lua base64 保存为图片文件

将获取到的base64字节流，保存为图片文件，源码如下：

local bs = "base64图片编码后数据"

bs = string.gsub(bs,"data:image/png;base64,","")

local ff = base64.decode(bs)

local file = io.open("a.png", "wb")
file:write(ff)
file:close()