What is Buffer in NodeJS and detailed explanation of usage examples

The so-called buffer Buffer means "temporary storage area", which is a section of memory that temporarily stores input and output data.

The JS language itself only has a string data type and no binary data type, so NodeJS provides a global constructor Buffer that is equivalent to String to provide operations on binary data. In addition to reading the file to get an instance of Buffer, it can also be constructed directly, for example:

　var buffer = new Buffer([ 0x68, 0x65, 0x6c, 0x6c, 0x6f ]) ;

Buffer is similar to a string. In addition to using the .length attribute to get the byte length, you can also use the [index] method. Read the bytes at the specified position, for example:

buffer[0] ; // 0x68;

Buffer and string can be converted to each other, for example, you can use the specified encoding to convert binary data into a string:

var str = buffer.toString("utf-8");  // hello

Convert the string to Binary data in the specified encoding:

var buffer= new Buffer("hello", "utf-8") ; // <Buffer 68 65 6c 6c 6f>

A little difference:

There is an important difference between Buffer and string. The string is read-only, and any modification to the string results in a new string, while the original string remains unchanged.

As for Buffer, it is more like a C language array that can perform pointer operations. For example, you can use the [index] method to directly modify the bytes at a certain position.

The slice method does not return a new Buffer, but more like returning a pointer to a position in the middle of the original Buffer, as shown below.

[ 0x68, 0x65, 0x6c, 0x6c, 0x6f ]
^ ^ ^
| bin bin.slice(2)
Therefore, modifications to the Buffer returned by the slice method will Acts on the original Buffer, for example:

 var buffer= new Buffer([ 0x68, 0x65, 0x6c, 0x6c, 0x6f ]) ;
 var sub = bin.slice(2) ;
 sub[0] = 0x65 ;
 console.log(buffer) ; //  <Buffer 68 65 65 6c 6f>

If you want to copy a Buffer, you must first create a new Buffer and copy the data in the original Buffer through the .copy method.

This is similar to applying for a new memory and copying the data in the existing memory. Below is an example.

var buffer= new Buffer([ 0x68, 0x65, 0x6c, 0x6c, 0x6f ]) ;
 var dup = new Buffer(bin.length) ;
 buffer.copy(dup) ;
 dup[0] = 0x48 ;
 console.log(buffer) ;  // <Buffer 68 65 6c 6c 6f>
 console.log(dup) ;  // <Buffer 48 65 65 6c 6f>

In short, Buffer extends the data processing capabilities of JS from strings to arbitrary binary data.

To summarize

(1), JavaScript is suitable for processing Unicode encoded data, but it is not friendly to the processing of binary data.

(2), so when processing TCP streams or file systems, it is necessary to process octet streams.
(3), Node has several methods for processing, creating and consuming octet streams.
(4), the original data is stored in a Buffer instance. A Buffer is similar to an integer array, but its memory is allocated outside the V8 stack. The size of a Buffer cannot be changed.
(5), the encoding types processed are: ascii, utf8, utf16le, ucs2 (alias of utf16le), base64, binary, hex.
(6), Buffer is a global element, and you can get a Buffer instance directly with new Buffer().

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