var ctrlCtxFn func(ctx context.Context, network, address string, c syscall.RawConn) error
	if sl.ListenConfig.Control != nil {
		ctrlCtxFn = func(ctx context.Context, network, address string, c syscall.RawConn) error {
			return sl.ListenConfig.Control(network, address, c)
		}
	}
	fd, err := internetSocket(ctx, sl.network, laddr, nil, syscall.SOCK_STREAM, proto, "listen", ctrlCtxFn)

		return nil, UnknownNetworkError(sl.network)
	}
	var ctrlCtxFn func(ctx context.Context, network, address string, c syscall.RawConn) error
	if sl.ListenConfig.Control != nil {
		ctrlCtxFn = func(ctx context.Context, network, address string, c syscall.RawConn) error {
			return sl.ListenConfig.Control(network, address, c)
		}
	}
	fd, err := internetSocket(ctx, network, laddr, nil, syscall.SOCK_RAW, proto, "listen", ctrlCtxFn)

The new type [KeepAliveConfig] permits fine-tuning the keep-alive
options for TCP connections, via a new [TCPConn.SetKeepAliveConfig]

	var ctrlCtxFn func(ctx context.Context, network, address string, c syscall.RawConn) error
	if sl.ListenConfig.Control != nil {
		ctrlCtxFn = func(ctx context.Context, network, address string, c syscall.RawConn) error {
			return sl.ListenConfig.Control(network, address, c)
		}
	}
	fd, err := unixSocket(ctx, sl.network, laddr, nil, "listen", ctrlCtxFn)
	if err != nil {
		return nil, err

	var ctrlCtxFn func(ctx context.Context, network, address string, c syscall.RawConn) error
	if sl.ListenConfig.Control != nil {
		ctrlCtxFn = func(ctx context.Context, network, address string, c syscall.RawConn) error {
			return sl.ListenConfig.Control(network, address, c)
		}
	}
	fd, err := internetSocket(ctx, sl.network, laddr, nil, syscall.SOCK_DGRAM, 0, "listen", ctrlCtxFn)

	}

	handler := func(ls *localServer, ln Listener) {
		for {
			c, err := ln.Accept()
			if err != nil {
				return
			}
			c.Close()
		}
	}
	ln := newLocalListener(t, "tcp", &ListenConfig{
		KeepAlive: -1, // prevent calling hook from accepting
	})
	ls := (&streamListener{Listener: ln}).newLocalServer()
	defer ls.teardown()
	if err := ls.buildup(handler); err != nil {
		t.Fatal(err)
	}

// It is possible to have a disconnected client in this tiny window of time.
func CheckPortAvailability(host, port string, opts TCPOptions) (err error) {
	lc := &net.ListenConfig{}

	ctx, cancel := context.WithTimeout(context.Background(), time.Second)
	defer cancel()

	l, err := lc.Listen(ctx, "tcp", net.JoinHostPort(host, port))
	if err != nil {
		return err
	}

// It is possible to have a disconnected client in this tiny window of time.
func CheckPortAvailability(host, port string, opts TCPOptions) (err error) {
	lc := &net.ListenConfig{
		Control: func(network, address string, c syscall.RawConn) error {
			c.Control(func(fdPtr uintptr) {
				if opts.Interface != "" {
					// When interface is specified look for specifically port availability on

func (sl *sysListener) listenTCP(ctx context.Context, laddr *TCPAddr) (*TCPListener, error) {
	fd, err := listenPlan9(ctx, sl.network, laddr)
	if err != nil {
		return nil, err
	}
	return &TCPListener{fd: fd, lc: sl.ListenConfig}, nil

package net

import (
	"bytes"
	"context"
	"errors"
	"syscall"
	"testing"
)

func newLocalListenerMPTCP(t *testing.T, envVar bool) Listener {
	lc := &ListenConfig{}

	if envVar {
		if !lc.MultipathTCP() {
			t.Fatal("MultipathTCP Listen is not on despite GODEBUG=multipathtcp=1")
		}
	} else {
		if lc.MultipathTCP() {
			t.Error("MultipathTCP should be off by default")