How to create a handler to SSE

sse_handler.go

func (h *Handler) Subscribe(c echo.Context) error {
	var epoch = time.Unix(0, 0).Format(time.RFC1123)

	c.Response().Header().Set(echo.HeaderContentType, "text/event-stream")
	c.Response().Header().Set("Cache-Control", "no-cache")
	c.Response().Header().Set("Connection", "keep-alive")
	c.Response().Header().Set("Expires", epoch)
	c.Response().Header().Set("Cache-Control", "no-cache, private, max-age=0")
	c.Response().Header().Set("Pragma", "no-cache")
	c.Response().Header().Set("X-Accel-Expires", "0")
	c.Response().WriteHeader(http.StatusOK)

	// knowWhenCloseConnectionClient is a listener to know when the user close the connection. e.g. close browser.
	knowWhenCloseConnectionClient := c.Request().Context().Done()
	client := h.sse.Subscribe(knowWhenCloseConnectionClient)
	defer h.sse.UnSubscribe(client)

	for {
		message := <-client.QueueMessages
		dataJSON, err := json.Marshal(message)
		if err != nil {
			log.Printf("Can't marshal message %v, error was %v", message, err)
			return c.JSON(http.StatusInternalServerError, err)
		}

		// Send message to client
		_, err = fmt.Fprintf(c.Response(), "data: %v\n\n", string(dataJSON))
		if err != nil {
			return err
		}

		c.Response().Flush()
	}
}