Invalid info Hash

Challenges
1

I’m stuck on the Tracker GET request on Stage #FI9.

I keep getting this reponse from the tracker URL:

d14:failure reason25:provided invalid infohashe

Here’s the info hash hexadecimal value I am extracting from the sample torrent file:
d69f91e6b2ae4c542468d1073a71d4ea13879a7f

The problem is unlikely to come from the info hash itself because I have double-checked it against the expected info hash hex value at step #RB2 and it matches perfectly. I also succesfully passed that step which would have been impossible without the right info hash value.

This is is how I extract the hex value of the info hash:

        const string infoMarker = "4:infod";
        var hashStart =
            encodedFile.IndexOf(infoMarker, StringComparison.Ordinal) + infoMarker.Length - 1;
        var chunk = bytes[hashStart..^1];
        InfoHash = SHA1.HashData(chunk);
        InfoHashHex = Convert.ToHexString(InfoHash).ToLower();

After that, all I do is URL encode the info hash bytes and add to the query params:

        var queryParams = new Dictionary<string, string>
        {
            { "info_hash", HttpUtility.UrlEncode(torrentFile.InfoHash) },
            { "peer_id", "22974793449159003000" },
            { "port", "6881" },
            { "uploaded", "0" },
            { "downloaded", "0" },
            { "left", torrentFile.Length },
            { "compact", "1" },
        };

The final endpoint to which I send a GET request looks like this:
http://bittorrent-test-tracker.codecrafters.io/announce?info_hash=%25d6%259f%2591%25e6%25b2%25aeLT%2524h%25d1%2507%253aq%25d4%25ea%2513%2587%259a%257f&peer_id=22974793449159003000&port=6881&uploaded=0&downloaded=0&left=92063&compact=1

I have tried encoding the InfoHash in a thousand different ways but to no avail. This ultimately seems like the right way to do it. Yet the CodeCrafter tells me its invalid.

Any tip would be appreciated, thanks.

2

Hi charlesmatte,
Can you try without HttpUtility.UrlEncode

1 Like
3

Hi sarp,

Thanks for pointing that out.

I was encoding the value twice, once with HttpUtility.UrlEncode(torrentFile.InfoHash) and a second time later through HttpUtility.ParseQueryString which automatically encodes the values.

I got rid of HttpUtility.ParseQueryString and it did the trick.

1 Like
4

Nice, glad you figured it out!

5

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