freeport.go

// SPDX-FileCopyrightText: Copyright The Lima Authors
// SPDX-License-Identifier: Apache-2.0

// Package freeport provides functions to find free localhost ports.
package freeport

import (
	"fmt"
	"net"
)

func TCP() (int, error) {
	lAddr0, err := net.ResolveTCPAddr("tcp4", "127.0.0.1:0")
	if err != nil {
		return 0, err
	}
	l, err := net.ListenTCP("tcp4", lAddr0)
	if err != nil {
		return 0, err
	}
	defer l.Close()
	lAddr := l.Addr()
	lTCPAddr, ok := lAddr.(*net.TCPAddr)
	if !ok {
		return 0, fmt.Errorf("expected *net.TCPAddr, got %v", lAddr)
	}
	port := lTCPAddr.Port
	if port <= 0 {
		return 0, fmt.Errorf("unexpected port %d", port)
	}
	return port, nil
}

func UDP() (int, error) {
	lAddr0, err := net.ResolveUDPAddr("udp4", "127.0.0.1:0")
	if err != nil {
		return 0, err
	}
	l, err := net.ListenUDP("udp4", lAddr0)
	if err != nil {
		return 0, err
	}
	defer l.Close()
	lAddr := l.LocalAddr()
	lUDPAddr, ok := lAddr.(*net.UDPAddr)
	if !ok {
		return 0, fmt.Errorf("expected *net.UDPAddr, got %v", lAddr)
	}
	port := lUDPAddr.Port
	if port <= 0 {
		return 0, fmt.Errorf("unexpected port %d", port)
	}
	return port, nil
}