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// Copyright 2009 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 freebsd linux netbsd openbsd windows

package net

import "syscall"

// 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 {
                la TCPAddr
                ok bool
        }{
                // IPv6 communication capability
                {TCPAddr{IP: ParseIP("::1")}, false},
                // IPv6 IPv4-mapped address communication capability
                {TCPAddr{IP: IPv4(127, 0, 0, 1)}, false},
        }

        for i := range probes {
                s, err := syscall.Socket(syscall.AF_INET6, syscall.SOCK_STREAM, syscall.IPPROTO_TCP)
                if err != nil {
                        continue
                }
                defer closesocket(s)
                sa, err := probes[i].la.toAddr().sockaddr(syscall.AF_INET6)
                if err != nil {
                        continue
                }
                err = syscall.Bind(s, sa)
                if err != nil {
                        continue
                }
                probes[i].ok = true
        }

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

// favoriteAddrFamily returns the appropriate address family to
// the given net, raddr, laddr and mode.  At first it figures
// address family out from the net.  If mode indicates "listen"
// and laddr.(type).IP is nil, it assumes that the user wants to
// make a passive connection with wildcard address family, both
// INET and INET6, and wildcard address.  Otherwise guess: if the
// addresses are IPv4 then returns INET, or else returns INET6.
func favoriteAddrFamily(net string, raddr, laddr sockaddr, mode string) int {
        switch net[len(net)-1] {
        case '4':
                return syscall.AF_INET
        case '6':
                return syscall.AF_INET6
        }

        if mode == "listen" {
                switch a := laddr.(type) {
                case *TCPAddr:
                        if a.IP == nil && supportsIPv6 {
                                return syscall.AF_INET6
                        }
                case *UDPAddr:
                        if a.IP == nil && supportsIPv6 {
                                return syscall.AF_INET6
                        }
                case *IPAddr:
                        if a.IP == nil && supportsIPv6 {
                                return syscall.AF_INET6
                        }
                }
        }

        if (laddr == nil || laddr.family() == syscall.AF_INET) &&
                (raddr == nil || raddr.family() == syscall.AF_INET) {
                return syscall.AF_INET
        }
        return syscall.AF_INET6
}

// Internet sockets (TCP, UDP)

// A sockaddr represents a TCP or UDP network address that can
// be converted into a syscall.Sockaddr.
type sockaddr interface {
        Addr
        sockaddr(family int) (syscall.Sockaddr, error)
        family() int
}

func internetSocket(net string, laddr, raddr sockaddr, sotype, proto int, mode string, toAddr func(syscall.Sockaddr) Addr) (fd *netFD, err error) {
        var oserr error
        var la, ra syscall.Sockaddr
        family := favoriteAddrFamily(net, raddr, laddr, mode)
        if laddr != nil {
                if la, oserr = laddr.sockaddr(family); oserr != nil {
                        goto Error
                }
        }
        if raddr != nil {
                if ra, oserr = raddr.sockaddr(family); oserr != nil {
                        goto Error
                }
        }
        fd, oserr = socket(net, family, sotype, proto, la, ra, toAddr)
        if oserr != nil {
                goto Error
        }
        return fd, nil

Error:
        addr := raddr
        if mode == "listen" {
                addr = laddr
        }
        return nil, &OpError{mode, net, addr, oserr}
}

func ipToSockaddr(family int, ip IP, port int) (syscall.Sockaddr, error) {
        switch family {
        case syscall.AF_INET:
                if len(ip) == 0 {
                        ip = IPv4zero
                }
                if ip = ip.To4(); ip == nil {
                        return nil, InvalidAddrError("non-IPv4 address")
                }
                s := new(syscall.SockaddrInet4)
                for i := 0; i < IPv4len; i++ {
                        s.Addr[i] = ip[i]
                }
                s.Port = port
                return s, nil
        case syscall.AF_INET6:
                if len(ip) == 0 {
                        ip = 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 all zeros.
                if ip.Equal(IPv4zero) {
                        ip = IPv6zero
                }
                if ip = ip.To16(); ip == nil {
                        return nil, InvalidAddrError("non-IPv6 address")
                }
                s := new(syscall.SockaddrInet6)
                for i := 0; i < IPv6len; i++ {
                        s.Addr[i] = ip[i]
                }
                s.Port = port
                return s, nil
        }
        return nil, InvalidAddrError("unexpected socket family")
}