lua中对字符串进行Base64加密的函数。备份！
function str2base64(str)
local b64chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/'
local s64 = ''
while #str > 0 do -- iterate through string
local bytes_num = 0 -- number of shifted bytes
local buf = 0 -- input buffer
for byte_cnt=1,3 do
buf = (buf * 256)
if #str > 0 then -- if string not empty, shift 1st byte to buf
buf = buf + string.byte(str, 1, 1)
str = string.sub(str, 2)
bytes_num = bytes_num + 1
end
end
for group_cnt=1,(bytes_num+1) do
b64char = math.fmod(math.floor(buf/262144), 64) + 1
s64 = s64 .. string.sub(b64chars, b64char, b64char)
buf = buf * 64
end
for fill_cnt=1,(3-bytes_num) do
s64 = s64 .. '='
end
end
return s64
end
