code: func (*wsNotificationManager) addAddrRequests(addrMap map[string]map[chan struct{}]*wsClient,
  	wsc *wsClient, addrs []string) {
  
  	for _, addr := range addrs {
  		// Track the request in the client as well so it can be quickly be
  		// removed on disconnect.
  		wsc.addrRequests[addr] = struct{}{}
  
  		// Add the client to the set of clients to notify when the
  		// outpoint is seen.  Create map as needed.
  		cmap, ok := addrMap[addr]
  		if !ok {
  			cmap = make(map[chan struct{}]*wsClient)
  			addrMap[addr] = cmap
  		}
  		cmap[wsc.quit] = wsc
  	}
  }
docs: // addAddrRequests adds the websocket client wsc to the address to client set
  // addrMap so wsc will be notified for any mempool or block transaction outputs
  // spending to any of the addresses in addrs.