Node中Buffer 常用API解读

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// Buffer.alloc 创建 Buffer
let buf1 = Buffer.alloc(6);

// Buffer.allocUnsafe 创建 Buffer
let buf2 = Buffer.allocUnsafe(6);

console.log(buf1); // <Buffer 00 00 00 00 00 00>
console.log(buf2); // <Buffer 00 e7 8f a0 00 00>
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let buf = Buffer.from("hello", "utf8");

console.log(buf); // <Buffer 68 65 6c 6c 6f>
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let buf = Buffer.from([1, 2, 3]);

console.log(buf); // <Buffer 01 02 03>
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let buf = Buffer.from([0xe4, 0xbd, 0xa0, 0xe5, 0xa5, 0xbd]);

console.log(buf); // <Buffer e4 bd a0 e5 a5 bd>
console.log(buf.toString("utf8")); // 你好
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let buf = Buffer.from(["1", "2", "3"]);

console.log(buf); // <Buffer 01 02 03>
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let buf1 = Buffer.from("hello", "utf8");

let buf2 = Buffer.from(buf1);

console.log(buf1); // <Buffer 68 65 6c 6c 6f>
console.log(buf2); // <Buffer 68 65 6c 6c 6f>
console.log(buf1 === buf2); // true
console.log(buf1[0] === buf2[0]); // false
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let arr1 = [1, 2, [3]];
let arr2 = arr1.slice();

arr2[2][0] = 5;
console.log(arr1); // [1, 2, [5]]
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let targetBuf = Buffer.alloc(6);
let sourceBuf = Buffer.from("你好", "utf8");

// 将 “你好” 复制到 targetBuf 中
sourceBuf.copy(targetBuf, 0, 0, 6);

console.log(targetBuf.toString()); // 你好
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let targetBuf = Buffer.alloc(3);
let sourceBuf = Buffer.from("你好", "utf8");

sourceBuf.copy(targetBuf, 0, 0, 6);
console.log(targetBuf.toString()); // 你
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// 数组
let arr = [1, 2, 3];
arr[3] = 4;
console.log(arr); // [1, 2, 3, 4]

arr.length = 5;
console.log(arr); // [1, 2, 3, 4, empty]


// Buffer
let buf = Buffer.alloc(3);
buf[3] = 0x00;
console.log(buf); // <Buffer 00 00 00>

buf.length = 5;
console.log(buf); // <Buffer 00 00 00>
console.log(buf.length); // 3
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Buffer.prototype.myCopy = function (target, targetStart, sourceStart, sourceEnd) {
    for(let i = 0; i < sourceEnd - sourceStart; i++) {
        target[targetStart + i] = this[sourceStart + i];
    }
}
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Buffer.myConcat = function (bufferList, len) {
    // 新 Buffer 的长度
    len = len || bufferList.reduce((prev, next) => prev + next.length, 0);

    let newBuf = Buffer.alloc(len); // 创建新 Buffer
    let index = 0; // 下次开始的索引

    // 循环存储 Buffer 的数组进行复制
    bufferList.forEach(buf => {
        buf.myCopy(newBuf, index, 0, buf.length);
        index += buf.length;
    });

    return newBuf;
}
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Buffer.prototype.split = function (sep) {
    let len = Buffer.from(sep).length; // 分隔符所占的字节数
    let result = []; // 返回的数组
    let start = 0; // 查找 Buffer 的起始位置
    let offset = 0; // 偏移量

    // 循环查找分隔符
    while ((offset = this.indexOf(sep, start)) !== -1) {
        // 将分隔符之前的部分截取出来存入
        result.push(this.slice(start, offset));
        start = offset + len;
    }

    // 处理剩下的部分
    return result.push(this.slice(start));
}
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let buf = Buffer.from("哈登爱篮球爱夜店", "utf8");
let bufs = buf.split("爱");

console.log(bufs);
// [ <Buffer e5 93 88 e7 99 bb>,
//   <Buffer e7 af ae e7 90 83>,
//   <Buffer e5 a4 9c e5 ba 97> ]

newBufs = bufs.map(buf => buf.toString());
console.log(newBufs); // [ '哈登', '篮球', '夜店' ]
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// 引入依赖
const fs = require("fs");
const path = require("path");

let buf = Buffer.from("你好", "utf8");
let result = fs.readFileSync(path.resolve(__dirname, "a.txt"));

console.log(buf); // <Buffer e4 bd a0 e5 a5 bd>
console.log(result); // <Buffer ef bb bf e4 bd a0 e5 a5 bd>
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function BOMStrip(result) {
    if (Buffer.isBuffer(result)) {
        // 如果读取的内容为 Buffer
        if (result[0] === 0xef && result[1] === 0xbb && result[2] === 0xbf) {
            // 若前三个字节是否和 BOM 头的前三字节相同，去掉 BOM 头
            return Buffer.slice(3);
        }
    } else {
        // 如果不是 Buffer
        if (result.charCodeAt(0) === 0xfeff) {
            // 判断第一项是否和 BOM 头的十六进制相同，去掉 BOM 头
            return result.slice(1);
        }
    }
}
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// 引入依赖
const fs = require("fs");
const path = require("path");

// 两种方式读文件
let result1 = fs.readFileSync(path.resolve(__dirname, "a.txt"));
let result2 = fs.readFileSync(path.resolve(__dirname, "a.txt"), "utf8");

console.log(BOMStrip(result1).toString()); // 你好
console.log(BOMStrip(result2)); // 你好
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let buf = Buffer.from("你好", "utf8");

let a = buf.slice(0, 2);
let b = buf.slice(2, 6);

console.log(a.toString()); // �
console.log(b.toString()); // �好
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// 引入依赖
const { StringDecoder } = require("string_decoder");

let buf = Buffer.from("你好", "utf8");

let a = buf.slice(0, 2);
let b = buf.slice(2, 6);

// 创建 StringDecoder 实例
let sd = new StringDecoder();

console.log(sd.write(a));
console.log(sd.write(b)); // 你好
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