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

net/base/network_quality_estimator.h

Index: net/base/network_quality_estimator.h
diff --git a/net/base/network_quality_estimator.h b/net/base/network_quality_estimator.h
index ecfa08af6b8341b3a9bb06897a89baa42651c7b7..c01f920c5b69b0359e4eb648655324fe75981d5d 100644
--- a/net/base/network_quality_estimator.h
+++ b/net/base/network_quality_estimator.h
@@ -7,6 +7,9 @@
 
 #include <stdint.h>
 
+#include <string>
+#include <vector>
+
 #include "base/gtest_prod_util.h"
 #include "base/macros.h"
 #include "base/threading/thread_checker.h"
@@ -43,11 +46,71 @@ class NET_EXPORT_PRIVATE NetworkQualityEstimator
   void NotifyDataReceived(const URLRequest& request,
                           int64_t prefilter_bytes_read);
 
+ protected:
+  // Returns true if cached network quality estimate was successfully read.

[bengr, 2015/06/01 20:39:35]

"if" -> "if the"

[tbansal1, 2015/06/01 21:56:51]

Done.

+  bool ReadCachedNetworkQualityEstimate();

[bengr, 2015/06/01 20:39:34]

You might want to bite the bullet now and make this interface asynchronous. You
will almost certainly need to do so if you expect to persist these cache
entries.

[tbansal1, 2015/06/01 21:56:51]

This CL is complete in the current form.
I would prefer to do it when doing the disk based caching.

[bengr, 2015/06/01 23:21:10]

Acknowledged.

[tbansal1, 2015/06/02 18:18:05]

Done.

+
+  // NetworkChangeNotifier::ConnectionTypeObserver implementation.
+  void OnConnectionTypeChanged(
+      NetworkChangeNotifier::ConnectionType type) override;
+
+  // Set the current network name for testing.
+  void SetCurrentNetworkNameForTests(const std::string& network_name);
+
+  // Returns the number of entries in the cache. Used only for testing.
+  uint32_t GetCacheSizeForTests() const;
+
+  // Updates the current network name to:
+  // WiFi SSID (if the user is connected to a WiFi access point and the SSID
+  // name is available), or
+  // The MCC/MNC 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.
+  // Updates the current network name to an empty string in all other cases or
+  // if the network name is not exposed by platform APIs.
+  // Virtualized for testing.
+  virtual void UpdateCurrentNetworkName();
+
  private:
   FRIEND_TEST_ALL_PREFIXES(NetworkQualityEstimatorTest,
                            TestPeakKbpsFastestRTTUpdates);
   FRIEND_TEST_ALL_PREFIXES(URLRequestTestHTTP, NetworkQualityEstimator);
 
+  // CachedNetworkQuality stores the quality of a previously seen network.
+  // A network is uniquely identified by combination of |connection_type_| and
+  // |network_name_|.
+  class CachedNetworkQuality {
+   public:
+    CachedNetworkQuality(NetworkChangeNotifier::ConnectionType connection_type,
+                         const std::string& network_name,
+                         int median_kbps,
+                         const base::TimeDelta& median_rtt);
+
+    virtual ~CachedNetworkQuality();
+
+    void UpdateNetworkQuality(int median_kbps,
+                              const base::TimeDelta& median_rtt);
+
+    bool MatchesNetwork(NetworkChangeNotifier::ConnectionType connection_type,
+                        const std::string& network_name) const;
+
+    // Median Kbps of this cached network.
+    int median_kbps_;
+
+    // Median RTT of this cached network.
+    base::TimeDelta median_rtt_;
+
+    // Time when this cache entry was last updated.
+    base::TimeTicks last_updated_;
+
+   private:
+    // Connection type of this cached network.
+    NetworkChangeNotifier::ConnectionType connection_type_;
+
+    // Name of this cached network.
+    std::string network_name_;
+  };
+
   // Tiny transfer sizes may give inaccurate throughput results.
   // Minimum size of the transfer over which the throughput is computed.
   static const int kMinTransferSizeInBytes = 10000;
@@ -65,9 +128,8 @@ class NET_EXPORT_PRIVATE NetworkQualityEstimator
   // used for network quality estimation.
   explicit NetworkQualityEstimator(bool allow_local_host_requests_for_tests);
 
-  // NetworkChangeNotifier::ConnectionTypeObserver implementation.
-  void OnConnectionTypeChanged(
-      NetworkChangeNotifier::ConnectionType type) override;
+  // 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.
@@ -87,12 +149,18 @@ class NET_EXPORT_PRIVATE NetworkQualityEstimator
   // 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_;
+
   // 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.
+  std::string current_network_name_;
+
   base::ThreadChecker thread_checker_;
 
   DISALLOW_COPY_AND_ASSIGN(NetworkQualityEstimator);