@substrate-system/bencode

bencode

A library for encoding and decoding bencoded data, according to the BitTorrent specification.

Contents

• About BEncoding
• Install
• Usage
  • Encoding
  • Decoding
• API
  • bencode.encode( data, [buffer], [offset] )
  • bencode.decode( data, [start], [end], [encoding] )
  • bencode.byteLength( value ) or bencode.encodingLength( value )

About BEncoding

from Wikipedia:

Bencode (pronounced like B encode) is the encoding used by the peer-to-peer file sharing system BitTorrent for storing and transmitting loosely structured data.

It supports four different types of values:

• byte strings
• integers
• lists
• dictionaries

Bencoding is most commonly used in torrent files. These metadata files are simply bencoded dictionaries.

Install

npm i -S @substrate-system/bencode

Usage

import bencode from '@substrate-system/bencode'

Encoding

const data = {
  string: 'Hello World',
  integer: 12345,
  dict: {
    key: 'This is a string within a dictionary'
  },
  list: [ 1, 2, 3, 4, 'string', 5, {} ]
}

const result = bencode.encode( data )

[!NOTE]
As of bencode@0.8.0, boolean values will be cast to integers (false -> 0, true -> 1).

Output

d4:dictd3:key36:This is a string within a dictionarye7:integeri12345e4:listli1ei2ei3ei4e6:stringi5edee6:string11:Hello Worlde

Decoding

import bencode from '@substrate-system/bencode'

var const = Buffer.from('d6:string11:Hello World7:integeri12345e4:dictd3:key36:This is a string within a dictionarye4:listli1ei2ei3ei4e6:stringi5edeee')
const result = bencode.decode(data)

Output

{
  string: <Buffer 48 65 6c 6c 6f 20 57 6f 72 6c 64>,
  integer: 12345,
  dict: {
    key: <Buffer 54 68 69 73 20 69 73 20 61 20 73 74 72 69 6e 67 20 77 69 74 68 69 6e 20 61 20 64 69 63 74 69 6f 6e 61 72 79>
  },
  list: [ 1, 2, 3, 4, <Buffer 73 74 72 69 6e 67>, 5, {} ]
}

Automagically convert bytestrings to strings:

const result = bencode.decode(data, 'utf8')

Output

{
  string: 'Hello World',
  integer: 12345,
  dict: {
    key: 'This is a string within a dictionary'
  },
  list: [ 1, 2, 3, 4, 'string', 5, {} ]
}

API

The API is compatible with the abstract-encoding specification.

bencode.encode( data, [buffer], [offset] )

function encode (
    data?:TypedArray|any[]|string|number|boolean|object|null,
    buffer?:Uint8Array,
    offset?:number
):Uint8Array|null

Returns Uint8Array.

bencode.decode( data, [start], [end], [encoding] )

type Decoded =
    | Record<string, any>
    | Array<any>
    | Uint8Array
    | string
    | number
    | null;

interface Decoder {
    (data:Uint8Array|string):Decoded
    (data:Uint8Array|string, encoding:string):Decoded
    (data:Uint8Array|string, start:number, encoding:string):Decoded
    (data:Uint8Array|string, start:number, end:number, encoding:string):Decoded
    data:Uint8Array|null;
    bytes;
    position:number;
    encoding:string|null;
    next:()=>any;
    dictionary:()=>any;
    list:()=>any;
    buffer:()=>Uint8Array|string;
    find:(ch:number)=>number|null;
    integer:()=>number;
}

const decode:Decoder = function decode (
    data:Uint8Array|string,
    start?:number|string,
    end?:number|string,
    encoding?:string
):Decoded

If encoding is set, bytestrings are automatically converted to strings.

Returns Object | Array | Buffer | String | Number

bencode.byteLength( value ) or bencode.encodingLength( value )

Buffer | Array | String | Object | Number | Boolean value