utf 8 - convertir cadena UTF-8 a ASCII en LUA puro

Question

Tengo una pregunta sobre el envío y recepción de datos con caracteres especiales. (Diéresis alemán)

Cuando envío la cadena "Café Zeezicht" con el siguiente código, en el lado del servidor, la cadena está activa.

Pero, ¿cómo puedo recibir y decodificar los datos de recepción que contienen los mismos caracteres? Ahora parece que le gusta "Caf? Zeezicht"

Estoy buscando una función LUA pura, porque no tengo la capacidad de cargar bibliotecas.

------------------------------------------------------------
-- Function voor converting ASCII naar UTF8
------------------------------------------------------------

-- return char as utf8 string
local function CodeToUTF8 (Unicode)
  if (Unicode == nil) then 
    return ""
  end

  if (Unicode < 0x20) then return '' ''; end;

    if (Unicode <= 0x7F) then return string.char(Unicode); end;

    if (Unicode <= 0x7FF) then
      local Byte0 = 0xC0 + math.floor(Unicode / 0x40);
      local Byte1 = 0x80 + (Unicode % 0x40);
      return string.char(Byte0, Byte1);
    end;

    if (Unicode <= 0xFFFF) then
      local Byte0 = 0xE0 +  math.floor(Unicode / 0x1000);
      local Byte1 = 0x80 + (math.floor(Unicode / 0x40) % 0x40);
      local Byte2 = 0x80 + (Unicode % 0x40);
      return string.char(Byte0, Byte1, Byte2);
    end;

    return "";    -- ignore UTF-32 for the moment
end;


-- convert ascii string to utf8 string
function AsciiToUTF8(str)
  result = ""
  for i = 1, #str do
    result = result .. CodeToUTF8(string.byte(str, i, i+1))
  end
  return result
end
------------------------------------------------------------
-- Einde Function voor converting ASCII naar UTF8
------------------------------------------------------------

Answer 1

local char, byte, pairs, floor = string.char, string.byte, pairs, math.floor
local table_insert, table_concat = table.insert, table.concat
local unpack = table.unpack or unpack

local function unicode_to_utf8(code)
   -- converts numeric UTF code (U+code) to UTF-8 string
   local t, h = {}, 128
   while code >= h do
      t[#t+1] = 128 + code%64
      code = floor(code/64)
      h = h > 32 and 32 or h/2
   end
   t[#t+1] = 256 - 2*h + code
   return char(unpack(t)):reverse()
end

local function utf8_to_unicode(utf8str, pos)
   -- pos = starting byte position inside input string (default 1)
   pos = pos or 1
   local code, size = utf8str:byte(pos), 1
   if code >= 0xC0 and code < 0xFE then
      local mask = 64
      code = code - 128
      repeat
         local next_byte = utf8str:byte(pos + size) or 0
         if next_byte >= 0x80 and next_byte < 0xC0 then
            code, size = (code - mask - 2) * 64 + next_byte, size + 1
         else
            code, size = utf8str:byte(pos), 1
         end
         mask = mask * 32
      until code < mask
   end
   -- returns code, number of bytes in this utf8 char
   return code, size
end

local map_1252_to_unicode = {
   [0x80] = 0x20AC,
   [0x81] = 0x81,
   [0x82] = 0x201A,
   [0x83] = 0x0192,
   [0x84] = 0x201E,
   [0x85] = 0x2026,
   [0x86] = 0x2020,
   [0x87] = 0x2021,
   [0x88] = 0x02C6,
   [0x89] = 0x2030,
   [0x8A] = 0x0160,
   [0x8B] = 0x2039,
   [0x8C] = 0x0152,
   [0x8D] = 0x8D,
   [0x8E] = 0x017D,
   [0x8F] = 0x8F,
   [0x90] = 0x90,
   [0x91] = 0x2018,
   [0x92] = 0x2019,
   [0x93] = 0x201C,
   [0x94] = 0x201D,
   [0x95] = 0x2022,
   [0x96] = 0x2013,
   [0x97] = 0x2014,
   [0x98] = 0x02DC,
   [0x99] = 0x2122,
   [0x9A] = 0x0161,
   [0x9B] = 0x203A,
   [0x9C] = 0x0153,
   [0x9D] = 0x9D,
   [0x9E] = 0x017E,
   [0x9F] = 0x0178,
   [0xA0] = 0x00A0,
   [0xA1] = 0x00A1,
   [0xA2] = 0x00A2,
   [0xA3] = 0x00A3,
   [0xA4] = 0x00A4,
   [0xA5] = 0x00A5,
   [0xA6] = 0x00A6,
   [0xA7] = 0x00A7,
   [0xA8] = 0x00A8,
   [0xA9] = 0x00A9,
   [0xAA] = 0x00AA,
   [0xAB] = 0x00AB,
   [0xAC] = 0x00AC,
   [0xAD] = 0x00AD,
   [0xAE] = 0x00AE,
   [0xAF] = 0x00AF,
   [0xB0] = 0x00B0,
   [0xB1] = 0x00B1,
   [0xB2] = 0x00B2,
   [0xB3] = 0x00B3,
   [0xB4] = 0x00B4,
   [0xB5] = 0x00B5,
   [0xB6] = 0x00B6,
   [0xB7] = 0x00B7,
   [0xB8] = 0x00B8,
   [0xB9] = 0x00B9,
   [0xBA] = 0x00BA,
   [0xBB] = 0x00BB,
   [0xBC] = 0x00BC,
   [0xBD] = 0x00BD,
   [0xBE] = 0x00BE,
   [0xBF] = 0x00BF,
   [0xC0] = 0x00C0,
   [0xC1] = 0x00C1,
   [0xC2] = 0x00C2,
   [0xC3] = 0x00C3,
   [0xC4] = 0x00C4,
   [0xC5] = 0x00C5,
   [0xC6] = 0x00C6,
   [0xC7] = 0x00C7,
   [0xC8] = 0x00C8,
   [0xC9] = 0x00C9,
   [0xCA] = 0x00CA,
   [0xCB] = 0x00CB,
   [0xCC] = 0x00CC,
   [0xCD] = 0x00CD,
   [0xCE] = 0x00CE,
   [0xCF] = 0x00CF,
   [0xD0] = 0x00D0,
   [0xD1] = 0x00D1,
   [0xD2] = 0x00D2,
   [0xD3] = 0x00D3,
   [0xD4] = 0x00D4,
   [0xD5] = 0x00D5,
   [0xD6] = 0x00D6,
   [0xD7] = 0x00D7,
   [0xD8] = 0x00D8,
   [0xD9] = 0x00D9,
   [0xDA] = 0x00DA,
   [0xDB] = 0x00DB,
   [0xDC] = 0x00DC,
   [0xDD] = 0x00DD,
   [0xDE] = 0x00DE,
   [0xDF] = 0x00DF,
   [0xE0] = 0x00E0,
   [0xE1] = 0x00E1,
   [0xE2] = 0x00E2,
   [0xE3] = 0x00E3,
   [0xE4] = 0x00E4,
   [0xE5] = 0x00E5,
   [0xE6] = 0x00E6,
   [0xE7] = 0x00E7,
   [0xE8] = 0x00E8,
   [0xE9] = 0x00E9,
   [0xEA] = 0x00EA,
   [0xEB] = 0x00EB,
   [0xEC] = 0x00EC,
   [0xED] = 0x00ED,
   [0xEE] = 0x00EE,
   [0xEF] = 0x00EF,
   [0xF0] = 0x00F0,
   [0xF1] = 0x00F1,
   [0xF2] = 0x00F2,
   [0xF3] = 0x00F3,
   [0xF4] = 0x00F4,
   [0xF5] = 0x00F5,
   [0xF6] = 0x00F6,
   [0xF7] = 0x00F7,
   [0xF8] = 0x00F8,
   [0xF9] = 0x00F9,
   [0xFA] = 0x00FA,
   [0xFB] = 0x00FB,
   [0xFC] = 0x00FC,
   [0xFD] = 0x00FD,
   [0xFE] = 0x00FE,
   [0xFF] = 0x00FF,
}
local map_unicode_to_1252 = {}
for code1252, code in pairs(map_1252_to_unicode) do
   map_unicode_to_1252[code] = code1252
end

function string.fromutf8(utf8str)
   local pos, result_1252 = 1, {}
   while pos <= #utf8str do
      local code, size = utf8_to_unicode(utf8str, pos)
      pos = pos + size
      code = code < 128 and code or map_unicode_to_1252[code] or (''?''):byte()
      table_insert(result_1252, char(code))
   end
   return table_concat(result_1252)
end

function string.toutf8(str1252)
   local result_utf8 = {}
   for pos = 1, #str1252 do
      local code = str1252:byte(pos)
      table_insert(result_utf8, unicode_to_utf8(map_1252_to_unicode[code] or code))
   end
   return table_concat(result_utf8)
end

Uso:

local str1252 = "1/128"  -- "one euro" in latin-1
local str_utf8 = str1252:toutf8()     -- "1/226/130/172" -- one euro in utf-8
local str1252_2 = str_utf8:fromutf8()