net.go

// Copyright (c) 2017-2021 Ivan Jelincic <parazyd@dyne.org>
//
// This file is part of tordam
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with this program. If not, see <https://www.gnu.org/licenses/>.

package tordam

import "net"

// GetAvailableListener is a helper function to return a *net.TCPAddr on some
// port that is available for listening on the system. It uses the :0 port
// which the kernel utilizes to return a random available port.
func GetAvailableListener() (*net.TCPAddr, error) {
	addr, err := net.ResolveTCPAddr("tcp4", "localhost:0")
	if err != nil {
		return nil, err
	}

	l, err := net.ListenTCP("tcp4", addr)
	if err != nil {
		return nil, err
	}
	defer l.Close()
	return l.Addr().(*net.TCPAddr), nil
}