sync: Introduce CryptographerProvider interface

sync/engine/cryptographer_provider.h

+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef SYNC_ENGINE_CRYPTOGRAPHER_PROVIDER_H_
+#define SYNC_ENGINE_CRYPTOGRAPHER_PROVIDER_H_
+
+#include "base/memory/scoped_ptr.h"
+#include "sync/base/sync_export.h"
+
+namespace syncer {
+
+class Cryptographer;
+class ScopedCryptographer;
+class ScopedCryptographerImpl;
+
+// An interface for providing clients with a ScopedCryptographer.
+//
+// Used to expose the syncable::Directory's cryptographer to clients that
+// would otherwise not have access to the Directory.
+class SYNC_EXPORT_PRIVATE CryptographerProvider {
+ public:
+  CryptographerProvider();
+  virtual ~CryptographerProvider();
+
+  virtual bool InitScopedCryptographer(ScopedCryptographer* scoped) = 0;
+};
+
+// A concrete class representing a cryptographer.
+//
+// Access to the cryptographer is lost when this class goes out of scope.
+class SYNC_EXPORT_PRIVATE ScopedCryptographer {

[Nicolas Zea, 2014/07/24 22:16:42]

I find this naming a bit confusing. ScopedCryptographer to me implies that it
destroys the cryptographer when it goes out of scope (a la scoped_ptr).

How about SharedCryptographer?

[rlarocque, 2014/07/24 22:23:13]

I was trying to get across the idea that the Cryptographer returned with Get()
is only valid as long as this item is on the stack.  I don't think that
SharedCryptographer conveys that same meaning.

Maybe ScopedCryptographerAccessor?  ScopedCryptographerReference?

[Nicolas Zea, 2014/07/24 22:34:19]

I see. Yeah, ScopedCryptographerRef seems better in that case.

+ public:
+  ScopedCryptographer();
+  ~ScopedCryptographer();
+
+  bool Initialize(ScopedCryptographerImpl* impl);
+  bool IsValid() const;
+  Cryptographer* Get() const;
+
+ private:
+  scoped_ptr<ScopedCryptographerImpl> scoped_cryptographer_impl_;
+
+  DISALLOW_COPY_AND_ASSIGN(ScopedCryptographer);
+};
+
+// An interface class used in the implementation of the ScopedCryptographer.
+//
+// We use this class to allow different implementations of
+// CryptographerProvider to implement InitScopedCryptographer in different
+// ways.  The ScopedCryptographer itself must be stack-allocated, so it can't
+// vary depending on which kind of CryptographerProvider is used to intialize
+// it.
+class SYNC_EXPORT_PRIVATE ScopedCryptographerImpl {
+ public:
+  ScopedCryptographerImpl();
+  virtual ~ScopedCryptographerImpl();
+
+  virtual Cryptographer* Get() const = 0;
+};
+
+}  // namespace syncer
+
+#endif  // SYNC_ENGINE_CRYPTOGRAPHER_PROVIDER_H_