diff --git a/multiplexer/filter/__init__.py b/multiplexer/filter/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/multiplexer/filter/filter.py b/multiplexer/filter/filter.py
new file mode 100644
index 0000000..fa4cc06
--- /dev/null
+++ b/multiplexer/filter/filter.py
@@ -0,0 +1,48 @@
+# Copyright (C) 2015-2016 The Software Heritage developers
+# See the AUTHORS file at the top-level directory of this distribution
+# License: GNU General Public License version 3, or any later version
+# See top-level LICENSE file for more information
+
+from ...objstorage import ObjStorage
+
+
+class ObjStorageFilter(ObjStorage):
+ """ Base implementation of a filter that allow inputs on ObjStorage or not
+
+ This class copy the API of ...objstorage in order to filter the inputs
+ of this class.
+ If the operation is allowed, return the result of this operation
+ applied to the destination implementation. Otherwise, just return
+ without any operation.
+
+ This class is an abstract base class for a classic read/write storage.
+ Filters can inherit from it and only redefine some methods in order
+ to change behavior.
+ """
+
+ def __init__(self, storage):
+ self.storage = storage
+
+ def __contains__(self, *args, **kwargs):
+ return self.storage.__contains__(*args, **kwargs)
+
+ def __iter__(self):
+ return self.storage.__iter__()
+
+ def __len__(self):
+ return self.storage.__len__()
+
+ def add(self, *args, **kwargs):
+ return self.storage.add(*args, **kwargs)
+
+ def restore(self, *args, **kwargs):
+ return self.storage.restore(*args, **kwargs)
+
+ def get(self, *args, **kwargs):
+ return self.storage.get(*args, **kwargs)
+
+ def check(self, *args, **kwargs):
+ return self.storage.check(*args, **kwargs)
+
+ def get_random(self, *args, **kwargs):
+ return self.storage.get_random(*args, **kwargs)
diff --git a/multiplexer/filter/id_filter.py b/multiplexer/filter/id_filter.py
new file mode 100644
index 0000000..b7faa30
--- /dev/null
+++ b/multiplexer/filter/id_filter.py
@@ -0,0 +1,99 @@
+# Copyright (C) 2015-2016 The Software Heritage developers
+# See the AUTHORS file at the top-level directory of this distribution
+# License: GNU General Public License version 3, or any later version
+# See top-level LICENSE file for more information
+
+import re
+
+from swh.core import hashutil
+
+from .filter import ObjStorageFilter
+from ...objstorage import ID_HASH_ALGO
+from ....exc import ObjNotFoundError
+
+
+def compute_hash(bytes):
+ """ Compute the hash of the given content.
+ """
+ # Checksum is missing, compute it on the fly.
+ h = hashutil._new_hash(ID_HASH_ALGO, len(bytes))
+ h.update(bytes)
+ return h.digest()
+
+
+class IdObjStorageFilter(ObjStorageFilter):
+ """ Filter that only allow operations if the object id match a requirement.
+
+ Even for read operations, check before if the id match the requirements.
+ This may prevent for unnecesary disk access.
+ """
+
+ def is_valid(self, obj_id):
+ """ Indicates if the given id is valid.
+ """
+ raise NotImplementedError('Implementations of an IdObjStorageFilter '
+ 'must have a "is_valid" method')
+
+ def __contains__(self, obj_id, *args, **kwargs):
+ if self.is_valid(obj_id):
+ return self.storage.__contains__(*args, obj_id=obj_id, **kwargs)
+ return False
+
+ def __len__(self):
+ return sum(1 for i in [id for id in self.storage if self.is_valid(id)])
+
+ def __iter__(self):
+ yield from filter(lambda id: self.is_valid(id), iter(self.storage))
+
+ def add(self, content, obj_id=None, check_presence=True, *args, **kwargs):
+ if obj_id is None:
+ obj_id = compute_hash(content)
+ if self.is_valid(obj_id):
+ return self.storage.add(content, *args, obj_id=obj_id, **kwargs)
+
+ def restore(self, content, obj_id=None, *args, **kwargs):
+ if obj_id is None:
+ obj_id = compute_hash(content)
+ if self.is_valid(obj_id):
+ return self.storage.restore(content, *args,
+ obj_id=obj_id, **kwargs)
+
+ def get(self, obj_id, *args, **kwargs):
+ if self.is_valid(obj_id):
+ return self.storage.get(*args, obj_id=obj_id, **kwargs)
+ raise ObjNotFoundError(obj_id)
+
+ def check(self, obj_id, *args, **kwargs):
+ if self.is_valid(obj_id):
+ return self.storage.check(*args, obj_id=obj_id, **kwargs)
+ raise ObjNotFoundError(obj_id)
+
+ def get_random(self, *args, **kwargs):
+ yield from filter(lambda id: self.is_valid(id),
+ self.storage.get_random(*args, **kwargs))
+
+
+class RegexIdObjStorageFilter(IdObjStorageFilter):
+ """ Filter that allow operations if the content's id as hex match a regex.
+ """
+
+ def __init__(self, storage, regex):
+ super().__init__(storage)
+ self.regex = re.compile(regex)
+
+ def is_valid(self, obj_id):
+ hex_obj_id = hashutil.hash_to_hex(obj_id)
+ return self.regex.match(hex_obj_id) is not None
+
+
+class PrefixIdObjStorageFilter(IdObjStorageFilter):
+ """ Filter that allow operations if the hexlified id have a given prefix.
+ """
+
+ def __init__(self, storage, prefix):
+ super().__init__(storage)
+ self.prefix = str(prefix)
+
+ def is_valid(self, obj_id):
+ hex_obj_id = hashutil.hash_to_hex(obj_id)
+ return str(hex_obj_id).startswith(self.prefix)
diff --git a/multiplexer/filter/read_write_filter.py b/multiplexer/filter/read_write_filter.py
new file mode 100644
index 0000000..e4821b9
--- /dev/null
+++ b/multiplexer/filter/read_write_filter.py
@@ -0,0 +1,17 @@
+# Copyright (C) 2015-2016 The Software Heritage developers
+# See the AUTHORS file at the top-level directory of this distribution
+# License: GNU General Public License version 3, or any later version
+# See top-level LICENSE file for more information
+
+from .filter import ObjStorageFilter
+
+
+class ReadObjStorageFilter(ObjStorageFilter):
+ """ Filter that disable write operation of the storage.
+ """
+
+ def add(self, *args, **kwargs):
+ return
+
+ def restore(self, *args, **kwargs):
+ return