Node.js Buffer (buffer)

JavaScript language itself only string data types, no binary data type.

But when dealing with streams like TCP stream or file, you must use the binary data. Therefore, in Node.js, the definition of a Buffer class that is used to create a specialized storage buffer binary data.

In the Node.js, Buffer class is released together with the Node kernel core library. Buffer Node.js library brings a raw data storage method allows Node.js handle binary data, whenever you need to handle I / O operations to move data Node.js when it is possible to use Buffer library . The original data stored in the instance Buffer class. A Buffer is similar to an array of integers, but it corresponds to a raw memory outside the V8 heap.

Create Buffer class

Node Buffer class can be created in several ways.

method 1

Create instance a length of 10 bytes Buffer:

var buf = new Buffer(10);

Method 2

Through a given array creation Buffer Example:

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

Method 3

Create Buffer instance by a string:

var buf = new Buffer("www.w3big.com", "utf-8");

utf-8 is the default encoding, in addition it also supports the following encodings: "ascii", "utf8", "utf16le", "ucs2", "base64" and "hex".

Write buffer

grammar

Node write buffer syntax is as follows:

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

parameter

Parameters are described below:

• string - the string buffer is written.

• offset - the index buffer to start writing, the default is 0.

• length - the number of bytes written, by default buffer.length

• encoding - the encoding used.The default is 'utf8'.

return value

Returns the size of the actual writing. If the buffer space, the only portion of the string is written.

Examples

buf = new Buffer(256);
len = buf.write("www.w3big.com");

console.log("写入字节数 : "+  len);

Implementation of the above code, the output is:

$node main.js
写入字节数 : 14

Reads data from the buffer

grammar

Node read buffer data syntax is as follows:

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

parameter

Parameters are described below:

• encoding - the encoding used.The default is 'utf8'.

• start - start reading index position specified, the default is 0.

• end - the end position, the default is the end of the buffer.

return value

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

Examples

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

console.log( buf.toString('ascii'));       // 输出: abcdefghijklmnopqrstuvwxyz
console.log( buf.toString('ascii',0,5));   // 输出: abcde
console.log( buf.toString('utf8',0,5));    // 输出: abcde
console.log( buf.toString(undefined,0,5)); // 使用 'utf8' 编码, 并输出: abcde

Implementation of the above code, the output is:

$ node main.js
abcdefghijklmnopqrstuvwxyz
abcde
abcde
abcde

Buffer will be converted to a JSON object

grammar

The Node Buffer into JSON object function syntax is as follows:

buf.toJSON()

return value

Returns JSON object.

Examples

var buf = new Buffer('www.w3big.com');
var json = buf.toJSON(buf);

console.log(json);

Implementation of the above code, the output is:

[ 119, 119, 119, 46, 114, 117, 110, 111, 111, 98, 46, 99, 111, 109 ]

Buffer Merge

grammar

Node buffer combined syntax is as follows:

Buffer.concat(list[, totalLength])

parameter

Parameters are described below:

• list - an array of objects for Buffer combined list.

• totalLength - after a specified total combined length of the Buffer object.

return value

Return multiple members of a merged new Buffer object.

Examples

var buffer1 = new Buffer('本教程 ');
var buffer2 = new Buffer('www.w3big.com');
var buffer3 = Buffer.concat([buffer1,buffer2]);
console.log("buffer3 内容: " + buffer3.toString());

Implementation of the above code, the output is:

buffer3 内容: 本教程 www.w3big.com

Comparison buffer

grammar

Node Buffer compare function syntax is as follows, the method introduced in Node.js v0.12.2 version:

buf.compare(otherBuffer);

parameter

Parameters are described below:

• otherBuffer - compared with bufBuffer objects to another object.

return value

It returns a number that representsbuf before otherBuffer,or after the same.

Examples

var buffer1 = new Buffer('ABC');
var buffer2 = new Buffer('ABCD');
var result = buffer1.compare(buffer2);

if(result < 0) {
   console.log(buffer1 + " 在 " + buffer2 + "之前");
}else if(result == 0){
   console.log(buffer1 + " 与 " + buffer2 + "相同");
}else {
   console.log(buffer1 + " 在 " + buffer2 + "之后");
}

Implementation of the above code, the output is:

ABC在ABCD之前

Copy buffer

grammar

Node buffer copy syntax is as follows:

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

parameter

Parameters are described below:

• targetBuffer - Buffer objects you want to copy.

• targetStart - digital, optional, default: 0

• sourceStart - digital, optional, default: 0

• sourceEnd - digital, optional, default: buffer.length

return value

No return value.

Examples

var buffer1 = new Buffer('ABC');
// 拷贝一个缓冲区
var buffer2 = new Buffer(3);
buffer1.copy(buffer2);
console.log("buffer2 content: " + buffer2.toString());

Implementation of the above code, the output is:

buffer2 content: ABC

Crop Buffer

Node buffer crop syntax is as follows:

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

parameter

Parameters are described below:

• start - numbers, optional, default: 0

• end - digital, optional, default: buffer.length

return value

Returns a new buffer, it is old and point to the same piece of memory buffer, but start from the index to the location of the cut end.

Examples

var buffer1 = new Buffer('w3big');
// 剪切缓冲区
var buffer2 = buffer1.slice(0,2);
console.log("buffer2 content: " + buffer2.toString());

Implementation of the above code, the output is:

buffer2 content: ru

Buffer length

grammar

Node buffer length calculation syntax is as follows:

buf.length;

return value

Back Buffer memory occupied by the object length.

Examples

var buffer = new Buffer('www.w3big.com');
//  缓冲区长度
console.log("buffer length: " + buffer.length);

Implementation of the above code, the output is:

buffer length: 14

Method Reference Manual

Following is a list Node.js Buffer module commonly used method (Note that some methods in the old version is not):

var b = new Buffer(6);
b.writeUIntBE(0x1234567890ab, 0, 6);
// <Buffer 12 34 56 78 90 ab>