// 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_
#pragma once

#include <vector>

#include "base/basictypes.h"
#include "base/memory/scoped_ptr.h"
#include "net/base/net_export.h"

namespace net {

// Represents a WebSocket frame header.
//
// Members of this class correspond to each element in WebSocket frame header
// (see http://tools.ietf.org/html/rfc6455#section-5.2).
struct NET_EXPORT_PRIVATE WebSocketFrameHeader {
  typedef int OpCode;
  static const OpCode kOpCodeContinuation;
  static const OpCode kOpCodeText;
  static const OpCode kOpCodeBinary;
  static const OpCode kOpCodeClose;
  static const OpCode kOpCodePing;
  static const OpCode kOpCodePong;

  // These values must be a compile-time constant. "enum hack" is used here
  // to make MSVC happy.
  enum {
    kBaseHeaderSize = 2,
    kMaximumExtendedLengthSize = 8,
    kMaskingKeyLength = 4
  };

  // Members below correspond to each item in WebSocket frame header.
  // See <http://tools.ietf.org/html/rfc6455#section-5.2> for details.
  bool final;
  bool reserved1;
  bool reserved2;
  bool reserved3;
  OpCode opcode;
  bool masked;
  uint64 payload_length;
};

// Contains payload data of part of a WebSocket frame.
//
// Payload of a WebSocket frame may be divided into multiple chunks.
// You need to look at |final_chunk| member variable to detect the end of a
// series of chunk objects of a WebSocket frame.
//
// Frame dissection is necessary to handle WebSocket frame stream containing
// abritrarily large frames in the browser process. Because the server may send
// a huge frame that doesn't fit in the memory, we cannot store the entire
// payload data in the memory.
//
// Users of this struct should treat WebSocket frames as a data stream; it's
// important to keep the frame data flowing, especially in the browser process.
// Users should not let the data stuck somewhere in the pipeline.
//
// This struct is used for reading WebSocket frame data (created by
// WebSocketFrameParser). To construct WebSocket frames, use functions below.
struct NET_EXPORT_PRIVATE WebSocketFrameChunk {
  WebSocketFrameChunk();
  ~WebSocketFrameChunk();

  // Non-null |header| is provided only if this chunk is the first part of
  // a series of chunks.
  scoped_ptr<WebSocketFrameHeader> header;

  // Indicates this part is the last chunk of a frame.
  bool final_chunk;

  // |data| is always unmasked even if the frame is masked.
  std::vector<char> data;
};

// Contains four-byte data representing "masking key" of WebSocket frames.
struct WebSocketMaskingKey {
  char key[WebSocketFrameHeader::kMaskingKeyLength];
};

// 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|.
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.
//
// A client must mask every WebSocket frame by XOR'ing the frame payload
// with four-byte random data (masking key). This function applies the masking
// to the given payload data.
//
// This function masks |data| with |masking_key|, assuming |data| is partial
// data starting from |frame_offset| bytes from the beginning of the payload
// data.
//
// Since frame masking is a reversible operation, this function can also be
// 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_