Fetch snippets from ChromeReader and show them on the NTP

components/ntp_snippets/ntp_snippets_fetcher.h

+// Copyright 2016 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 COMPONENTS_NTP_SNIPPETS_NTP_SNIPPETS_FETCHER_H_
+#define COMPONENTS_NTP_SNIPPETS_NTP_SNIPPETS_FETCHER_H_
+
+#include "base/callback.h"
+#include "base/callback_list.h"
+#include "base/files/file_path.h"
+#include "base/memory/weak_ptr.h"
+#include "base/observer_list.h"
+#include "base/sequenced_task_runner.h"
+#include "google_apis/gaia/oauth2_token_service.h"
+
+namespace net {
+class URLRequestContextGetter;
+class URLFetcher;
+class URLFetcherDelegate;
+}  // namespace net
+
+class SigninManager;
+
+namespace ntp_snippets {
+
+// Fetches snippet data for the NTP from the server
+class NTPSnippetsFetcher : public OAuth2TokenService::Consumer,
+                           public OAuth2TokenService::Observer,
+                           public net::URLFetcherDelegate {
+ public:
+  using SnippetsAvailableCallback = base::Callback<void(const base::FilePath&)>;
+  using SnippetsAvailableCallbackList =
+      base::CallbackList<void(const base::FilePath&)>;
+
+  NTPSnippetsFetcher(scoped_refptr<base::SequencedTaskRunner> file_task_runner,
+                     SigninManager* signin_manager,
+                     OAuth2TokenService* oauth2_token_service,
+                     net::URLRequestContextGetter* url_request_context_getter,
+                     const base::FilePath& base_download_path);
+  ~NTPSnippetsFetcher() override;
+
+  // Fetches snippets from the server. |overwrite| is true if existing snippets
+  // should be overwritten.
+  void FetchSnippets(bool overwrite);
+
+  // Adds a callback that is called when a new set of snippets are downloaded
+  scoped_ptr<SnippetsAvailableCallbackList::Subscription> AddCallback(
+      const SnippetsAvailableCallback& callback) WARN_UNUSED_RESULT;
+
+ private:
+  void StartTokenRequest();
+  void NotifyObservers();
+  void OnDownloadSnippetsDone(bool success);
+  void OnFileExistsCheckDone(bool exists);
+  void OnFileMoveDone(bool success);
+  void StartFetch();
+
+  // OAuth2TokenService::Consumer overrides:
+  void OnGetTokenSuccess(const OAuth2TokenService::Request* request,
+                         const std::string& access_token,
+                         const base::Time& expiration_time) override;
+  void OnGetTokenFailure(const OAuth2TokenService::Request* request,
+                         const GoogleServiceAuthError& error) override;
+
+  // OAuth2TokenService::Observer overrides:
+  void OnRefreshTokenAvailable(const std::string& account_id) override;
+
+  // URLFetcherDelegate implementation.
+  void OnURLFetchComplete(const net::URLFetcher* source) override;
+
+  // The SequencedTaskRunner on which file system operations will be run.
+  scoped_refptr<base::SequencedTaskRunner> file_task_runner_;
+
+  // Holds the URL request context. Not owned.
+  net::URLRequestContextGetter* url_request_context_getter_;

[mmenke, 2016/02/18 16:51:11]

You should hold onto a reference to this, or modify your architecture so you
don't need to keep a pointer to it, to make sure it always exists when you're
fetching something.  Note that this doesn't delay teardown of the network stack,
but if the network stack is torn down, requests will just cleanly fail, as long
as you're not using an invalid URLRequestContextGetter pointer.

Since NTPSnippetsFetchers are owned by a service keyed on the profile, they
should be deleted just before the URLRequestConext is, but I think it's best not
to have that implicit dependency on shutdown ordering, since we can easily avoid
it.

[May, 2016/02/19 14:49:02]

Thanks for the explanation, turned into a scoped_refptr

+
+  scoped_ptr<net::URLFetcher> url_fetcher_;
+  scoped_ptr<SigninManager> signin_manager_;
+  scoped_ptr<OAuth2TokenService> token_service_;
+  scoped_ptr<OAuth2TokenService::Request> oauth_request_;
+
+  base::FilePath download_path_;
+  bool waiting_for_refresh_token_;
+
+  SnippetsAvailableCallbackList callback_list_;
+
+  base::WeakPtrFactory<NTPSnippetsFetcher> weak_ptr_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(NTPSnippetsFetcher);
+};
+}  // namespace ntp_snippets
+
+#endif  // COMPONENTS_NTP_SNIPPETS_NTP_SNIPPETS_FETCHER_H_