About Buffer in Node.js

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

But when dealing with 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 dedicated to storing binary data.

In Node.js, the Buffer class is the core library that ships with the Node kernel. The Buffer library brings to Node.js a way to store raw data, allowing Node.js to work with binary data, it is possible to use the Buffer library whenever data moving in I/O operations needs to be processed in Node.js .

Raw data is stored in an instance of the Buffer class.

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

Create the Buffer class

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

Method 1

Create a Buffer instance of length 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 to a Node buffer is as follows:

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

parameter

The parameters are described as follows:

• string - String to write to buffer.
• offset - The index value at which to start writing to the buffer, defaults to 0.
• length - number of bytes written, default is buffer.length
• encoding - The encoding used. Defaults to 'utf8'.

return value

Returns the size actually written. If the buffer space is insufficient, only part of the string will be written.
instance

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 buffer

Syntax

The syntax for reading Node buffer data is as follows:

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

parameter

The parameters are described as follows:

• encoding - the encoding to use. Defaults to 'utf8'.
• start - Specifies the index position to start reading, defaults to 0.
• end - the end position, defaults to the end of the buffer.

return value

Decodes buffer data and returns a string using 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

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 a JSON object.

instance

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

Execute the above code, the output result is:

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

buffer merge

Syntax

The syntax for Node buffer coalescing is as follows:

Buffer.concat(list[, totalLength])

parameter

The parameters are described as follows:

• list - a list of arrays of Buffer objects to merge.
• totalLength - Specifies the total length of the merged Buffer objects.

return value

Returns a new Buffer object with multiple members merged.

instance

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 for Node Buffer comparison is as follows, which was introduced in Node.js v0.12.2:

buf.compare(otherBuffer);

parameter

The parameters are described as follows:

• otherBuffer - Another Buffer object to compare with the buf

return value

Returns a number representing buf in otherBuffer before, or after 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");
}

Execute the above code, the output result is:

ABC在ABCD之前

copy buffer

Syntax

The Node buffer copy syntax is as follows:

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

parameter

The parameters are described as follows:

• targetBuffer - the Buffer object to copy.
• targetStart - number, optional, default: 0
• sourceStart - number, optional, default: 0
• sourceEnd - number, optional, default: buffer.length

return value

There is no return value.

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());

Execute the above code, the output result is:

buffer2 content: ABC

buffer clipping

The Node buffer clipping syntax is as follows:

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

parameter

The parameters are described as follows:

• start - number, optional, default: 0
• end - number, optional, default: buffer.length

return value

Returns a new buffer that points to the same memory as the old buffer, but is cut from index start 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());

Execute the above code, the output result is:

buffer2 content: yo

buffer length

syntax Node Buffer length calculation syntax is as follows:

buf.length;

return value

Returns the length of memory occupied by the Buffer object.

instance

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

Execute the above code, the output result is:

buffer length: 15

~

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