internal static (BEncodedDictionary torrent, InfoHash infohash) DecodeTorrent(RawReader reader)
{
var torrent = new BEncodedDictionary();
if (reader.ReadByte() != 'd')
{
throw new BEncodingException("Invalid data found. Aborting"); // Remove the leading 'd'
}
int read;
InfoHash infoHash = null;
// We can save a few resizes and array copies if we pre-allocate
// a buffer and then get the memory stream to write to it. We
// can trivially pass the final set of bytes to the hash function then.
byte[] capturedDataBytes = null;
MemoryStream capturedDataStream = null;
while ((read = reader.ReadByte()) != -1 && read != 'e')
{
BEncodedValue value;
var key = (BEncodedString)Decode(reader, read); // keys have to be BEncoded strings
if ((read = reader.ReadByte()) == 'd')
{
if (InfoKey.Equals(key))
{
capturedDataBytes = new byte[reader.Length - reader.Position];
capturedDataStream = new MemoryStream(capturedDataBytes, true);
capturedDataStream.WriteByte((byte)'d');
reader.BeginCaptureData(capturedDataStream);
}
value = DecodeDictionary(reader, reader.StrictDecoding);
if (InfoKey.Equals(key))
{
reader.EndCaptureData();
using var hasher = SHA1.Create();
infoHash = new InfoHash(hasher.ComputeHash(capturedDataBytes, 0, (int)capturedDataStream.Position));
}
}
else
{
value = Decode(reader, read); // the value is a BEncoded value
}
torrent.Add(key, value);
}
if (read != 'e') // remove the trailing 'e'
{
throw new BEncodingException("Invalid data found. Aborting");
}
return(torrent, infoHash);
}