Base64

-- Base64 Encoder / Decoder
-- By KillaVanilla

local alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"

local function sixBitToBase64(input)
    return string.sub(alphabet, input+1, input+1)
end

local function base64ToSixBit(input)
    for i=1, 64 do
        if input == string.sub(alphabet, i, i) then
            return i-1
        end
    end
end

local function octetToBase64(o1, o2, o3)
    local i1 = sixBitToBase64(bit.brshift(bit.band(o1, 0xFC), 2))
    local i2 = "A"
    local i3 = "="
    local i4 = "="
    if o2 then
        i2 = sixBitToBase64(bit.bor( bit.blshift(bit.band(o1, 3), 4), bit.brshift(bit.band(o2, 0xF0), 4) ))
        if not o3 then
            i3 = sixBitToBase64(bit.blshift(bit.band(o2, 0x0F), 2))
        else
            i3 = sixBitToBase64(bit.bor( bit.blshift(bit.band(o2, 0x0F), 2), bit.brshift(bit.band(o3, 0xC0), 6) ))
        end
    else
        i2 = sixBitToBase64(bit.blshift(bit.band(o1, 3), 4))
    end
    if o3 then
        i4 = sixBitToBase64(bit.band(o3, 0x3F))
    end

    return i1..i2..i3..i4
end

-- octet 1 needs characters 1/2
-- octet 2 needs characters 2/3
-- octet 3 needs characters 3/4

local function base64ToThreeOctet(s1)
    local c1 = base64ToSixBit(string.sub(s1, 1, 1))
    local c2 = base64ToSixBit(string.sub(s1, 2, 2))
    local c3 = 0
    local c4 = 0
    local o1 = 0
    local o2 = 0
    local o3 = 0
    if string.sub(s1, 3, 3) == "=" then
        c3 = nil
        c4 = nil
    elseif string.sub(s1, 4, 4) == "=" then
        c3 = base64ToSixBit(string.sub(s1, 3, 3))
        c4 = nil
    else
        c3 = base64ToSixBit(string.sub(s1, 3, 3))
        c4 = base64ToSixBit(string.sub(s1, 4, 4))
    end
    o1 = bit.bor( bit.blshift(c1, 2), bit.brshift(bit.band( c2, 0x30 ), 4) )
    if c3 then
        o2 = bit.bor( bit.blshift(bit.band(c2, 0x0F), 4), bit.brshift(bit.band( c3, 0x3C ), 2) )
    else
        o2 = nil
    end
    if c4 then
        o3 = bit.bor( bit.blshift(bit.band(c3, 3), 6), c4 )
    else
        o3 = nil
    end
    return o1, o2, o3
end

local function splitIntoBlocks(bytes)
    local blockNum = 1
    local blocks = {}
    for i=1, #bytes, 3 do
        blocks[blockNum] = {bytes[i], bytes[i+1], bytes[i+2]}
        --[[
        if #blocks[blockNum] < 3 then
            for j=#blocks[blockNum]+1, 3 do
                table.insert(blocks[blockNum], 0)
            end
        end
        ]]
        blockNum = blockNum+1
    end
    return blocks
end

function encode(bytes)
    local blocks = splitIntoBlocks(bytes)
    local output = ""
    for i=1, #blocks do
        output = output..octetToBase64( unpack(blocks[i]) )
    end
    return output
end

function decode(str)
    local bytes = {}
    local blocks = {}
    local blockNum = 1
    for i=1, #str, 4 do
        blocks[blockNum] = string.sub(str, i, i+3)
        blockNum = blockNum+1
    end
    for i=1, #blocks do
        local o1, o2, o3 = base64ToThreeOctet(blocks[i])
        table.insert(bytes, o1)
        table.insert(bytes, o2)
        table.insert(bytes, o3)
    end
    -- Remove padding:
    --[[
    for i=#bytes, 1, -1 do
        if bytes[i] ~= 0 then
            break
        else
            bytes[i] = nil
        end
    end
    ]]
    return bytes
end