About Node.js buffers

This is the 8th day of my participation in the First Challenge 2022. For details: First Challenge 2022.

preface

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

But when dealing with things like TCP streams or file streams, you must use binary data. Therefore, in Node.js, a Buffer class is defined to create a Buffer dedicated to binary data.

In Node.js, the Buffer class is the core library shipped with the Node kernel. The Buffer library gives Node.js a way to store raw data, allows Node.js to work with binary data, and is likely to be used whenever data needs to be moved during I/O operations in Node.js.

The 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 block of raw memory outside of V8 heap memory.

Create the Buffer class

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

Method 1

Create a Buffer with a length of 10 bytes:

var buf = new Buffer(10);
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Method 2

Create a Buffer instance from the given array:

var buf = new Buffer([10.20.30.40.50]);
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Methods 3

Create a Buffer instance from a string:

var buf = new Buffer("bianchengsanmei"."utf-8");
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Utf-8 is the default encoding, but it also supports “ASCII “,” UTF8 “, “UTF16LE “,” UCS2 “, “base64”, and “HEX”.

Write buffer

grammar

The syntax for writing to the Node buffer looks like this:

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

The parameters are described as follows:

• String – A string written to the buffer.
• Offset – The index at which the buffer starts writing. The default value is 0.
• Length – Number of bytes to be written. The default is buffer.length
• Encoding – Specifies the encoding used. The default is ‘utf8’.

The return value

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

buf = new Buffer(256);
len = buf.write("bi");
len = buf.write("bianchengsanmei");
 
console.log("Bytes written:"+  len);
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Execute the above code and the output is:

$node main.js Number of bytes written:15
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Read data from the buffer

grammar

The syntax for reading Node buffer data looks like this:

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

The parameters are described as follows:

• Encoding – Specifies the encoding used. The default is ‘utf8’.

• Start – Specifies the index position to start reading. Default is 0.

• End – The end position, the default is the end of the buffer.

The return value

Decodes buffer data and returns a string using the specified encoding.

The instance

buf = new Buffer(26);
for (var i = 0 ; i < 26 ; i++) {
  buf[i] = i + 97;
}
 
console.log( buf.toString('ascii'));       / / output: abcdefghijklmnopqrstuvwxyz
console.log( buf.toString('ascii'.0.5));   // output: abcde
console.log( buf.toString('utf8'.0.5));    // output: abcde
console.log( buf.toString(undefined.0.5)); // Encode with 'utf8' and print: abcde
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Execute the above code and the output is:

$ node main.js
abcdefghijklmnopqrstuvwxyz
abcde
abcde
abcde
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Convert Buffer to JSON objects

grammar

The syntax of the Node Buffer function to convert a Node Buffer to a JSON object is as follows:

buf.toJSON()
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The return value

Returns a JSON object.

The instance

var buf = new Buffer('bianchengsanmei');
var json = buf.toJSON(buf);
 
console.log(json);
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Execute the above code and the output is:

{ type: 'Buffer'.data: [ 119.119.119.46.119.51.99.115.99.104.111.111.108.46.99.110]}Copy the code

Buffer merge

grammar

The syntax for Node buffer merging looks like this:

Buffer.concat(list[, totalLength])
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parameter

The parameters are described as follows:

• List – An array of Buffer objects used for merging.
• TotalLength – specifies the totalLength of the merged Buffer object.

The return value

Returns a new Buffer object whose members are merged.

The instance

var buffer1 = new Buffer(Programming samadhi);
var buffer2 = new Buffer('bi');
var buffer2 = new Buffer('bianchengsanmei');
var buffer3 = Buffer.concat([buffer1,buffer2]);
console.log("Buffer3 contents: + buffer3.toString());
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Execute the above code and the output is:

Buffer3 Content: Programming Samadhi BianchengsanmeiCopy the code

Buffer comparison

grammar

The syntax of the Node Buffer comparison function is shown below, which was introduced in Node.js v0.12.2:

buf.compare(otherBuffer);
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parameter

The parameters are described as follows:

• OtherBuffer – Another Buffer object compared to the BUF object.

The return value

Returns a number indicating that buF precedes, follows, or is the same as otherBuffer.

The instance

var buffer1 = new Buffer('ABC');
var buffer2 = new Buffer('ABCD');
var result = buffer1.compare(buffer2);
 
if(result < 0) {
   console.log(buffer1 + "In" + buffer2 + "Before");
}else if(result == 0) {console.log(buffer1 + " 与 " + buffer2 + "The same");
}else {
   console.log(buffer1 + "In" + buffer2 + "After");
}
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Execute the above code and the output is:

ABC comes before ABCDCopy the code

Copy buffer

grammar

The Node buffer copy syntax looks like this:

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

The return value

No return value.

The instance

var buffer1 = new Buffer('ABC');
// Copy a buffer
var buffer2 = new Buffer(3);
buffer1.copy(buffer2);
console.log("buffer2 content: " + buffer2.toString());
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Execute the above code and the output is:

buffer2 content: ABC
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Buffer clipping

The Node buffer clipping syntax looks like this:

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

The parameters are described as follows:

• Start – Optional number. Default: 0
• End – Number, optional, default: buffer.length

The return value

Returns a new buffer that points to the same block of memory as the old buffer but is clipped from index start to end.

The instance

var buffer1 = new Buffer('youj');
// Cut the buffer
var buffer2 = buffer1.slice(0.2);
console.log("buffer2 content: " + buffer2.toString());

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Execute the above code and the output is:

buffer2 content: yo
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Buffer length

Syntax Node buffer length calculation syntax looks like this:

buf.length;
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The return value

Returns the length of memory occupied by the Buffer object.

The instance

var buffer = new Buffer('bianchengsanmei');
// Buffer length
console.log("buffer length: " + buffer.length);
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Execute the above code and the output is:

buffer length: 15
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~

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