Buffer和字符串间的转换

• 字符串转Buffer。Buffer.from(str, [encoding])
• Buffer转字符串。buf.toString([encoding], [start], [end])

其中，支持的encoding编码：ASCII、UTF-8、UTF-16LE/UCS-2、Base64、Binary、Hex。

var str = "Hello 你好";
var bufStr = Buffer.from(str);
var bufUTF8 = Buffer.from(str, "utf-8");
console.log(str.length);// 8
console.log(bufStr.length); // 12
console.log(bufStr); // <Buffer 48 65 6c 6c 6f 20 e4 bd a0 e5 a5 bd>
console.log(bufUTF8.length); // 12
console.log(bufUTF8); // <Buffer 48 65 6c 6c 6f 20 e4 bd a0 e5 a5 bd