Implement throttling logic for fetching affiliation information.

components/password_manager/core/browser/affiliation_fetch_throttler.h

+// Copyright 2015 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_PASSWORD_MANAGER_CORE_BROWSER_AFFILIATION_FETCH_THROTTLER_H_
+#define COMPONENTS_PASSWORD_MANAGER_CORE_BROWSER_AFFILIATION_FETCH_THROTTLER_H_
+
+#include "base/gtest_prod_util.h"
+#include "base/macros.h"
+#include "base/memory/ref_counted.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/memory/weak_ptr.h"
+#include "net/base/backoff_entry.h"
+#include "net/base/network_change_notifier.h"
+
+namespace base {
+class TickClock;
+class SingleThreadTaskRunner;
+}  // namespace base
+
+namespace password_manager {
+
+class AffiliationFetchThrottlerDelegate;
+
+// Implements the throttling logic that the AffiliationBackend will use when it
+// needs to issue requests over the network to fetch affiliation information.
+//
+// This class manages only the scheduling of the requests. It is up to the
+// consumer (the AffiliationBackend) to actually assemble and send the requests,
+// to report back about their success or failure, and to retry them if desired.
+// The process goes like this:
+//   1.) The consumer calls SignalNetworkRequestNeeded().
+//   2.) Once appropriate, OnCanSendNetworkRequest() is called on the delegate.
+//   3.) The consumer sends the request, and waits until it completes.
+//   4.) The consumer calls InformOfNetworkRequestComplete().
+// Note that only a single request at a time is supported.
+//
+// If the request fails in Step 3, the consumer should not automatically retry
+// it. Instead it should always proceed to Step 4, and then -- if retrying the
+// request is desired -- proceed immediately to Step 1. That is, it should act
+// as if another request was needed right away.
+//
+// Essentially, this class implements exponential backoff in case of network and
+// server errors with the additional constraint that no requests will be issued
+// in the first place while there is known to be no network connectivity. This
+// prevents the exponential backoff delay from growing huge during long offline
+// periods, so that requests will not be held back for too long after
+// connectivity is restored.
+class AffiliationFetchThrottler
+    : public net::NetworkChangeNotifier::ConnectionTypeObserver {
+ public:
+  // Creates an instance that will use |tick_clock| as its tick source, and will
+  // post to |task_runner| to call the |delegate|'s OnSendNetworkRequest().

[mmenke, 2015/01/30 19:50:41]

Should mention the delegate must outlive the throttler.

[engedy, 2015/01/30 20:23:13]

Done.

+  AffiliationFetchThrottler(
+      AffiliationFetchThrottlerDelegate* delegate,
+      const scoped_refptr<base::SingleThreadTaskRunner>& task_runner,
+      scoped_ptr<base::TickClock> tick_clock);
+  ~AffiliationFetchThrottler() override;
+
+  // Signals to the throttling logic that a network request is needed, and that
+  // OnCanSendNetworkRequest() should be called as soon as the request can be
+  // sent.

[mmenke, 2015/01/30 19:50:41]

Think it's worth noting that OnCanSendNetworkRequest will always be called
asynchronously.

[engedy, 2015/01/30 20:23:13]

Done.

+  //
+  // Calls to this method will be ignored when a request is already known to be
+  // needed or while a request is in flight. To signal that another request will
+  // be needed right away after the current one, call this method after calling
+  // InformOfNetworkRequestComplete().
+  void SignalNetworkRequestNeeded();
+
+  // Informs the back-off logic that the in-flight network request has been
+  // completed, either with |success| or not.
+  void InformOfNetworkRequestComplete(bool success);
+
+ private:
+  FRIEND_TEST_ALL_PREFIXES(AffiliationFetchThrottlerTest, FailedRequests);
+  FRIEND_TEST_ALL_PREFIXES(AffiliationFetchThrottlerTest,
+                           GracePeriodAfterConnectivityIsRestored);
+  FRIEND_TEST_ALL_PREFIXES(AffiliationFetchThrottlerTest,
+                           GracePeriodAfterConnectivityIsRestored2);
+  FRIEND_TEST_ALL_PREFIXES(AffiliationFetchThrottlerTest,
+                           GracePeriodAfterConnectivityIsRestored3);
+  FRIEND_TEST_ALL_PREFIXES(AffiliationFetchThrottlerTest,
+                           ConnectivityLostDuringBackoff);
+  FRIEND_TEST_ALL_PREFIXES(AffiliationFetchThrottlerTest,
+                           ConnectivityLostAndRestoredDuringBackoff);
+  FRIEND_TEST_ALL_PREFIXES(AffiliationFetchThrottlerTest, FlakyConnectivity);
+  FRIEND_TEST_ALL_PREFIXES(AffiliationFetchThrottlerTest,
+                           ConnectivityLostDuringRequest);
+  FRIEND_TEST_ALL_PREFIXES(AffiliationFetchThrottlerTest,
+                           ConnectivityLostAndRestoredDuringRequest);
+  FRIEND_TEST_ALL_PREFIXES(AffiliationFetchThrottlerTest,
+                           ConnectivityLostAndRestoredDuringRequest2);
+
+  enum State { IDLE, FETCH_NEEDED, FETCH_IN_FLIGHT };
+
+  // Exponential backoff parameters in case of network and server errors
+  static const net::BackoffEntry::Policy kBackoffPolicy;
+
+  // Minimum delay before sending the first request once network connectivity is
+  // restored. The fuzzing factor in |kBackoffParameters.jitter_factor| applies.
+  static const int64_t kGracePeriodAfterReconnectMs;
+
+  // Ensures that OnBackoffDelayExpiredCallback() is scheduled to be called back
+  // once the |exponential_backoff_| delay expires.
+  void EnsureCallbackIsScheduled();
+
+  // Called back when the |exponential_backoff_| delay expires.
+  void OnBackoffDelayExpiredCallback();
+
+  // net::NetworkChangeNotifier::ConnectionTypeObserver:
+  void OnConnectionTypeChanged(
+      net::NetworkChangeNotifier::ConnectionType type) override;
+
+  AffiliationFetchThrottlerDelegate* delegate_;
+  scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
+  State state_;
+  bool has_network_connectivity_;
+  bool is_fetch_scheduled_;
+  scoped_ptr<base::TickClock> tick_clock_;
+  scoped_ptr<net::BackoffEntry> exponential_backoff_;
+  base::WeakPtrFactory<AffiliationFetchThrottler> weak_ptr_factory_;

[mmenke, 2015/01/30 19:50:41]

Suggest a blank line before the factory, as it should always go last.

[engedy, 2015/01/30 20:23:13]

Done.

+
+  DISALLOW_COPY_AND_ASSIGN(AffiliationFetchThrottler);
+};
+
+}  // namespace password_manager
+
+#endif  // COMPONENTS_PASSWORD_MANAGER_CORE_BROWSER_AFFILIATION_FETCH_THROTTLER_H_