class PDF::Reader::Buffer

def find_first_xref_offset

table in the underlying IO stream.
objects in the file. This method attempts to locate the byte offset of the xref
The Xref table in a PDF file acts as an aid for finding the location of various
############################################################################### 
def find_first_xref_offset
  @io.seek(-1024, IO::SEEK_END) rescue seek(0)
  data = @io.read(1024)
  # the PDF 1.7 spec (section #3.4) says that EOL markers can be either \r, \n, or both.
  # To ensure we find the xref offset correctly, change all possible options to a 
  # standard format
  data = data.gsub("\r\n","\n").gsub("\n\r","\n").gsub("\r","\n")
  lines = data.split(/\n/).reverse
  eof_index = nil
  lines.each_with_index do |line, index|
    if line =~ /^%%EOF\r?$/
      eof_index = index
      break
    end
  end
  raise MalformedPDFError, "PDF does not contain EOF marker" if eof_index.nil?
  raise MalformedPDFError, "PDF EOF marker does not follow offset" if eof_index >= lines.size-1
  lines[eof_index+1].to_i
end