1 // Copyright (c) 2011 The Chromium Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style license that can be 3 // found in the LICENSE file. 4 5 // SdchFilter applies open_vcdiff content decoding to a datastream. 6 // This decoding uses a pre-cached dictionary of text fragments to decode 7 // (expand) the stream back to its original contents. 8 // 9 // This SdchFilter internally uses open_vcdiff/vcdec library to do decoding. 10 // 11 // SdchFilter is also a subclass of Filter. See the latter's header file 12 // filter.h for sample usage. 13 14 #ifndef NET_BASE_SDCH_FILTER_H_ 15 #define NET_BASE_SDCH_FILTER_H_ 16 #pragma once 17 18 #include <string> 19 20 #include "base/memory/scoped_ptr.h" 21 #include "net/base/filter.h" 22 #include "net/base/sdch_manager.h" 23 24 namespace open_vcdiff { 25 class VCDiffStreamingDecoder; 26 } 27 28 namespace net { 29 30 class SdchFilter : public Filter { 31 public: 32 virtual ~SdchFilter(); 33 34 // Initializes filter decoding mode and internal control blocks. 35 bool InitDecoding(Filter::FilterType filter_type); 36 37 // Decode the pre-filter data and writes the output into |dest_buffer| 38 // The function returns FilterStatus. See filter.h for its description. 39 // 40 // Upon entry, *dest_len is the total size (in number of chars) of the 41 // destination buffer. Upon exit, *dest_len is the actual number of chars 42 // written into the destination buffer. 43 virtual FilterStatus ReadFilteredData(char* dest_buffer, int* dest_len); 44 45 private: 46 // Internal status. Once we enter an error state, we stop processing data. 47 enum DecodingStatus { 48 DECODING_UNINITIALIZED, 49 WAITING_FOR_DICTIONARY_SELECTION, 50 DECODING_IN_PROGRESS, 51 DECODING_ERROR, 52 META_REFRESH_RECOVERY, // Decoding error being handled by a meta-refresh. 53 PASS_THROUGH, // Non-sdch content being passed without alteration. 54 }; 55 56 // Only to be instantiated by Filter::Factory. 57 explicit SdchFilter(const FilterContext& filter_context); 58 friend class Filter; 59 60 // Identify the suggested dictionary, and initialize underlying decompressor. 61 Filter::FilterStatus InitializeDictionary(); 62 63 // Move data that was internally buffered (after decompression) to the 64 // specified dest_buffer. 65 int OutputBufferExcess(char* const dest_buffer, size_t available_space); 66 67 // Context data from the owner of this filter. 68 const FilterContext& filter_context_; 69 70 // Tracks the status of decoding. 71 // This variable is initialized by InitDecoding and updated only by 72 // ReadFilteredData. 73 DecodingStatus decoding_status_; 74 75 // The underlying decoder that processes data. 76 // This data structure is initialized by InitDecoding and updated in 77 // ReadFilteredData. 78 scoped_ptr<open_vcdiff::VCDiffStreamingDecoder> vcdiff_streaming_decoder_; 79 80 // In case we need to assemble the hash piecemeal, we have a place to store 81 // a part of the hash until we "get all 8 bytes plus a null." 82 std::string dictionary_hash_; 83 84 // After assembling an entire dictionary hash (the first 9 bytes of the 85 // sdch payload, we check to see if it is plausible, meaning it has a null 86 // termination, and has 8 characters that are possible in a net-safe base64 87 // encoding. If the hash is not plausible, then the payload is probably not 88 // an SDCH encoded bundle, and various error recovery strategies can be 89 // attempted. 90 bool dictionary_hash_is_plausible_; 91 92 // We hold an in-memory copy of the dictionary during the entire decoding, as 93 // it is used directly by the VC-DIFF decoding system. 94 // That char* data is part of the dictionary_ we hold a reference to. 95 scoped_refptr<SdchManager::Dictionary> dictionary_; 96 97 // The decoder may demand a larger output buffer than the target of 98 // ReadFilteredData so we buffer the excess output between calls. 99 std::string dest_buffer_excess_; 100 // To avoid moving strings around too much, we save the index into 101 // dest_buffer_excess_ that has the next byte to output. 102 size_t dest_buffer_excess_index_; 103 104 // To get stats on activities, we keep track of source and target bytes. 105 // Visit about:histograms/Sdch to see histogram data. 106 size_t source_bytes_; 107 size_t output_bytes_; 108 109 // Error recovery in content type may add an sdch filter type, in which case 110 // we should gracefully perform pass through if the format is incorrect, or 111 // an applicable dictionary can't be found. 112 bool possible_pass_through_; 113 114 // The URL that is currently being filtered. 115 // This is used to restrict use of a dictionary to a specific URL or path. 116 GURL url_; 117 118 // To facilitate error recovery, allow filter to know if content is text/html 119 // by checking within this mime type (we may do a meta-refresh via html). 120 std::string mime_type_; 121 122 DISALLOW_COPY_AND_ASSIGN(SdchFilter); 123 }; 124 125 } // namespace net 126 127 #endif // NET_BASE_SDCH_FILTER_H_ 128