BencodeNET

A .NET library for encoding and decoding bencode.

Usage

Torrents

Working with torrent files:

// Decode torrent by specifying the file path
TorrentFile torrent = Bencode.DecodeTorrentFile("C:\ubuntu.torrent");

// Alternatively, handle the stream yourself
using (var stream = File.OpenRead("C:\ubuntu.torrent"))
{
    torrent = Bencode.DecodeTorrentFile(stream);
}

// Calculate the info hash
string infoHash = torrent.CalculateInfoHash();
// "B415C913643E5FF49FE37D304BBB5E6E11AD5101"

// You can also calculate the info hash with this static method
TorrentFile.CalculateInfoHash(BDictionary info)

The following fields are available directly on the TorrentFile itself and parsed to a default .NET type where applicable:

Announce : string
AnnounceList : BList
Comment : string
CreatedBy : string
CreationDate : DateTime
Encoding : string
Info : BDictionary

If you need to access other fields you can access them by their key:

BString keyWithStringValue = torrent["key with string value"];

// The default fields are also accessible here
BDictionary info = torrent["info"];
BString announce = torrent["announce"]
BList announceList = torrent["announce-list"]

Decoding

Simple decoding of a bencoded string:

BString bstring = Bencode.DecodeString("12:Hello World!");
// "Hello World!"

BNumber bnumber = Bencode.DecodeNumber("i42e");
// 42

BList blist = Bencode.DecodeList("l3:foo3:bari42ee");
// { "foo", "bar", 42 }

BDictionary bdictionary = Bencode.DecodeDictionary("d3:fooi42e5:Hello6:World!e");
// { { "foo", 42 }, { "Hello", "World" } }

If you are unsure of the type you can just use the generic Bencode.Decode:

IBObject bobject = Bencode.Decode("12:Hello World!");

if (bobject is BString)
{
    // The decoded object is a string
}

It is also possible to decode directly from a stream instead, for example a FileStream:

using (var fs = File.OpenRead("Ubuntu.torrent"))
{
    BDictionary bdictionary = Bencode.DecodeDictionary(fs);
}

Encoding

var bstring = new BString("Hello World!");
bstring.Encode();    // "12:Hello World!"

var bnumber = new BNumber(42);
bnumber.Encode();    // "i42e"

var blist = new BList { "foo", 42, "bar" };
blist.Encode();      // "l3:fooi42e3:bare"

var bdictionary = new BDictionary { { "foo", 42 }, { "Hello", "World!" } };
bdictionary.Encode() // "d3:fooi42e5:Hello6:World!e"

It is also possible to encode directly to a stream:

using (var fs = File.OpenWrite("MyTorrent.torrent"))
{
    bobject.EncodeToStream(fs);
}

String Character Encoding

By default Encoding.UTF8 is used when rendering strings.

When decoding a string directly the encoding is used to convert the string to an array of bytes.

If no encoding is passed to ToString it will use the encoding the BString was created/decoded with.

// Using the default encoding from Bencode.DefaultEncoding (UTF8)
var bstring = Bencode.DecodeString("21:æøå äö èéê ñ");
bstring.ToString()              // "æøå äö èéê ñ"
bstring.ToString(Encoding.UTF8) // "æøå äö èéê ñ"

// Using ISO-8859-1
bstring = Bencode.DecodeString("12:æøå äö èéê ñ", Encoding.GetEncoding("ISO-8859-1"));
bstring.ToString();              // "æøå äö èéê ñ"
bstring.ToString(Encoding.UTF8); // "??? ?? ??? ?"

If you decode a bencoded stream that is not using UTF8 and you don't specify the encoding, then ToString without parameters will use Encoding.UTF8 to try to render the BString and you will not get the expected result.

var bytes = Encoding.GetEncoding("ISO-8859-1").GetBytes("12:æøå äö èéê ñ");
using (var ms = new MemoryStream(bytes))
{
    // When not specifying an encoding, ToString will use Bencode.DefaultEncoding (UTF8)
    var bstring = Bencode.DecodeString(ms);
    bstring.ToString();
    // "??? ?? ??? ?"
    
    // Pass your desired encoding to ToString to override the encoding used to render the string
    bstring.ToString(Encoding.GetEncoding("ISO-8859-1"));
    // "æøå äö èéê ñ"

    // If you specify an encoding when decoding, ToString will use that as the default when rendering the string
    bstring = Bencode.DecodeString(ms, Encoding.GetEncoding("ISO-8859-1"));
    bstring.ToString();
    // "æøå äö èéê ñ"
}

When you encode an object directly to a stream (IBObject.EncodeToStream) the encoding is irrelevant.

However, when encoding to a string (IBObject.Encode) you can specify the encoding used to render the string. BString.Encode without specifying an encoding will use the encoding the BString was created with. For all the other types Bencode.DefaultEncoding will be used.

Note: Using BList.Encode and BDictionary.Encode will render all contained BString using Bencode.DefaultEncoding irregardless of the encoding of the BString itself.

var blist = new BList();
blist.Add(new BString("æøå äö èéê ñ", Encoding.GetEncoding("ISO-8859-1")));
blist.Encode();                                   // "l12:??? ?? ??? ?e"
blist.Encode(Encoding.UTF8);                      // "l12:??? ?? ??? ?e
blist.Encode(Encoding.GetEncoding("ISO-8859-1")); // "l12:æøå äö èéê ñe""

If you want to use another encoding than UTF8 as the default encoding you can set Bencode.DefaultEncoding to your desired encoding.

Bencode.DefaultEncoding = Encoding.ASCII;

Note: Bencode.DefaultEncoding is a static property and is used by all static methods of the Bencode class when no encoding is supplied.

SamuelFisher / BencodeNET