Class: FilesHunter::Decoders::JPEG

Inherits:
BeginPatternDecoder show all
Defined in:
lib/fileshunter/Decoders/JPEG.rb

Overview

JPEG decoder has to be among the last ones to be decoded, as a truncated JPEG followed by other files can consume all files in its truncated data. JPEG files can contain TIFF files

Constant Summary collapse

MARKER_PREFIX = 
"\xFF".force_encoding(Encoding::ASCII_8BIT)
END_MARKER = 
"\xD9".force_encoding(Encoding::ASCII_8BIT)
MARKERS_WITHOUT_PAYLOAD = 
[
  "\xD8".force_encoding(Encoding::ASCII_8BIT),
  "\xD9".force_encoding(Encoding::ASCII_8BIT)
]
MARKER_WITH_ENTROPY_DATA = 
"\xDA".force_encoding(Encoding::ASCII_8BIT)
MARKER_APP0 = 
"\xE0".force_encoding(Encoding::ASCII_8BIT)
MARKER_APP1 = 
"\xE1".force_encoding(Encoding::ASCII_8BIT)
MARKER_SOF0 = 
"\xC0".force_encoding(Encoding::ASCII_8BIT)
MARKER_SOF3 = 
"\xC3".force_encoding(Encoding::ASCII_8BIT)
MARKER_DHT = 
"\xC4".force_encoding(Encoding::ASCII_8BIT)
MARKER_SOS = 
"\xDA".force_encoding(Encoding::ASCII_8BIT)
MARKER_DQT = 
"\xDB".force_encoding(Encoding::ASCII_8BIT)
MARKERS_IGNORED_IN_ENTROPY_DATA = 
[
  "\x00".force_encoding(Encoding::ASCII_8BIT),
  "\xD0".force_encoding(Encoding::ASCII_8BIT),
  "\xD1".force_encoding(Encoding::ASCII_8BIT),
  "\xD2".force_encoding(Encoding::ASCII_8BIT),
  "\xD3".force_encoding(Encoding::ASCII_8BIT),
  "\xD4".force_encoding(Encoding::ASCII_8BIT),
  "\xD5".force_encoding(Encoding::ASCII_8BIT),
  "\xD6".force_encoding(Encoding::ASCII_8BIT),
  "\xD7".force_encoding(Encoding::ASCII_8BIT),
  "\xFF".force_encoding(Encoding::ASCII_8BIT)
]
MARKERS_IGNORED_IN_ENTROPY_DATA_REGEXP = 
Regexp.new("#{MARKER_PREFIX}[^#{MARKERS_IGNORED_IN_ENTROPY_DATA.join}]", nil, 'n')
JFIF_HEADER = 
"JFIF\x00".force_encoding(Encoding::ASCII_8BIT)
JFXX_HEADER = 
"JFXX\x00".force_encoding(Encoding::ASCII_8BIT)
EXIF_HEADER = 
"Exif\x00\x00".force_encoding(Encoding::ASCII_8BIT)
VALID_EXTENSION_CODES = 
[ 16, 17, 19 ]

Instance Method Summary collapse

Methods inherited from BeginPatternDecoder

#find_segments

Methods inherited from FilesHunter::Decoder

#segments_found, #setup

Instance Method Details

#decode(offset) ⇒ Object 



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# File 'lib/fileshunter/Decoders/JPEG.rb', line 48

def decode(offset)
  ending_offset = nil

  cursor = offset + 2
  nbr_segments = 0
  quantisation_tables_id = []
  huffman_ac_tables_id = []
  huffman_dc_tables_id = []
  found_sos = false
  found_sof = false
  while (ending_offset == nil)
    # Here cursor is at the beginning of the next marker
    # Read the 2 next bytes: they should be FF ??
    log_debug "@#{cursor} Decoding next offset: #{@data[cursor..cursor+1].inspect}"
    invalid_data("@#{cursor} - Did not get a valid marker definition: #{@data[cursor..cursor+1].inspect}") if (@data[cursor] != MARKER_PREFIX)
    c_1 = @data[cursor+1]
    invalid_data("@#{cursor} - Invalid marker: #{c_1.ord}") if (c_1.ord < 192)
    # Does this marker have a payload?
    if (MARKERS_WITHOUT_PAYLOAD.include?(c_1))
      # No payload
      log_debug "=== No payload"
      # Get to the next bytes
      cursor += 2
      # Check if we arrived at the end
      ending_offset = cursor if (c_1 == END_MARKER)
    else
      # There is a payload
      # Read its length
      size = BinData::Uint16be.read(@data[cursor+2..cursor+3])
      log_debug "=== Payload of size #{size}"
      case c_1
      when MARKER_APP0
        # Application specific data
        log_debug "@#{cursor} - Found APP0 marker"
        # Usually used for JFIF
        case @data[cursor+4..cursor+8]
        when JFIF_HEADER
          invalid_data("@#{cursor} - Invalid size for JFIF marker: #{size}") if (size < 16)
          version_major = @data[cursor+9].ord
          version_minor = @data[cursor+10].ord
          units = @data[cursor+11].ord
          invalid_data("@#{cursor} - Invalid units: #{units}") if (units > 2)
          width = BinData::Uint16be.read(@data[cursor+12..cursor+13])
          invalid_data("@#{cursor} - Invalid width: #{width}") if (width == 0)
          height = BinData::Uint16be.read(@data[cursor+14..cursor+15])
          invalid_data("@#{cursor} - Invalid height: #{height}") if (height == 0)
          jfif_metadata = {
            :version_major => version_major,
            :version_minor => version_minor,
            :units => units,
            :width => width,
            :height => height
          }
          if (size > 16)
            width_thumb = BinData::Uint16be.read(@data[cursor+16..cursor+17])
            height_thumb = BinData::Uint16be.read(@data[cursor+18..cursor+19])
            jfif_metadata.merge!(
              :width_thumb => width_thumb,
              :height_thumb => height_thumb
            )
          end
          metadata( :jfif_metadata => jfif_metadata )
        when JFXX_HEADER
          extension_code = @data[cursor+9].ord
          invalid_data("@#{cursor} - Invalid extension code: #{extension_code}") if (!VALID_EXTENSION_CODES.include?(extension_code))
          metadata( :jfxx_metadata => { :extension_code => extension_code } )
        end
      when MARKER_APP1
        # Application specific data
        log_debug "@#{cursor} - Found APP1 marker"
        # Usually used for Exif
        case @data[cursor+4..cursor+9]
        when EXIF_HEADER
          # Read a TIFF file from cursor+10
          require 'fileshunter/Decoders/TIFF'
          invalid_data("@#{cursor} - Invalid TIFF header") if (@data[cursor+10..cursor+13].index(FilesHunter::Decoders::TIFF::BEGIN_PATTERN_TIFF) != 0)
          tiff_decoder = FilesHunter::Decoders::TIFF.new
          tiff_decoder.setup(FilesHunter::get_segments_analyzer, @data, cursor+10, cursor+2+size)
          tiff_decoder.accept_no_image_data
          begin
            tiff_decoder.find_segments
          rescue InvalidDataError, TruncatedDataError, AccessAfterDataError
            # Invalid TIFF data
            invalid_data("@#{cursor} - Invalid TIFF data: #{$!}")
          end
          segments = tiff_decoder.segments_found
          invalid_data("@#{cursor} - No valid TIFF segment found for Exif") if segments.empty?
          invalid_data("@#{cursor} - Not a valid TIFF segment found for Exif. Found #{segments[0].extensions.inspect}.") if (!segments[0].extensions.include?(:tif))
          invalid_data("@#{cursor} - Truncated TIFF segment found for Exif.") if (segments[0].truncated)
          invalid_data("@#{cursor} - TIFF segment (@#{segments[0].begin_offset}) not found at the beginning of Exif (#{cursor+10}).") if (segments[0].begin_offset != cursor+10)
          #invalid_data("@#{cursor} - TIFF segment not ending (#{segments[0].end_offset}) at the end of Exif (#{cursor+2+size}).") if (segments[0].end_offset != cursor+2+size)
          metadata( :exif_metadata => segments[0].metadata )
          found_relevant_data([:jpg, :thm])
        end
      when MARKER_SOF0..MARKER_SOF3
        # SOF: Start of Frame
        log_debug "@#{cursor} - Found SOF marker"
        invalid_data("@#{cursor} - Found several SOF markers") if found_sof
        invalid_data("@#{cursor} - Found a SOF marker after the SOS marker") if found_sos
        found_sof = true
        sample_precision = @data[cursor+4].ord
        invalid_data("@#{cursor} - Invalid sample precision: #{sample_precision}") if ((sample_precision != 8) and (sample_precision != 12))
        image_height = BinData::Uint16be.read(@data[cursor+5..cursor+6])
        image_width = BinData::Uint16be.read(@data[cursor+7..cursor+8])
        metadata(
          :image_height => image_height,
          :image_width => image_width
        )
        nbr_components = @data[cursor+9].ord
        invalid_data("@#{cursor} - Invalid number of components: #{nbr_components}") if (nbr_components == 0)
        # Check that quantisation tables have been defined
        nbr_components.times do |idx_component|
          sampling = @data[cursor+11+idx_component*3].ord
          horizontal_sampling = ((sampling & 0b11110000) >> 4)
          vertical_sampling = (sampling & 0b00001111)
          invalid_data("@#{cursor} - Invalid horizontal sampling: #{horizontal_sampling}") if (horizontal_sampling == 0)
          invalid_data("@#{cursor} - Invalid vertical sampling: #{vertical_sampling}") if (vertical_sampling == 0)
          dqt_id = @data[cursor+12+idx_component*3].ord
          invalid_data("@#{cursor} - Missing quantisation table ID #{dqt_id}") if (!quantisation_tables_id.include?(dqt_id))
        end
      when MARKER_DHT
        # DHT: Define Huffman tables
        log_debug "@#{cursor} - Found DHT marker"
        end_cursor = cursor + 2 + size
        dht_cursor = cursor + 4
        while (dht_cursor < end_cursor)
          header_byte = @data[dht_cursor].ord
          huffman_type = ((header_byte & 0b11110000) >> 4)
          invalid_data("@#{cursor} - Unknown Huffman table type: #{huffman_type}") if (huffman_type > 1)
          if (huffman_type == 0)
            huffman_dc_table_id = (header_byte & 0b00001111)
            #invalid_data("@#{cursor} - Huffman DC table id #{huffman_dc_table_id} already defined.") if (huffman_dc_tables_id.include?(huffman_dc_table_id))
            huffman_dc_tables_id << huffman_dc_table_id
            log_debug "@#{cursor} - Found Huffman DC table: #{huffman_dc_table_id}"
          else
            huffman_ac_table_id = (header_byte & 0b00001111)
            #invalid_data("@#{cursor} - Huffman AC table id #{huffman_ac_table_id} already defined.") if (huffman_ac_tables_id.include?(huffman_ac_table_id))
            huffman_ac_tables_id << huffman_ac_table_id
            log_debug "@#{cursor} - Found Huffman AC table: #{huffman_ac_table_id}"
          end
          nbr_elements = 0
          @data[dht_cursor+1..dht_cursor+16].bytes.each do |nbr_element_for_depth|
            nbr_elements += nbr_element_for_depth
          end
          dht_cursor += 17 + nbr_elements
          invalid_data("@#{dqt_cursor} - End of Huffman table was supposed to be @#{end_cursor}.") if (dht_cursor > end_cursor)
        end
      when MARKER_SOS
        # SOS: Start of Scan
        log_debug "@#{cursor} - Found SOS marker"
        #invalid_data("@#{cursor} - SOS marker begins whereas no Huffman DC table has been defined.") if (huffman_dc_tables_id.empty?)
        #invalid_data("@#{cursor} - SOS marker begins whereas no Huffman AC table has been defined.") if (huffman_ac_tables_id.empty?)
        invalid_data("@#{cursor} - SOS marker begins whereas no quantisation table has been defined.") if (quantisation_tables_id.empty?)
        invalid_data("@#{cursor} - SOS marker begins whereas no SOF marker has been encountered.") if (!found_sof)
        found_sos = true
        nbr_components = @data[cursor+4].ord
        invalid_data("@#{cursor} - Invalid number of components: #{nbr_components}") if (nbr_components == 0)
        nbr_components.times do |idx_component|
          huffman_table_ids = @data[cursor+6+2*idx_component].ord
          huffman_dc_table_id = ((huffman_table_ids & 0b11110000) >> 4)
          huffman_ac_table_id = (huffman_table_ids & 0b00001111)
          #invalid_data("@#{cursor} - Unknown DC Huffman table: #{huffman_dc_table_id}") if (!huffman_dc_tables_id.include?(huffman_dc_table_id))
          #invalid_data("@#{cursor} - Unknown AC Huffman table: #{huffman_ac_table_id}") if (!huffman_ac_tables_id.include?(huffman_ac_table_id))
        end
      when MARKER_DQT
        # DQT: Define quantisation tables
        log_debug "@#{cursor} - Found DQT marker"
        end_cursor = cursor + 2 + size
        dqt_cursor = cursor + 4
        while (dqt_cursor < end_cursor)
          header_byte = @data[dqt_cursor].ord
          precision = ((header_byte & 0b11110000) >> 4)
          quantisation_table_id = (header_byte & 0b00001111)
          invalid_data("@#{cursor} - Quantisation table id #{quantisation_table_id} already defined.") if (quantisation_tables_id.include?(quantisation_table_id))
          quantisation_tables_id << quantisation_table_id
          log_debug "@#{cursor} - Found quantisation table: #{quantisation_table_id}"
          dqt_cursor += 1 + 64*((precision == 0) ? 1 : 2)
          invalid_data("@#{dqt_cursor} - End of quantisation table was supposed to be @#{end_cursor}.") if (dqt_cursor > end_cursor)
        end
      else
        log_debug "@#{cursor} - Found ignored marker: #{c_1.inspect}"
      end
      # Does it have entropy data?
      if (c_1 == MARKER_WITH_ENTROPY_DATA)
        # There is entropy data
        found_relevant_data([:jpg, :thm])
        # Find the next marker that is FF xx, with xx being different than 00, D0..D7 and FF
        cursor = @data.index(MARKERS_IGNORED_IN_ENTROPY_DATA_REGEXP, cursor + 2 + size, 2)
        log_debug "=== Entropy data gets to cursor #{cursor.inspect}"
        truncated_data("@#{cursor} - Truncated entropy data segment", @end_offset) if (cursor == nil)
      else
        # No entropy data: just get to the next segment
        cursor += 2 + size
      end
    end
    nbr_segments += 1
    progress(cursor)
  end
  metadata( :nbr_segments => nbr_segments )

  return ending_offset
end

#get_begin_pattern ⇒ Object 



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# File 'lib/fileshunter/Decoders/JPEG.rb', line 44

def get_begin_pattern
  return "\xFF\xD8\xFF".force_encoding(Encoding::ASCII_8BIT)
end