Introduce WebSocketDeflatePredictor.

net/websockets/websocket_deflate_predictor.h

+// Copyright 2013 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_WEBSOCKETS_WEBSOCKET_DEFLATE_PREDICTOR_H_
+#define NET_WEBSOCKETS_WEBSOCKET_DEFLATE_PREDICTOR_H_
+
+#include "base/basictypes.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/memory/scoped_vector.h"
+#include "net/base/net_export.h"
+
+namespace net {
+
+struct WebSocketFrame;
+
+// WebSocketDeflatePredictor is an interface class used for judging whether
+// a WebSocketDeflateStream should compress a message or not.
+class NET_EXPORT_PRIVATE WebSocketDeflatePredictor {
+ public:
+  enum Result {
+    // Deflate and send the message.
+    DEFLATE,
+    // Do not deflate and send the original message.
+    DO_NOT_DEFLATE,
+    // Try compressing the message and send the smaller one of the original
+    // and the compressed message.
+    // Returning this result implies that the deflater is running on
+    // DoNotTakeOverContext mode and the entire message is visible.
+    TRY_DEFLATE,
+  };
+
+  virtual ~WebSocketDeflatePredictor() {}
+
+  // Predicts and returns whether the deflater should deflate the message
+  // which begins with |frames[frame_index]| or not.
+  // frames[(frame_index + 1):] consists of future frames.
+  // |frames[frame_index]| must be the first frame of a data message,
+  // but future frames may contain control message frames.

[Adam Rice, 2013/10/25 13:05:25]

You might want to mention that if frame_index is the last frame, then
frames[frame_index + 1] won't exist. But that is pretty obvious, so maybe not
worth saying.

[yhirano, 2013/10/28 01:42:46]

I intended to use Python notation which will work for |a[len(a):]|.
Done.

+  virtual Result Predict(const ScopedVector<WebSocketFrame>& frames,
+                         size_t frame_index) = 0;
+
+  // Records frame data for future prediction.
+  // Only data frames should be recorded. Do not pass control frames' data.
+  // All input data frames must be recorded in order.
+  virtual void RecordProcessedDataFrame(const WebSocketFrame* frame) = 0;
+
+  // Records frame data for future prediction.
+  // Only data frames should be recorded. Do not pass control frames' data.
+  // All sent data frames must be recorded in order regardless of whether
+  // they are compressed or not.
+  virtual void RecordSentDataFrame(const WebSocketFrame* frame) = 0;
+};
+
+}  // namespace net
+
+#endif  // NET_WEBSOCKETS_WEBSOCKET_DEFLATE_PREDICTOR_H_