Add a function that calculates the size of WebSocket frame header.

net/websockets/websocket_frame.h

 // Copyright (c) 2012 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_FRAME_H_
 #define NET_WEBSOCKETS_WEBSOCKET_FRAME_H_
 
 #include <vector>
 
 #include "base/basictypes.h"
@@ skipping 68 matching lines @@
   // |data| is always unmasked even if the frame is masked. |data| might be
   // null in the first chunk.
   scoped_refptr<IOBufferWithSize> data;
 };
 
 // Contains four-byte data representing "masking key" of WebSocket frames.
 struct WebSocketMaskingKey {
   char key[WebSocketFrameHeader::kMaskingKeyLength];
 };
 
+// Returns the size of WebSocket frame header. The size of WebSocket frame
+// header varies from 2 bytes to 14 bytes depending on the payload length
+// and maskedness.
+NET_EXPORT_PRIVATE int GetWebSocketFrameHeaderSize(
+    const WebSocketFrameHeader& header);
+
 // Writes wire format of a WebSocket frame header into |output|, and returns
 // the number of bytes written.
 //
 // WebSocket frame format is defined at:
 // <http://tools.ietf.org/html/rfc6455#section-5.2>. This function writes
 // everything but payload data in a WebSocket frame to |buffer|.
 //
 // If |header->masked| is true, |masking_key| must point to a valid
 // WebSocketMaskingKey object containing the masking key for that frame
 // (possibly generated by GenerateWebSocketMaskingKey() function below).
 // Otherwise, |masking_key| must be NULL.
 //
-// |buffer| should have enough size to contain the frame header. Size of a
-// frame header varies from 2 bytes to 14 bytes depending on the payload length
-// and maskedness. If the size of |buffer| is insufficient, this function
-// returns ERR_INVALID_ARGUMENT and does not write any data to |buffer|.
+// |buffer| should have enough size to contain the frame header.
+// GetWebSocketFrameHeaderSize() can be used to know the size of header
+// beforehand. If the size of |buffer| is insufficient, this function returns
+// ERR_INVALID_ARGUMENT and does not write any data to |buffer|.
 NET_EXPORT_PRIVATE int WriteWebSocketFrameHeader(
     const WebSocketFrameHeader& header,
     const WebSocketMaskingKey* masking_key,
     char* buffer,
     int buffer_size);
 
 // Generates a masking key suitable for use in a new WebSocket frame.
 NET_EXPORT_PRIVATE WebSocketMaskingKey GenerateWebSocketMaskingKey();
 
 // Masks WebSocket frame payload.
@@ skipping 10 matching lines @@
 // used for unmasking a WebSocket frame.
 NET_EXPORT_PRIVATE void MaskWebSocketFramePayload(
     const WebSocketMaskingKey& masking_key,
     uint64 frame_offset,
     char* data,
     int data_size);
 
 }  // namespace net
 
 #endif  // NET_WEBSOCKETS_WEBSOCKET_FRAME_H_