Node.js - Buffers

Node.js - Buffers

Pure JavaScript is friendly to Unicode, but for binary data this is not so. It is essential to handle octet streams while dealing with TCP streams or the file system. Node provides a buffer class that provides instances for storing raw data similar to an array of integers which corresponds to an allocation of raw memory outside the V8 heap.

Buffer class is a global class that can be accessed within an application without the buffer module being imported.

Creating Buffers

Node buffer can be developed in a number of ways.

Next is the syntax to construct a 10-byte uninitiated buffer-

var buf = new Buffer(10);

The syntax to create a buffer from a given array follows –

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

The syntax follows to construct a buffer from a given string and optionally encode type –

var buf = new Buffer("Simply Easy Learning", "utf-8");

Although "utf8" is the default encoding, you can use "ascii," "utf16le," "utf8," "ucs2," "base64" or "hex."

Writing to Buffers

The method to write to a Node Buffer is syntaxed below

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

Parameters Value

The description of the parameters used is here-

This method returns written octet numbers. If there is not enough space in the buffer to suit the whole string, a section of the string is written.

buf = new Buffer(256);
len = buf.write("Hello Phptpoint");
console.log("Octets written : "+  len);

Reading from Buffers

Following is the method syntax for reading data from a Node Buffer –

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

Parameter Values

This method decodes and returns a string from encoded buffer data using the encoding of the specified character set.

buf = new Buffer(22);
for (var i = 0 ; i < 22 ; i++) 
{
buf[i] = i + 97;
}
console.log( buf.toString('ascii'));    
console.log( buf.toString('ascii',0,5));   
console.log( buf.toString('utf8',0,5));   
console.log( buf.toString(undefined,0,5));

Convert Buffer to JSON

Following is the method syntax for converting a Node Buffer to JSON object –

buf.toJSON()

This method returns the Buffer instance a JSON-representation.

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

Concatenate Buffers

The method to concatenate node buffers to a single node buffer is syntaxed below.

Buffer.concat(list[, totalLength])

Parameter Value

The description of the parameters is used here-

This method returns an instance of a Buffer.

var buffer1 = new Buffer('Phptpoint ');
var buffer2 = new Buffer('Hello phptpoint');
var buffer3 = Buffer.concat([buffer1,buffer2]);
console.log("buffer3 content: " + buffer3.toString());

Compare Buffers

Following is the method syntax for comparing two Node buffers –

buf.compare(otherBuffer);

Parameter Values

The description of the parameters is used here-

Returns a number that indicates whether it is in sort order before or after, or is the same as the otherBuffer.

var buffer1 = new Buffer('WXY');
var buffer2 = new Buffer('WXYZ');
var result = buffer1.compare(buffer2);
if(result < 0) {
console.log(buffer1 +" comes before " + buffer2);
} else if(result === 0) {
console.log(buffer1 +" is same as " + buffer2);
} else {
console.log(buffer1 +" comes after " + buffer2);
}

Copy Buffer

The method for copying a node buffer is syntaxed below –

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

Parameter Values

The description of the parameters is used here-

No value for return. Copies data in the target buffer from a region of this buffer to a region even if the target memory region overlaps with the source. If undefined, the default parameters for targetStart and sourceStart are 0, while default to buffer.length is for sourceEnd.

var buffer1 = new Buffer('XYZ');
//copy a buffer
var buffer2 = new Buffer(3);
buffer1.copy(buffer2);
console.log("buffer2 content: " + buffer2.toString());\

Slice Buffer

Following is the method syntax for getting a node buffer sub-buffer –

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

Parameter Values

The description of the parameters is used here-

Returns a new buffer referring to the same memory as the old one but offsetting and cropped by the indexes start (defaults to 0) and end (defaults to buffer.length). Negative indexes start at buffer ends.

var buffer1 = new Buffer('Phptpoint');
//slicing a buffer
var buffer2 = buffer1.slice(0,9);
console.log("buffer2 content: " + buffer2.toString());

Buffer Length

The syntax of the method to get a node buffer size in bytes follows –

buf.length;

Returns in Bytes the size of a buffer

var buffer = new Buffer('phptpoint');
//length of the buffer
console.log("buffer length: " + buffer.length);

Class Methods