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08_Buffers.md

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Buffers in Node.js

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() 은 쓰여진 octet 의 수를 return 한다

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

: toString은 encoding 된 buffer data를 지정한 character set으로 return 한다!

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

: Buffer instance를 JSON 형식으로 return 한다!


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()은 Buffer instance를 return 한다


ex)

buffer_concat.js

var buffer1 = new Buffer('지금은 저녁 11시 ');
var buffer2 = new Buffer('배가 고프다');
var buffer3 = Buffer.concat([buffer1,buffer2]);

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

Result

$ node buffer_concat.js 
buffer3 content: 지금은 저녁 11시 배가 고프다


Compare Buffers


Syntax

buf.compare(otherBuffer);

Parameters

  • otherBuffer
    • 위의 syntax 예시에서 buf와 비교할 다른 buffer

Return Value

  • buf과 otherBuffer를 비교할 때
    • 같으면 return 0
    • sort 한 후 otherBuffer 가 buf 보다 더 앞에 오면 1
    • sort 한 후 otherBuffer 가 buf 보다 더 뒤에 오면 -1

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

: return 값 없음~!


ex)

buffer_copy.js

var buffer1 = new Buffer('몇시에 잘까?');

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

Result

$ node buffer_copy.js 
buffer2 content: 몇시에 잘까?


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