encoding.lua

local ffi = require "ffi"
local kernel32 = ffi.load("kernel32")

ffi.cdef [[
    int Beep(int x, int y);
    typedef unsigned int UINT;
    typedef unsigned int DWORD;
    typedef const char * LPCSTR;
    typedef char * LPSTR;
    typedef wchar_t * LPWSTR;
    typedef const wchar_t * LPCWSTR;
    typedef int * LPBOOL;

    int WideCharToMultiByte(UINT CodePage,
        DWORD    dwFlags,
        LPCWSTR   lpWideCharStr, int cchWideChar,
        LPSTR  lpMultiByteStr, int cbMultiByte,
        LPCSTR  lpDefaultChar,
        LPBOOL lpUsedDefaultChar);

    int MultiByteToWideChar(UINT CodePage,
        DWORD    dwFlags,
        LPCSTR   lpMultiByteStr, int cbMultiByte,
        LPWSTR  lpWideCharStr, int cchWideChar);
]]

local CP_UTF8 = 65001

local function to_utf16(s)
    local needed = kernel32.MultiByteToWideChar(CP_UTF8, 0, s, -1, nil, 0)
    local buf = ffi.new("wchar_t[?]", needed)
    local written = kernel32.MultiByteToWideChar(CP_UTF8, 0, s, -1, buf, needed)
    return ffi.string(ffi.cast("char *", buf), written * 2)
end

local function to_utf8(s)
    local needed = kernel32.WideCharToMultiByte(CP_UTF8, 0, s, -1, nil, 0, nil, nil)
    local buf = ffi.new("char[?]", needed)
    local written = kernel32.WideCharToMultiByte(CP_UTF8, 0, s, -1, buf, needed, nil, nil)
    return ffi.string(buf, written - 1)
end

return { to_utf8 = to_utf8, to_utf16 = to_utf16 }