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.
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.
9 // This SdchFilter internally uses open_vcdiff/vcdec library to do decoding.
11 // SdchFilter is also a subclass of Filter. See the latter's header file
12 // filter.h for sample usage.
14 #ifndef NET_FILTER_SDCH_FILTER_H_
15 #define NET_FILTER_SDCH_FILTER_H_
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"
24 namespace open_vcdiff {
25 class VCDiffStreamingDecoder;
30 class NET_EXPORT_PRIVATE SdchFilter : public Filter {
32 ~SdchFilter() override;
34 // Initializes filter decoding mode and internal control blocks.
35 bool InitDecoding(Filter::FilterType filter_type);
37 // Decode the pre-filter data and writes the output into |dest_buffer|
38 // The function returns FilterStatus. See filter.h for its description.
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;
46 // Internal status. Once we enter an error state, we stop processing data.
48 DECODING_UNINITIALIZED,
49 WAITING_FOR_DICTIONARY_SELECTION,
52 META_REFRESH_RECOVERY, // Decoding error being handled by a meta-refresh.
53 PASS_THROUGH, // Non-sdch content being passed without alteration.
56 // Only to be instantiated by Filter::Factory.
57 explicit SdchFilter(const FilterContext& filter_context);
60 // Identify the suggested dictionary, and initialize underlying decompressor.
61 Filter::FilterStatus InitializeDictionary();
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);
67 // Context data from the owner of this filter.
68 const FilterContext& filter_context_;
70 // Tracks the status of decoding.
71 // This variable is initialized by InitDecoding and updated only by
73 DecodingStatus decoding_status_;
75 // The underlying decoder that processes data.
76 // This data structure is initialized by InitDecoding and updated in
78 scoped_ptr<open_vcdiff::VCDiffStreamingDecoder> vcdiff_streaming_decoder_;
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_;
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
90 bool dictionary_hash_is_plausible_;
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_;
97 // We keep a copy of the URLRequestContext for use in the destructor, (at
98 // which point GetURLRequestContext() will likely return null because of
99 // the disassociation of the URLRequest from the URLRequestJob). This is
100 // safe because the URLRequestJob (and any filters) are guaranteed to be
101 // deleted before the URLRequestContext is destroyed.
102 const URLRequestContext* const url_request_context_;
104 // The decoder may demand a larger output buffer than the target of
105 // ReadFilteredData so we buffer the excess output between calls.
106 std::string dest_buffer_excess_;
107 // To avoid moving strings around too much, we save the index into
108 // dest_buffer_excess_ that has the next byte to output.
109 size_t dest_buffer_excess_index_;
111 // To get stats on activities, we keep track of source and target bytes.
112 // Visit about:histograms/Sdch to see histogram data.
113 size_t source_bytes_;
114 size_t output_bytes_;
116 // Error recovery in content type may add an sdch filter type, in which case
117 // we should gracefully perform pass through if the format is incorrect, or
118 // an applicable dictionary can't be found.
119 bool possible_pass_through_;
121 // The URL that is currently being filtered.
122 // This is used to restrict use of a dictionary to a specific URL or path.
125 // To facilitate error recovery, allow filter to know if content is text/html
126 // by checking within this mime type (we may do a meta-refresh via html).
127 std::string mime_type_;
129 DISALLOW_COPY_AND_ASSIGN(SdchFilter);
134 #endif // NET_FILTER_SDCH_FILTER_H_