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// Copyright (c) 2006-2008 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.
// SdchFilter applies open_vcdiff content decoding to a datastream.
// This decoding uses a pre-cached dictionary of text fragments to decode
// (expand) the stream back to its original contents.
//
// This SdchFilter internally uses open_vcdiff/vcdec library to do decoding.
//
// SdchFilter is also a subclass of Filter. See the latter's header file
// filter.h for sample usage.
#ifndef NET_BASE_SDCH_FILTER_H_
#define NET_BASE_SDCH_FILTER_H_
#include <string>
#include "base/scoped_ptr.h"
#include "net/base/filter.h"
#include "net/base/sdch_manager.h"
class SafeOutputStringInterface;
namespace open_vcdiff {
class VCDiffStreamingDecoder;
}
class SdchFilter : public Filter {
public:
SdchFilter();
virtual ~SdchFilter();
// Initializes filter decoding mode and internal control blocks.
bool InitDecoding();
// Decode the pre-filter data and writes the output into |dest_buffer|
// The function returns FilterStatus. See filter.h for its description.
//
// Upon entry, *dest_len is the total size (in number of chars) of the
// destination buffer. Upon exit, *dest_len is the actual number of chars
// written into the destination buffer.
virtual FilterStatus ReadFilteredData(char* dest_buffer, int* dest_len);
private:
// Internal status. Once we enter an error state, we stop processing data.
enum DecodingStatus {
DECODING_UNINITIALIZED,
WAITING_FOR_DICTIONARY_SELECTION,
DECODING_IN_PROGRESS,
DECODING_ERROR
};
// Identify the suggested dictionary, and initialize underlying decompressor.
Filter::FilterStatus InitializeDictionary();
// Move data that was internally buffered (after decompression) to the
// specified dest_buffer.
int OutputBufferExcess(char* const dest_buffer, size_t available_space);
// Tracks the status of decoding.
// This variable is initialized by InitDecoding and updated only by
// ReadFilteredData.
DecodingStatus decoding_status_;
// The underlying decoder that processes data.
// This data structure is initialized by InitDecoding and updated in
// ReadFilteredData.
scoped_ptr<open_vcdiff::VCDiffStreamingDecoder> vcdiff_streaming_decoder_;
// In case we need to assemble the hash piecemeal, we have a place to store
// a part of the hash until we "get all 8 bytes."
std::string dictionary_hash_;
// We hold an in-memory copy of the dictionary during the entire decoding.
// The char* data is embedded in a RefCounted dictionary_.
SdchManager::Dictionary* dictionary_;
// The decoder may demand a larger output buffer than the target of
// ReadFilteredData so we buffer the excess output between calls.
std::string dest_buffer_excess_;
// To avoid moving strings around too much, we save the index into
// dest_buffer_excess_ that has the next byte to output.
size_t dest_buffer_excess_index_;
// To get stats on activities, we keep track of source and target bytes.
// Visit about:histograms/Sdch to see histogram data.
size_t source_bytes_;
size_t output_bytes_;
DISALLOW_COPY_AND_ASSIGN(SdchFilter);
};
#endif // NET_BASE_SDCH_FILTER_H_
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