local base64 = {}
function extract( v, from, width )
local w = 0
local flag = 2^from
for i = 0, width-1 do
local flag2 = flag + flag
if v % flag2 >= flag then
w = w + 2^i
end
flag = flag2
end
return w
end
function base64.makeencoder( s62, s63, spad )
local encoder = {}
for b64code, char in pairs{[0]='A','B','C','D','E','F','G','H','I','J',
'K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y',
'Z','a','b','c','d','e','f','g','h','i','j','k','l','m','n',
'o','p','q','r','s','t','u','v','w','x','y','z','0','1','2',
'3','4','5','6','7','8','9',s62 or '+',s63 or'/',spad or'='} do
encoder[b64code] = char:byte()
end
return encoder
end
function base64.makedecoder( s62, s63, spad )
local decoder = {}
for b64code, charcode in pairs( base64.makeencoder( s62, s63, spad )) do
decoder[charcode] = b64code
end
return decoder
end
local DEFAULT_ENCODER = base64.makeencoder()
local DEFAULT_DECODER = base64.makedecoder()
local char, concat = string.char, table.concat
function base64.encode( str, encoder, usecaching )
encoder = encoder or DEFAULT_ENCODER
local t, k, n = {}, 1, #str
local lastn = n % 3
local cache = {}
for i = 1, n-lastn, 3 do
local a, b, c = str:byte( i, i+2 )
local v = a*0x10000 + b*0x100 + c
local s
if usecaching then
s = cache[v]
if not s then
s = char(encoder[extract(v,18,6)], encoder[extract(v,12,6)], encoder[extract(v,6,6)], encoder[extract(v,0,6)])
cache[v] = s
end
else
s = char(encoder[extract(v,18,6)], encoder[extract(v,12,6)], encoder[extract(v,6,6)], encoder[extract(v,0,6)])
end
t[k] = s
k = k + 1
end
if lastn == 2 then
local a, b = str:byte( n-1, n )
local v = a*0x10000 + b*0x100
t[k] = char(encoder[extract(v,18,6)], encoder[extract(v,12,6)], encoder[extract(v,6,6)], encoder[64])
elseif lastn == 1 then
local v = str:byte( n )*0x10000
t[k] = char(encoder[extract(v,18,6)], encoder[extract(v,12,6)], encoder[64], encoder[64])
end
return concat( t )
end
function base64.decode( b64, decoder, usecaching )
decoder = decoder or DEFAULT_DECODER
local pattern = '[^%w%+%/%=]'
if decoder then
local s62, s63
for charcode, b64code in pairs( decoder ) do
if b64code == 62 then s62 = charcode
elseif b64code == 63 then s63 = charcode
end
end
pattern = ('[^%%w%%%s%%%s%%=]'):format( char(s62), char(s63) )
end
b64 = b64:gsub( pattern, '' )
local cache = usecaching and {}
local t, k = {}, 1
local n = #b64
local padding = b64:sub(-2) == '==' and 2 or b64:sub(-1) == '=' and 1 or 0
for i = 1, padding > 0 and n-4 or n, 4 do
local a, b, c, d = b64:byte( i, i+3 )
local s
if usecaching then
local v0 = a*0x1000000 + b*0x10000 + c*0x100 + d
s = cache[v0]
if not s then
local v = decoder[a]*0x40000 + decoder[b]*0x1000 + decoder[c]*0x40 + decoder[d]
s = char( extract(v,16,8), extract(v,8,8), extract(v,0,8))
cache[v0] = s
end
else
local v = decoder[a]*0x40000 + decoder[b]*0x1000 + decoder[c]*0x40 + decoder[d]
s = char( extract(v,16,8), extract(v,8,8), extract(v,0,8))
end
t[k] = s
k = k + 1
end
if padding == 1 then
local a, b, c = b64:byte( n-3, n-1 )
local v = decoder[a]*0x40000 + decoder[b]*0x1000 + decoder[c]*0x40
t[k] = char( extract(v,16,8), extract(v,8,8))
elseif padding == 2 then
local a, b = b64:byte( n-3, n-2 )
local v = decoder[a]*0x40000 + decoder[b]*0x1000
t[k] = char( extract(v,16,8))
end
return concat( t )
end
return base64