Class: SectionStripper

Inherits:
Object
  • Object
show all
Defined in:
lib/kindlestrip.rb

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(datain, verbose = true) ⇒ SectionStripper

Returns a new instance of SectionStripper.



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# File 'lib/kindlestrip.rb', line 119

def initialize(datain, verbose = true)
  @verbose = verbose
  if datain[0x3C...0x3C+8] != "BOOKMOBI"
    raise StripException, "invalid file format"
  end
  @num_sections, = datain[76...78].unpack("n")

  # get mobiheader and check SRCS section number and count
  offset0, = datain.unpack("@78N")
  offset1, = datain.unpack("@86N")
  mobiheader = datain[offset0 ... offset1]
  srcs_secnum, srcs_cnt = mobiheader.unpack("@224NN")
  if srcs_secnum == 0xffffffff || srcs_cnt == 0
    raise StripException, "File doesn't contain the sources section."
  end

  puts "Found SRCS section number %d, and count %d" % [srcs_secnum, srcs_cnt] if @verbose
  # find its offset and length
  _next = srcs_secnum + srcs_cnt
  srcs_offset, = datain.unpack("@#{78+srcs_secnum*8}NN")
  next_offset, = datain.unpack("@#{78+_next*8}NN")
  srcs_length = next_offset - srcs_offset
  if datain[srcs_offset ... srcs_offset+4] != "SRCS"
    raise StripException, "SRCS section num does not point to SRCS."
  end
  puts "   beginning at offset %0x and ending at offset %0x" % [srcs_offset, srcs_length] if @verbose

  # it appears bytes 68-71 always contain (2*num_sections) + 1
  # this is not documented anyplace at all but it appears to be some sort of next 
  # available unique_id used to identify specific sections in the palm db
  @data_file = datain[0, 68] + [(@num_sections - srcs_cnt) * 2 + 1].pack("N")
  @data_file += datain[72...76]

  # write out the number of sections reduced by srtcs_cnt
  @data_file = @data_file + [@num_sections - srcs_cnt].pack("n")

  # we are going to remove srcs_cnt SRCS sections so the offset of every entry in the table
  # up to the srcs secnum must begin 8 bytes earlier per section removed (each table entry is 8 )
  delta = -8 * srcs_cnt
  srcs_secnum.times do |i|
    offset, flgval = datain.unpack("@#{78+i*8}NN")
    offset += delta
    @data_file += [offset].pack("N") + [flgval].pack("N")
  end

  # for every record after the srcs_cnt SRCS records we must start it
  # earlier by 8*srcs_cnt + the length of the srcs sections themselves)
  delta = delta - srcs_length
  (srcs_secnum + srcs_cnt ... @num_sections).each do |i|
    offset, = datain.unpack("@#{78+i*8}NN")
    offset += delta
    flgval = 2 * (i - srcs_cnt)
    @data_file += [offset].pack("N") + [flgval].pack("N")
  end

  # now pad it out to begin right at the first offset
  # typically this is 2 bytes of nulls
  first_offset, = @data_file.unpack("@78NN")
  @data_file += "\0" * (first_offset - @data_file.length)

  # now finally add on every thing up to the original src_offset
  @data_file += datain[offset0...srcs_offset]
  
  # and everything afterwards
  @data_file += datain[srcs_offset + srcs_length .. -1]

  #store away the SRCS section in case the user wants it output
  @stripped_data_header = datain[srcs_offset ... srcs_offset + 16]
  @stripped_data = datain[srcs_offset + 16 ... srcs_offset + srcs_length]

  # update the number of sections count
  @num_section = @num_sections - srcs_cnt

  # update the srcs_secnum and srcs_cnt in the mobiheader
  offset0, = @data_file.unpack("@78NN")
  offset1, = @data_file.unpack("@86NN")
  mobiheader = @data_file[offset0 ... offset1]
  mobiheader = mobiheader[0, 0xe0] + [-1].pack("N") + [0].pack("N") + mobiheader[0xe8 .. -1]

  # if K8 mobi, handle metadata 121 in old mobiheader
  mobiheader = updateEXTH121(srcs_secnum, srcs_cnt, mobiheader)
  @data_file = @data_file[0, offset0] + mobiheader + @data_file[offset1 .. -1]
  puts "done" if @verbose
end

Class Method Details

.strip(infile, outfile = nil, verbose = true) ⇒ Object 



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# File 'lib/kindlestrip.rb', line 216

def self.strip(infile, outfile = nil, verbose = true)
  outfile = infile unless outfile
  data_file = File.binread(infile)
  stripped_file = new(data_file, verbose)
  File.binwrite(outfile, stripped_file.get_result)
  stripped_file
end

Instance Method Details

#get_header ⇒ Object 



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# File 'lib/kindlestrip.rb', line 212

def get_header
  @stripped_data_header
end

#get_result ⇒ Object 



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# File 'lib/kindlestrip.rb', line 204

def get_result
  @data_file
end

#get_stripped_data ⇒ Object 



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# File 'lib/kindlestrip.rb', line 208

def get_stripped_data
  @stripped_data
end

#load_section(section) ⇒ Object 



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# File 'lib/kindlestrip.rb', line 59

def load_section(section)
  if section + 1 == @num_sections
    endoff = @data_file.length
  else
    endoff = @sections[section + 1][0]
  end
  off = @sections[section][0]
  @data_file[off...endoff]
end

#patch(off, _new) ⇒ Object 



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# File 'lib/kindlestrip.rb', line 69

def patch(off, _new)
  @data_file = @data_file[0, off] + new + @data_file[off + _new.length .. -1]
end

#patch_section(section, _new, in_off = 0) ⇒ Object 



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# File 'lib/kindlestrip.rb', line 77

def patch_section(section, _new, in_off = 0)
  if section + 1 == @num_sections
    endoff = @data_file.length
  else
    endoff = @sections[section + 1][0]
  end
  raise unless off + in_off + _new.length <= endoff
  patch(off + in_off, _new)
end

#strip(off, len) ⇒ Object 



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# File 'lib/kindlestrip.rb', line 73

def strip(off, len)
  @data_file = @data_file[0, off] + @data_file[off + len .. -1]
end

#updateEXTH121(srcs_secnum, srcs_cnt, mobiheader) ⇒ Object 



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# File 'lib/kindlestrip.rb', line 87

def updateEXTH121(srcs_secnum, srcs_cnt, mobiheader)
  mobi_length, = mobiheader[0x14...0x18].unpack("N")
  exth_flag, = mobiheader[0x80...0x84].unpack("N")
  exth = "NONE"
  begin
    if exth_flag & 0x40 != 0
      exth = mobiheader[16 + mobi_length .. -1]
      if exth.length >= 4 && exth[0, 4] == "EXTH"
        nitems, = exth[8...12].unpack("N")
        pos = 12
        nitems.times do
          type, size = exth[pos ... pos + 8].unpack("NN")
          #puts "#{type}, #{size}"
          if type == 121
            boundaryptr, = exth[pos + 8 ... pos + size].unpack("N")
            if srcs_secnum <= boundaryptr
              boundaryptr -= srcs_cnt
              prefix = mobiheader[0, 16 + mobi_length + pos + 8]
              suffix = mobiheader[16 + mobi_length + pos + 8 + 4 .. -1]
              nval = [boundaryptr].pack("N")
              mobiheader = prefix + nval + suffix
            end
          end
          pos += size
        end
      end
    end
  rescue
  end
  mobiheader
end