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 ScopedCryptographerRef;
+class ScopedCryptographerImpl;
+
+// An interface for providing clients with a ScopedCryptographerRef.
+//
+// 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 InitScopedCryptographerRef(ScopedCryptographerRef* scoped) = 0;
+};
+
+// A concrete class representing a cryptographer.

[Nicolas Zea, 2014/07/25 20:03:30]

nit: perhaps "representing a cryptographer" should be "representing a
cryptographer reference"

[rlarocque, 2014/07/25 20:18:17]

Done.

+//
+// Access to the cryptographer is lost when this class goes out of scope.
+class SYNC_EXPORT_PRIVATE ScopedCryptographerRef {
+ public:
+  ScopedCryptographerRef();
+  ~ScopedCryptographerRef();
+
+  bool Initialize(ScopedCryptographerImpl* impl);
+  bool IsValid() const;
+  Cryptographer* Get() const;
+
+ private:
+  scoped_ptr<ScopedCryptographerImpl> scoped_cryptographer_impl_;
+
+  DISALLOW_COPY_AND_ASSIGN(ScopedCryptographerRef);
+};
+
+// An interface class used in the implementation of the ScopedCryptographerRef.
+//
+// We use this class to allow different implementations of
+// CryptographerProvider to implement InitScopedCryptographer in different
+// ways.  The ScopedCryptographerRef 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 {

[Nicolas Zea, 2014/07/25 20:03:30]

nit: this is the actual getter, not so much an impl in my mind.
CryptographerGetter might make more sense as a name.

[rlarocque, 2014/07/25 20:18:17]

Maybe Impl isn't the right suffix, given how we tend to use it for implementers
of interfaces.  I don't think Getter makes sense either, though.  In the
Directory case, the ScopedCryptographerImpl embeds the scoped transaction.  That
seems like more than a getter.

How about an "Internal(s)" suffix?

+ public:
+  ScopedCryptographerImpl();
+  virtual ~ScopedCryptographerImpl();
+
+  virtual Cryptographer* Get() const = 0;
+};
+
+}  // namespace syncer
+
+#endif  // SYNC_ENGINE_CRYPTOGRAPHER_PROVIDER_H_