async def force_close_channel(self, chan_id):
    chan = self._channels[chan_id]
    tx = chan.force_close_tx()
    (await self.network.broadcast_transaction(tx))
    chan.set_state(ChannelState.FORCE_CLOSING)
    return tx.txid()
async def force_close_channel(self, chan_id):
    chan = self._channels[chan_id]
    tx = chan.force_close_tx()
    (await self.network.broadcast_transaction(tx))
    chan.set_state(ChannelState.FORCE_CLOSING)
    return tx.txid()