arcast/pkg/server/broadcast.go

package server

import (
	"context"
	"log"
	"net/http"
	"sync"

	"github.com/go-chi/chi/v5"
	"github.com/gorilla/websocket"
	"github.com/pkg/errors"
	"gitlab.com/wpetit/goweb/logger"
)

var (
	upgrader = websocket.Upgrader{}
	channels = &channelMap{
		index: make(map[string]map[*websocket.Conn]struct{}),
	}
)

func (s *Server) handleBroadcast(w http.ResponseWriter, r *http.Request) {
	ctx := r.Context()

	c, err := upgrader.Upgrade(w, r, nil)
	if err != nil {
		log.Print("upgrade:", err)
		return
	}

	channelID := chi.URLParam(r, "channelID")
	channels.Add(channelID, c)

	defer func() {
		channels.Remove(channelID, c)

		if err := c.Close(); err != nil && !websocket.IsCloseError(err, 1001) {
			logger.Error(ctx, "could not close connection", logger.E(errors.WithStack(err)))
		}
	}()

	for {
		messageType, message, err := c.ReadMessage()
		if err != nil {
			logger.Error(ctx, "could not read message", logger.E(errors.WithStack(err)))
			break
		}

		logger.Debug(ctx, "broadcasting message", logger.F("message", message), logger.F("messageType", messageType))

		channels.Send(ctx, channelID, messageType, message, c)
	}
}

type channelMap struct {
	mutex sync.RWMutex
	index map[string]map[*websocket.Conn]struct{}
}

func (m *channelMap) Remove(channelID string, conn *websocket.Conn) {
	m.mutex.Lock()
	defer m.mutex.Unlock()

	conns, exists := m.index[channelID]
	if !exists {
		return
	}

	delete(conns, conn)
	if len(conns) == 0 {
		delete(m.index, channelID)
	}
}

func (m *channelMap) Add(channelID string, conn *websocket.Conn) {
	m.mutex.Lock()
	defer m.mutex.Unlock()

	conns, exists := m.index[channelID]
	if !exists {
		conns = make(map[*websocket.Conn]struct{})
	}

	conns[conn] = struct{}{}
	m.index[channelID] = conns
}

func (m *channelMap) Send(ctx context.Context, channelID string, messageType int, message []byte, except *websocket.Conn) {
	m.mutex.RLock()
	defer m.mutex.RUnlock()

	conns, exists := m.index[channelID]
	if !exists {
		return
	}

	for c := range conns {
		if except == c {
			continue
		}

		if err := c.WriteMessage(messageType, message); err != nil {
			logger.Error(ctx, "could not write message", logger.E(errors.WithStack(err)))
		}
	}
}