Add in-memory caching of network quality estimates across network changes.

net/base/network_quality_estimator.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 NET_BASE_NETWORK_QUALITY_ESTIMATOR_H_
 #define NET_BASE_NETWORK_QUALITY_ESTIMATOR_H_
 
 #include <stdint.h>
 
 #include "base/gtest_prod_util.h"
 #include "base/macros.h"
 #include "base/threading/thread_checker.h"
 #include "base/time/time.h"
 #include "net/base/network_change_notifier.h"
 
 namespace net {
 
+// CachedNetworkQuality stores the quality of a previously seen network.
+// A network is uniquely identified by combination of |connection_type| and
+// |network_name|.
+struct NET_EXPORT_PRIVATE CachedNetworkQuality {

[mmenke, 2015/05/28 15:25:02]

Since a subclass for testing only needs to be able to calculate the size of a
vector of these, NET_EXPORT_PRIVATE seems overkill.  Just add a protected method
to NetworkQualityEstimator, and have the subclass expose it with a "using"
directive.

[mmenke, 2015/05/28 15:25:02]

This should be a protected or private class - private seems better, see next
comment.

[tbansal1, 2015/05/29 02:27:23]

Done.

[tbansal1, 2015/05/29 02:27:24]

Done.

+  CachedNetworkQuality(NetworkChangeNotifier::ConnectionType connection_type,
+                       std::string network_name,
+                       int median_kbps,
+                       int median_rtt_milliseconds);
+
+  ~CachedNetworkQuality();
+
+  void UpdateNetworkQuality(int updated_median_kbps,
+                            int updated_median_rtt_milliseconds);
+
+  // Connection type of this cached network.
+  NetworkChangeNotifier::ConnectionType connection_type;
+
+  // Name of this cached network.
+  std::string network_name;
+
+  // Median Kbps of this cached network.
+  int median_kbps;
+
+  // Median RTT (in milliseconds) of this cached network.
+  int median_rtt_milliseconds;
+
+  // Time when this cache entry was last updated.
+  base::TimeTicks last_updated;
+};
+
 struct NetworkQuality;
 
 // NetworkQualityEstimator provides network quality estimates (quality of the
 // full paths to all origins that have been connected to).
 // The estimates are based on the observed organic traffic.
 // A NetworkQualityEstimator instance is attached to URLRequestContexts and
 // observes the traffic of URLRequests spawned from the URLRequestContexts.
 // A single instance of NQE can be attached to multiple URLRequestContexts,
 // thereby increasing the single NQE instance's accuracy by providing more
 // observed traffic characteristics.
@@ skipping 12 matching lines @@
   // |prefilter_bytes_read| is the count of the bytes received prior to
   // applying filters (e.g. decompression, SDCH) from request creation time
   // until now.
   void NotifyDataReceived(const URLRequest& request,
                           int64_t prefilter_bytes_read);
 
  private:
   FRIEND_TEST_ALL_PREFIXES(NetworkQualityEstimatorTest,
                            TestPeakKbpsFastestRTTUpdates);
   FRIEND_TEST_ALL_PREFIXES(URLRequestTestHTTP, NetworkQualityEstimator);
+  friend class NetworkQualityEstimatorTest;

[mmenke, 2015/05/28 15:25:02]

Should not need to friend a subclass.  Just make protected accessors for
anything it needs.

[tbansal1, 2015/05/29 02:27:24]

Done.

 
   // Tiny transfer sizes may give inaccurate throughput results.
   // Minimum size of the transfer over which the throughput is computed.
   static const int kMinTransferSizeInBytes = 10000;
 
   // Minimum duration (in microseconds) of the transfer over which the
   // throughput is computed.
   static const int kMinRequestDurationMicroseconds = 1000;
 
   // Construct a NetworkQualityEstimator instance allowing for test
   // configuration.
   // Registers for network type change notifications so estimates can be kept
   // network specific.
   // |allow_local_host_requests_for_tests| should only be true when testing
   // against local HTTP server and allows the requests to local host to be
   // used for network quality estimation.
   explicit NetworkQualityEstimator(bool allow_local_host_requests_for_tests);
 
   // NetworkChangeNotifier::ConnectionTypeObserver implementation.
   void OnConnectionTypeChanged(
       NetworkChangeNotifier::ConnectionType type) override;
 
+  // Returns the current network name:
+  // WiFi SSID (if the user is connected to a WiFi access point and the SSID
+  // name is available), or
+  // The MCCMNC code of the cellular carrier if the device is connected to a
+  // cellular network, or
+  // "ethernet" if the device is connected to an Ethernet network.
+  // Returns empty string in all other cases or if the network name is not
+  // exposed by platform APIs.
+  // Virtualized for testing.
+  virtual std::string GetCurrentNetworkName() const;

[mmenke, 2015/05/28 15:25:02]

include <string>

[tbansal1, 2015/05/29 02:27:24]

Done.

+
+  // Returns true if cached network quality estimate was successfully read.
+  bool ReadCachedNetworkQualityEstimate();
+
+  // Write the estimated quality of the current network to the cache.
+  void CacheNetworkQualityEstimate();
+
   // Determines if the requests to local host can be used in estimating the
   // network quality. Set to true only for tests.
   const bool allow_localhost_requests_;
 
   // Time when last connection change was observed.
   base::TimeTicks last_connection_change_;
 
   // Last value passed to |OnConnectionTypeChanged|. This indicates the
   // current connection type.
   NetworkChangeNotifier::ConnectionType current_connection_type_;
 
   // Set if any network data has been received since last connectivity change.
   bool bytes_read_since_last_connection_change_;
 
   // Fastest round-trip-time (RTT) since last connectivity change. RTT measured
   // from URLRequest creation until first byte received.
   base::TimeDelta fastest_RTT_since_last_connection_change_;
 
+  // Cache to store quality of previously seen networks.
+  std::vector<CachedNetworkQuality> cached_network_quality_;

[mmenke, 2015/05/28 15:25:03]

include <vector>

[tbansal1, 2015/05/29 02:27:24]

Done.

+
   // Rough measurement of downlink peak Kbps witnessed since last connectivity
   // change. The accuracy is decreased by ignoring these factors:
   // 1) Multiple URLRequests can occur concurrently.
   // 2) The transfer time includes at least one RTT while no bytes are read.
   uint64_t peak_kbps_since_last_connection_change_;
 
+  // Name of the current network as returned by GetCurrentNetworkName.
+  std::string current_network_name_;
+
   base::ThreadChecker thread_checker_;
 
   DISALLOW_COPY_AND_ASSIGN(NetworkQualityEstimator);
 };
 
 }  // namespace net
 
 #endif  // NET_BASE_NETWORK_QUALITY_ESTIMATOR_H_