function getEncoding (label) {
  if (!label) {
    return 'failure'
  }

  // 1. Remove any leading and trailing ASCII whitespace from label.
  // 2. If label is an ASCII case-insensitive match for any of the
  //    labels listed in the table below, then return the
  //    corresponding encoding; otherwise return failure.
  switch (label.trim().toLowerCase()) {
    case 'unicode-1-1-utf-8':
    case 'unicode11utf8':
    case 'unicode20utf8':
    case 'utf-8':
    case 'utf8':
    case 'x-unicode20utf8':
      return 'UTF-8'
    case '866':
    case 'cp866':
    case 'csibm866':
    case 'ibm866':
      return 'IBM866'
    case 'csisolatin2':
    case 'iso-8859-2':
    case 'iso-ir-101':
    case 'iso8859-2':
    case 'iso88592':
    case 'iso_8859-2':
    case 'iso_8859-2:1987':
    case 'l2':
    case 'latin2':
      return 'ISO-8859-2'
    case 'csisolatin3':
    case 'iso-8859-3':
    case 'iso-ir-109':
    case 'iso8859-3':
    case 'iso88593':
    case 'iso_8859-3':
    case 'iso_8859-3:1988':
    case 'l3':
    case 'latin3':
      return 'ISO-8859-3'
    case 'csisolatin4':
    case 'iso-8859-4':
    case 'iso-ir-110':
    case 'iso8859-4':
    case 'iso88594':
    case 'iso_8859-4':
    case 'iso_8859-4:1988':
    case 'l4':
    case 'latin4':
      return 'ISO-8859-4'
    case 'csisolatincyrillic':
    case 'cyrillic':
    case 'iso-8859-5':
    case 'iso-ir-144':
    case 'iso8859-5':
    case 'iso88595':
    case 'iso_8859-5':
    case 'iso_8859-5:1988':
      return 'ISO-8859-5'
    case 'arabic':
    case 'asmo-708':
    case 'csiso88596e':
    case 'csiso88596i':
    case 'csisolatinarabic':
    case 'ecma-114':
    case 'iso-8859-6':
    case 'iso-8859-6-e':
    case 'iso-8859-6-i':
    case 'iso-ir-127':
    case 'iso8859-6':
    case 'iso88596':
    case 'iso_8859-6':
    case 'iso_8859-6:1987':
      return 'ISO-8859-6'
    case 'csisolatingreek':
    case 'ecma-118':
    case 'elot_928':
    case 'greek':
    case 'greek8':
    case 'iso-8859-7':
    case 'iso-ir-126':
    case 'iso8859-7':
    case 'iso88597':
    case 'iso_8859-7':
    case 'iso_8859-7:1987':
    case 'sun_eu_greek':
      return 'ISO-8859-7'
    case 'csiso88598e':
    case 'csisolatinhebrew':
    case 'hebrew':
    case 'iso-8859-8':
    case 'iso-8859-8-e':
    case 'iso-ir-138':
    case 'iso8859-8':
    case 'iso88598':
    case 'iso_8859-8':
    case 'iso_8859-8:1988':
    case 'visual':
      return 'ISO-8859-8'
    case 'csiso88598i':
    case 'iso-8859-8-i':
    case 'logical':
      return 'ISO-8859-8-I'
    case 'csisolatin6':
    case 'iso-8859-10':
    case 'iso-ir-157':
    case 'iso8859-10':
    case 'iso885910':
    case 'l6':
    case 'latin6':
      return 'ISO-8859-10'
    case 'iso-8859-13':
    case 'iso8859-13':
    case 'iso885913':
      return 'ISO-8859-13'
    case 'iso-8859-14':
    case 'iso8859-14':
    case 'iso885914':
      return 'ISO-8859-14'
    case 'csisolatin9':
    case 'iso-8859-15':
    case 'iso8859-15':
    case 'iso885915':
    case 'iso_8859-15':
    case 'l9':
      return 'ISO-8859-15'
    case 'iso-8859-16':
      return 'ISO-8859-16'
    case 'cskoi8r':
    case 'koi':
    case 'koi8':
    case 'koi8-r':
    case 'koi8_r':
      return 'KOI8-R'
    case 'koi8-ru':
    case 'koi8-u':
      return 'KOI8-U'
    case 'csmacintosh':
    case 'mac':
    case 'macintosh':
    case 'x-mac-roman':
      return 'macintosh'
    case 'iso-8859-11':
    case 'iso8859-11':
    case 'iso885911':
    case 'tis-620':
    case 'windows-874':
      return 'windows-874'
    case 'cp1250':
    case 'windows-1250':
    case 'x-cp1250':
      return 'windows-1250'
    case 'cp1251':
    case 'windows-1251':
    case 'x-cp1251':
      return 'windows-1251'
    case 'ansi_x3.4-1968':
    case 'ascii':
    case 'cp1252':
    case 'cp819':
    case 'csisolatin1':
    case 'ibm819':
    case 'iso-8859-1':
    case 'iso-ir-100':
    case 'iso8859-1':
    case 'iso88591':
    case 'iso_8859-1':
    case 'iso_8859-1:1987':
    case 'l1':
    case 'latin1':
    case 'us-ascii':
    case 'windows-1252':
    case 'x-cp1252':
      return 'windows-1252'
    case 'cp1253':
    case 'windows-1253':
    case 'x-cp1253':
      return 'windows-1253'
    case 'cp1254':
    case 'csisolatin5':
    case 'iso-8859-9':
    case 'iso-ir-148':
    case 'iso8859-9':
    case 'iso88599':
    case 'iso_8859-9':
    case 'iso_8859-9:1989':
    case 'l5':
    case 'latin5':
    case 'windows-1254':
    case 'x-cp1254':
      return 'windows-1254'
    case 'cp1255':
    case 'windows-1255':
    case 'x-cp1255':
      return 'windows-1255'
    case 'cp1256':
    case 'windows-1256':
    case 'x-cp1256':
      return 'windows-1256'
    case 'cp1257':
    case 'windows-1257':
    case 'x-cp1257':
      return 'windows-1257'
    case 'cp1258':
    case 'windows-1258':
    case 'x-cp1258':
      return 'windows-1258'
    case 'x-mac-cyrillic':
    case 'x-mac-ukrainian':
      return 'x-mac-cyrillic'
    case 'chinese':
    case 'csgb2312':
    case 'csiso58gb231280':
    case 'gb2312':
    case 'gb_2312':
    case 'gb_2312-80':
    case 'gbk':
    case 'iso-ir-58':
    case 'x-gbk':
      return 'GBK'
    case 'gb18030':
      return 'gb18030'
    case 'big5':
    case 'big5-hkscs':
    case 'cn-big5':
    case 'csbig5':
    case 'x-x-big5':
      return 'Big5'
    case 'cseucpkdfmtjapanese':
    case 'euc-jp':
    case 'x-euc-jp':
      return 'EUC-JP'
    case 'csiso2022jp':
    case 'iso-2022-jp':
      return 'ISO-2022-JP'
    case 'csshiftjis':
    case 'ms932':
    case 'ms_kanji':
    case 'shift-jis':
    case 'shift_jis':
    case 'sjis':
    case 'windows-31j':
    case 'x-sjis':
      return 'Shift_JIS'
    case 'cseuckr':
    case 'csksc56011987':
    case 'euc-kr':
    case 'iso-ir-149':
    case 'korean':
    case 'ks_c_5601-1987':
    case 'ks_c_5601-1989':
    case 'ksc5601':
    case 'ksc_5601':
    case 'windows-949':
      return 'EUC-KR'
    case 'csiso2022kr':
    case 'hz-gb-2312':
    case 'iso-2022-cn':
    case 'iso-2022-cn-ext':
    case 'iso-2022-kr':
    case 'replacement':
      return 'replacement'
    case 'unicodefffe':
    case 'utf-16be':
      return 'UTF-16BE'
    case 'csunicode':
    case 'iso-10646-ucs-2':
    case 'ucs-2':
    case 'unicode':
    case 'unicodefeff':
    case 'utf-16':
    case 'utf-16le':
      return 'UTF-16LE'
    case 'x-user-defined':
      return 'x-user-defined'
    default: return 'failure'
  }
}
@see https://encoding.spec.whatwg.org/#concept-encoding-get
@param {string|undefined} label