Node.js Buffer

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

But when dealing with TCP streams 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. . Raw data is stored in instances of the Buffer class. A Buffer is similar to an integer array, but it corresponds to a piece of raw memory outside of 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 through a string:

var buf = new Buffer("www.php.cn", "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, default is buffer.length

• encoding - The encoding to use. 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("www.php.cn");

console.log("写入字节数 : "+  len);

Execute the above code, the output result is:

$node main.js
写入字节数 : 14

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 used. 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('ascii'));       // 输出: abcdefghijklmnopqrstuvwxyz
console.log( buf.toString('ascii',0,5));   // 输出: abcde
console.log( buf.toString('utf8',0,5));    // 输出: abcde
console.log( buf.toString(undefined,0,5)); // 使用 'utf8' 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('www.php.cn');
var json = buf.toJSON(buf);

console.log(json);

Execute the above code, the output result is:

[ 119, 119, 119, 46, 114, 117, 110, 111, 111, 98, 46, 99, 111, 109 ]

Buffer merge

Syntax

Node buffer The syntax of zone merging is as follows:

Buffer.concat(list[, totalLength])

Parameters

The parameters are described as follows:

• list - Array list of Buffer objects used for merging.

• totalLength - Specifies the total length of the merged Buffer object.

Return value

Returns a new Buffer object that combines multiple members.

Example

var buffer1 = new Buffer('php中文网 ');
var buffer2 = new Buffer('www.php.cn');
var buffer3 = Buffer.concat([buffer1,buffer2]);
console.log("buffer3 内容: " + buffer3.toString());

Execute the above code, the output result is:

buffer3 内容: php中文网 www.php.cn

Buffer comparison

Syntax

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

buf.compare(otherBuffer);

Parameters

The parameters are described as follows:

• otherBuffer - Another Buffer object compared to 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 The area copy syntax is as follows:

buf.copy(targetBuffer[, 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

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());

buffer2 content: ABC

buf.slice([start[, end]])

• start - number, optional, default: 0

• end - number, optional, default: buffer.length

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

buffer2 content: ru

buf.length;

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

buffer length: 14

var b = new Buffer(6);
b.writeUIntBE(0x1234567890ab, 0, 6);
// <Buffer 12 34 56 78 90 ab>