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| 1 // Copyright 2014 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_FILTER_SDCH_FILTER_H_ | |
| 15 #define NET_FILTER_SDCH_FILTER_H_ | |
| 16 | |
| 17 #include <string> | |
| 18 | |
| 19 #include "base/memory/scoped_ptr.h" | |
| 20 #include "net/base/net_export.h" | |
| 21 #include "net/base/sdch_manager.h" | |
| 22 #include "net/filter/filter.h" | |
| 23 | |
| 24 namespace open_vcdiff { | |
| 25 class VCDiffStreamingDecoder; | |
| 26 } | |
| 27 | |
| 28 namespace net { | |
| 29 | |
| 30 class NET_EXPORT_PRIVATE SdchFilter : public Filter { | |
| 31 public: | |
| 32 ~SdchFilter() override; | |
| 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 FilterStatus ReadFilteredData(char* dest_buffer, int* dest_len) override; | |
| 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 SdchFilter(FilterType type, 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 // Add SDCH Problem to net-log and record histogram. | |
| 68 void LogSdchProblem(SdchProblemCode problem); | |
| 69 | |
| 70 // Context data from the owner of this filter. | |
| 71 const FilterContext& filter_context_; | |
| 72 | |
| 73 // Tracks the status of decoding. | |
| 74 // This variable is initialized by InitDecoding and updated only by | |
| 75 // ReadFilteredData. | |
| 76 DecodingStatus decoding_status_; | |
| 77 | |
| 78 // The underlying decoder that processes data. | |
| 79 // This data structure is initialized by InitDecoding and updated in | |
| 80 // ReadFilteredData. | |
| 81 scoped_ptr<open_vcdiff::VCDiffStreamingDecoder> vcdiff_streaming_decoder_; | |
| 82 | |
| 83 // In case we need to assemble the hash piecemeal, we have a place to store | |
| 84 // a part of the hash until we "get all 8 bytes plus a null." | |
| 85 std::string dictionary_hash_; | |
| 86 | |
| 87 // After assembling an entire dictionary hash (the first 9 bytes of the | |
| 88 // sdch payload, we check to see if it is plausible, meaning it has a null | |
| 89 // termination, and has 8 characters that are possible in a net-safe base64 | |
| 90 // encoding. If the hash is not plausible, then the payload is probably not | |
| 91 // an SDCH encoded bundle, and various error recovery strategies can be | |
| 92 // attempted. | |
| 93 bool dictionary_hash_is_plausible_; | |
| 94 | |
| 95 // Validity of this pointer is guaranteed by either the FilterContext holding | |
| 96 // a containing SdchManager::DictionarySet, or this object holding a | |
| 97 // container in |unexpected_dictionary_handle_| below. | |
| 98 const SdchManager::Dictionary *dictionary_; | |
| 99 | |
| 100 // We keep a copy of the URLRequestContext for use in the destructor, (at | |
| 101 // which point GetURLRequestContext() will likely return null because of | |
| 102 // the disassociation of the URLRequest from the URLRequestJob). This is | |
| 103 // safe because the URLRequestJob (and any filters) are guaranteed to be | |
| 104 // deleted before the URLRequestContext is destroyed. | |
| 105 const URLRequestContext* const url_request_context_; | |
| 106 | |
| 107 // The decoder may demand a larger output buffer than the target of | |
| 108 // ReadFilteredData so we buffer the excess output between calls. | |
| 109 std::string dest_buffer_excess_; | |
| 110 // To avoid moving strings around too much, we save the index into | |
| 111 // dest_buffer_excess_ that has the next byte to output. | |
| 112 size_t dest_buffer_excess_index_; | |
| 113 | |
| 114 // To get stats on activities, we keep track of source and target bytes. | |
| 115 // Visit about:histograms/Sdch to see histogram data. | |
| 116 size_t source_bytes_; | |
| 117 size_t output_bytes_; | |
| 118 | |
| 119 // Error recovery in content type may add an sdch filter type, in which case | |
| 120 // we should gracefully perform pass through if the format is incorrect, or | |
| 121 // an applicable dictionary can't be found. | |
| 122 bool possible_pass_through_; | |
| 123 | |
| 124 // The URL that is currently being filtered. | |
| 125 // This is used to restrict use of a dictionary to a specific URL or path. | |
| 126 GURL url_; | |
| 127 | |
| 128 // To facilitate error recovery, allow filter to know if content is text/html | |
| 129 // by checking within this mime type (we may do a meta-refresh via html). | |
| 130 std::string mime_type_; | |
| 131 | |
| 132 // If the response was encoded with a dictionary different than those | |
| 133 // advertised (e.g. a cached response using an old dictionary), this | |
| 134 // variable preserves that dictionary from deletion during decoding. | |
| 135 scoped_ptr<SdchManager::DictionarySet> unexpected_dictionary_handle_; | |
| 136 | |
| 137 DISALLOW_COPY_AND_ASSIGN(SdchFilter); | |
| 138 }; | |
| 139 | |
| 140 } // namespace net | |
| 141 | |
| 142 #endif // NET_FILTER_SDCH_FILTER_H_ | |
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