net/filter/sdch_filter.h

   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_