关于Node.js中Buffer的一些你可能不知道的用法

fs.readFile('filename', function (err, buf) {
 // <Buffer 2f 2a 2a 0a 20 2a 20 53 75 ... >
});

var bufs = [];
conn.on('data', function (buf) {
 bufs.push(buf);
});
conn.on('end', function () {
 // 接收数据结束后，拼接所有收到的 Buffer 对象
 var buf = Buffer.concat(bufs);
});

console.log(new Buffer('hello, world!').toString('base64'));
// 转换成 base64 字符串：aGVsbG8sIHdvcmxkIQ==

console.log(new Buffer('aGVsbG8sIHdvcmxkIQ==', 'base64').toString());
// 还原 base64 字符串：hello, world!

console.log(new Buffer('hello, world!').toString('hex'));
// 转换成十六进制字符串：68656c6c6f2c20776f726c6421

console.log(new Buffer('68656c6c6f2c20776f726c6421', 'hex').toString());
// 还原十六进制字符串：hello, world!

// 分配一个 2G-1 字节的数据
// 单次分配内存超过此值会抛出异常 RangeError: Invalid typed array length
var buf = new Buffer(1024 * 1024 * 1024 - 1);

var buf = new Buffer(6);

buf.writeUIntBE(1447656645380, 0, 6);
// <Buffer 01 51 0f 0f 63 04>

buf.readUIntBE(0, 6);
// 1447656645380

100001,1001,99
100002,1001,67
100003,1001,88

// 读取一条记录
// buf Buffer 对象
// offset 本条记录在 Buffer 对象的开始位置
// data {number, lesson, score}
function writeRecord (buf, offset, data) {
 buf.writeUIntBE(data.number, offset, 3);
 buf.writeUInt16BE(data.lesson, offset   3);
 buf.writeInt8(data.score, offset   5);
}

// 写入一条记录
// buf Buffer 对象
// offset 本条记录在 Buffer 对象的开始位置
function readRecord (buf, offset) {
 return {
 number: buf.readUIntBE(offset, 3),
 lesson: buf.readUInt16BE(offset   3),
 score: buf.readInt8(offset   5)
 };
}

// 写入记录列表
// list 记录列表，每一条包含 {number, lesson, score}
function writeList (list) {
 var buf = new Buffer(list.length * 6);
 var offset = 0;
 for (var i = 0; i < list.length; i  ) {
 writeRecord(buf, offset, list[i]);
 offset  = 6;
 }
 return buf;
}

// 读取记录列表
// buf Buffer 对象
function readList (buf) {
 var offset = 0;
 var list = [];
 while (offset < buf.length) {
 list.push(readRecord(buf, offset));
 offset  = 6;
 }
 return list;
}

var list = [
 {number: 100001, lesson: 1001, score: 99},
 {number: 100002, lesson: 1001, score: 88},
 {number: 100003, lesson: 1001, score: 77},
 {number: 100004, lesson: 1001, score: 66},
 {number: 100005, lesson: 1001, score: 55},
];
console.log(list);

var buf = writeList(list);
console.log(buf);
// 输出 <Buffer 01 86 a1 03 e9 63 01 86 a2 03 e9 58 01 86 a3 03 e9 4d 01 86 a4 03 e9 42 01 86 a5 03 e9 37>

var ret = readList(buf);
console.log(ret);
/* 输出
[ { number: 100001, lesson: 1001, score: 99 },
 { number: 100002, lesson: 1001, score: 88 },
 { number: 100003, lesson: 1001, score: 77 },
 { number: 100004, lesson: 1001, score: 66 },
 { number: 100005, lesson: 1001, score: 55 } ]
*/

$ npm install lei-proto --save

var parsePorto = require('lei-proto');

// 生成指定记录结构的数据编码/解码器
var record = parsePorto([
 ['number', 'uint', 3],
 ['lesson', 'uint', 2],
 ['score', 'uint', 1]
]);

function readList (buf) {
 var list = [];
 var offset = 0;
 while (offset < buf.length) {
 list.push(record.decode(buf.slice(offset, offset   6)));
 offset  = 6;
 }
 return list;
}

function writeList (list) {
 return Buffer.concat(list.map(record.encodeEx));
}

<Buffer 01 86 a1 03 e9 63 01 86 a2 03 e9 58 01 86 a3 03 e9 4d 01 86 a4 03 e9 42 01 86 a5 03 e9 37>
[ { number: 100001, lesson: 1001, score: 99 },
 { number: 100002, lesson: 1001, score: 88 },
 { number: 100003, lesson: 1001, score: 77 },
 { number: 100004, lesson: 1001, score: 66 },
 { number: 100005, lesson: 1001, score: 55 } ]