefResolutionError as e:\n                raise_invalid(self.request, name='schema', description=str(e))\n\n            # Assign the schema version to the record.\n            schema_timestamp = self._collection[self.model.modified_field]\n            new[self.schema_field] = schema_timestamp\n\n        # Validate also from the record:schema field defined on the bucket.\n        validate_from_bucket_schema_or_400(new, resource_name=\"record\", request=self.request,\n                                           ignore_fields=internal_fields)\n\n        return new\n\n    def collection_get(self):\n        result = super().collection_get()\n        self._handle_cache_expires(self.request.response)\n        return result\n\n    def get(self):\n        result = super().get()\n        self._handle_cache_expires(self.request.response)\n        return result\n\n    def _handle_cache_expires(self, response):\n        \"\"\"If the parent collection defines a ``cache_expires`` attribute,\n        then cache-control response headers are sent.\n\n        .. note::\n\n            Those headers are also sent if the\n            ``kinto.record_cache_expires_seconds`` setting is defined.\n        \"\"\"\n        is_anonymous = Authenticated not in self.request.effective_principals\n        if not is_anonymous:\n            return\n\n        cache_expires = self._collection.get('cache_expires')\n        if cache_expires is None:\n            by_bucket = '{}_record_cache_expires_seconds'.format(self.bucket_id)\n            by_collection = '{}_{}_record_cache_expires_seconds'.format(\n                self.bucket_id, self.collection_id)\n            settings = self.request.registry.settings\n            cache_expires = settings.get(by_collection,\n                                         settings.get(by_bucket))\n\n        if cache_expires is not None:\n            response.cache_expires(seconds=int(cache_expires))\n", "path": "kinto/views/records.py"}], "after_files": [{"content": "from pyramid.security import Authenticated\nfrom pyramid.settings import asbool\n\nfrom kinto.core import resource, utils\nfrom kinto.core.errors import raise_invalid\nfrom kinto.views import object_exists_or_404\nfrom kinto.schema_validation import (validate_from_bucket_schema_or_400, validate_schema,\n                                     ValidationError, RefResolutionError)\n\n\n_parent_path = '/buckets/{{bucket_id}}/collections/{{collection_id}}'\n\n\n@resource.register(name='record',\n                   collection_path=_parent_path + '/records',\n                   record_path=_parent_path + '/records/{{id}}')\nclass Record(resource.ShareableResource):\n\n    schema_field = 'schema'\n\n    def __init__(self, request, **kwargs):\n        # Before all, first check that the parent collection exists.\n        # Check if already fetched before (in batch).\n        collections = request.bound_data.setdefault('collections', {})\n        collection_uri = self.get_parent_id(request)\n        if collection_uri not in collections:\n            # Unknown yet, fetch from storage.\n            bucket_uri = utils.instance_uri(request, 'bucket', id=self.bucket_id)\n            collection = object_exists_or_404(request,\n                                              collection_id='collection',\n                                              parent_id=bucket_uri,\n                                              object_id=self.collection_id)\n            collections[collection_uri] = collection\n        self._collection = collections[collection_uri]\n\n        super().__init__(request, **kwargs)\n\n    def get_parent_id(self, request):\n        self.bucket_id = request.matchdict['bucket_id']\n        self.collection_id = request.matchdict['collection_id']\n        return utils.instance_uri(request, 'collection',\n                                  bucket_id=self.bucket_id,\n                                  id=self.collection_id)\n\n    def process_record(self, new, old=None):\n        \"\"\"Validate records against collection or bucket schema, if any.\"\"\"\n        new = super().process_record(new, old)\n\n        # Is schema validation enabled?\n        settings = self.request.registry.settings\n        schema_validation = 'experimental_collection_schema_validation'\n        if not asbool(settings.get(schema_validation)):\n            return new\n\n        # Remove internal and auto-assigned fields from schemas and record.\n        internal_fields = (self.model.id_field,\n                           self.model.modified_field,\n                           self.schema_field,\n                           self.model.permissions_field)\n\n        # The schema defined on the collection will be validated first.\n        if 'schema' in self._collection:\n            schema = self._collection['schema']\n\n            try:\n                validate_schema(new, schema, ignore_fields=internal_fields)\n            except ValidationError as e:\n                raise_invalid(self.request, name=e.field, description=e.message)\n            except RefResolutionError as e:\n                raise_invalid(self.request, name='schema', description=str(e))\n\n            # Assign the schema version to the record.\n            schema_timestamp = self._collection[self.model.modified_field]\n            new[self.schema_field] = schema_timestamp\n\n        # Validate also from the record:schema field defined on the bucket.\n        validate_from_bucket_schema_or_400(new, resource_name=\"record\", request=self.request,\n                                           ignore_fields=internal_fields)\n\n        return new\n\n    def collection_get(self):\n        result = super().collection_get()\n        self._handle_cache_expires(self.request.response)\n        return result\n\n    def get(self):\n        result = super().get()\n        self._handle_cache_expires(self.request.response)\n        return result\n\n    def _handle_cache_expires(self, response):\n        \"\"\"If the parent collection defines a ``cache_expires`` attribute,\n        then cache-control response headers are sent.\n\n        .. note::\n\n            Those headers are also sent if the\n            ``kinto.record_cache_expires_seconds`` setting is defined.\n        \"\"\"\n        is_anonymous = Authenticated not in self.request.effective_principals\n        if not is_anonymous:\n            return\n\n        cache_expires = self._collection.get('cache_expires')\n        if cache_expires is None:\n            by_collection = '{}.{}.record_cache_expires_seconds'.format(\n                self.bucket_id, self.collection_id)\n            by_bucket = '{}.record_cache_expires_seconds'.format(self.bucket_id)\n            by_collection_legacy = '{}_{}_record_cache_expires_seconds'.format(\n                self.bucket_id, self.collection_id)\n            by_bucket_legacy = '{}_record_cache_expires_seconds'.format(self.bucket_id)\n            settings = self.request.registry.settings\n            for s in (by_collection, by_bucket, by_collection_legacy, by_bucket_legacy):\n                cache_expires = settings.get(s)\n                if cache_expires is not None:\n                    break\n        if cache_expires is not None:\n            response.cache_expires(seconds=int(cache_expires))\n", "path": "kinto/views/records.py"}]}