Buffers

Pure JavaScript is Unicode friendly, but it is not so for binary data.

While dealing with TCP streams or the file system, it's necessary to handle octet streams.

• Node provides Buffer class which provides instances to store raw data similar to an array of integers but corresponds to a raw memory allocation outside the V8 heap.

• Buffer class is a global class that can be accessed in an application without importing the buffer module

1. Creating Buffers

Node Buffer can be constructed in a variety of ways!

Method 1

var buf = new Buffer(10);

• Create an uninitiated Buffer of 10 octets

Method 2

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

• Create a Buffer from a given array

Method 3

var buf = new Buffer('Strin')

• Create a Buffer from a given string and optionally encoding type

2. Writing to Buffers

Syntax

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

Parameters

• string

  • string data to be written to buffer

• offset

  • index of the buffer to start writing at

  • default value is 0

• length

  • number of bytes to write

  • defaults to buffer.length

• encoding

  • encoding to use

  • default is utf8

Return Value

: .write() returns the number of octets written

ex)

buffer_write.js

buf = new Buffer(256);
len = buf.write("Buffer write method test~! ^____^")

console.log("Octets written : "+ len);

Result

$ node buffer_write.js
Octets written : 33
(node:20416) [DEP0005] DeprecationWarning: Buffer() is deprecated due to security and usability issues. Please use the Buffer.alloc(), Buffer.allocUnsafe(), or Buffer.from() methods instead.

3. Reading from Buffers

Syntax

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

Parameters

• encoding

  • encoding to use

  • default is utf8

• start

  • beginning index to start reading

  • defaults is to 0

• end

  • end index to end reading

  • default is complete buffer

Return Value

: toString returns the encoded buffer data in the specified character set!

ex)

buffer_toString.js

buf = new Buffer(26);
for (var i = 0 ; i < 26 ; i++) {
  buf[i] = i + 97;
}

console.log( buf.toString('ascii'));       // outputs: abcdefghijklmnopqrstuvwxyz
console.log( buf.toString('ascii',0,5));   // outputs: abcde
console.log( buf.toString('utf8',0,5));    // outputs: abcde
console.log( buf.toString(undefined,0,5)); // encoding defaults to 'utf8', outputs abcde

4. Convert Buffer to JSON

Syntax

buf.toJSON()

Return Value

: Returns the Buffer instance in JSON format!

ex)

buffer_toJSON.js

var buf = new Buffer('Make it into JSON object');
var json = buf.toJSON(buf);

console.log(json);

result

$ node buffer_toJSON.js
{ type: 'Buffer',
  data:
   [ 77,
     97,
     107,
     101,
     32,
     105,
     116,
     32,
     105,
     110,
     116,
     111,
     32,
     74,
     83,
     79,
     78,
     32,
     111,
     98,
     106,
     101,
     99,
     116 ] }

5. Concatenate Buffers

Syntax

Buffer.concat(list[, totalLength])

Parameters

• list

  • Array List of Buffer objects to be concatenated.

• totalLength

  • This is the total length of the buffers when concatenated.

Return Value

: .concat() returns a Buffer instance

ex)

buffer_concat.js

var buffer1 = new Buffer('It is now 11 PM ');
var buffer2 = new Buffer('I am hungry');
var buffer3 = Buffer.concat([buffer1,buffer2]);

console.log("buffer3 content: " + buffer3.toString());

Result

$ node buffer_concat.js
buffer3 content: It is now 11 PM I am hungry

Compare Buffers

Syntax

buf.compare(otherBuffer);

Parameters

• otherBuffer

  • Another buffer to compare with buf in the syntax example above

Return Value

• When comparing buf and otherBuffer

  • Returns 0 if they are equal

  • Returns 1 if otherBuffer comes before buf after sorting

  • Returns -1 if otherBuffer comes after buf after sorting

ex)

buffer_compare.js

const buf1 = Buffer.from('ABC');
const buf2 = Buffer.from('BCD');
const buf3 = Buffer.from('ABCD');

console.log(buf1.compare(buf1));
// Prints: 0
console.log(buf1.compare(buf2));
// Prints: -1
console.log(buf1.compare(buf3));
// Prints: -1
console.log(buf2.compare(buf1));
// Prints: 1
console.log(buf2.compare(buf3));
// Prints: 1
console.log([buf1, buf2, buf3].sort(Buffer.compare));
// Prints: [ <Buffer 41 42 43>, <Buffer 41 42 43 44>, <Buffer 42 43 44> ]
// (This result is equal to: [buf1, buf3, buf2].)

Result

$ node buffer_compare.js
0
-1
-1
1
1
[ <Buffer 41 42 43>, <Buffer 41 42 43 44>, <Buffer 42 43 44> ]

Copy Buffer

Syntax

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

Parameters

• targetBuffer

  • Buffer object where buffer will be copied.

• targetStart

  • Number, Optional

  • Default: 0

• sourceStart

  • Number, Optional

  • Default: 0

• sourceEnd

  • Number, Optional

  • Default: buffer.length

Return Value

: No return value!

ex)

buffer_copy.js

var buffer1 = new Buffer('What time shall I sleep?');

//copy a buffer
var buffer2 = new Buffer(20);
buffer1.copy(buffer2);
console.log("buffer2 content: " + buffer2.toString());

Result

$ node buffer_copy.js
buffer2 content: What time shall I sleep?

Slice Buffer

Syntax

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

Parameters

• start − Number, Optional, Default: 0

• end − Number, Optional, Default: buffer.length

Return Value

Returns a new buffer which references the same memory as the old one, but offset and cropped by the start (defaults to 0) and end (defaults to buffer.length) indexes. Negative indexes start from the end of the buffer.

ex)

buffer_slice.js

var buffer1 = new Buffer('Slice this buffer');

//slicing a buffer
var buffer2 = buffer1.slice(0,10);
console.log("buffer2 content: " + buffer2.toString());

Result

$ node buffer_slice.js
buffer2 content: Slice this