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_dictionary.h"
  22 #include "net/base/sdch_manager.h"
  23 #include "net/filter/filter.h"
  24
  25 namespace open_vcdiff {
  26 class VCDiffStreamingDecoder;
  27 }
  28
  29 namespace net {
  30
  31 class NET_EXPORT_PRIVATE SdchFilter : public Filter {
  32  public:
  33   ~SdchFilter() override;
  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   FilterStatus ReadFilteredData(char* dest_buffer, int* dest_len) override;
  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   // Only to be instantiated by Filter::Factory.
  58   SdchFilter(FilterType type, const FilterContext& filter_context);
  59   friend class Filter;
  60
  61   // Identify the suggested dictionary, and initialize underlying decompressor.
  62   Filter::FilterStatus InitializeDictionary();
  63
  64   // Move data that was internally buffered (after decompression) to the
  65   // specified dest_buffer.
  66   int OutputBufferExcess(char* const dest_buffer, size_t available_space);
  67
  68   // Add SDCH Problem to net-log and record histogram.
  69   void LogSdchProblem(SdchProblemCode problem);
  70
  71   // Context data from the owner of this filter.
  72   const FilterContext& filter_context_;
  73
  74   // Tracks the status of decoding.
  75   // This variable is initialized by InitDecoding and updated only by
  76   // ReadFilteredData.
  77   DecodingStatus decoding_status_;
  78
  79   // The underlying decoder that processes data.
  80   // This data structure is initialized by InitDecoding and updated in
  81   // ReadFilteredData.
  82   scoped_ptr<open_vcdiff::VCDiffStreamingDecoder> vcdiff_streaming_decoder_;
  83
  84   // After the encoded response SDCH header is read, this variable contains
  85   // the server hash with trailing null byte.
  86   std::string dictionary_hash_;
  87
  88   // After assembling an entire dictionary hash (the first 9 bytes of the
  89   // sdch payload, we check to see if it is plausible, meaning it has a null
  90   // termination, and has 8 characters that are possible in a net-safe base64
  91   // encoding. If the hash is not plausible, then the payload is probably not
  92   // an SDCH encoded bundle, and various error recovery strategies can be
  93   // attempted.
  94   bool dictionary_hash_is_plausible_;
  95
  96   // We keep a copy of the URLRequestContext for use in the destructor, (at
  97   // which point GetURLRequestContext() will likely return null because of
  98   // the disassociation of the URLRequest from the URLRequestJob). This is
  99   // safe because the URLRequestJob (and any filters) are guaranteed to be
 100   // deleted before the URLRequestContext is destroyed.
 101   const URLRequestContext* const url_request_context_;
 102
 103   // The decoder may demand a larger output buffer than the target of
 104   // ReadFilteredData so we buffer the excess output between calls.
 105   std::string dest_buffer_excess_;
 106   // To avoid moving strings around too much, we save the index into
 107   // dest_buffer_excess_ that has the next byte to output.
 108   size_t dest_buffer_excess_index_;
 109
 110   // To get stats on activities, we keep track of source and target bytes.
 111   // Visit about:histograms/Sdch to see histogram data.
 112   size_t source_bytes_;
 113   size_t output_bytes_;
 114
 115   // Error recovery in content type may add an sdch filter type, in which case
 116   // we should gracefully perform pass through if the format is incorrect, or
 117   // an applicable dictionary can't be found.
 118   bool possible_pass_through_;
 119
 120   // The URL that is currently being filtered.
 121   // This is used to restrict use of a dictionary to a specific URL or path.
 122   GURL url_;
 123
 124   // To facilitate error recovery, allow filter to know if content is text/html
 125   // by checking within this mime type (we may do a meta-refresh via html).
 126   std::string mime_type_;
 127
 128   // If the response was encoded with a dictionary different than those
 129   // advertised (e.g. a cached response using an old dictionary), this
 130   // variable preserves that dictionary from deletion during decoding.
 131   scoped_ptr<SdchManager::DictionarySet> unexpected_dictionary_handle_;
 132
 133   DISALLOW_COPY_AND_ASSIGN(SdchFilter);
 134 };
 135
 136 }  // namespace net
 137
 138 #endif  // NET_FILTER_SDCH_FILTER_H_