node. JS Cache

node. js buffer (buffer)

The JavaScript language itself has only a string data type and no binary data type.

However, when processing a TCP stream or file stream, you must use the binary data. Therefore, in node. js, a buffer class is defined that is used to create a buffer that is dedicated to storing the binary data.

In node. js, the Buffer class is the core library that is published with the Node kernel. The buffer library provides a way for node. JS to store the raw data, allowing node. js to process the binary data, possibly using the buffer library whenever data moved in the I/O operation needs to be handled in node. js. The raw data is stored in an instance of the Buffer class. A Buffer is similar to an array of integers, but it corresponds to a piece of raw memory outside of the V8 heap memory.

Buffer and character encoding

A Buffer instance is typically used to represent a sequence of encoded characters, such as UTF-8, UCS2, Base64, or hexadecimal encoded data. By using an explicit character encoding, you can convert a Buffer instance to a normal JavaScript string.

Const BUF = buffer.from (' Runoob ', ' ASCII ');//Output 72756e6f6f62console.log (buf.tostring (' hex '));//Output CnVub29iconsole.log (buf.tostring (' base64 '));

　　

The character encodings currently supported by node. JS include:

• ASCII -supports only 7-bit ASCII data. This encoding is very fast if the setting is removed from the high.

• UTF8 -multibyte-encoded Unicode characters. Many web pages and other document formats use UTF-8.

• Utf16le -2 or 4 bytes, a small-endian encoded Unicode character. Support for proxy pairs (u+10000 to U+10FFFF).

• Alias of UCS2 - utf16le .

• Base64 -Base64 encoding.

• latin1 -a way to encode Buffer into a byte-encoded string.

• binary -the alias of the latin1 .

• Hex -encodes each byte as a two hexadecimal character.

Convert Buffer to JSON object syntax

The function syntax for converting Node Buffer to a JSON object is formatted as follows:

BUF.  ToJSON()  

When a Buffer instance is serialized, Json.stringify () implicitly invokes the ToJSON ().

return value

Returns a JSON object.

Instance

Const BUF = Buffer.from ([0x1, 0x2, 0x3, 0x4, 0x5]); Const JSON = json.stringify (BUF);//output: {"type": "Buffer", "Data": [N/A, 4,5]}console.log (JSON); const COPY = Json.parse (JSON, (key, value) + {  return value && value.type = = = Buff Er '?    Buffer.from (value.data):    value;}); /output: <buffer 05>console.log (copy);

　　

Execute the above code and the output is:

{"type": "Buffer", "Data": [1,2,3,4,5]}<buffer 05>

　　

Buffer clipping

The Node buffer clipping syntax is as follows:

BUF.  Slice([start[,end]])      

Parameters

The parameters are described as follows:

• Start -number, optional, default: 0

• End -number, optional, default: Buffer.length

return value

Returns a new buffer that points to the same piece of memory as the old buffer, but cuts from the index start to end.

Instance

var buffer1 = buffer.from (' Runoob ');//shear buffer var buffer2 = Buffer1.slice (0,2); Console.log ("Buffer2 content:" + buffer2.to String ());

　　

Execute the above code and the output is:

Buffer2 Content:ru

　　

The clipping function returns the actual buffer or part of the original buffer, which operates in the same memory area as the original buffer.

Crop var buffer_origin = buffer.from (' Runoob '), var buffer_slice = Buffer_origin.slice (0,2); Console.log ("Buffer slice Content: "+buffer_slice.tostring ()"); Console.log ("Buffer origin content:" +buffer_origin.tostring ()); Buffer_ Slice.write ("Wirte"); Write buffer slice//before cropping with the original string change Console.log ("Buffer slice content:" +buffer_slice.tostring ()); Console.log ("Buffer Origin content: "+buffer_origin.tostring ()");

　　

Output:

Buffer Slice Content:rubuffer origin Content:runoobbuffer slice Content:wibuffer origin Content:winoob

　　

You can see that the write operation returned to the crop  is also written to the original . 

Excerpt from: http://www.runoob.com/nodejs/nodejs-buffer.html

node. JS Cache