Feature: Handling server canceled observation

[arvindh123]

Is your feature request related to a problem? Please describe.

Canceled observation by server are not detected and handled by CLI

Describe the feature you are requesting, as well as the possible use case(s) for it.

Detecting the server canceled observer

We should retrieve the observer on each time the function is called
If there is no Observe option is not found , then server has canceled the observer ("This need to verify with coap protocol spec")

// Receive receives a message.
func (c Client) Receive(path string, verbose bool, opts ...message.Option) (mux.Observation, error) {
	ctx, cancel := context.WithTimeout(context.Background(), time.Minute)
	defer cancel()

	return c.conn.Observe(ctx, path, func(res *pool.Message) {
		body, err := res.ReadBody()
		if err != nil {
			fmt.Println("Error reading message body: ", err)
			return
		}
		bodySize, err := res.BodySize()
		if err != nil {
			fmt.Println("Error getting body size: ", err)
			return
		}
		if _, err := res.Observe(); err != nil {
			if !errors.Is(err, message.ErrOptionNotFound) {
				fmt.Println("Error getting Observer: ", err)
			}
			cancel()
			return
		}

		if bodySize == 0 {
			fmt.Println("Received observe")
		}
		switch verbose {
		case true:
			fmt.Printf(verboseFmt,
				time.Now().Format(time.RFC1123),
				res.Code(),
				res.Type(),
				res.Token(),
				res.MessageID(),
				bodySize)
			if len(body) > 0 {
				fmt.Printf("Payload: %s\n\n", string(body))
			}
		case false:
			if len(body) > 0 {
				fmt.Printf("Payload: %s\n", string(body))
			}
		}
	}, opts...)
}

In the above same code, difference highlighted version:

// Receive receives a message.
func (c Client) Receive(path string, verbose bool, opts ...message.Option) (mux.Observation, error) {
	ctx, cancel := context.WithTimeout(context.Background(), time.Minute)
	defer cancel()

	return c.conn.Observe(ctx, path, func(res *pool.Message) {
		body, err := res.ReadBody()
		if err != nil {
			fmt.Println("Error reading message body: ", err)
			return
		}
		bodySize, err := res.BodySize()
		if err != nil {
			fmt.Println("Error getting body size: ", err)
			return
		}
+		if _, err := res.Observe(); err != nil {
+			if !errors.Is(err, message.ErrOptionNotFound) {
+				fmt.Println("Error getting Observer: ", err)
+			}
+			cancel()
+			return
+		}

		if bodySize == 0 {
			fmt.Println("Received observe")
		}
		switch verbose {
		case true:
			fmt.Printf(verboseFmt,
				time.Now().Format(time.RFC1123),
				res.Code(),
				res.Type(),
				res.Token(),
				res.MessageID(),
				bodySize)
			if len(body) > 0 {
				fmt.Printf("Payload: %s\n\n", string(body))
			}
		case false:
			if len(body) > 0 {
				fmt.Printf("Payload: %s\n", string(body))
			}
		}
	}, opts...)
}

Indicate the importance of this feature to you.

Must-have

Anything else?

No response