More implementation details of extension content verification

extensions/browser/content_hash_fetcher.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 EXTENSIONS_BROWSER_CONTENT_HASH_FETCHER_H_
+#define EXTENSIONS_BROWSER_CONTENT_HASH_FETCHER_H_
+
+#include "base/scoped_observer.h"
+#include "extensions/browser/content_verifier_delegate.h"
+#include "extensions/browser/extension_registry_observer.h"
+#include "extensions/common/extension.h"
+
+namespace content {
+class BrowserContext;
+}
+
+namespace extensions {
+
+class ExtensionRegistry;
+
+// This class is responsible for getting signed expected hashes for use in
+// extension content verification. As extensions are loaded it will fetch and
+// parse/validate/cache this data as needed, including calculating expected
+// hashes for each block of each file within an extension. (These unsigned leaf
+// node block level hashes will always be checked at time of use use to make
+// sure they match the signed treehash root hash).
+class ContentHashFetcher : public ExtensionRegistryObserver {
+ public:
+  // The consumer of this class needs to ensure that context and delegate
+  // outlive this object.
+  ContentHashFetcher(content::BrowserContext* context,
+                     ContentVerifierDelegate* delegate);
+  virtual ~ContentHashFetcher();
+
+  // Begins the process of trying to fetch any needed verified contents, and
+  // listening for extension load/unload.
+  void Start();
+
+  // Explicitly ask to fetch hashes for |extension|.
+  void DoFetch(const Extension* extension);
+
+  // ExtensionRegistryObserver interface
+  virtual void OnExtensionLoaded(content::BrowserContext* browser_context,
+                                 const Extension* extension) OVERRIDE;
+  virtual void OnExtensionUnloaded(
+      content::BrowserContext* browser_context,
+      const Extension* extension,
+      UnloadedExtensionInfo::Reason reason) OVERRIDE;
+
+ private:
+  content::BrowserContext* context_;
+  ContentVerifierDelegate* delegate_;
+
+  // For observing the ExtensionRegistry.
+  ScopedObserver<ExtensionRegistry, ExtensionRegistryObserver> observer_;
+
+  DISALLOW_COPY_AND_ASSIGN(ContentHashFetcher);
+};
+
+}  // namespace extensions
+
+#endif  // EXTENSIONS_BROWSER_CONTENT_HASH_FETCHER_H_