add WebSocket support for real-time delivery updates with JWT authentication and automatic reconnection

backend/internal/ws/client.go

@@ -0,0 +1,74 @@
+package ws
+
+import (
+	"time"
+
+	"github.com/gorilla/websocket"
+)
+
+const (
+	writeWait  = 10 * time.Second
+	pongWait   = 60 * time.Second
+	pingPeriod = (pongWait * 9) / 10
+)
+
+type Client struct {
+	hub  *Hub
+	conn *websocket.Conn
+	send chan []byte
+}
+
+func NewClient(hub *Hub, conn *websocket.Conn) *Client {
+	return &Client{
+		hub:  hub,
+		conn: conn,
+		send: make(chan []byte, 256),
+	}
+}
+
+// ReadPump keeps the connection alive and handles pong frames.
+// We don't expect real messages from the client (read-only WS).
+func (c *Client) ReadPump() {
+	defer func() {
+		c.hub.Unregister(c)
+		c.conn.Close()
+	}()
+	c.conn.SetReadLimit(512)
+	c.conn.SetReadDeadline(time.Now().Add(pongWait))
+	c.conn.SetPongHandler(func(string) error {
+		c.conn.SetReadDeadline(time.Now().Add(pongWait))
+		return nil
+	})
+	for {
+		if _, _, err := c.conn.ReadMessage(); err != nil {
+			break
+		}
+	}
+}
+
+// WritePump sends messages from hub to the client and pings to keep alive.
+func (c *Client) WritePump() {
+	ticker := time.NewTicker(pingPeriod)
+	defer func() {
+		ticker.Stop()
+		c.conn.Close()
+	}()
+	for {
+		select {
+		case msg, ok := <-c.send:
+			c.conn.SetWriteDeadline(time.Now().Add(writeWait))
+			if !ok {
+				c.conn.WriteMessage(websocket.CloseMessage, nil)
+				return
+			}
+			if err := c.conn.WriteMessage(websocket.TextMessage, msg); err != nil {
+				return
+			}
+		case <-ticker.C:
+			c.conn.SetWriteDeadline(time.Now().Add(writeWait))
+			if err := c.conn.WriteMessage(websocket.PingMessage, nil); err != nil {
+				return
+			}
+		}
+	}
+}