Set entry['torrent_info_hash'] from magnet URI

[ropery]

I think the info_hash is the best identifier of an entry (much more reliable than title or URL). For example, the seen_info_hash plugin runs during the modify phase after the torrent plugin has set the torrent_info_hash of accepted entries to avoid duplicates. I request a (builtin) magnet plugin that sets entry['torrent_info_hash'] from entry['url'] if it's a magnet URI.

Since some sites since long have stopped providing torrent files but a simple magnet link only, I think this is a useful feature.

[ropery]

OK, this works for me:

from __future__ import unicode_literals, division, absolute_import
import logging
import re

from flexget import plugin
from flexget.event import event

log = logging.getLogger('modify_magnet_btih')

class MagnetBtih(object):
    """Sets torrent_info_hash from magnet url."""

    @plugin.priority(255)
    def on_task_modify(self, task, config):
        for entry in task.accepted:
            if entry['url'].startswith('magnet:'):
                info_hash_search = re.search('btih:([0-9a-f]+)', entry['url'], re.IGNORECASE)
                if info_hash_search:
                    entry['torrent_info_hash'] = info_hash_search.group(1).upper()

@event('plugin.register')
def register_plugin():
    plugin.register(MagnetBtih, 'magnet_btih', builtin=True, api_ver=2)

I put it in flexget/plugins/modify/. This code does not consider the case where the torrent_info_hash of the entry is already set, such as in the case of the torrentz and kat plugins.

BTW, there seems to be a typo in modify/torrent.py, where it says "modif_torrent".

[gazpachoking]

Added in feb9805ff0a827be7aa2052fc50fa73da30bd171, thanks!