What is buffer? The following article will give you an in-depth understanding of the buffer module in Nodejs, and introduce the methods of creating, copying, splicing, intercepting, filling Buffers, and converting Buffers and Strings. I hope it will be helpful to everyone!
We know that JS has corresponding method APIs for operating strings, arrays, numbers, Boolean values, etc., while in Node, file operations, network communications, database operations, and data transmission are also required. and other capabilities; files are represented in binary form at the storage level, and data transmission in http requests and responses is also transmitted in binary data, so the current JS capabilities alone are not enough, which is why Node## The buffer module is provided in #.
That is: giving NodeJS the ability to manipulate binary data like strings. Buffer is also calledtemporary storage area, which is a section of memory that temporarily stores input and output binary data.
Talk about the core module in Nodejs: stream module (see how to use), we learned that when reading large files, Generally, it is not read into the memory all at once, but a data block is read in the form of a stream, and the continuous data blocks form the concept of data stream. During the process of reading and writing data blocks, the data will first be stored in the memory of buffer (temporary buffer area) to be processed.
1.1 Understand buffer memory allocation
#The memory allocation of the buffer object is not in the heap memory of V8, but at the C level of Node Implement memory application; in order to efficiently use the application to obtain memory, Node adopts the slab allocation mechanism (a dynamic memory management mechanism).1. 2 The global nature of the buffer
Node has already installed the buffer into the memory when the process starts and puts it into the global The object can be introduced without require when using it, but it is still officially recommended to reference it explicitly through the import or require statement.2.1 Buffer.alloc(size[, fill[, encoding]])
Parameters:
import { Buffer } from 'buffer';
const buf = Buffer.alloc(8);
console.log(buf);
// <Buffer 00 00 00 00 00 00 00 00>2.2 Buffer.allocUnsafe(size)
Parameters:import { Buffer } from 'buffer';
const buf = Buffer.allocUnsafe(8);
console.log(buf);
// <Buffer e8 bf 99 e6 98 af e4 b8 80 e6>2.3 Buffer.from(string[, encoding])
Create a new buffer containing the incoming stringParameters:
import { Buffer } from 'buffer';
const buf = Buffer.from('hello buffer');
console.log(buf);
// <Buffer 68 65 6c 6c 6f 20 62 75 66 66 65 72>2.4 Buffer.from(array)
Use bytes in the range0 – 255 array to allocate new Buffer.
import { Buffer } from 'buffer';
const array = [0x62, 0x78, 0x84];
const buf = Buffer.from(array);
console.log(buf);
// <Buffer 62 78 84>3.1 Buffer.from(buffer)
Parameters:import { Buffer } from 'buffer';
// 新建
const buf1 = Buffer.alloc(10, 2);
// 复制
const buf2 = Buffer.from(buf1);
console.log(buf1);
// <Buffer 02 02 02 02 02 02 02 02 02 02>
console.log(buf2);
// <Buffer 02 02 02 02 02 02 02 02 02 02>3.2 buf.copy(target[, targetStart[, sourceStart[, sourceEnd]]] )
Copy the buf instance to the target targetimport { Buffer } from 'buffer';
const buf1 = Buffer.alloc(10, 2);
const buf2 = Buffer.allocUnsafe(10)
// 将buf1复制到buf2
buf1.copy(buf2);
console.log(buf1);
// <Buffer 02 02 02 02 02 02 02 02 02 02>
console.log(buf2);
// <Buffer 02 02 02 02 02 02 02 02 02 02>4.1 Buffer.concat(list[, totalLength])
Returns a new buffer in which all buffer instances in the list are connected togetherParameters:Note:
import { Buffer } from 'buffer';
const buf1 = Buffer.alloc(4, 2);
const buf2 = Buffer.alloc(4, 3);
const buf3 = Buffer.concat([buf1, buf2]);
console.log(buf1); // <Buffer 02 02 02 02>
console.log(buf2); // <Buffer 03 03 03 03>
console.log(buf3); // <Buffer 02 02 02 02 03 03 03 03>##5.1 buf.slice([start[, end]])Return a new Buffer instance from the buf instance. The returned new Buffer instance is only a reference to the source buf instance, that is, modifications to the newly returned instance will affect the original Buffer instance
Parameters ：
import { Buffer } from 'buffer';
const buf1 = Buffer.alloc(10, 2);
// 截取
const buf2 = buf1.slice(1,4);
// 截取部分修改
buf2[0] = 0x63;
console.log(buf1);
// <Buffer 02 63 02 02 02 02 02 02 02 02>
console.log(buf2);
// <Buffer 63 02 02>6.1 buf.fill(value[, offset[, end]][, encoding])
参数：
import { Buffer } from 'buffer';
const buf1 = Buffer.allocUnsafe(8).fill(2);
console.log(buf1);
// <Buffer 02 02 02 02 02 02 02 02>6.2 buf.write(string[, offset[, length]][, encoding])
根据 encoding 中的字符编码将 string 写入 buf 的 offset 处。
注意：length 参数是要写入的字节数。 如果 buf 没有足够的空间来容纳整个字符串，则只会写入 string 的一部分
参数：
import { Buffer } from 'buffer';
// buf1 length为12
const buf1 = Buffer.alloc(12, 3);
// write offset大于buf1.length,写入无效
buf1.write('hello', 12);
console.log(buf1);
// <Buffer 03 03 03 03 03 03 03 03 03 03 03 03>
// 部分写入
buf1.write('hello', 10);
// <Buffer 03 03 03 03 03 03 03 03 03 03 68 65>7.1 Buffer.isBuffer(obj)
检验传入obj是否为buffer
import { Buffer } from 'buffer';
const buf1 = Buffer.alloc(12, 3);
console.log(Buffer.isBuffer(buf1));
// true7.2 Buffer.isEncoding(encoding)
检查传入的编码名称是否被Buffer所支持
import { Buffer } from 'buffer';
console.log(Buffer.isEncoding('utf-8'))
// trueBuffer转String
8.1 buf.toString([encoding[, start[, end]]])
参数：
import { Buffer } from 'buffer';
const buf1 = Buffer.allocUnsafe(26)
for (let i = 0; i < 26; i++) {
// 97 是 'a' 的十进制 ASCII 值。
buf1[i] = i + 97;
}
console.log(buf1.toString())
// abcdefghijklmnopqrstuvwxyzString转Buffer
8.2 Buffer.from(string[, encoding])
参数：
import { Buffer } from 'buffer';
const buf = Buffer.from('hello buffer');
console.log(buf);
// <Buffer 68 65 6c 6c 6f 20 62 75 66 66 65 72>9.1 与Array类似点
9.2 与Array不同之处
更多node相关知识，请访问：nodejs 教程！！
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