A closer look at Buffers in Node.js

This article will give you an in-depth understanding of Buffer (buffer) in Node.js. It will introduce various ways to create the Buffer class, methods of writing to the buffer, etc. I hope it will be useful to everyone. Helped!

#The JavaScript language itself only has string data types, not binary data types.

But when processing streams like TCP or file streams, binary data must be used. Therefore, in Node.js, a Buffer class is defined, which is used to create a buffer area specifically for storing binary data.

In Node.js, the Buffer class is a core library released with the Node kernel. The Buffer library brings a method of storing raw data to Node.js, allowing Node.js to process binary data. Whenever you need to process data moved during I/O operations in Node.js, it is possible to use the Buffer library .

The original data is stored in an instance of the Buffer class.

A Buffer is similar to an integer array, but it corresponds to a piece of original memory outside the V8 heap memory.

Creating the Buffer class

The Node Buffer class can be created in a variety of ways.

Method 1

Create a Buffer instance with a length of 10 bytes:

var buf = new Buffer(10);

Method 2

Create a Buffer instance from the given array:

var buf = new Buffer([10, 20, 30, 40, 50]);

Method 3

Create a Buffer instance from a string:

var buf = new Buffer("bianchengsanmei", "utf-8");

utf-8 is the default encoding, and it also supports the following encodings: "ascii", "utf8", "utf16le", "ucs2", "base64" and "hex".

Write buffer

Syntax

The syntax for writing Node buffer is as follows:

buf.write(string[, offset[, length]][, encoding])

Parameters

The parameters are described as follows:

• string - The string written to the buffer.
• offset - The index value at which the buffer starts to be written, default is 0.
• length - Number of bytes written, defaults to buffer.length
• encoding - Encoding used. Defaults to 'utf8' .

Return value

Returns the actual written size. If there is insufficient buffer space, only part of the string will be written.
Example

buf = new Buffer(256);
len = buf.write("bi");
len = buf.write("bianchengsanmei"); 
console.log("写入字节数 : "+  len);

Execute the above code, the output result is:

$node main.js
写入字节数 : 15

Read data from the buffer

Syntax

The syntax for reading Node buffer data is as follows:

buf.toString([encoding[,start[,end]]])

Parameters

The parameters are described as follows:

• encoding - the encoding to use. Defaults to 'utf8' .

• start - Specifies the index position to start reading, default is 0.

• end - End position, defaults to the end of the buffer.

Return Value

Decode the buffer data and return a string using the specified encoding.

Example

buf = new Buffer(26);
for (var i = 0 ; i < 26 ; i++) {
  buf[i] = i + 97;
}
 
console.log( buf.toString(&#39;ascii&#39;));       // 输出: abcdefghijklmnopqrstuvwxyz
console.log( buf.toString(&#39;ascii&#39;,0,5));   // 输出: abcde
console.log( buf.toString(&#39;utf8&#39;,0,5));    // 输出: abcde
console.log( buf.toString(undefined,0,5)); // 使用 &#39;utf8&#39; 编码, 并输出: abcde

Execute the above code, the output result is:

$ node main.js
abcdefghijklmnopqrstuvwxyz
abcde
abcde
abcde

Convert Buffer to JSON object

Syntax

The function syntax format for converting Node Buffer to JSON object is as follows:

buf.toJSON()

Return value

Returns JSON object.

Example

var buf = new Buffer('bianchengsanmei');
var json = buf.toJSON(buf);
 
console.log(json);

Execute the above code, the output result is:

{
  type: 'Buffer',
  data: [
     98, 105, 97, 110, 99, 104, 101, 110, 103, 115, 97, 110, 109, 101, 105
  ]
}

Buffer merge

Syntax

The syntax of Node buffer merging is as follows:

Buffer.concat(list[, totalLength])

Parameters

The parameters are described as follows:

• list - an array list of Buffer objects used for merging.
• totalLength - Specifies the total length of the combined Buffer objects.

Return value

Returns a new Buffer object that combines multiple members.

Example

var buffer1 = new Buffer('编程三昧 ');
var buffer2 = new Buffer('bi');
var buffer2 = new Buffer('bianchengsanmei');
var buffer3 = Buffer.concat([buffer1,buffer2]);
console.log("buffer3 内容: " + buffer3.toString());

Execute the above code, the output result is:

buffer3 内容: 编程三昧 bianchengsanmei

Buffer comparison

Syntax

The function syntax of Node Buffer comparison is as follows. This method was introduced in Node.js v0.12.2 version:

buf.compare(otherBuffer);

Parameters

Parameters The description is as follows:

• otherBuffer - Another Buffer object compared with the buf object.

Return Value

Returns a number indicating that buf is before, after, or the same as otherBuffer.

Example

var buffer1 = new Buffer('ABC');
var buffer2 = new Buffer('ABCD');
var result = buffer1.compare(buffer2);
 
if(result < 0) {
   console.log(buffer1 + " 在 " + buffer2 + "之前");
}else if(result == 0){
   console.log(buffer1 + " 与 " + buffer2 + "相同");
}else {
   console.log(buffer1 + " 在 " + buffer2 + "之后");
}

Execute the above code, the output result is:

ABC在ABCD之前

Copy buffer

Syntax

Node buffer copy syntax is as follows:

buf.copy(target[, targetStart[, sourceStart[, sourceEnd]]])

Parameters

The parameters are described as follows:

• targetBuffer - The Buffer object to be copied.
• targetStart - number, optional, default: 0
• sourceStart - number, optional, default: 0
• sourceEnd - number, optional, default: buffer.length

Return value

No return value.

Example

var buffer1 = new Buffer('ABC');
// 拷贝一个缓冲区
var buffer2 = new Buffer(3);
buffer1.copy(buffer2);
console.log("buffer2 content: " + buffer2.toString());

Execute the above code, the output result is:

buffer2 content: ABC

缓冲区裁剪

Node 缓冲区裁剪语法如下所示：

buf.slice([start[, end]])

参数

参数描述如下：

• start - 数字, 可选, 默认: 0
• end - 数字, 可选, 默认: buffer.length

返回值

返回一个新的缓冲区，它和旧缓冲区指向同一块内存，但是从索引 start 到 end 的位置剪切。

实例

var buffer1 = new Buffer('youj');
// 剪切缓冲区
var buffer2 = buffer1.slice(0,2);
console.log("buffer2 content: " + buffer2.toString());

执行以上代码，输出结果为：

buffer2 content: yo

缓冲区长度

语法 Node 缓冲区长度计算语法如下所示：

buf.length;

返回值

返回 Buffer 对象所占据的内存长度。

实例

var buffer = new Buffer('bianchengsanmei');
//  缓冲区长度
console.log("buffer length: " + buffer.length);

执行以上代码，输出结果为：

buffer length: 15

~

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