conn.go
func (c *Conn) MiddlewareFunc(middleware ...func(ctx *ReqCtx) error) {
	c.middleware = append(c.middleware, middleware...)
}
func (c *Conn) MiddlewareFunc(middleware ...func(ctx *ReqCtx) error) {
	c.middleware = append(c.middleware, middleware...)
}
// MiddlewareFunc registers middleware function to handle incoming request messages.