Javascript Torrent File Parsing

Question

To date, I've not found any suitable .torrent file parsers coded in javascript, therefore I began creating my own.

So far, I was able to recode a php bdecoder in javascript, one issue I found is that larger .torrent files (like the second one in http://www.vuze.com/content/channel.php?id=53&name=Scam%20School%20(Quicktime%20HD)) sometimes result in Uncaught RangeError: Maximum call stack size exceeded errors in chrome. Is there a method to have the bdecode function run less recursively?

Along with this issue, I haven't been able to accurately produce an info hash for the '.torrent' files which decoded successfully. I hash the info dictionary beginning right after the info name and ending at the e 'closing tag'. However, this results in incorrect hashes compared to that of actual bittorrent clients. Am I reading the file incorrectly?

Current code: http://jsfiddle.net/e23YQ/

Thanks.

Answer 1

Reading the torrent file using readAsTest or readAsBinaryString (which is deprecated) will not suffice for generating an accurate info hash. In order to keep things as native as possible, you must read the file as an ArrayBuffer and parse using Uint8Arrays. While parsing, save the beginning and ending offsets of the info dictionary for generating the info hash.

In order to generate an accurate info hash, you must use a javascript implementation of Sha-1 which allows for hashing of ArrayBuffers. Rusha seemed to be a viable option. Using the digestFromArrayBuffer in Rusha with a slice of the initial ArrayBuffer containing the info dictionary, we get an accurate info hash.

Using an ArrayBuffer eliminated the stackoverflow issue I was having earlier.

This is the adjusted code: http://jsfiddle.net/e23YQ/5/