Source File
	sockopt_bsd.go

Belonging Package
	net

// Copyright 2011 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// +build darwin dragonfly freebsd netbsd openbsd

package net

import (
	"os"
	"runtime"
	"syscall"
)

func setDefaultSockopts(s, family, sotype int, ipv6only bool) error {
	if runtime.GOOS == "dragonfly" && sotype != syscall.SOCK_RAW {
		// On DragonFly BSD, we adjust the ephemeral port
		// range because unlike other BSD systems its default
		// port range doesn't conform to IANA recommendation
		// as described in RFC 6056 and is pretty narrow.
		switch family {
		case syscall.AF_INET:
			syscall.SetsockoptInt(s, syscall.IPPROTO_IP, syscall.IP_PORTRANGE, syscall.IP_PORTRANGE_HIGH)
		case syscall.AF_INET6:
			syscall.SetsockoptInt(s, syscall.IPPROTO_IPV6, syscall.IPV6_PORTRANGE, syscall.IPV6_PORTRANGE_HIGH)
		}
	}
	if supportsIPv4map() && family == syscall.AF_INET6 && sotype != syscall.SOCK_RAW {
		// Allow both IP versions even if the OS default
		// is otherwise. Note that some operating systems
		// never admit this option.
		syscall.SetsockoptInt(s, syscall.IPPROTO_IPV6, syscall.IPV6_V6ONLY, boolint(ipv6only))
	}
	if (sotype == syscall.SOCK_DGRAM || sotype == syscall.SOCK_RAW) && family != syscall.AF_UNIX {
		// Allow broadcast.
		return os.NewSyscallError("setsockopt", syscall.SetsockoptInt(s, syscall.SOL_SOCKET, syscall.SO_BROADCAST, 1))
	}
	return nil
}

func setDefaultListenerSockopts(s int) error {
	// Allow reuse of recently-used addresses.
	return os.NewSyscallError("setsockopt", syscall.SetsockoptInt(s, syscall.SOL_SOCKET, syscall.SO_REUSEADDR, 1))
}

func setDefaultMulticastSockopts(s int) error {
	// Allow multicast UDP and raw IP datagram sockets to listen
	// concurrently across multiple listeners.
	if err := syscall.SetsockoptInt(s, syscall.SOL_SOCKET, syscall.SO_REUSEADDR, 1); err != nil {
		return os.NewSyscallError("setsockopt", err)
	}
	// Allow reuse of recently-used ports.
	// This option is supported only in descendants of 4.4BSD,
	// to make an effective multicast application that requires
	// quick draw possible.
	return os.NewSyscallError("setsockopt", syscall.SetsockoptInt(s, syscall.SOL_SOCKET, syscall.SO_REUSEPORT, 1))
}

The pages are generated with Golds v0.2.8-preview. (GOOS=darwin GOARCH=arm64)