// 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.

package net

import (
	
	
	
)

// BUG(rsc,mikio): On DragonFly BSD and OpenBSD, listening on the
// "tcp" and "udp" networks does not listen for both IPv4 and IPv6
// connections. This is due to the fact that IPv4 traffic will not be
// routed to an IPv6 socket - two separate sockets are required if
// both address families are to be supported.
// See inet6(4) for details.

type ipStackCapabilities struct {
	sync.Once             // guards following
	ipv4Enabled           bool
	ipv6Enabled           bool
	ipv4MappedIPv6Enabled bool
}

var ipStackCaps ipStackCapabilities

// supportsIPv4 reports whether the platform supports IPv4 networking
// functionality.
func supportsIPv4() bool {
	ipStackCaps.Once.Do(ipStackCaps.probe)
	return ipStackCaps.ipv4Enabled
}

// supportsIPv6 reports whether the platform supports IPv6 networking
// functionality.
func supportsIPv6() bool {
	ipStackCaps.Once.Do(ipStackCaps.probe)
	return ipStackCaps.ipv6Enabled
}

// supportsIPv4map reports whether the platform supports mapping an
// IPv4 address inside an IPv6 address at transport layer
// protocols. See RFC 4291, RFC 4038 and RFC 3493.
func supportsIPv4map() bool {
	ipStackCaps.Once.Do(ipStackCaps.probe)
	return ipStackCaps.ipv4MappedIPv6Enabled
}

// An addrList represents a list of network endpoint addresses.
type addrList []Addr

// isIPv4 reports whether addr contains an IPv4 address.
func isIPv4( Addr) bool {
	switch addr := .(type) {
	case *TCPAddr:
		return .IP.To4() != nil
	case *UDPAddr:
		return .IP.To4() != nil
	case *IPAddr:
		return .IP.To4() != nil
	}
	return false
}

// isNotIPv4 reports whether addr does not contain an IPv4 address.
func isNotIPv4( Addr) bool { return !isIPv4() }

// forResolve returns the most appropriate address in address for
// a call to ResolveTCPAddr, ResolveUDPAddr, or ResolveIPAddr.
// IPv4 is preferred, unless addr contains an IPv6 literal.
func ( addrList) (,  string) Addr {
	var  bool
	switch  {
	case "ip":
		// IPv6 literal (addr does NOT contain a port)
		 = count(, ':') > 0
	case "tcp", "udp":
		// IPv6 literal. (addr contains a port, so look for '[')
		 = count(, '[') > 0
	}
	if  {
		return .first(isNotIPv4)
	}
	return .first(isIPv4)
}

// first returns the first address which satisfies strategy, or if
// none do, then the first address of any kind.
func ( addrList) ( func(Addr) bool) Addr {
	for ,  := range  {
		if () {
			return 
		}
	}
	return [0]
}

// partition divides an address list into two categories, using a
// strategy function to assign a boolean label to each address.
// The first address, and any with a matching label, are returned as
// primaries, while addresses with the opposite label are returned
// as fallbacks. For non-empty inputs, primaries is guaranteed to be
// non-empty.
func ( addrList) ( func(Addr) bool) (,  addrList) {
	var  bool
	for ,  := range  {
		 := ()
		if  == 0 ||  ==  {
			 = 
			 = append(, )
		} else {
			 = append(, )
		}
	}
	return
}

// filterAddrList applies a filter to a list of IP addresses,
// yielding a list of Addr objects. Known filters are nil, ipv4only,
// and ipv6only. It returns every address when the filter is nil.
// The result contains at least one address when error is nil.
func filterAddrList( func(IPAddr) bool,  []IPAddr,  func(IPAddr) Addr,  string) (addrList, error) {
	var  addrList
	for ,  := range  {
		if  == nil || () {
			 = append(, ())
		}
	}
	if len() == 0 {
		return nil, &AddrError{Err: errNoSuitableAddress.Error(), Addr: }
	}
	return , nil
}

// ipv4only reports whether addr is an IPv4 address.
func ipv4only( IPAddr) bool {
	return .IP.To4() != nil
}

// ipv6only reports whether addr is an IPv6 address except IPv4-mapped IPv6 address.
func ipv6only( IPAddr) bool {
	return len(.IP) == IPv6len && .IP.To4() == nil
}

// SplitHostPort splits a network address of the form "host:port",
// "host%zone:port", "[host]:port" or "[host%zone]:port" into host or
// host%zone and port.
//
// A literal IPv6 address in hostport must be enclosed in square
// brackets, as in "[::1]:80", "[::1%lo0]:80".
//
// See func Dial for a description of the hostport parameter, and host
// and port results.
func ( string) (,  string,  error) {
	const (
		   = "missing port in address"
		 = "too many colons in address"
	)
	 := func(,  string) (,  string,  error) {
		return "", "", &AddrError{Err: , Addr: }
	}
	,  := 0, 0

	// The port starts after the last colon.
	 := last(, ':')
	if  < 0 {
		return (, )
	}

	if [0] == '[' {
		// Expect the first ']' just before the last ':'.
		 := bytealg.IndexByteString(, ']')
		if  < 0 {
			return (, "missing ']' in address")
		}
		switch  + 1 {
		case len():
			// There can't be a ':' behind the ']' now.
			return (, )
		case :
			// The expected result.
		default:
			// Either ']' isn't followed by a colon, or it is
			// followed by a colon that is not the last one.
			if [+1] == ':' {
				return (, )
			}
			return (, )
		}
		 = [1:]
		,  = 1, +1 // there can't be a '[' resp. ']' before these positions
	} else {
		 = [:]
		if bytealg.IndexByteString(, ':') >= 0 {
			return (, )
		}
	}
	if bytealg.IndexByteString([:], '[') >= 0 {
		return (, "unexpected '[' in address")
	}
	if bytealg.IndexByteString([:], ']') >= 0 {
		return (, "unexpected ']' in address")
	}

	 = [+1:]
	return , , nil
}

func splitHostZone( string) (,  string) {
	// The IPv6 scoped addressing zone identifier starts after the
	// last percent sign.
	if  := last(, '%');  > 0 {
		,  = [:], [+1:]
	} else {
		 = 
	}
	return
}

// JoinHostPort combines host and port into a network address of the
// form "host:port". If host contains a colon, as found in literal
// IPv6 addresses, then JoinHostPort returns "[host]:port".
//
// See func Dial for a description of the host and port parameters.
func (,  string) string {
	// We assume that host is a literal IPv6 address if host has
	// colons.
	if bytealg.IndexByteString(, ':') >= 0 {
		return "[" +  + "]:" + 
	}
	return  + ":" + 
}

// internetAddrList resolves addr, which may be a literal IP
// address or a DNS name, and returns a list of internet protocol
// family addresses. The result contains at least one address when
// error is nil.
func ( *Resolver) ( context.Context, ,  string) (addrList, error) {
	var (
		        error
		,  string
		    int
	)
	switch  {
	case "tcp", "tcp4", "tcp6", "udp", "udp4", "udp6":
		if  != "" {
			if , ,  = SplitHostPort();  != nil {
				return nil, 
			}
			if ,  = .LookupPort(, , );  != nil {
				return nil, 
			}
		}
	case "ip", "ip4", "ip6":
		if  != "" {
			 = 
		}
	default:
		return nil, UnknownNetworkError()
	}
	 := func( IPAddr) Addr {
		switch  {
		case "tcp", "tcp4", "tcp6":
			return &TCPAddr{IP: .IP, Port: , Zone: .Zone}
		case "udp", "udp4", "udp6":
			return &UDPAddr{IP: .IP, Port: , Zone: .Zone}
		case "ip", "ip4", "ip6":
			return &IPAddr{IP: .IP, Zone: .Zone}
		default:
			panic("unexpected network: " + )
		}
	}
	if  == "" {
		return addrList{(IPAddr{})}, nil
	}

	// Try as a literal IP address, then as a DNS name.
	,  := .lookupIPAddr(, , )
	if  != nil {
		return nil, 
	}
	// Issue 18806: if the machine has halfway configured
	// IPv6 such that it can bind on "::" (IPv6unspecified)
	// but not connect back to that same address, fall
	// back to dialing 0.0.0.0.
	if len() == 1 && [0].IP.Equal(IPv6unspecified) {
		 = append(, IPAddr{IP: IPv4zero})
	}

	var  func(IPAddr) bool
	if  != "" && [len()-1] == '4' {
		 = ipv4only
	}
	if  != "" && [len()-1] == '6' {
		 = ipv6only
	}
	return filterAddrList(, , , )
}

func loopbackIP( string) IP {
	if  != "" && [len()-1] == '6' {
		return IPv6loopback
	}
	return IP{127, 0, 0, 1}
}