[feat] implementation for send side congestion controller

src/qos/alr_detector.h

@@ -0,0 +1,60 @@
+/*
+ * @Author: DI JUNKUN
+ * @Date: 2025-01-14
+ * Copyright (c) 2025 by DI JUNKUN, All Rights Reserved.
+ */
+
+#ifndef _ALR_DETECTOR_H_
+#define _ALR_DETECTOR_H_
+
+#include <stddef.h>
+#include <stdint.h>
+
+#include <memory>
+#include <optional>
+
+#include "interval_budget.h"
+
+struct AlrDetectorConfig {
+  // Sent traffic ratio as a function of network capacity used to determine
+  // application-limited region. ALR region start when bandwidth usage drops
+  // below kAlrStartUsageRatio and ends when it raises above
+  // kAlrEndUsageRatio. NOTE: This is intentionally conservative at the moment
+  // until BW adjustments of application limited region is fine tuned.
+  double bandwidth_usage_ratio = 0.65;
+  double start_budget_level_ratio = 0.80;
+  double stop_budget_level_ratio = 0.50;
+};
+// Application limited region detector is a class that utilizes signals of
+// elapsed time and bytes sent to estimate whether network traffic is
+// currently limited by the application's ability to generate traffic.
+//
+// AlrDetector provides a signal that can be utilized to adjust
+// estimate bandwidth.
+// Note: This class is not thread-safe.
+class AlrDetector {
+ public:
+  AlrDetector(AlrDetectorConfig config);
+  AlrDetector();
+  ~AlrDetector();
+
+  void OnBytesSent(size_t bytes_sent, int64_t send_time_ms);
+
+  // Set current estimated bandwidth.
+  void SetEstimatedBitrate(int bitrate_bps);
+
+  // Returns time in milliseconds when the current application-limited region
+  // started or empty result if the sender is currently not application-limited.
+  std::optional<int64_t> GetApplicationLimitedRegionStartTime() const;
+
+ private:
+  friend class GoogCcStatePrinter;
+  const AlrDetectorConfig conf_;
+
+  std::optional<int64_t> last_send_time_ms_;
+
+  IntervalBudget alr_budget_;
+  std::optional<int64_t> alr_started_time_ms_;
+};
+
+#endif