ipsock_posix.go

// Copyright 2014 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 linux nacl netbsd openbsd solaris windows

// Internet protocol family sockets for POSIX

package nett

import (
	"net"
	"syscall"
)

func probeIPv4Stack() bool {
	s, err := syscall.Socket(syscall.AF_INET, syscall.SOCK_STREAM, syscall.IPPROTO_TCP)
	switch err {
	case syscall.EAFNOSUPPORT, syscall.EPROTONOSUPPORT:
		return false
	case nil:
		closesocket(s)
	}
	return true
}

// Should we try to use the IPv4 socket interface if we're
// only dealing with IPv4 sockets?  As long as the host system
// understands IPv6, it's okay to pass IPv4 addresses to the IPv6
// interface.  That simplifies our code and is most general.
// Unfortunately, we need to run on kernels built without IPv6
// support too.  So probe the kernel to figure it out.
//
// probeIPv6Stack probes both basic IPv6 capability and IPv6 IPv4-
// mapping capability which is controlled by IPV6_V6ONLY socket
// option and/or kernel state "net.inet6.ip6.v6only".
// It returns two boolean values.  If the first boolean value is
// true, kernel supports basic IPv6 functionality.  If the second
// boolean value is true, kernel supports IPv6 IPv4-mapping.
func probeIPv6Stack() (supportsIPv6, supportsIPv4map bool) {
	var probes = []struct {
		laddr net.TCPAddr
		value int
		ok    bool
	}{
		// IPv6 communication capability
		{laddr: net.TCPAddr{IP: net.ParseIP("::1")}, value: 1},
		// IPv6 IPv4-mapped address communication capability
		{laddr: net.TCPAddr{IP: net.IPv4(127, 0, 0, 1)}, value: 0},
	}

	for i := range probes {
		s, err := syscall.Socket(syscall.AF_INET6, syscall.SOCK_STREAM, syscall.IPPROTO_TCP)
		if err != nil {
			continue
		}
		defer closesocket(s)
		syscall.SetsockoptInt(s, syscall.IPPROTO_IPV6, syscall.IPV6_V6ONLY, probes[i].value)
		sa, err := tcpSockaddr(probes[i].laddr, syscall.AF_INET6)
		if err != nil {
			continue
		}
		if err := syscall.Bind(s, sa); err != nil {
			continue
		}
		probes[i].ok = true
	}

	return probes[0].ok, probes[1].ok
}

func tcpSockaddr(a net.TCPAddr, family int) (syscall.Sockaddr, error) {
	return ipToSockaddr(family, a.IP, a.Port, a.Zone)
}

func ipToSockaddr(family int, ip net.IP, port int, zone string) (syscall.Sockaddr, error) {
	switch family {
	case syscall.AF_INET:
		if len(ip) == 0 {
			ip = net.IPv4zero
		}
		if ip = ip.To4(); ip == nil {
			return nil, net.InvalidAddrError("non-IPv4 address")
		}
		sa := new(syscall.SockaddrInet4)
		for i := 0; i < net.IPv4len; i++ {
			sa.Addr[i] = ip[i]
		}
		sa.Port = port
		return sa, nil
	case syscall.AF_INET6:
		if len(ip) == 0 {
			ip = net.IPv6zero
		}
		// IPv4 callers use 0.0.0.0 to mean "announce on any available address".
		// In IPv6 mode, Linux treats that as meaning "announce on 0.0.0.0",
		// which it refuses to do.  Rewrite to the IPv6 unspecified address.
		if ip.Equal(net.IPv4zero) {
			ip = net.IPv6zero
		}
		if ip = ip.To16(); ip == nil {
			return nil, net.InvalidAddrError("non-IPv6 address")
		}
		sa := new(syscall.SockaddrInet6)
		for i := 0; i < net.IPv6len; i++ {
			sa.Addr[i] = ip[i]
		}
		sa.Port = port
		sa.ZoneId = uint32(zoneToInt(zone))
		return sa, nil
	}
	return nil, net.InvalidAddrError("unexpected socket family")
}

func zoneToInt(zone string) int {
	if zone == "" {
		return 0
	}
	if ifi, err := net.InterfaceByName(zone); err == nil {
		return ifi.Index
	}
	n, _, _ := dtoi(zone, 0)
	return n
}