quiche/http2/adapter/window_manager.h

#ifndef QUICHE_HTTP2_ADAPTER_WINDOW_MANAGER_H_
#define QUICHE_HTTP2_ADAPTER_WINDOW_MANAGER_H_

#include <stddef.h>

#include <functional>

#include "quiche/common/platform/api/quiche_export.h"

namespace http2 {
namespace adapter {

namespace test {
class WindowManagerPeer;
}

// This class keeps track of a HTTP/2 flow control window, notifying a listener
// when a window update needs to be sent. This class is not thread-safe.
class QUICHE_EXPORT_PRIVATE WindowManager {
 public:
  // A WindowUpdateListener is invoked when it is time to send a window update.
  using WindowUpdateListener = std::function<void(int64_t)>;

  // Invoked to determine whether to call the listener based on the window
  // limit, window size, and delta that would be sent.
  using ShouldWindowUpdateFn =
      std::function<bool(int64_t limit, int64_t size, int64_t delta)>;

  WindowManager(int64_t window_size_limit, WindowUpdateListener listener,
                ShouldWindowUpdateFn should_window_update_fn = {},
                bool update_window_on_notify = true);

  int64_t CurrentWindowSize() const { return window_; }
  int64_t WindowSizeLimit() const { return limit_; }

  // Called when the window size limit is changed (typically via settings) but
  // no window update should be sent.
  void OnWindowSizeLimitChange(int64_t new_limit);

  // Sets the window size limit to |new_limit| and notifies the listener to
  // update as necessary.
  void SetWindowSizeLimit(int64_t new_limit);

  // Increments the running total of data bytes buffered. Returns true iff there
  // is more window remaining.
  bool MarkDataBuffered(int64_t bytes);

  // Increments the running total of data bytes that have been flushed or
  // dropped. Invokes the listener if the current window is smaller than some
  // threshold and there is quota available to send.
  void MarkDataFlushed(int64_t bytes);

  // Convenience method, used when incoming data is immediately dropped or
  // ignored.
  void MarkWindowConsumed(int64_t bytes) {
    MarkDataBuffered(bytes);
    MarkDataFlushed(bytes);
  }

  // Increments the window size without affecting the limit. Useful if this end
  // of a stream or connection issues a one-time WINDOW_UPDATE.
  void IncreaseWindow(int64_t delta) { window_ += delta; }

 private:
  friend class test::WindowManagerPeer;

  void MaybeNotifyListener();

  // The upper bound on the flow control window. The GFE attempts to maintain a
  // window of this size at the peer as data is proxied through.
  int64_t limit_;

  // The current flow control window that has not been advertised to the peer
  // and not yet consumed. The peer can send this many bytes before becoming
  // blocked.
  int64_t window_;

  // The amount of data already buffered, which should count against the flow
  // control window upper bound.
  int64_t buffered_;

  WindowUpdateListener listener_;

  ShouldWindowUpdateFn should_window_update_fn_;

  bool update_window_on_notify_;
};

}  // namespace adapter
}  // namespace http2

#endif  // QUICHE_HTTP2_ADAPTER_WINDOW_MANAGER_H_