Implementing preload=metadata for video

webkit/glue/media/defer_strategy.h

+// Copyright (c) 2011 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 WEBKIT_GLUE_DEFER_STRATEGY_H_
+#define WEBKIT_GLUE_DEFER_STRATEGY_H_
+
+#include "base/singleton.h"
+
+namespace webkit_glue {
+
+class BufferedResourceLoader;
+
+class DeferStrategy {
+ public:
+  // Checks to see if loader should defer loading based on its state.
+  // Defers loader if needed.
+  // Returns true deferring was enabled, false otherwise.
+  virtual bool EnableDeferIfNeeded(BufferedResourceLoader* loader) const = 0;
+
+  // Checks to see if loader should stop deferring based on its state.
+  // Disables deferring if needed.
+  // Returns true deferring was disabled, false otherwise.
+  virtual bool DisableDeferIfNeeded(BufferedResourceLoader* loader) const = 0;
+
+  // Returns true if this strategy will ever allow resource deferring. This is
+  // used by BufferedResourceLoader to determine how much data should be
+  // stored in its in-memory buffer.
+  virtual bool AllowsDeferring() const { return true; };
+
+  // Toggles the defer settings for the resource loader.
+  // Returns true if defer setting was toggled, false otherwise.
+  static bool ToggleDefer(BufferedResourceLoader* loader);
+};
+
+// Never defer resource loading; keep buffering until all data has been
+// received.
+class NeverDeferStrategy : public DeferStrategy {
+ public:
+  static NeverDeferStrategy* GetInstance();
+  virtual bool EnableDeferIfNeeded(BufferedResourceLoader* loader) const;
+  virtual bool DisableDeferIfNeeded(BufferedResourceLoader* loader) const;
+  virtual bool AllowsDeferring() const { return false; };
+};
+
+// Buffer up until a threshold determined by the resource loader.
+class ThresholdDeferStrategy : public DeferStrategy {
+ public:
+  static ThresholdDeferStrategy* GetInstance();
+  virtual bool EnableDeferIfNeeded(BufferedResourceLoader* loader) const;
+  virtual bool DisableDeferIfNeeded(BufferedResourceLoader* loader) const;
+};
+
+// Buffer only what is requested by the read requests on the loader.
+class ReadThenDeferStrategy : public DeferStrategy {
+ public:
+  static ReadThenDeferStrategy* GetInstance();
+  virtual bool EnableDeferIfNeeded(BufferedResourceLoader* loader) const;
+  virtual bool DisableDeferIfNeeded(BufferedResourceLoader* loader) const;
+};
+
+};
+
+#endif  // WEBKIT_GLUE_DEFER_STRATEGY_H_