Bencode Parser

A lightweight JavaScript library for encoding and decoding Bencode format. Bencode is the encoding used by the BitTorrent protocol for storing and transmitting loosely structured data.

Features

• ✅ Full Bencode support (integers, strings, lists, dictionaries)
• ✅ Simple and intuitive API
• ✅ Zero dependencies
• ✅ ES6 module support
• ✅ Bidirectional conversion (encode & decode)

Installation

Clone or download this repository:

git clone https://github.com/VrajVed/Bencode-Parser.git
cd Bencode-Parser

Usage

Importing

import BencodeParser from './bencoder.js';

Encoding

Convert JavaScript values to Bencode format:

// Encode an integer
BencodeParser.encode(42);
// Output: 'i42e'

// Encode a string
BencodeParser.encode('spam');
// Output: '4:spam'

// Encode an array
BencodeParser.encode([1, 2, 3]);
// Output: 'li1ei2ei3ee'

// Encode an object
BencodeParser.encode({ key: 'value' });
// Output: 'd3:key5:valuee'

// Encode nested structures
BencodeParser.encode({ 
  name: 'example', 
  size: 1024, 
  files: ['file1.txt', 'file2.txt'] 
});
// Output: 'd5:filesli9:file1.txti9:file2.txtee4:name7:example4:sizei1024ee'

Decoding

Convert Bencode strings back to JavaScript:

// Decode an integer
BencodeParser.decode('i42e');
// Output: 42

// Decode a string
BencodeParser.decode('4:spam');
// Output: 'spam'

// Decode a list
BencodeParser.decode('li1ei2ei3ee');
// Output: [1, 2, 3]

// Decode a dictionary
BencodeParser.decode('d3:key5:valuee');
// Output: { key: 'value' }

Alternative API (Instance-based)

You can also create a parser instance for decoding:

const parser = new BencodeParser('i42e');
const result = parser.parse();
console.log(result); // 42

Bencode Format

Bencode supports four data types:

Type	Format	Example	JavaScript Equivalent
Integer	i<number>e	i42e	42
String	<length>:<string>	4:spam	"spam"
List	l<items>e	li1ei2ee	[1, 2]
Dictionary	d<key><value>...e	d3:key5:valuee	{key: "value"}

API Reference

BencodeParser.encode(value)

Encodes a JavaScript value into Bencode format.

Parameters:

• value (number|string|array|object) - The value to encode

Returns: String - The Bencode encoded string

Throws: Error if the value type is not supported

BencodeParser.decode(bencodedString)

Decodes a Bencode string into a JavaScript value.

Parameters:

• bencodedString (string) - The Bencode string to decode

Returns: number|string|array|object - The decoded JavaScript value

Throws: Error if the Bencode format is invalid

new BencodeParser(data)

Creates a parser instance (for manual parsing).

Parameters:

• data (string) - The Bencode string to parse

parser.parse()

Parses the Bencode string provided to the constructor.

Returns: number|string|array|object - The parsed JavaScript value

Examples

Round-trip Conversion

const original = { 
  name: 'MyTorrent', 
  size: 2048, 
  files: ['video.mp4', 'subtitle.srt'] 
};

const encoded = BencodeParser.encode(original);
console.log(encoded);
// 'd5:filesli9:video.mp4i12:subtitle.srtee4:name9:MyTorrent4:sizei2048ee'

const decoded = BencodeParser.decode(encoded);
console.log(decoded);
// { name: 'MyTorrent', size: 2048, files: ['video.mp4', 'subtitle.srt'] }

Working with Torrent Files

// Typical torrent metadata structure
const torrentInfo = {
  announce: 'http://tracker.example.com:8080/announce',
  info: {
    name: 'example.iso',
    length: 1073741824,
    'piece length': 262144
  }
};

const encoded = BencodeParser.encode(torrentInfo);
// This can now be written to a .torrent file

Running Tests

node index.js

Contributing

Contributions are welcome! Feel free to open issues or submit pull requests.

Author

VrajVed

Resources

• BitTorrent Protocol Specification
• Bencode Wikipedia

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Created for educational purposes to learn about parsing and encoding.