lua之base64的解码和编码（三种方案实现）

概述

由于涉及到java 与 lua 之间传递字节数组，如果直接传递的话会导致json解析失败，所以需要将字节数组加密为字符串，这样可以保证数据的完整传输。
在网上找到了多个版本的lua base64的编解码代码，经过逐个测试最终方案3解决了我的问题。

方案1：

调用decodeBase64解码测试的时候经常返回nil值
参考：http://www.cnblogs.com/decode1234/p/8505001.html

-- lbase64加密和解密算法
local function encodeBase64(source_str)
    local b64chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/'
    local s64 = ''
    local str = source_str

    while #str > 0 do
        local bytes_num = 0
        local buf = 0

        for byte_cnt=1,3 do
            buf = (buf * 256)
            if #str > 0 then
                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
            local 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

local function decodeBase64(str64)
    local b64chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/'
    local temp={}
    for i=1,64 do
        temp[string.sub(b64chars,i,i)] = i
    end
    temp['=']=0
    local str=""
    for i=1,#str64,4 do
        if i>#str64 then
            break
        end
        local data = 0
        local str_count=0
        for j=0,3 do
            local str1=string.sub(str64,i+j,i+j)
            if not temp[str1] then
                return
            end
            if temp[str1] < 1 then
                data = data * 64
            else
                data = data * 64 + temp[str1]-1
                str_count = str_count + 1
            end
        end
        for j=16,0,-8 do
            if str_count > 0 then
                str=str..string.char(math.floor(data/math.pow(2,j)))
                data=math.mod(data,math.pow(2,j))
                str_count = str_count - 1
            end
        end
    end

    local last = tonumber(string.byte(str, string.len(str), string.len(str)))
    if last == 0 then
        str = string.sub(str, 1, string.len(str) - 1)
    end
    return str
end

方案2：

参考：http://www.cnblogs.com/sjns/p/9958737.html

测试ZZBase64.decode解码的时候，提示local num = a * 262144 + b * 4096 + c * 64 + d语句中的a为nil值

ZZBase64 = {}
local string = string

ZZBase64.__code = {
    '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', '+', '/',
};
ZZBase64.__decode = {}
for k,v in pairs(ZZBase64.__code) do
    ZZBase64.__decode[string.byte(v,1)] = k - 1
end

function ZZBase64.encode(text)
    local len = string.len(text)
    local left = len % 3
    len = len - left
    local res = {}
    local index  = 1
    for i = 1, len, 3 do
        local a = string.byte(text, i )
        local b = string.byte(text, i + 1)
        local c = string.byte(text, i + 2)
        -- num = a<<16 + b<<8 + c
        local num = a * 65536 + b * 256 + c
        for j = 1, 4 do
            --tmp = num >> ((4 -j) * 6)
            local tmp = math.floor(num / (2 ^ ((4-j) * 6)))
            --curPos = tmp&0x3f
            local curPos = tmp % 64 + 1
            res[index] = ZZBase64.__code[curPos]
            index = index + 1
        end
    end
    
    if left == 1 then
        ZZBase64.__left1(res, index, text, len)
    elseif left == 2 then
        ZZBase64.__left2(res, index, text, len)
    end
    return table.concat(res)
end

function ZZBase64.__left2(res, index, text, len)
    local num1 = string.byte(text, len + 1)
    num1 = num1 * 1024 --lshift 10
    local num2 = string.byte(text, len + 2)
    num2 = num2 * 4 --lshift 2
    local num = num1 + num2
    
    local tmp1 = math.floor(num / 4096) --rShift 12
    local curPos = tmp1 % 64 + 1
    res[index] = ZZBase64.__code[curPos]
    
    local tmp2 = math.floor(num / 64)
    curPos = tmp2 % 64 + 1
    res[index + 1] = ZZBase64.__code[curPos]
    
    curPos = num % 64 + 1
    res[index + 2] = ZZBase64.__code[curPos]
    
    res[index + 3] = "="
end

function ZZBase64.__left1(res, index,text, len)
    local num = string.byte(text, len + 1)
    num = num * 16
    
    tmp = math.floor(num / 64)
    local curPos = tmp % 64 + 1
    res[index ] = ZZBase64.__code[curPos]
    
    curPos = num % 64 + 1
    res[index + 1] = ZZBase64.__code[curPos]
    
    res[index + 2] = "="
    res[index + 3] = "="
end

function ZZBase64.decode(text)
    local len = string.len(text)
    local left = 0
    if string.sub(text, len - 1) == "==" then
        left = 2
        len = len - 4
    elseif string.sub(text, len) == "=" then
        left = 1
        len = len - 4
    end
    
    local res = {}
    local index = 1
    local decode = ZZBase64.__decode
    for i =1, len, 4 do
        local a = decode[string.byte(text,i    )]
        local b = decode[string.byte(text,i + 1)]
        local c = decode[string.byte(text,i + 2)]
        local d = decode[string.byte(text,i + 3)]
        
        --num = a<<18 + b<<12 + c<<6 + d
        local num = a * 262144 + b * 4096 + c * 64 + d
        
        local e = string.char(num % 256)
        num = math.floor(num / 256)
        local f = string.char(num % 256)
        num = math.floor(num / 256)
        res[index ] = string.char(num % 256)
        res[index + 1] = f
        res[index + 2] = e
        index = index + 3
    end
    
    if left == 1 then
        ZZBase64.__decodeLeft1(res, index, text, len)
    elseif left == 2 then
        ZZBase64.__decodeLeft2(res, index, text, len)
    end
    return table.concat(res)
end

function ZZBase64.__decodeLeft1(res, index, text, len)
    local decode = ZZBase64.__decode
    local a = decode[string.byte(text, len + 1)]
    local b = decode[string.byte(text, len + 2)]
    local c = decode[string.byte(text, len + 3)]
    local num = a * 4096 + b * 64 + c
    
    local num1 = math.floor(num / 1024) % 256
    local num2 = math.floor(num / 4) % 256
    res[index] = string.char(num1)
    res[index + 1] = string.char(num2)
end

function ZZBase64.__decodeLeft2(res, index, text, len)
    local decode = ZZBase64.__decode
    local a = decode[string.byte(text, len + 1)]
    local b = decode[string.byte(text, len + 2)]
    local num = a * 64 + b
    num = math.floor(num / 16)
    res[index] = string.char(num)
end

return ZZBase64

方案3：

http://lua-users.org/wiki/BaseSixtyFour
测试编解码ok

base64 = {}

local b='ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/' -- You will need this for encoding/decoding

-- encoding
function base64.enc(data)
    return ((data:gsub('.', function(x) 
        local r,b='',x:byte()
        for i=8,1,-1 do r=r..(b%2^i-b%2^(i-1)>0 and '1' or '0') end
        return r;
    end)..'0000'):gsub('%d%d%d?%d?%d?%d?', function(x)
        if (#x < 6) then return '' end
        local c=0
        for i=1,6 do c=c+(x:sub(i,i)=='1' and 2^(6-i) or 0) end
        return b:sub(c+1,c+1)
    end)..({ '', '==', '=' })[#data%3+1])
end

-- decoding
function base64.dec(data)
    data = string.gsub(data, '[^'..b..'=]', '')
    return (data:gsub('.', function(x)
        if (x == '=') then return '' end
        local r,f='',(b:find(x)-1)
        for i=6,1,-1 do r=r..(f%2^i-f%2^(i-1)>0 and '1' or '0') end
        return r;
    end):gsub('%d%d%d?%d?%d?%d?%d?%d?', function(x)
        if (#x ~= 8) then return '' end
        local c=0
        for i=1,8 do c=c+(x:sub(i,i)=='1' and 2^(8-i) or 0) end
            return string.char(c)
    end))
end

return base64