Add OverlayObjectStore.

dulwich/object_store.py

@@ -1245,3 +1245,59 @@ def commit_tree_changes(object_store, tree, changes):
             tree[name] = (stat.S_IFDIR, subtree.id)
     object_store.add_object(tree)
     return tree
+
+
+class OverlayObjectStore(BaseObjectStore):
+    """Object store that can overlay multiple object stores."""
+
+    def __init__(self, bases, add_store=None):
+        self.bases = bases
+        self.add_store = add_store
+
+    def add_object(self, object):
+        if self.add_store is None:
+            raise NotImplementedError(self.add_object)
+        return self.add_store.add_object(object)
+
+    def add_objects(self, objects):
+        if self.add_store is None:
+            raise NotImplementedError(self.add_object)
+        return self.add_store.add_objects(objects)
+
+    @property
+    def packs(self):
+        ret = []
+        for b in self.bases:
+            ret.extend(b.packs)
+        return ret
+
+    def __iter__(self):
+        done = set()
+        for b in self.bases:
+            for o_id in b:
+                if o_id not in done:
+                    yield o_id
+                    done.add(o_id)
+
+    def get_raw(self, sha_id):
+        for b in self.bases:
+            try:
+                return b.get_raw(sha_id)
+            except KeyError:
+                pass
+        else:
+            raise KeyError(sha_id)
+
+    def contains_packed(self, sha):
+        for b in self.bases:
+            if b.contains_packed(sha):
+                return True
+        else:
+            return False
+
+    def contains_loose(self, sha):
+        for b in self.bases:
+            if b.contains_loose(sha):
+                return True
+        else:
+            return False

dulwich/tests/test_object_store.py

@@ -44,6 +44,7 @@ from dulwich.objects import (
 from dulwich.object_store import (
     DiskObjectStore,
     MemoryObjectStore,
+    OverlayObjectStore,
     ObjectStoreGraphWalker,
     commit_tree_changes,
     tree_lookup_path,
@@ -213,6 +214,14 @@ class ObjectStoreTests(object):
         self.store.close()
 
 
+class OverlayObjectStoreTests(ObjectStoreTests, TestCase):
+
+    def setUp(self):
+        TestCase.setUp(self)
+        self.bases = [MemoryObjectStore(), MemoryObjectStore()]
+        self.store = OverlayObjectStore(self.bases, self.bases[0])
+
+
 class MemoryObjectStoreTests(ObjectStoreTests, TestCase):
 
     def setUp(self):