Node3-2 base API ---- Buffer (buffer)

Buffer (buffer)

Buffer for processing the binary data stream
Examples of similar integer array, a fixed size (after instantiation, is how much it can not be changed)
C ++ code in physical memory allocation of foreign V8
Buffer is a global variable, no need to require the use of references

// Common a predetermined length, the default is filled with zeros 
the console.log (Buffer.alloc (10 )); 
the console.log (Buffer.alloc ( 20 is ));
 // with 2 filled 
console.log (Buffer.alloc (5, 2 ));
 // create a length of 5, uninitialized Buffer. This method than calling Buffer.alloc () faster, 
// but Buffer returned instance may contain old data, so need to use fill () or write () rewritten. 
the console.log (Buffer.allocUnsafe (5,2 )); 
the console.log (Buffer.from ([ l, 2,3 ])); 
the console.log (Buffer.from ( 'Test' ));
 // specified encoding 
console.log (Buffer.from ( 'test', 'base64'));

operation result

Static properties and methods (Buffer own class attributes and methods) [common]

Buffer.byteLength & Buffer.isBuffer() & Buffer.concat()

// 实际占了几个字节
console.log(Buffer.byteLength('test'));
//一个中文三个字节
console.log(Buffer.byteLength('测试'));

console.log(Buffer.isBuffer({}));
console.log(Buffer.isBuffer(Buffer.from([1,2,3])));

const buf1 = Buffer.from('This')
const buf2 = Buffer.from(' is ')
const buf3 = Buffer.from('a ')
const buf4 = Buffer.from('test ')
const buf5 = Buffer.from('!')

const buf = Buffer.concat([buf1,buf2,buf3,buf4,buf5])
console.log(buf.toString());

operation result:

Examples of common attributes and methods (six kinds)

buf.length buf.toString() buf.fill()

buf.equals() buf.indexOf() buf.copy()

// 1.buf.length      
const Buffer.from buf = ( 'Test A This IS!' ) 
The console.log (to buf.length); // 15 
const = BUF2 Buffer.alloc (10 ); 
const buf3 = Buffer.allocUnsafe (10); // default is not filled 
BUF2 [0] = 2 // demonstrated below, even if the default is not filled, but the length is controlled according to the size of your start created, regardless of the contents is not filled with filling 
console.log (buf2. length); // 10 
the console.log (buf3.length); // 10 // 2.buf.toString () 
the console.log (buf.toString ()); // default. 8 This IS-A UTF Test 
Console. log (buf.toString ( 'Base64')); // VGhpcyBpcyBhIHRlc3Qh //





3.buf.fill () alloc 0 are populated automatically, but can fill () to fill another value 
const = buf4 is Buffer.allocUnsafe (10 ) 
the console.log (buf4 is); 
the console.log (buf4.fill ( 10, 2,6)); // fill (filled image content, where to start, where to end) 


// 4.buf.equals () Buffer two contents are equal 
const = BUF5 Buffer.from ( 'Test' ) 
buf6 const   = Buffer.from ( 'Test' ) 
const buf7   = Buffer.from ( 'Test!' ) 

the console.log (buf5.equals (buf6)); // to true 
the console.log (buf5.equals (buf7)); // to false 

// 5.buf.indexOf () Test = BUF5 
the console.log (buf5.indexOf ( 'S')); // find the location of the index returns (starting from 0)
the console.log (buf5.indexOf ( 'A')); // can not find it returns -1 

// 6.buf.copy () 
const = BUF8 Buffer.allocUnsafe (10) .fill ( '*' ) 
const buf9 Buffer.allocUnsafe = (10) .fill ( '!' )
 // copy 'buf8' to the first data byte 3-6 'buf9' fourth offset start 
buf8.copy (buf9,4,3,6 ) 
console.log (buf9.toString ()); // !!!! *** !!!

// garbled

const StringDecoder = require('string_decoder').StringDecoder

// decoder Custom

const decoder = new StringDecoder('utf8')

const buf = Buffer.from ( 'Chinese string!');

for(let i =0 ;i<buf.length ; i+=5){

const b = Buffer.allocUnsafe(5)

buf.copy(b,0,i)

console.log (b.toString ()); // distortion

}

for(let i =0 ;i<buf.length ; i+=5){

const b = Buffer.allocUnsafe(5)

buf.copy(b,0,i)

// print with a decoder to determine the content of print

console.log (decoder.write (b)); // no distortion

}

// decoder does not realize that they deal with Chinese (byte width),

Node3-2 base API ---- Buffer (buffer)

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