1 files changed, 89 insertions, 0 deletions
diff --git a/dom/media/MediaChannelStatistics.h b/dom/media/MediaChannelStatistics.h
new file mode 100644
index 0000000000..9a3636cef2
--- /dev/null
+++ b/dom/media/MediaChannelStatistics.h
@@ -0,0 +1,89 @@
+/* vim:set ts=2 sw=2 sts=2 et cindent: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#if !defined(MediaChannelStatistics_h_)
+#  define MediaChannelStatistics_h_
+
+#  include "mozilla/TimeStamp.h"
+
+namespace mozilla {
+
+// Number of bytes we have accumulated before we assume the connection download
+// rate can be reliably calculated. 57 Segments at IW=3 allows slow start to
+// reach a CWND of 30 (See bug 831998)
+static const int64_t RELIABLE_DATA_THRESHOLD = 57 * 1460;
+
+/**
+ * This class is useful for estimating rates of data passing through
+ * some channel. The idea is that activity on the channel "starts"
+ * and "stops" over time. At certain times data passes through the
+ * channel (usually while the channel is active; data passing through
+ * an inactive channel is ignored). The GetRate() function computes
+ * an estimate of the "current rate" of the channel, which is some
+ * kind of average of the data passing through over the time the
+ * channel is active.
+ *
+ * All methods take "now" as a parameter so the user of this class can
+ * control the timeline used.
+ */
+class MediaChannelStatistics {
+ public:
+  MediaChannelStatistics() = default;
+  MediaChannelStatistics(const MediaChannelStatistics&) = default;
+  MediaChannelStatistics& operator=(const MediaChannelStatistics&) = default;
+
+  void Reset() {
+    mLastStartTime = TimeStamp();
+    mAccumulatedTime = TimeDuration(0);
+    mAccumulatedBytes = 0;
+    mIsStarted = false;
+  }
+  void Start() {
+    if (mIsStarted) return;
+    mLastStartTime = TimeStamp::Now();
+    mIsStarted = true;
+  }
+  void Stop() {
+    if (!mIsStarted) return;
+    mAccumulatedTime += TimeStamp::Now() - mLastStartTime;
+    mIsStarted = false;
+  }
+  void AddBytes(int64_t aBytes) {
+    if (!mIsStarted) {
+      // ignore this data, it may be related to seeking or some other
+      // operation we don't care about
+      return;
+    }
+    mAccumulatedBytes += aBytes;
+  }
+  double GetRateAtLastStop(bool* aReliable) const {
+    double seconds = mAccumulatedTime.ToSeconds();
+    *aReliable =
+        (seconds >= 1.0) || (mAccumulatedBytes >= RELIABLE_DATA_THRESHOLD);
+    if (seconds <= 0.0) return 0.0;
+    return static_cast<double>(mAccumulatedBytes) / seconds;
+  }
+  double GetRate(bool* aReliable) const {
+    TimeDuration time = mAccumulatedTime;
+    if (mIsStarted) {
+      time += TimeStamp::Now() - mLastStartTime;
+    }
+    double seconds = time.ToSeconds();
+    *aReliable =
+        (seconds >= 3.0) || (mAccumulatedBytes >= RELIABLE_DATA_THRESHOLD);
+    if (seconds <= 0.0) return 0.0;
+    return static_cast<double>(mAccumulatedBytes) / seconds;
+  }
+
+ private:
+  int64_t mAccumulatedBytes = 0;
+  TimeDuration mAccumulatedTime;
+  TimeStamp mLastStartTime;
+  bool mIsStarted = false;
+};
+
+}  // namespace mozilla
+
+#endif  // MediaChannelStatistics_h_