Add a QuicSustainedBandwidthEstimator class. Not yet used.

net/quic/quic_sustained_bandwidth_recorder.h

+// Copyright (c) 2014 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_QUIC_QUIC_SUSTAINED_BANDWIDTH_RECORDER_H_
+#define NET_QUIC_QUIC_SUSTAINED_BANDWIDTH_RECORDER_H_
+
+#include "base/logging.h"
+#include "net/quic/quic_bandwidth.h"
+#include "net/quic/quic_time.h"
+
+namespace net {
+
+// This class keeps track of a sustained bandwidth estimate to ultimately send
+// to the client in a server config update message. A sustained bandwidth
+// estimate is only marked as valid if the QuicSustainedBandwidthRecorder has
+// been given uninterrupted reliable estimates over a certain period of time.
+class NET_EXPORT_PRIVATE QuicSustainedBandwidthRecorder {
+ public:
+  QuicSustainedBandwidthRecorder();
+
+  // As long as |is_reliable_estimate| is consistently true, multiple calls to
+  // this method over a 3 * srtt period results in storage of a valid sustained
+  // bandwidth estimate.
+  // |time_now| is used as a max bandwidth timestamp if needed.
+  void RecordEstimate(bool is_reliable_estimate,
+                      QuicBandwidth bandwidth,
+                      QuicTime estimate_time,
+                      QuicWallTime wall_time,
+                      QuicTime::Delta srtt);
+
+  bool HasEstimate() const {
+    return has_estimate_;
+  }
+
+  QuicBandwidth BandwidthEstimate() const {
+    DCHECK(has_estimate_);
+    return bandwidth_estimate_;
+  }
+
+  QuicBandwidth MaxBandwidthEstimate() const {
+    DCHECK(has_estimate_);
+    return max_bandwidth_estimate_;
+  }
+
+  int32 MaxBandwidthTimestamp() const {

[ramant (doing other things), 2014/08/15 02:35:35]

rjshade@: should we use int64 instead of int32?

[Robbie Shade, 2014/08/15 12:08:38]

Yep, thanks!

[ramant (doing other things), 2014/08/15 17:54:18]

Great. Will submit the change to the internal source tree first.

thanks
raman

+    DCHECK(has_estimate_);
+    return max_bandwidth_timestamp_;
+  }
+
+ private:
+  // True if we have been able to calculate sustained bandwidth, over at least
+  // one recording period (3 * rtt).
+  bool has_estimate_;
+
+  // True if the last call to RecordEstimate had a reliable estimate.
+  bool is_recording_;
+
+  // The latest sustained bandwidth estimate.
+  QuicBandwidth bandwidth_estimate_;
+
+  // The maximum sustained bandwidth seen over the lifetime of the connection.
+  QuicBandwidth max_bandwidth_estimate_;
+
+  // Timestamp indicating when the max_bandwidth_estimate_ was seen.
+  int32 max_bandwidth_timestamp_;
+
+  // Timestamp marking the beginning of the latest recording period.
+  QuicTime start_time_;
+
+  DISALLOW_COPY_AND_ASSIGN(QuicSustainedBandwidthRecorder);
+};
+
+}  // namespace net
+
+#endif  // NET_QUIC_QUIC_SUSTAINED_BANDWIDTH_RECORDER_H_