Shutdown gracefully shuts down the server without interrupting any active connections. Shutdown works by first closing all open listeners, then closing all idle connections, and then waiting indefinitely for connections to return to idle and then shut down. If the provided context expires before the shutdown is complete, Shutdown returns the context's error, otherwise it returns any error returned from closing the Server's underlying Listener(s).
When Shutdown is called, Serve, ListenAndServe, and ListenAndServeTLS immediately return ErrServerClosed. Make sure the program doesn't exit and waits instead for Shutdown to return.
Shutdown does not attempt to close nor wait for hijacked connections such as WebSockets. The caller of Shutdown should separately notify such long-lived connections of shutdown and wait for them to close, if desired. See RegisterOnShutdown for a way to register shutdown notification functions.
Once Shutdown has been called on a server, it may not be reused; future calls to methods such as Serve will return ErrServerClosed.
