refactor _join implementation
refactor _join implementation

smarthomekit/dpark,304471720/dpark,Mignet/dpark,douban/dpark,zzl0/dpark,dogeyes/dpark,quxiaolong1504/dpark,windreamer/dpark,dogeyes/dpark,mageia/dpark,windreamer/dpark,yhj630520/dpark,ee08b397/dpark,304471720/dpark,yanheven/dpark,veritynoob/dpark,304471720/dpark,douban/dpark,veritynoob/dpark,smarthomekit/dpark,fe11x/dpark,yanheven/dpark,Mignet/dpark,junmoa/dpark,yhj630520/dpark,mageia/dpark,fe11x/dpark,daishaowei/dpark,junmoa/dpark,douban/dpark,yhj630520/dpark,zzl0/dpark,douban/dpark,windreamer/dpark,smarthomekit/dpark,dogeyes/dpark,windreamer/dpark,veritynoob/dpark,daishaowei/dpark,douban/dpark,oceanjack/dpark,oceanjack/dpark,quxiaolong1504/dpark