Node .js Buffer (Buffer)

Node .js Buffer (Buffer)

The JavaScript language itself has only string data types and no binary data types.

However, binary data must be used when working with streams like TCP or file. So in the node .js, a Buffer class is defined that creates a cache that holds binary data specifically.

In node .js, the Buffer class is the core library that is released with the Node kernel. T he Buffer library .js a way for Node.js to store raw data, allowing Node.js to process binary data, making it possible to use the Buffer library whenever you need to process data moved in an I/O operation in Node.js T he raw 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 raw memory outside of V8 heap memory.

Create a Buffer class

The Node Buffer class can be created in a number 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 a given array:

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

Method 3

Create a Buffer instance with a string:

var buf = new Buffer("www.w3cschool.cn", "utf-8");

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

Write to the buffer

Grammar

The syntax for writing to the Node buffer is as follows:

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

Parameters

The parameters are described as follows:

• String - A string written to the buffer.

• offset - The index value at which the buffer starts writing, which defaults to 0.

• length - The number of bytes written, which defaults to buffer.length

• encoding - the code used. The default is 'utf8'.

Returns a value

Returns the size of the actual write. If there is not enough space for buffer, only part of the string is written.

Instance

buf = new Buffer(256);
len = buf.write("www.w3cschool.cn");

console.log("写入字节数 : "+  len);

The above code is executed and the output is:

$node main.js
写入字节数 : 16

Read the data from the buffer

Grammar

The syntax for reading Node buffer data is as follows:

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

Parameters

The parameters are described as follows:

• encoding - the code used. The default is 'utf8'.

• Start - Specifies the index location where the reading begins, which defaults to 0.

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

Returns a value

Decode the buffer data and return the string with the specified encoding.

Instance

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

The above code is executed and the output is:

$ node main.js
abcdefghijklmnopqrstuvwxyz
abcde
abcde
abcde

Convert Buffer to a JSON object

Grammar

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

buf.toJSON()

Returns a value

Returns the JSON object.

Instance

var buf = new Buffer('www.w3cschool.cn');
var json = buf.toJSON(buf);

console.log(json);

The above code is executed and the output is:

{ type: 'Buffer',
  data: [ 119, 119, 119, 46, 119, 51, 99, 115, 99, 104, 111, 111, 108, 46, 99, 110 ] }

Buffer merge

Grammar

The syntax for node buffer merge is as follows:

Buffer.concat(list[, totalLength])

Parameters

The parameters are described as follows:

• List - An array of Buffer objects for consolidation.

• TotalLength - Specifies the total length of the merged Buffalo object.

Returns a value

Returns a new Buffer object that is merged by multiple members.

Instance

var buffer1 = new Buffer('W3Cschool教程 ');
var buffer2 = new Buffer('www.w3cschool.cn');
var buffer3 = Buffer.concat([buffer1,buffer2]);
console.log("buffer3 内容: " + buffer3.toString());

The above code is executed and the output is:

buffer3 内容: W3Cschool教程 www.w3cschool.cn

Buffer comparison

Grammar

The function syntax of the Node Buffer comparison is as follows, and the method .js in node v0.12.2:

buf.compare(otherBuffer);

Parameters

The parameters are described as follows:

• otherBuffer - another Buffer object compared to the buf object.

Returns a value

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

Instance

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");
}

The above code is executed and the output is:

ABC在ABCD之前

Copy buffer

Grammar

The Node buffer copy syntax looks like this:

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

Parameters

The parameters are described as follows:

• TargetBuffer - Buffer object to copy.

• TargetStart - number, optional, default: 0

• SourceStart - Digital, Optional, Default: 0

• SourceEnd - Digital, Optional, Default: buffer.length

Returns a value

No value was returned.

Instance

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());

The above code is executed and the output is:

buffer2 content: ABC

Buffer cropping

The Node buffer crop syntax looks like this:

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

Parameters

The parameters are described as follows:

• start - number, optional, default: 0

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

Returns a value

Returns a new buffer that points to the same piece of memory as the old buffer, but is cut from the position where the index starts to end.

Instance

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

The above code is executed and the output is:

buffer2 content: yo

The length of the buffer

Grammar

The Node buffer length calculation syntax is as follows:

buf.length;

Returns a value

Returns the length of memory occupied by the Buffer object.

Instance

var buffer = new Buffer('www.w3cschool.cn');
//  缓冲区长度
console.log("buffer length: " + buffer.length);

The above code is executed and the output is:

buffer length: 16

Method reference manual

The following are .js methods commonly used by Node and the Buffer module (note that some methods were not available in older versions):

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