From d5f94b76986615b255b77b2a7b7ed336e5ad4838 Mon Sep 17 00:00:00 2001
From: Emiliano Ciavatta
Date: Wed, 7 Oct 2020 14:58:48 +0200
Subject: Implement notifications

---
 notification_controller.go | 165 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 165 insertions(+)
 create mode 100644 notification_controller.go

(limited to 'notification_controller.go')

diff --git a/notification_controller.go b/notification_controller.go
new file mode 100644
index 0000000..88c9e8c
--- /dev/null
+++ b/notification_controller.go
@@ -0,0 +1,165 @@
+package main
+
+import (
+	"github.com/gin-gonic/gin"
+	"github.com/gorilla/websocket"
+	log "github.com/sirupsen/logrus"
+	"net"
+	"net/http"
+	"time"
+)
+
+const (
+	InsertNotification = "insert"
+	UpdateNotification = "update"
+	DeleteNotification = "delete"
+
+	writeWait      = 10 * time.Second
+	pongWait       = 60 * time.Second
+	pingPeriod     = (pongWait * 9) / 10
+	maxMessageSize = 512
+)
+
+type NotificationController struct {
+	upgrader           websocket.Upgrader
+	clients            map[net.Addr]*client
+	broadcast          chan interface{}
+	register           chan *client
+	unregister         chan *client
+	applicationContext *ApplicationContext
+}
+
+func NewNotificationController(applicationContext *ApplicationContext) *NotificationController {
+	return &NotificationController{
+		upgrader: websocket.Upgrader{
+			ReadBufferSize:  1024,
+			WriteBufferSize: 1024,
+		},
+		clients:            make(map[net.Addr]*client),
+		broadcast:          make(chan interface{}),
+		register:           make(chan *client),
+		unregister:         make(chan *client),
+		applicationContext: applicationContext,
+	}
+}
+
+type client struct {
+	conn                   *websocket.Conn
+	send                   chan interface{}
+	notificationController *NotificationController
+}
+
+func (wc *NotificationController) NotificationHandler(w http.ResponseWriter, r *http.Request) error {
+	conn, err := wc.upgrader.Upgrade(w, r, nil)
+	if err != nil {
+		log.WithError(err).Error("failed to set websocket upgrade")
+		return err
+	}
+
+	client := &client{
+		conn:                   conn,
+		send:                   make(chan interface{}),
+		notificationController: wc,
+	}
+	wc.register <- client
+	go client.readPump()
+	go client.writePump()
+
+	return nil
+}
+
+func (wc *NotificationController) Run() {
+	for {
+		select {
+		case client := <-wc.register:
+			wc.clients[client.conn.RemoteAddr()] = client
+			payload := gin.H{"event": "connected", "message": gin.H{
+				"version":           wc.applicationContext.Version,
+				"is_configured":     wc.applicationContext.IsConfigured,
+				"connected_clients": len(wc.clients),
+			}}
+			client.send <- payload
+			log.WithField("connected_clients", len(wc.clients)).
+				WithField("remote_address", client.conn.RemoteAddr()).
+				Info("[+] a websocket client connected")
+		case client := <-wc.unregister:
+			if _, ok := wc.clients[client.conn.RemoteAddr()]; ok {
+				close(client.send)
+				_ = client.conn.WriteMessage(websocket.CloseMessage, nil)
+				_ = client.conn.Close()
+				delete(wc.clients, client.conn.RemoteAddr())
+				log.WithField("connected_clients", len(wc.clients)).
+					WithField("remote_address", client.conn.RemoteAddr()).
+					Info("[-] a websocket client disconnected")
+			}
+		case payload := <-wc.broadcast:
+			for _, client := range wc.clients {
+				select {
+				case client.send <- payload:
+				default:
+					close(client.send)
+					delete(wc.clients, client.conn.RemoteAddr())
+				}
+			}
+		}
+	}
+}
+
+func (wc *NotificationController) Notify(event string, eventType string, message interface{}) {
+	wc.broadcast <- gin.H{"event": event, "event_type": eventType, "message": message}
+}
+
+func (c *client) readPump() {
+	c.conn.SetReadLimit(maxMessageSize)
+	if err := c.conn.SetReadDeadline(time.Now().Add(pongWait)); err != nil {
+		c.close()
+		return
+	}
+	c.conn.SetPongHandler(func(string) error { return c.conn.SetReadDeadline(time.Now().Add(pongWait)) })
+	for {
+		if _, _, err := c.conn.ReadMessage(); err != nil {
+			if websocket.IsUnexpectedCloseError(err, websocket.CloseGoingAway) {
+				log.WithError(err).WithField("remote_address", c.conn.RemoteAddr()).
+					Warn("unexpected websocket disconnection")
+			}
+			break
+		}
+	}
+
+	c.close()
+}
+
+func (c *client) writePump() {
+	ticker := time.NewTicker(pingPeriod)
+	defer ticker.Stop()
+
+	for {
+		select {
+		case payload, ok := <-c.send:
+			if !ok {
+				return
+			}
+			if err := c.conn.SetWriteDeadline(time.Now().Add(writeWait)); err != nil {
+				c.close()
+				return
+			}
+			if err := c.conn.WriteJSON(payload); err != nil {
+				c.close()
+				return
+			}
+		case <-ticker.C:
+			if err := c.conn.SetWriteDeadline(time.Now().Add(writeWait)); err != nil {
+				c.close()
+				return
+			}
+			if err := c.conn.WriteMessage(websocket.PingMessage, nil); err != nil {
+				c.close()
+				return
+			}
+		}
+	}
+}
+
+func (c *client) close() {
+	c.notificationController.unregister <- c
+}
-- 
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