SixArm/sixarm_ruby_magic_number_type

# -*- coding: utf-8 -*-
=begin rdoc
Please see README
=end

class String

  # We implement magic number type by using a lookup hash.
  # This is fast enough for our needs; it could be optimized.
  #
  # The key is a string that encodes the first bits.
  # The value is a symbol that indicates the magic type.
  #
  # See:
  #  - IO#magic_number_type
  #  - File.magic_number_type
  #
  # Quirks:
  #   - JPEG adjustment:
  #     - Some cameras put JPEG Exif data in bytes 3 & 4,
  #       so we only check the first two bytes of a JPEG.
  #   - TIFF has two possible matches:
  #     - II.. Intel little ending ("II2A00")
  #     - MM.. Motorola big endian ("MM002A")
  #
  # TODO change from hash implementation to binary tree
  #
  MagicNumberTypeHash = {
    "<!doctyp" => :html,
    "<html" => :html,
    "<?xml" => :xml,
    "<MakerFile" => :adobe_framemaker,
    "BC" => :bitcode,
    "BM" => :bitmap,
    "BZ" => :bzip,
    "SIMPLE"=> :fits,
    "GIF8" => :gif,
    "GKSM" => :gks,
    ["01DA"].pack('H*') => :iris_rgb,
    ["F10040BB"].pack('H*') => :itc,
    ["FFD8"].pack('H*') => :jpeg,
    "IIN1" => :niff,
    "MThd" => :midi,
    "%PDF" => :pdf,
    "VIEW" => :pm,
    ["89504E470D0A1A0A"].pack('H*') => :png,
    "Y" + ["A6"].pack('H*') + "j" + ["95"].pack('H*') => :sun_rasterfile,
    "II" + ["2A00"].pack('H*') => :tiff,  # II means Intel format, then 42 little-endian
    "MM" + ["002A"].pack('H*') => :tiff,  # MM means Motorola format, then 42 big-endian
    "gimp xcf" => :gimp_xcf,
    "#FIG" => :xfig,
    "/* XPM */" => :xpm,
    ["1F9D"].pack('H*') => :compress,
    ["1F8B"].pack('H*') => :gzip,
    "\x1F\xA0" => :tar_file_using_lzh_compression,
    "PK\x03\x04" => :pkzip,
    "7Z\xBC\xAF\x27\x1C" => :seven_zip,
    "MZ" => :dos_os2_windows_executable,
    ".ELF" => :unix_elf,
    "\x99\x00" => :pgp_public_ring,
    "\x95\x01" => :pgp_security_ring,
    "\x95\x00" => :pgp_security_ring,
    "\xA6\x00" => :pgp_encrypted_data,
    "\xD0\xCF\x11\xE0" => :docfile,
    #TODO matroska seems to have multiple magic file types-- diagnose and fix
    #"\x1a\x45\xdf\xa3\xa3\x42\x86\x81\x01\x42\xf7\x81\x01\x42\xf2\x81\x04\x42\xf3\x81\x08\x42\x82\x88matroska" => :matroska_stream,
    ".RTS COMPRESSED IMAGE" => :runtime_software_disk_image,
    "WS" => :wordstar_document,
    "!BDN" => :microsoft_outlook_personal_folder_file,
    "# Disk Descripto" => :vmware_disk_description,
    "# Microsoft Developer Studio" => :microsoft_developer_studio,
    "#!AMR" => :adaptive_multi_rate,
    "#?RADIANCE." => :radiance_high_dynamic_range_image_file,
    "%!PS-Adobe-3.0 EPSF-3.0" => :encapsulated_postscript,
    "8BPS" => :adobe_photoshop,
    "\x00\xBF" => :adobe_flash_shared_object,  # Typically a flash cookie
    "\x00\x00\x00\x14ftypisom" => :iso_base_media,  # ISO Base Media file (MPEG-4) v1
    "\x00\x00\x00\x14ftypqt" => :quicktime_movie,
    "\x00\x00\x00\x14fty3gp5" => :mpeg4_video,
    "\x00\x00\x00\x14ftymp42" => :mpeg4_video_quicktime,
    "\x00\x00\x00\x14ftyM4A" => :app_lossless_audio_codec,
    "\x00\x01\x00\x00MYISAM DATABASE" => :msisam_database,  # e.g. Microsoft Money
    "\x00\x01\x00\x00Standard ACE DB" => :microsoft_access_ace_db,
    "\x00\x01\x00\x00Standard Jet DB" => :microsoft_access_jet_db,
    "\x00\x01BA" => :palm_address_book,
    "\x00\x01BD" => :palm_date_book,
    "\x01\x0F\x00\x00" => :microsoft_sql_server_2000,
    "(This file must be converted with BinHex" => :binhex,
    "***  Installation Started" => :symantec_wise_installer_log_file,
    ".REC" => :realplayer_video,
    ".RMF" => :realplayer_media,
    "01ORDNANCE SURVEY" => :national_transfer_format_map,
    "\x31\xBE" => :microsoft_write,
    "\x32\xBE" => :microsoft_write,
    "4" + ["CDB2A1"].pack('H*') => :tcpdump,
    ":VERSION" => :surfplan_kite_project,
    "AC10" => :autocad,
    ".snd" => :sun_microsystems_law_audio_file,
    # Short ones below that would mask longer ones above
    "\x23\x21" => :shebang,
    "%!" => :postscript
  }

  MagicNumberTypeMaxLength = 64  # Longest key


  # Detect the data type by checking various "magic number" conventions
  # for the introductory bytes of a data stream
  #
  # Return the "magic number" as a symbol:
  #  - :bitmap = Bitmap image file, typical extension ".bmp"
  #  - :gzip = Unix GZIP compressed data, typical extension ".gz"
  #  - :postscript = Postscript pages, typical extension ".ps"
  #
  # Return nil if there's no match for any known magic number.
  #
  # Examples:
  #   "BM".magic_number_type => :bitmap
  #   "GIF8".magic_numer_type => :gif
  #   "\xa6\x00".magic_number_type => :pgp_encrypted_data
  #
  # TODO change from hash implementation to binary tree
  #
  def magic_number_type
    String::MagicNumberTypeHash.each_pair do |byte_string,type_symbol|
      return type_symbol if byte_string==self.byteslice(0,byte_string.length)
    end
    return nil
  end

  protected

end