def __init__(self, url, callback, timeout, max_connections=30):
"""
If the URL conforms to a magnet link, the .torrent info is
downloaded and returned to CALLBACK.
"""
# _callback is called when the metadata is retrieved.
self._callback = callback
dn, xt, trs = self.parse_url(url)
# _name is the unicode name suggested for the swarm.
assert dn is None or isinstance(dn, unicode), "DN has invalid type: %s" % type(dn)
self._name = dn
# _info_hash is the 20 byte binary info hash that identifies
# the swarm.
assert isinstance(xt, str), "XT has invalid type: %s" % type(xt)
assert len(xt) == 20, "XT has invalid length: %d" % len(xt)
self._info_hash = xt
# _tracker is an optional tracker address.
self._trackers = trs
# _swarm is a MiniBitTorrent.MiniSwarm instance that connects
# to peers to retrieve the metadata.
self.magnet_handler = MagnetHandler.get_instance()
self.magnet_handler.add_magnet(self, timeout)
self._swarm = MiniSwarm(self._info_hash, self.magnet_handler.get_raw_server(), self.metainfo_retrieved, max_connections=max_connections)
