//功能 将数据流转换为二进制流
//参数 base64:对应数据流
function base64ToArrayBuffer(base64) {
var binaryString = window.atob(base64);
var binaryLen = binaryString.length;
var bytes = new Uint8Array(binaryLen);
for (var i = 0; i < binaryLen; i++) {
var ascii = binaryString.charCodeAt(i);
bytes[i] = ascii;
}
return bytes;
}