Add Peer ID for Free Download Manager (FDM)

[kholia]

Based on experiments with FDM 5.1.32 running on Windows 10.

FDM uses Azureus-style peer ID with -FD prefix.

This fixes issue #335.

[mention-bot]

@kholia, thanks for your PR! By analyzing the history of the files in this pull request, we identified @mikedld, @Charlesk and @titer to be potential reviewers.

[kholia]

Before this commit,

After this commit,

[mikedld]

What are those "R" and "W" letters for? Maybe worth decoding as well?

[mikedld]

Could it be that they're using an alphanumeric sequence for the third version part? If we take a sequence of "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ" (it may also include lowercase letters, have no idea) then "W" is 32nd (starting from 0) char there, and I see you were testing with "5.1.32" (so third part is 32).

[kholia]

I think you are right.

>>> import string
>>> 
>>> table = string.digits + string.ascii_uppercase
>>> table
'0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ'
>>> table.index('W')
32
>>> table.index('R')
27

The -FD51R prefix reported in issues #335 was associated with FDM v5.1.27 (note that the R value maps perfectly to27).

It does seem that R and W values indicate the third version part. I can't locate the source code for FDM v5 series to confirm these findings 100%. Also, lowercase letters might indeed be involved in this versioning scheme.

Overall, I am not sure if decoding the third version part matters at all.

[Encombe]

If we take a sequence of "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ" (it may also include lowercase letters, have no idea)

The number encoding is probably from: http://forums.degreez.net/viewtopic.php?t=7070

TheSHAD0W
Post subject: BitTornado peer ID spec
...
First off, all numerical coding is in a custom base-64 format. This format isn't standard, but was developed in order to be URL-safe. This reduces the quoting required in the announce, which reduces bandwidth needed. The digits of this base-64 format are:
0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz.-

See also: https://wiki.theory.org/index.php/BitTorrentSpecification#peer_id

Might as well also add BI = BiglyBT https://github.com/BiglySoftware/BiglyBT
which is a fork of Vuze done by Vuze former main developers

[kholia]

I have now implemented decoding of the third version part from the Peer ID in the latest commit. FDM seems to be using 0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz-_.!~*() table for encoding the third version part.

I will squash the commits in this PR once the changes look good.

[kholia]

Here is FDM in action with the latest commit,

[kholia]

I have squashed the commits. This PR should be all set now. Thanks!