src/net/ip.go - go - Git at Google

 // 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.

 // IP address manipulations
 //
 // IPv4 addresses are 4 bytes; IPv6 addresses are 16 bytes.
 // An IPv4 address can be converted to an IPv6 address by
 // adding a canonical prefix (10 zeros, 2 0xFFs).
 // This library accepts either size of byte slice but always
 // returns 16-byte addresses.

 package net

 import "errors"

 // IP address lengths (bytes).
 const (
 	IPv4len = 4
 	IPv6len = 16
 )

 // An IP is a single IP address, a slice of bytes.
 // Functions in this package accept either 4-byte (IPv4)
 // or 16-byte (IPv6) slices as input.
 //
 // Note that in this documentation, referring to an
 // IP address as an IPv4 address or an IPv6 address
 // is a semantic property of the address, not just the
 // length of the byte slice: a 16-byte slice can still
 // be an IPv4 address.
 type IP []byte

 // An IP mask is an IP address.
 type IPMask []byte

 // An IPNet represents an IP network.
 type IPNet struct {
 	IP   IP     // network number
 	Mask IPMask // network mask
 }

 // IPv4 returns the IP address (in 16-byte form) of the
 // IPv4 address a.b.c.d.
 func IPv4(a, b, c, d byte) IP {
 	p := make(IP, IPv6len)
 	copy(p, v4InV6Prefix)
 	p[12] = a
 	p[13] = b
 	p[14] = c
 	p[15] = d
 	return p
 }

 var v4InV6Prefix = []byte{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0xff, 0xff}

 // IPv4Mask returns the IP mask (in 4-byte form) of the
 // IPv4 mask a.b.c.d.
 func IPv4Mask(a, b, c, d byte) IPMask {
 	p := make(IPMask, IPv4len)
 	p[0] = a
 	p[1] = b
 	p[2] = c
 	p[3] = d
 	return p
 }

 // CIDRMask returns an IPMask consisting of `ones' 1 bits
 // followed by 0s up to a total length of `bits' bits.
 // For a mask of this form, CIDRMask is the inverse of IPMask.Size.
 func CIDRMask(ones, bits int) IPMask {
 	if bits != 8*IPv4len && bits != 8*IPv6len {
 		return nil
 	}
 	if ones < 0 || ones > bits {
 		return nil
 	}
 	l := bits / 8
 	m := make(IPMask, l)
 	n := uint(ones)
 	for i := 0; i < l; i++ {
 		if n >= 8 {
 			m[i] = 0xff
 			n -= 8
 			continue
 		}
 		m[i] = ^byte(0xff >> n)
 		n = 0
 	}
 	return m
 }

 // Well-known IPv4 addresses
 var (
 	IPv4bcast     = IPv4(255, 255, 255, 255) // broadcast
 	IPv4allsys    = IPv4(224, 0, 0, 1)       // all systems
 	IPv4allrouter = IPv4(224, 0, 0, 2)       // all routers
 	IPv4zero      = IPv4(0, 0, 0, 0)         // all zeros
 )

 // Well-known IPv6 addresses
 var (
 	IPv6zero                   = IP{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}
 	IPv6unspecified            = IP{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}
 	IPv6loopback               = IP{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1}
 	IPv6interfacelocalallnodes = IP{0xff, 0x01, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0x01}
 	IPv6linklocalallnodes      = IP{0xff, 0x02, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0x01}
 	IPv6linklocalallrouters    = IP{0xff, 0x02, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0x02}
 )

 // IsUnspecified returns true if ip is an unspecified address.
 func (ip IP) IsUnspecified() bool {
 	if ip.Equal(IPv4zero) || ip.Equal(IPv6unspecified) {
 		return true
 	}
 	return false
 }

 // IsLoopback returns true if ip is a loopback address.
 func (ip IP) IsLoopback() bool {
 	if ip4 := ip.To4(); ip4 != nil && ip4[0] == 127 {
 		return true
 	}
 	return ip.Equal(IPv6loopback)
 }

 // IsMulticast returns true if ip is a multicast address.
 func (ip IP) IsMulticast() bool {
 	if ip4 := ip.To4(); ip4 != nil && ip4[0]&0xf0 == 0xe0 {
 		return true
 	}
 	return ip[0] == 0xff
 }

 // IsInterfaceLinkLocalMulticast returns true if ip is
 // an interface-local multicast address.
 func (ip IP) IsInterfaceLocalMulticast() bool {
 	return len(ip) == IPv6len && ip[0] == 0xff && ip[1]&0x0f == 0x01
 }

 // IsLinkLocalMulticast returns true if ip is a link-local
 // multicast address.
 func (ip IP) IsLinkLocalMulticast() bool {
 	if ip4 := ip.To4(); ip4 != nil && ip4[0] == 224 && ip4[1] == 0 && ip4[2] == 0 {
 		return true
 	}
 	return ip[0] == 0xff && ip[1]&0x0f == 0x02
 }

 // IsLinkLocalUnicast returns true if ip is a link-local
 // unicast address.
 func (ip IP) IsLinkLocalUnicast() bool {
 	if ip4 := ip.To4(); ip4 != nil && ip4[0] == 169 && ip4[1] == 254 {
 		return true
 	}
 	return ip[0] == 0xfe && ip[1]&0xc0 == 0x80
 }

 // IsGlobalUnicast returns true if ip is a global unicast
 // address.
 func (ip IP) IsGlobalUnicast() bool {
 	return !ip.IsUnspecified() &&
 		!ip.IsLoopback() &&
 		!ip.IsMulticast() &&
 		!ip.IsLinkLocalUnicast()
 }

 // Is p all zeros?
 func isZeros(p IP) bool {
 	for i := 0; i < len(p); i++ {
 		if p[i] != 0 {
 			return false
 		}
 	}
 	return true
 }

 // To4 converts the IPv4 address ip to a 4-byte representation.
 // If ip is not an IPv4 address, To4 returns nil.
 func (ip IP) To4() IP {
 	if len(ip) == IPv4len {
 		return ip
 	}
 	if len(ip) == IPv6len &&
 		isZeros(ip[0:10]) &&
 		ip[10] == 0xff &&
 		ip[11] == 0xff {
 		return ip[12:16]
 	}
 	return nil
 }

 // To16 converts the IP address ip to a 16-byte representation.
 // If ip is not an IP address (it is the wrong length), To16 returns nil.
 func (ip IP) To16() IP {
 	if len(ip) == IPv4len {
 		return IPv4(ip[0], ip[1], ip[2], ip[3])
 	}
 	if len(ip) == IPv6len {
 		return ip
 	}
 	return nil
 }

 // Default route masks for IPv4.
 var (
 	classAMask = IPv4Mask(0xff, 0, 0, 0)
 	classBMask = IPv4Mask(0xff, 0xff, 0, 0)
 	classCMask = IPv4Mask(0xff, 0xff, 0xff, 0)
 )

 // DefaultMask returns the default IP mask for the IP address ip.
 // Only IPv4 addresses have default masks; DefaultMask returns
 // nil if ip is not a valid IPv4 address.
 func (ip IP) DefaultMask() IPMask {
 	if ip = ip.To4(); ip == nil {
 		return nil
 	}
 	switch true {
 	case ip[0] < 0x80:
 		return classAMask
 	case ip[0] < 0xC0:
 		return classBMask
 	default:
 		return classCMask
 	}
 }

 func allFF(b []byte) bool {
 	for _, c := range b {
 		if c != 0xff {
 			return false
 		}
 	}
 	return true
 }

 // Mask returns the result of masking the IP address ip with mask.
 func (ip IP) Mask(mask IPMask) IP {
 	if len(mask) == IPv6len && len(ip) == IPv4len && allFF(mask[:12]) {
 		mask = mask[12:]
 	}
 	if len(mask) == IPv4len && len(ip) == IPv6len && bytesEqual(ip[:12], v4InV6Prefix) {
 		ip = ip[12:]
 	}
 	n := len(ip)
 	if n != len(mask) {
 		return nil
 	}
 	out := make(IP, n)
 	for i := 0; i < n; i++ {
 		out[i] = ip[i] & mask[i]
 	}
 	return out
 }

 // String returns the string form of the IP address ip.
 // If the address is an IPv4 address, the string representation
 // is dotted decimal ("74.125.19.99").  Otherwise the representation
 // is IPv6 ("2001:4860:0:2001::68").
 func (ip IP) String() string {
 	p := ip

 	if len(ip) == 0 {
 		return "<nil>"
 	}

 	// If IPv4, use dotted notation.
 	if p4 := p.To4(); len(p4) == IPv4len {
 		return itod(uint(p4[0])) + "." +
 			itod(uint(p4[1])) + "." +
 			itod(uint(p4[2])) + "." +
 			itod(uint(p4[3]))
 	}
 	if len(p) != IPv6len {
 		return "?"
 	}

 	// Find longest run of zeros.
 	e0 := -1
 	e1 := -1
 	for i := 0; i < IPv6len; i += 2 {
 		j := i
 		for j < IPv6len && p[j] == 0 && p[j+1] == 0 {
 			j += 2
 		}
 		if j > i && j-i > e1-e0 {
 			e0 = i
 			e1 = j
 			i = j
 		}
 	}
 	// The symbol "::" MUST NOT be used to shorten just one 16 bit 0 field.
 	if e1-e0 <= 2 {
 		e0 = -1
 		e1 = -1
 	}

 	const maxLen = len("ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff")
 	b := make([]byte, 0, maxLen)

 	// Print with possible :: in place of run of zeros
 	for i := 0; i < IPv6len; i += 2 {
 		if i == e0 {
 			b = append(b, ':', ':')
 			i = e1
 			if i >= IPv6len {
 				break
 			}
 		} else if i > 0 {
 			b = append(b, ':')
 		}
 		b = appendHex(b, (uint32(p[i])<<8)|uint32(p[i+1]))
 	}
 	return string(b)
 }

 // ipEmptyString is like ip.String except that it returns
 // an empty string when ip is unset.
 func ipEmptyString(ip IP) string {
 	if len(ip) == 0 {
 		return ""
 	}
 	return ip.String()
 }

 // MarshalText implements the encoding.TextMarshaler interface.
 // The encoding is the same as returned by String.
 func (ip IP) MarshalText() ([]byte, error) {
 	if len(ip) == 0 {
 		return []byte(""), nil
 	}
 	if len(ip) != IPv4len && len(ip) != IPv6len {
 		return nil, errors.New("invalid IP address")
 	}
 	return []byte(ip.String()), nil
 }

 // UnmarshalText implements the encoding.TextUnmarshaler interface.
 // The IP address is expected in a form accepted by ParseIP.
 func (ip *IP) UnmarshalText(text []byte) error {
 	if len(text) == 0 {
 		*ip = nil
 		return nil
 	}
 	s := string(text)
 	x := ParseIP(s)
 	if x == nil {
 		return &ParseError{"IP address", s}
 	}
 	*ip = x
 	return nil
 }

 // Equal returns true if ip and x are the same IP address.
 // An IPv4 address and that same address in IPv6 form are
 // considered to be equal.
 func (ip IP) Equal(x IP) bool {
 	if len(ip) == len(x) {
 		return bytesEqual(ip, x)
 	}
 	if len(ip) == IPv4len && len(x) == IPv6len {
 		return bytesEqual(x[0:12], v4InV6Prefix) && bytesEqual(ip, x[12:])
 	}
 	if len(ip) == IPv6len && len(x) == IPv4len {
 		return bytesEqual(ip[0:12], v4InV6Prefix) && bytesEqual(ip[12:], x)
 	}
 	return false
 }

 func bytesEqual(x, y []byte) bool {
 	if len(x) != len(y) {
 		return false
 	}
 	for i, b := range x {
 		if y[i] != b {
 			return false
 		}
 	}
 	return true
 }

 // If mask is a sequence of 1 bits followed by 0 bits,
 // return the number of 1 bits.
 func simpleMaskLength(mask IPMask) int {
 	var n int
 	for i, v := range mask {
 		if v == 0xff {
 			n += 8
 			continue
 		}
 		// found non-ff byte
 		// count 1 bits
 		for v&0x80 != 0 {
 			n++
 			v <<= 1
 		}
 		// rest must be 0 bits
 		if v != 0 {
 			return -1
 		}
 		for i++; i < len(mask); i++ {
 			if mask[i] != 0 {
 				return -1
 			}
 		}
 		break
 	}
 	return n
 }

 // Size returns the number of leading ones and total bits in the mask.
 // If the mask is not in the canonical form--ones followed by zeros--then
 // Size returns 0, 0.
 func (m IPMask) Size() (ones, bits int) {
 	ones, bits = simpleMaskLength(m), len(m)*8
 	if ones == -1 {
 		return 0, 0
 	}
 	return
 }

 // String returns the hexadecimal form of m, with no punctuation.
 func (m IPMask) String() string {
 	if len(m) == 0 {
 		return "<nil>"
 	}
 	buf := make([]byte, len(m)*2)
 	for i, b := range m {
 		buf[i*2], buf[i*2+1] = hexDigit[b>>4], hexDigit[b&0xf]
 	}
 	return string(buf)
 }

 func networkNumberAndMask(n *IPNet) (ip IP, m IPMask) {
 	if ip = n.IP.To4(); ip == nil {
 		ip = n.IP
 		if len(ip) != IPv6len {
 			return nil, nil
 		}
 	}
 	m = n.Mask
 	switch len(m) {
 	case IPv4len:
 		if len(ip) != IPv4len {
 			return nil, nil
 		}
 	case IPv6len:
 		if len(ip) == IPv4len {
 			m = m[12:]
 		}
 	default:
 		return nil, nil
 	}
 	return
 }

 // Contains reports whether the network includes ip.
 func (n *IPNet) Contains(ip IP) bool {
 	nn, m := networkNumberAndMask(n)
 	if x := ip.To4(); x != nil {
 		ip = x
 	}
 	l := len(ip)
 	if l != len(nn) {
 		return false
 	}
 	for i := 0; i < l; i++ {
 		if nn[i]&m[i] != ip[i]&m[i] {
 			return false
 		}
 	}
 	return true
 }

 // Network returns the address's network name, "ip+net".
 func (n *IPNet) Network() string { return "ip+net" }

 // String returns the CIDR notation of n like "192.168.100.1/24"
 // or "2001:DB8::/48" as defined in RFC 4632 and RFC 4291.
 // If the mask is not in the canonical form, it returns the
 // string which consists of an IP address, followed by a slash
 // character and a mask expressed as hexadecimal form with no
 // punctuation like "192.168.100.1/c000ff00".
 func (n *IPNet) String() string {
 	nn, m := networkNumberAndMask(n)
 	if nn == nil || m == nil {
 		return "<nil>"
 	}
 	l := simpleMaskLength(m)
 	if l == -1 {
 		return nn.String() + "/" + m.String()
 	}
 	return nn.String() + "/" + itod(uint(l))
 }

 // Parse IPv4 address (d.d.d.d).
 func parseIPv4(s string) IP {
 	var p [IPv4len]byte
 	i := 0
 	for j := 0; j < IPv4len; j++ {
 		if i >= len(s) {
 			// Missing octets.
 			return nil
 		}
 		if j > 0 {
 			if s[i] != '.' {
 				return nil
 			}
 			i++
 		}
 		var (
 			n  int
 			ok bool
 		)
 		n, i, ok = dtoi(s, i)
 		if !ok || n > 0xFF {
 			return nil
 		}
 		p[j] = byte(n)
 	}
 	if i != len(s) {
 		return nil
 	}
 	return IPv4(p[0], p[1], p[2], p[3])
 }

 // parseIPv6 parses s as a literal IPv6 address described in RFC 4291
 // and RFC 5952.  It can also parse a literal scoped IPv6 address with
 // zone identifier which is described in RFC 4007 when zoneAllowed is
 // true.
 func parseIPv6(s string, zoneAllowed bool) (ip IP, zone string) {
 	ip = make(IP, IPv6len)
 	ellipsis := -1 // position of ellipsis in p
 	i := 0         // index in string s

 	if zoneAllowed {
 		s, zone = splitHostZone(s)
 	}

 	// Might have leading ellipsis
 	if len(s) >= 2 && s[0] == ':' && s[1] == ':' {
 		ellipsis = 0
 		i = 2
 		// Might be only ellipsis
 		if i == len(s) {
 			return ip, zone
 		}
 	}

 	// Loop, parsing hex numbers followed by colon.
 	j := 0
 	for j < IPv6len {
 		// Hex number.
 		n, i1, ok := xtoi(s, i)
 		if !ok || n > 0xFFFF {
 			return nil, zone
 		}

 		// If followed by dot, might be in trailing IPv4.
 		if i1 < len(s) && s[i1] == '.' {
 			if ellipsis < 0 && j != IPv6len-IPv4len {
 				// Not the right place.
 				return nil, zone
 			}
 			if j+IPv4len > IPv6len {
 				// Not enough room.
 				return nil, zone
 			}
 			ip4 := parseIPv4(s[i:])
 			if ip4 == nil {
 				return nil, zone
 			}
 			ip[j] = ip4[12]
 			ip[j+1] = ip4[13]
 			ip[j+2] = ip4[14]
 			ip[j+3] = ip4[15]
 			i = len(s)
 			j += IPv4len
 			break
 		}

 		// Save this 16-bit chunk.
 		ip[j] = byte(n >> 8)
 		ip[j+1] = byte(n)
 		j += 2

 		// Stop at end of string.
 		i = i1
 		if i == len(s) {
 			break
 		}

 		// Otherwise must be followed by colon and more.
 		if s[i] != ':' || i+1 == len(s) {
 			return nil, zone
 		}
 		i++

 		// Look for ellipsis.
 		if s[i] == ':' {
 			if ellipsis >= 0 { // already have one
 				return nil, zone
 			}
 			ellipsis = j
 			if i++; i == len(s) { // can be at end
 				break
 			}
 		}
 	}

 	// Must have used entire string.
 	if i != len(s) {
 		return nil, zone
 	}

 	// If didn't parse enough, expand ellipsis.
 	if j < IPv6len {
 		if ellipsis < 0 {
 			return nil, zone
 		}
 		n := IPv6len - j
 		for k := j - 1; k >= ellipsis; k-- {
 			ip[k+n] = ip[k]
 		}
 		for k := ellipsis + n - 1; k >= ellipsis; k-- {
 			ip[k] = 0
 		}
 	} else if ellipsis >= 0 {
 		// Ellipsis must represent at least one 0 group.
 		return nil, zone
 	}
 	return ip, zone
 }

 // A ParseError represents a malformed text string and the type of string that was expected.
 type ParseError struct {
 	Type string
 	Text string
 }

 func (e *ParseError) Error() string {
 	return "invalid " + e.Type + ": " + e.Text
 }

 // ParseIP parses s as an IP address, returning the result.
 // The string s can be in dotted decimal ("74.125.19.99")
 // or IPv6 ("2001:4860:0:2001::68") form.
 // If s is not a valid textual representation of an IP address,
 // ParseIP returns nil.
 func ParseIP(s string) IP {
 	for i := 0; i < len(s); i++ {
 		switch s[i] {
 		case '.':
 			return parseIPv4(s)
 		case ':':
 			ip, _ := parseIPv6(s, false)
 			return ip
 		}
 	}
 	return nil
 }

 // ParseCIDR parses s as a CIDR notation IP address and mask,
 // like "192.168.100.1/24" or "2001:DB8::/48", as defined in
 // RFC 4632 and RFC 4291.
 //
 // It returns the IP address and the network implied by the IP
 // and mask.  For example, ParseCIDR("192.168.100.1/16") returns
 // the IP address 192.168.100.1 and the network 192.168.0.0/16.
 func ParseCIDR(s string) (IP, *IPNet, error) {
 	i := byteIndex(s, '/')
 	if i < 0 {
 		return nil, nil, &ParseError{"CIDR address", s}
 	}
 	addr, mask := s[:i], s[i+1:]
 	iplen := IPv4len
 	ip := parseIPv4(addr)
 	if ip == nil {
 		iplen = IPv6len
 		ip, _ = parseIPv6(addr, false)
 	}
 	n, i, ok := dtoi(mask, 0)
 	if ip == nil || !ok || i != len(mask) || n < 0 || n > 8*iplen {
 		return nil, nil, &ParseError{"CIDR address", s}
 	}
 	m := CIDRMask(n, 8*iplen)
 	return ip, &IPNet{IP: ip.Mask(m), Mask: m}, nil
 }
	// 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.

	// IP address manipulations
	//
	// IPv4 addresses are 4 bytes; IPv6 addresses are 16 bytes.
	// An IPv4 address can be converted to an IPv6 address by
	// adding a canonical prefix (10 zeros, 2 0xFFs).
	// This library accepts either size of byte slice but always
	// returns 16-byte addresses.

	package net

	import "errors"

	// IP address lengths (bytes).
	const (
	IPv4len = 4
	IPv6len = 16
	)

	// An IP is a single IP address, a slice of bytes.
	// Functions in this package accept either 4-byte (IPv4)
	// or 16-byte (IPv6) slices as input.
	//
	// Note that in this documentation, referring to an
	// IP address as an IPv4 address or an IPv6 address
	// is a semantic property of the address, not just the
	// length of the byte slice: a 16-byte slice can still
	// be an IPv4 address.
	type IP []byte

	// An IP mask is an IP address.
	type IPMask []byte

	// An IPNet represents an IP network.
	type IPNet struct {
	IP IP // network number
	Mask IPMask // network mask
	}

	// IPv4 returns the IP address (in 16-byte form) of the
	// IPv4 address a.b.c.d.
	func IPv4(a, b, c, d byte) IP {
	p := make(IP, IPv6len)
	copy(p, v4InV6Prefix)
	p[12] = a
	p[13] = b
	p[14] = c
	p[15] = d
	return p
	}

	var v4InV6Prefix = []byte{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0xff, 0xff}

	// IPv4Mask returns the IP mask (in 4-byte form) of the
	// IPv4 mask a.b.c.d.
	func IPv4Mask(a, b, c, d byte) IPMask {
	p := make(IPMask, IPv4len)
	p[0] = a
	p[1] = b
	p[2] = c
	p[3] = d
	return p
	}

	// CIDRMask returns an IPMask consisting of `ones' 1 bits
	// followed by 0s up to a total length of `bits' bits.
	// For a mask of this form, CIDRMask is the inverse of IPMask.Size.
	func CIDRMask(ones, bits int) IPMask {
	if bits != 8IPv4len && bits != 8IPv6len {
	return nil
	}
	if ones < 0 \|\| ones > bits {
	return nil
	}
	l := bits / 8
	m := make(IPMask, l)
	n := uint(ones)
	for i := 0; i < l; i++ {
	if n >= 8 {
	m[i] = 0xff
	n -= 8
	continue
	}
	m[i] = ^byte(0xff >> n)
	n = 0
	}
	return m
	}

	// Well-known IPv4 addresses
	var (
	IPv4bcast = IPv4(255, 255, 255, 255) // broadcast
	IPv4allsys = IPv4(224, 0, 0, 1) // all systems
	IPv4allrouter = IPv4(224, 0, 0, 2) // all routers
	IPv4zero = IPv4(0, 0, 0, 0) // all zeros
	)

	// Well-known IPv6 addresses
	var (
	IPv6zero = IP{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}
	IPv6unspecified = IP{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}
	IPv6loopback = IP{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1}
	IPv6interfacelocalallnodes = IP{0xff, 0x01, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0x01}
	IPv6linklocalallnodes = IP{0xff, 0x02, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0x01}
	IPv6linklocalallrouters = IP{0xff, 0x02, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0x02}
	)

	// IsUnspecified returns true if ip is an unspecified address.
	func (ip IP) IsUnspecified() bool {
	if ip.Equal(IPv4zero) \|\| ip.Equal(IPv6unspecified) {
	return true
	}
	return false
	}

	// IsLoopback returns true if ip is a loopback address.
	func (ip IP) IsLoopback() bool {
	if ip4 := ip.To4(); ip4 != nil && ip4[0] == 127 {
	return true
	}
	return ip.Equal(IPv6loopback)
	}

	// IsMulticast returns true if ip is a multicast address.
	func (ip IP) IsMulticast() bool {
	if ip4 := ip.To4(); ip4 != nil && ip4[0]&0xf0 == 0xe0 {
	return true
	}
	return ip[0] == 0xff
	}

	// IsInterfaceLinkLocalMulticast returns true if ip is
	// an interface-local multicast address.
	func (ip IP) IsInterfaceLocalMulticast() bool {
	return len(ip) == IPv6len && ip[0] == 0xff && ip[1]&0x0f == 0x01
	}

	// IsLinkLocalMulticast returns true if ip is a link-local
	// multicast address.
	func (ip IP) IsLinkLocalMulticast() bool {
	if ip4 := ip.To4(); ip4 != nil && ip4[0] == 224 && ip4[1] == 0 && ip4[2] == 0 {
	return true
	}
	return ip[0] == 0xff && ip[1]&0x0f == 0x02
	}

	// IsLinkLocalUnicast returns true if ip is a link-local
	// unicast address.
	func (ip IP) IsLinkLocalUnicast() bool {
	if ip4 := ip.To4(); ip4 != nil && ip4[0] == 169 && ip4[1] == 254 {
	return true
	}
	return ip[0] == 0xfe && ip[1]&0xc0 == 0x80
	}

	// IsGlobalUnicast returns true if ip is a global unicast
	// address.
	func (ip IP) IsGlobalUnicast() bool {
	return !ip.IsUnspecified() &&
	!ip.IsLoopback() &&
	!ip.IsMulticast() &&
	!ip.IsLinkLocalUnicast()
	}

	// Is p all zeros?
	func isZeros(p IP) bool {
	for i := 0; i < len(p); i++ {
	if p[i] != 0 {
	return false
	}
	}
	return true
	}

	// To4 converts the IPv4 address ip to a 4-byte representation.
	// If ip is not an IPv4 address, To4 returns nil.
	func (ip IP) To4() IP {
	if len(ip) == IPv4len {
	return ip
	}
	if len(ip) == IPv6len &&
	isZeros(ip[0:10]) &&
	ip[10] == 0xff &&
	ip[11] == 0xff {
	return ip[12:16]
	}
	return nil
	}

	// To16 converts the IP address ip to a 16-byte representation.
	// If ip is not an IP address (it is the wrong length), To16 returns nil.
	func (ip IP) To16() IP {
	if len(ip) == IPv4len {
	return IPv4(ip[0], ip[1], ip[2], ip[3])
	}
	if len(ip) == IPv6len {
	return ip
	}
	return nil
	}

	// Default route masks for IPv4.
	var (
	classAMask = IPv4Mask(0xff, 0, 0, 0)
	classBMask = IPv4Mask(0xff, 0xff, 0, 0)
	classCMask = IPv4Mask(0xff, 0xff, 0xff, 0)
	)

	// DefaultMask returns the default IP mask for the IP address ip.
	// Only IPv4 addresses have default masks; DefaultMask returns
	// nil if ip is not a valid IPv4 address.
	func (ip IP) DefaultMask() IPMask {
	if ip = ip.To4(); ip == nil {
	return nil
	}
	switch true {
	case ip[0] < 0x80:
	return classAMask
	case ip[0] < 0xC0:
	return classBMask
	default:
	return classCMask
	}
	}

	func allFF(b []byte) bool {
	for _, c := range b {
	if c != 0xff {
	return false
	}
	}
	return true
	}

	// Mask returns the result of masking the IP address ip with mask.
	func (ip IP) Mask(mask IPMask) IP {
	if len(mask) == IPv6len && len(ip) == IPv4len && allFF(mask[:12]) {
	mask = mask[12:]
	}
	if len(mask) == IPv4len && len(ip) == IPv6len && bytesEqual(ip[:12], v4InV6Prefix) {
	ip = ip[12:]
	}
	n := len(ip)
	if n != len(mask) {
	return nil
	}
	out := make(IP, n)
	for i := 0; i < n; i++ {
	out[i] = ip[i] & mask[i]
	}
	return out
	}

	// String returns the string form of the IP address ip.
	// If the address is an IPv4 address, the string representation
	// is dotted decimal ("74.125.19.99"). Otherwise the representation
	// is IPv6 ("2001:4860:0:2001::68").
	func (ip IP) String() string {
	p := ip

	if len(ip) == 0 {
	return "<nil>"
	}

	// If IPv4, use dotted notation.
	if p4 := p.To4(); len(p4) == IPv4len {
	return itod(uint(p4[0])) + "." +
	itod(uint(p4[1])) + "." +
	itod(uint(p4[2])) + "." +
	itod(uint(p4[3]))
	}
	if len(p) != IPv6len {
	return "?"
	}

	// Find longest run of zeros.
	e0 := -1
	e1 := -1
	for i := 0; i < IPv6len; i += 2 {
	j := i
	for j < IPv6len && p[j] == 0 && p[j+1] == 0 {
	j += 2
	}
	if j > i && j-i > e1-e0 {
	e0 = i
	e1 = j
	i = j
	}
	}
	// The symbol "::" MUST NOT be used to shorten just one 16 bit 0 field.
	if e1-e0 <= 2 {
	e0 = -1
	e1 = -1
	}

	const maxLen = len("ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff")
	b := make([]byte, 0, maxLen)

	// Print with possible :: in place of run of zeros
	for i := 0; i < IPv6len; i += 2 {
	if i == e0 {
	b = append(b, ':', ':')
	i = e1
	if i >= IPv6len {
	break
	}
	} else if i > 0 {
	b = append(b, ':')
	}
	b = appendHex(b, (uint32(p[i])<<8)\|uint32(p[i+1]))
	}
	return string(b)
	}

	// ipEmptyString is like ip.String except that it returns
	// an empty string when ip is unset.
	func ipEmptyString(ip IP) string {
	if len(ip) == 0 {
	return ""
	}
	return ip.String()
	}

	// MarshalText implements the encoding.TextMarshaler interface.
	// The encoding is the same as returned by String.
	func (ip IP) MarshalText() ([]byte, error) {
	if len(ip) == 0 {
	return []byte(""), nil
	}
	if len(ip) != IPv4len && len(ip) != IPv6len {
	return nil, errors.New("invalid IP address")
	}
	return []byte(ip.String()), nil
	}

	// UnmarshalText implements the encoding.TextUnmarshaler interface.
	// The IP address is expected in a form accepted by ParseIP.
	func (ip *IP) UnmarshalText(text []byte) error {
	if len(text) == 0 {
	*ip = nil
	return nil
	}
	s := string(text)
	x := ParseIP(s)
	if x == nil {
	return &ParseError{"IP address", s}
	}
	*ip = x
	return nil
	}

	// Equal returns true if ip and x are the same IP address.
	// An IPv4 address and that same address in IPv6 form are
	// considered to be equal.
	func (ip IP) Equal(x IP) bool {
	if len(ip) == len(x) {
	return bytesEqual(ip, x)
	}
	if len(ip) == IPv4len && len(x) == IPv6len {
	return bytesEqual(x[0:12], v4InV6Prefix) && bytesEqual(ip, x[12:])
	}
	if len(ip) == IPv6len && len(x) == IPv4len {
	return bytesEqual(ip[0:12], v4InV6Prefix) && bytesEqual(ip[12:], x)
	}
	return false
	}

	func bytesEqual(x, y []byte) bool {
	if len(x) != len(y) {
	return false
	}
	for i, b := range x {
	if y[i] != b {
	return false
	}
	}
	return true
	}

	// If mask is a sequence of 1 bits followed by 0 bits,
	// return the number of 1 bits.
	func simpleMaskLength(mask IPMask) int {
	var n int
	for i, v := range mask {
	if v == 0xff {
	n += 8
	continue
	}
	// found non-ff byte
	// count 1 bits
	for v&0x80 != 0 {
	n++
	v <<= 1
	}
	// rest must be 0 bits
	if v != 0 {
	return -1
	}
	for i++; i < len(mask); i++ {
	if mask[i] != 0 {
	return -1
	}
	}
	break
	}
	return n
	}

	// Size returns the number of leading ones and total bits in the mask.
	// If the mask is not in the canonical form--ones followed by zeros--then
	// Size returns 0, 0.
	func (m IPMask) Size() (ones, bits int) {
	ones, bits = simpleMaskLength(m), len(m)*8
	if ones == -1 {
	return 0, 0
	}
	return
	}

	// String returns the hexadecimal form of m, with no punctuation.
	func (m IPMask) String() string {
	if len(m) == 0 {
	return "<nil>"
	}
	buf := make([]byte, len(m)*2)
	for i, b := range m {
	buf[i2], buf[i2+1] = hexDigit[b>>4], hexDigit[b&0xf]
	}
	return string(buf)
	}

	func networkNumberAndMask(n *IPNet) (ip IP, m IPMask) {
	if ip = n.IP.To4(); ip == nil {
	ip = n.IP
	if len(ip) != IPv6len {
	return nil, nil
	}
	}
	m = n.Mask
	switch len(m) {
	case IPv4len:
	if len(ip) != IPv4len {
	return nil, nil
	}
	case IPv6len:
	if len(ip) == IPv4len {
	m = m[12:]
	}
	default:
	return nil, nil
	}
	return
	}

	// Contains reports whether the network includes ip.
	func (n *IPNet) Contains(ip IP) bool {
	nn, m := networkNumberAndMask(n)
	if x := ip.To4(); x != nil {
	ip = x
	}
	l := len(ip)
	if l != len(nn) {
	return false
	}
	for i := 0; i < l; i++ {
	if nn[i]&m[i] != ip[i]&m[i] {
	return false
	}
	}
	return true
	}

	// Network returns the address's network name, "ip+net".
	func (n *IPNet) Network() string { return "ip+net" }

	// String returns the CIDR notation of n like "192.168.100.1/24"
	// or "2001:DB8::/48" as defined in RFC 4632 and RFC 4291.
	// If the mask is not in the canonical form, it returns the
	// string which consists of an IP address, followed by a slash
	// character and a mask expressed as hexadecimal form with no
	// punctuation like "192.168.100.1/c000ff00".
	func (n *IPNet) String() string {
	nn, m := networkNumberAndMask(n)
	if nn == nil \|\| m == nil {
	return "<nil>"
	}
	l := simpleMaskLength(m)
	if l == -1 {
	return nn.String() + "/" + m.String()
	}
	return nn.String() + "/" + itod(uint(l))
	}

	// Parse IPv4 address (d.d.d.d).
	func parseIPv4(s string) IP {
	var p [IPv4len]byte
	i := 0
	for j := 0; j < IPv4len; j++ {
	if i >= len(s) {
	// Missing octets.
	return nil
	}
	if j > 0 {
	if s[i] != '.' {
	return nil
	}
	i++
	}
	var (
	n int
	ok bool
	)
	n, i, ok = dtoi(s, i)
	if !ok \|\| n > 0xFF {
	return nil
	}
	p[j] = byte(n)
	}
	if i != len(s) {
	return nil
	}
	return IPv4(p[0], p[1], p[2], p[3])
	}

	// parseIPv6 parses s as a literal IPv6 address described in RFC 4291
	// and RFC 5952. It can also parse a literal scoped IPv6 address with
	// zone identifier which is described in RFC 4007 when zoneAllowed is
	// true.
	func parseIPv6(s string, zoneAllowed bool) (ip IP, zone string) {
	ip = make(IP, IPv6len)
	ellipsis := -1 // position of ellipsis in p
	i := 0 // index in string s

	if zoneAllowed {
	s, zone = splitHostZone(s)
	}

	// Might have leading ellipsis
	if len(s) >= 2 && s[0] == ':' && s[1] == ':' {
	ellipsis = 0
	i = 2
	// Might be only ellipsis
	if i == len(s) {
	return ip, zone
	}
	}

	// Loop, parsing hex numbers followed by colon.
	j := 0
	for j < IPv6len {
	// Hex number.
	n, i1, ok := xtoi(s, i)
	if !ok \|\| n > 0xFFFF {
	return nil, zone
	}

	// If followed by dot, might be in trailing IPv4.
	if i1 < len(s) && s[i1] == '.' {
	if ellipsis < 0 && j != IPv6len-IPv4len {
	// Not the right place.
	return nil, zone
	}
	if j+IPv4len > IPv6len {
	// Not enough room.
	return nil, zone
	}
	ip4 := parseIPv4(s[i:])
	if ip4 == nil {
	return nil, zone
	}
	ip[j] = ip4[12]
	ip[j+1] = ip4[13]
	ip[j+2] = ip4[14]
	ip[j+3] = ip4[15]
	i = len(s)
	j += IPv4len
	break
	}

	// Save this 16-bit chunk.
	ip[j] = byte(n >> 8)
	ip[j+1] = byte(n)
	j += 2

	// Stop at end of string.
	i = i1
	if i == len(s) {
	break
	}

	// Otherwise must be followed by colon and more.
	if s[i] != ':' \|\| i+1 == len(s) {
	return nil, zone
	}
	i++

	// Look for ellipsis.
	if s[i] == ':' {
	if ellipsis >= 0 { // already have one
	return nil, zone
	}
	ellipsis = j
	if i++; i == len(s) { // can be at end
	break
	}
	}
	}

	// Must have used entire string.
	if i != len(s) {
	return nil, zone
	}

	// If didn't parse enough, expand ellipsis.
	if j < IPv6len {
	if ellipsis < 0 {
	return nil, zone
	}
	n := IPv6len - j
	for k := j - 1; k >= ellipsis; k-- {
	ip[k+n] = ip[k]
	}
	for k := ellipsis + n - 1; k >= ellipsis; k-- {
	ip[k] = 0
	}
	} else if ellipsis >= 0 {
	// Ellipsis must represent at least one 0 group.
	return nil, zone
	}
	return ip, zone
	}

	// A ParseError represents a malformed text string and the type of string that was expected.
	type ParseError struct {
	Type string
	Text string
	}

	func (e *ParseError) Error() string {
	return "invalid " + e.Type + ": " + e.Text
	}

	// ParseIP parses s as an IP address, returning the result.
	// The string s can be in dotted decimal ("74.125.19.99")
	// or IPv6 ("2001:4860:0:2001::68") form.
	// If s is not a valid textual representation of an IP address,
	// ParseIP returns nil.
	func ParseIP(s string) IP {
	for i := 0; i < len(s); i++ {
	switch s[i] {
	case '.':
	return parseIPv4(s)
	case ':':
	ip, _ := parseIPv6(s, false)
	return ip
	}
	}
	return nil
	}

	// ParseCIDR parses s as a CIDR notation IP address and mask,
	// like "192.168.100.1/24" or "2001:DB8::/48", as defined in
	// RFC 4632 and RFC 4291.
	//
	// It returns the IP address and the network implied by the IP
	// and mask. For example, ParseCIDR("192.168.100.1/16") returns
	// the IP address 192.168.100.1 and the network 192.168.0.0/16.
	func ParseCIDR(s string) (IP, *IPNet, error) {
	i := byteIndex(s, '/')
	if i < 0 {
	return nil, nil, &ParseError{"CIDR address", s}
	}
	addr, mask := s[:i], s[i+1:]
	iplen := IPv4len
	ip := parseIPv4(addr)
	if ip == nil {
	iplen = IPv6len
	ip, _ = parseIPv6(addr, false)
	}
	n, i, ok := dtoi(mask, 0)
	if ip == nil \|\| !ok \|\| i != len(mask) \|\| n < 0 \|\| n > 8*iplen {
	return nil, nil, &ParseError{"CIDR address", s}
	}
	m := CIDRMask(n, 8*iplen)
	return ip, &IPNet{IP: ip.Mask(m), Mask: m}, nil
	}