hub.go

package main

import "log"

type message struct {
	data []byte
	room string
	sender *connection
}

type subscription struct {
	conn *connection
	room string
}

// hub maintains the set of active connections and broadcasts messages to the
// connections.
type hub struct {
	// Registered connections.
	rooms map[string]map[*connection]bool

	// Inbound messages from the connections.
	broadcast chan message

	// Register requests from the connections.
	register chan subscription

	// Unregister requests from connections.
	unregister chan subscription
}

var h = hub{
	broadcast:  make(chan message),
	register:   make(chan subscription),
	unregister: make(chan subscription),
	rooms:      make(map[string]map[*connection]bool),
}

func (h *hub) run() {
	for {
		select {
		case s := <-h.register:
			connections := h.rooms[s.room]
			if connections == nil {
				connections = make(map[*connection]bool)
				h.rooms[s.room] = connections
			}
			h.rooms[s.room][s.conn] = true

			log.Printf("Registered room: %s", s.room)

			// Send a warning to the connections of the room if there are more than two connections
			if len(h.rooms[s.room]) > 2 {
				log.Printf("Warning! More than 2 connections in room %s", s.room)

				m := message{[]byte(
					"{\"command\": \"showWarning\", " +
					"\"msg\": \"More than 2 connections are using this token! Are multiple instances of QOwnNotes active?\"}"),
					s.room, nil}
				sendMessage(m)
			}
		case s := <-h.unregister:
			connections := h.rooms[s.room]
			if connections != nil {
				if _, ok := connections[s.conn]; ok {
					delete(connections, s.conn)
					close(s.conn.send)
					if len(connections) == 0 {
						delete(h.rooms, s.room)
					}
				}
			}
		case m := <-h.broadcast:
			sendMessage(m)
		}
	}
}

func sendMessage(m message) {
	connections := h.rooms[m.room]
	for c := range connections {
		// Don't send sender the message back
		if c == m.sender {
			continue
		}

		select {
		case c.send <- m.data:
		default:
			close(c.send)
			delete(connections, c)
			if len(connections) == 0 {
				delete(h.rooms, m.room)
			}
		}
	}
}