chrome/browser/extensions/external_loader.h

// Copyright (c) 2012 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 CHROME_BROWSER_EXTENSIONS_EXTERNAL_LOADER_H_
#define CHROME_BROWSER_EXTENSIONS_EXTERNAL_LOADER_H_

#include <memory>

#include "base/files/file_path.h"
#include "base/macros.h"
#include "base/memory/ref_counted.h"

namespace base {
class DictionaryValue;
}

namespace extensions {
class ExternalProviderImpl;

// Base class for gathering a list of external extensions. Subclasses
// implement loading from registry, JSON file, policy.
// Instances are owned by ExternalProviderImpl objects.
// Instances are created on the UI thread and expect public method calls from
// the UI thread. Some subclasses introduce new methods that are executed on the
// FILE thread.
// The sequence of loading the extension list:
// 1.) StartLoading() - checks if a loading task is already running
// 2.) Load() - implemented in subclasses
// 3.) LoadFinished()
// 4.) owner_->SetPrefs()
class ExternalLoader : public base::RefCountedThreadSafe<ExternalLoader> {
 public:
  ExternalLoader();

  // Specifies the provider that owns this object.
  void Init(ExternalProviderImpl* owner);

  // Called by the owner before it gets deleted.
  void OwnerShutdown();

  // Initiates the possibly asynchronous loading of extension list.
  // Implementations of this method should call LoadFinished with results.
  virtual void StartLoading() = 0;

  // Some external providers allow relative file paths to local CRX files.
  // Subclasses that want this behavior should override this method to
  // return the absolute path from which relative paths should be resolved.
  // By default, return an empty path, which indicates that relative paths
  // are not allowed.
  virtual const base::FilePath GetBaseCrxFilePath();

 protected:
  virtual ~ExternalLoader();

  // Notifies the provider that the list of extensions has been loaded.
  virtual void LoadFinished(std::unique_ptr<base::DictionaryValue> prefs);

  // Notifies the provider that the list of extensions has been updated.
  virtual void OnUpdated(std::unique_ptr<base::DictionaryValue> updated_prefs);

  // Returns true if this loader has an owner.
  // This is useful to know if calling LoadFinished/OnUpdated will propagate
  // prefs to our owner.
  bool has_owner() const { return owner_ != nullptr; }

 private:
  friend class base::RefCountedThreadSafe<ExternalLoader>;

  ExternalProviderImpl* owner_;  // weak

  DISALLOW_COPY_AND_ASSIGN(ExternalLoader);
};

}  // namespace extensions

#endif  // CHROME_BROWSER_EXTENSIONS_EXTERNAL_LOADER_H_