Renamed IStorageDB to IStorageWrapper and expanded it to provide

methods for transforming and untransforming data records. This was
needed to make storage wrappers that transform data work with
conflict resolution.

src/CHANGES.txt

@@ -32,6 +32,11 @@ New Features
   - You can now pass None (rather than a storage or file name) to get
     a database with a mapping storage.
 
+- Renamed IStorageDB to IStorageWrapper and expanded it to provide
+  methods for transforming and untransforming data records. This was
+  needed to make storage wrappers that transform data work with
+  conflict resolution.
+
 Bugs Fixed
 ----------
 

src/ZEO/StorageServer.py

@@ -778,6 +778,7 @@ class StorageServerDB:
     def invalidateCache(self):
         self.server._invalidateCache(self.storage_id)
 
+    transform_record_data = untransform_record_data = lambda self, data: data
 
 class StorageServer:
 

src/ZODB/ConflictResolution.py

@@ -53,6 +53,7 @@ def find_global(*args):
 
 def state(self, oid, serial, prfactory, p=''):
     p = p or self.loadSerial(oid, serial)
+    p = self._crs_wrapper.untransform_record_data(p)
     file = StringIO(p)
     unpickler = Unpickler(file)
     unpickler.find_global = find_global
@@ -80,13 +81,13 @@ class IPersistentReference(zope.interface.Interface):
 
     def __cmp__(other):
         '''if other is equivalent reference, return 0; else raise ValueError.
-        
+
         Equivalent in this case means that oid and database_name are the same.
 
         If either is a weak reference, we only support `is` equivalence, and
         otherwise raise a ValueError even if the datbase_names and oids are
         the same, rather than guess at the correct semantics.
-        
+
         It is impossible to sort reliably, since the actual persistent
         class may have its own comparison, and we have no idea what it is.
         We assert that it is reasonably safe to assume that an object is
@@ -135,7 +136,7 @@ class PersistentReference(object):
 
     def __cmp__(self, other):
         if self is other or (
-            isinstance(other, PersistentReference) and 
+            isinstance(other, PersistentReference) and
             self.oid == other.oid and
             self.database_name == other.database_name and
             not self.weak and
@@ -179,6 +180,7 @@ def tryToResolveConflict(self, oid, committedSerial, oldSerial, newpickle,
     # class_tuple, old, committed, newstate = ('',''), 0, 0, 0
     try:
         prfactory = PersistentReferenceFactory()
+        newpickle = self._crs_wrapper.untransform_record_data(newpickle)
         file = StringIO(newpickle)
         unpickler = Unpickler(file)
         unpickler.find_global = find_global
@@ -215,7 +217,7 @@ def tryToResolveConflict(self, oid, committedSerial, oldSerial, newpickle,
         pickler.inst_persistent_id = persistent_id
         pickler.dump(meta)
         pickler.dump(resolved)
-        return file.getvalue(1)
+        return self._crs_wrapper.transform_record_data(file.getvalue(1))
     except (ConflictError, BadClassName):
         return None
     except:
@@ -227,7 +229,11 @@ def tryToResolveConflict(self, oid, committedSerial, oldSerial, newpickle,
         logger.error("Unexpected error", exc_info=True)
         return None
 
-class ConflictResolvingStorage:
+class ConflictResolvingStorage(object):
     "Mix-in class that provides conflict resolution handling for storages"
 
     tryToResolveConflict = tryToResolveConflict
+
+    def registerDB(self, wrapper):
+        self._crs_wrapper = wrapper
+        super(ConflictResolvingStorage, self).registerDB(wrapper)

src/ZODB/DB.py

@@ -705,6 +705,8 @@ class DB(object):
         """
         self._connectionMap(lambda c: c.invalidateCache())
 
+    transform_record_data = untransform_record_data = lambda self, data: data
+
     def objectCount(self):
         return len(self.storage)
 

src/ZODB/interfaces.py

@@ -287,23 +287,32 @@ class IConnection(Interface):
         """
 
 
-class IStorageDB(Interface):
-    """Database interface exposed to storages
+class IStorageWrapper(Interface):
+    """Storage wrapper interface
 
-    This interface provides 2 facilities:
+    This interface provides 3 facilities:
 
     - Out-of-band invalidation support
 
-      A storage can notify it's database of object invalidations that
+      A storage can notify it's wrapper of object invalidations that
       don't occur due to direct operations on the storage.  Currently
       this is only used by ZEO client storages to pass invalidation
       messages sent from a server.
 
-    - Record-reference extraction.
+    - Record-reference extraction
 
       The references method can be used to extract referenced object
       IDs from a database record.  This can be used by storages to
-      provide more advanced garbage collection.
+      provide more advanced garbage collection.  A wrapper storage
+      that transforms data will provide a references method that
+      untransforms data passed to it and then pass the data to the
+      layer above it.
+
+    - Record transformation
+
+      A storage wrapper may transform data, for example for
+      compression or encryption.  Methods are provided to transform or
+      untransform data.
 
     This interface may be implemented by storage adapters or other
     intermediaries.  For example, a storage adapter that provides
@@ -337,6 +346,16 @@ class IStorageDB(Interface):
         be created and returned.
         """
 
+    def transform_record_data(data):
+        """Return transformed data
+        """
+
+    def untransform_record_data(data):
+        """Return untransformed data
+        """
+
+IStorageDB = IStorageWrapper # for backward compatibility
+
 
 class IDatabase(IStorageDB):
     """ZODB DB.
@@ -595,12 +614,18 @@ class IStorage(Interface):
         revisions.
         """
 
-    def registerDB(db):
-        """Register an IStorageDB.
+    def registerDB(wrapper):
+        """Register a storage wrapper IStorageWrapper.
+
+        The passed object is a wrapper object that provides an upcall
+        interface to support composition.
 
         Note that, for historical reasons, an implementation may
         require a second argument, however, if required, the None will
         be passed as the second argument.
+
+        Also, for historical reasons, this is called registerDB rather
+        than register_wrapper.
         """
 
     def sortKey():

src/ZODB/tests/ConflictResolution.py

@@ -53,9 +53,15 @@ class PCounter4(PCounter):
     def _p_resolveConflict(self, oldState, savedState):
         raise RuntimeError("Can't get here; not enough args")
 
+class StorageWrapper:
+
+    transform_record_data = untransform_record_data = lambda self, data: data
+
 class ConflictResolvingStorage:
 
     def checkResolve(self):
+        self._storage.registerDB(StorageWrapper())
+
         obj = PCounter()
         obj.inc()
 
@@ -76,6 +82,8 @@ class ConflictResolvingStorage:
         self.assertEqual(inst._value, 5)
 
     def checkUnresolvable(self):
+        self._storage.registerDB(StorageWrapper())
+
         obj = PCounter2()
         obj.inc()
 
@@ -97,11 +105,15 @@ class ConflictResolvingStorage:
             self.fail("Expected ConflictError")
 
     def checkZClassesArentResolved(self):
+        self._storage.registerDB(StorageWrapper())
+
         from ZODB.ConflictResolution import find_global, BadClassName
         dummy_class_tuple = ('*foobar', ())
         self.assertRaises(BadClassName, find_global, '*foobar', ())
 
     def checkBuggyResolve1(self):
+        self._storage.registerDB(StorageWrapper())
+
         obj = PCounter3()
         obj.inc()
 
@@ -120,6 +132,8 @@ class ConflictResolvingStorage:
                           oid, revid=revid1, data=zodb_pickle(obj))
 
     def checkBuggyResolve2(self):
+        self._storage.registerDB(StorageWrapper())
+
         obj = PCounter4()
         obj.inc()
 
@@ -144,6 +158,8 @@ class ConflictResolvingTransUndoStorage:
         # TransactionalUndoStorage test suite.  Except here, conflict
         # resolution should allow us to undo the transaction anyway.
 
+        self._storage.registerDB(StorageWrapper())
+
         obj = PCounter()
         obj.inc()
         oid = self._storage.new_oid()
@@ -166,6 +182,8 @@ class ConflictResolvingTransUndoStorage:
         # TransactionalUndoStorage test suite.  Except here, conflict
         # resolution should allow us to undo the transaction anyway.
 
+        self._storage.registerDB(StorageWrapper())
+
         obj = PCounter2()
         obj.inc()
         oid = self._storage.new_oid()