1 // Copyright (c) 2006-2008 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 17 #include <string> 18 19 #include "base/scoped_ptr.h" 20 #include "net/base/filter.h" 21 #include "net/base/sdch_manager.h" 22 23 class SafeOutputStringInterface; 24 25 namespace open_vcdiff { 26 class VCDiffStreamingDecoder; 27 } 28 29 class SdchFilter : public Filter { 30 public: 31 explicit SdchFilter(const FilterContext& filter_context); 32 33 virtual ~SdchFilter(); 34 35 // Initializes filter decoding mode and internal control blocks. 36 bool InitDecoding(Filter::FilterType filter_type); 37 38 // Decode the pre-filter data and writes the output into |dest_buffer| 39 // The function returns FilterStatus. See filter.h for its description. 40 // 41 // Upon entry, *dest_len is the total size (in number of chars) of the 42 // destination buffer. Upon exit, *dest_len is the actual number of chars 43 // written into the destination buffer. 44 virtual FilterStatus ReadFilteredData(char* dest_buffer, int* dest_len); 45 46 private: 47 // Internal status. Once we enter an error state, we stop processing data. 48 enum DecodingStatus { 49 DECODING_UNINITIALIZED, 50 WAITING_FOR_DICTIONARY_SELECTION, 51 DECODING_IN_PROGRESS, 52 DECODING_ERROR, 53 META_REFRESH_RECOVERY, // Decoding error being handled by a meta-refresh. 54 PASS_THROUGH, // Non-sdch content being passed without alteration. 55 }; 56 57 // Identify the suggested dictionary, and initialize underlying decompressor. 58 Filter::FilterStatus InitializeDictionary(); 59 60 // Move data that was internally buffered (after decompression) to the 61 // specified dest_buffer. 62 int OutputBufferExcess(char* const dest_buffer, size_t available_space); 63 64 // Tracks the status of decoding. 65 // This variable is initialized by InitDecoding and updated only by 66 // ReadFilteredData. 67 DecodingStatus decoding_status_; 68 69 // The underlying decoder that processes data. 70 // This data structure is initialized by InitDecoding and updated in 71 // ReadFilteredData. 72 scoped_ptr<open_vcdiff::VCDiffStreamingDecoder> vcdiff_streaming_decoder_; 73 74 // In case we need to assemble the hash piecemeal, we have a place to store 75 // a part of the hash until we "get all 8 bytes plus a null." 76 std::string dictionary_hash_; 77 78 // After assembling an entire dictionary hash (the first 9 bytes of the 79 // sdch payload, we check to see if it is plausible, meaning it has a null 80 // termination, and has 8 characters that are possible in a net-safe base64 81 // encoding. If the hash is not plausible, then the payload is probably not 82 // an SDCH encoded bundle, and various error recovery strategies can be 83 // attempted. 84 bool dictionary_hash_is_plausible_; 85 86 // We hold an in-memory copy of the dictionary during the entire decoding, as 87 // it is used directly by the VC-DIFF decoding system. 88 // That char* data is part of the dictionary_ we hold a reference to. 89 scoped_refptr<SdchManager::Dictionary> dictionary_; 90 91 // The decoder may demand a larger output buffer than the target of 92 // ReadFilteredData so we buffer the excess output between calls. 93 std::string dest_buffer_excess_; 94 // To avoid moving strings around too much, we save the index into 95 // dest_buffer_excess_ that has the next byte to output. 96 size_t dest_buffer_excess_index_; 97 98 // To get stats on activities, we keep track of source and target bytes. 99 // Visit about:histograms/Sdch to see histogram data. 100 size_t source_bytes_; 101 size_t output_bytes_; 102 103 // Error recovery in content type may add an sdch filter type, in which case 104 // we should gracefully perform pass through if the format is incorrect, or 105 // an applicable dictionary can't be found. 106 bool possible_pass_through_; 107 108 // The URL that is currently being filtered. 109 // This is used to restrict use of a dictionary to a specific URL or path. 110 GURL url_; 111 112 // To facilitate error recovery, allow filter to know if content is text/html 113 // by checking within this mime type (we may do a meta-refresh via html). 114 std::string mime_type_; 115 116 DISALLOW_COPY_AND_ASSIGN(SdchFilter); 117 }; 118 119 #endif // NET_BASE_SDCH_FILTER_H_ 120