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 (
 	"internal/bytealg"
 	"internal/itoa"
 	"net/netip"
 )

 // 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 IPMask is a bitmask that can be used to manipulate
 // IP addresses for IP addressing and routing.
 //
 // See type [IPNet] and func [ParseCIDR] for details.
 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) // limited 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 reports whether ip is an unspecified address, either
 // the IPv4 address "0.0.0.0" or the IPv6 address "::".
 func (ip IP) IsUnspecified() bool {
 	return ip.Equal(IPv4zero) || ip.Equal(IPv6unspecified)
 }

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

 // IsPrivate reports whether ip is a private address, according to
 // RFC 1918 (IPv4 addresses) and RFC 4193 (IPv6 addresses).
 func (ip IP) IsPrivate() bool {
 	if ip4 := ip.To4(); ip4 != nil {
 		// Following RFC 1918, Section 3. Private Address Space which says:
 		//   The Internet Assigned Numbers Authority (IANA) has reserved the
 		//   following three blocks of the IP address space for private internets:
 		//     10.0.0.0        -   10.255.255.255  (10/8 prefix)
 		//     172.16.0.0      -   172.31.255.255  (172.16/12 prefix)
 		//     192.168.0.0     -   192.168.255.255 (192.168/16 prefix)
 		return ip4[0] == 10 ||
 			(ip4[0] == 172 && ip4[1]&0xf0 == 16) ||
 			(ip4[0] == 192 && ip4[1] == 168)
 	}
 	// Following RFC 4193, Section 8. IANA Considerations which says:
 	//   The IANA has assigned the FC00::/7 prefix to "Unique Local Unicast".
 	return len(ip) == IPv6len && ip[0]&0xfe == 0xfc
 }

 // IsMulticast reports whether ip is a multicast address.
 func (ip IP) IsMulticast() bool {
 	if ip4 := ip.To4(); ip4 != nil {
 		return ip4[0]&0xf0 == 0xe0
 	}
 	return len(ip) == IPv6len && ip[0] == 0xff
 }

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

 // IsLinkLocalMulticast reports whether ip is a link-local
 // multicast address.
 func (ip IP) IsLinkLocalMulticast() bool {
 	if ip4 := ip.To4(); ip4 != nil {
 		return ip4[0] == 224 && ip4[1] == 0 && ip4[2] == 0
 	}
 	return len(ip) == IPv6len && ip[0] == 0xff && ip[1]&0x0f == 0x02
 }

 // IsLinkLocalUnicast reports whether ip is a link-local
 // unicast address.
 func (ip IP) IsLinkLocalUnicast() bool {
 	if ip4 := ip.To4(); ip4 != nil {
 		return ip4[0] == 169 && ip4[1] == 254
 	}
 	return len(ip) == IPv6len && ip[0] == 0xfe && ip[1]&0xc0 == 0x80
 }

 // IsGlobalUnicast reports whether ip is a global unicast
 // address.
 //
 // The identification of global unicast addresses uses address type
 // identification as defined in RFC 1122, RFC 4632 and RFC 4291 with
 // the exception of IPv4 directed broadcast addresses.
 // It returns true even if ip is in IPv4 private address space or
 // local IPv6 unicast address space.
 func (ip IP) IsGlobalUnicast() bool {
 	return (len(ip) == IPv4len || len(ip) == IPv6len) &&
 		!ip.Equal(IPv4bcast) &&
 		!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 {
 	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 && bytealg.Equal(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.
 // It returns one of 4 forms:
 //   - "<nil>", if ip has length 0
 //   - dotted decimal ("192.0.2.1"), if ip is an IPv4 or IP4-mapped IPv6 address
 //   - IPv6 conforming to RFC 5952 ("2001:db8::1"), if ip is a valid IPv6 address
 //   - the hexadecimal form of ip, without punctuation, if no other cases apply
 func (ip IP) String() string {
 	if len(ip) == 0 {
 		return "<nil>"
 	}

 	if len(ip) != IPv4len && len(ip) != IPv6len {
 		return "?" + hexString(ip)
 	}
 	// If IPv4, use dotted notation.
 	if p4 := ip.To4(); len(p4) == IPv4len {
 		return netip.AddrFrom4([4]byte(p4)).String()
 	}
 	return netip.AddrFrom16([16]byte(ip)).String()
 }

 func hexString(b []byte) string {
 	s := make([]byte, len(b)*2)
 	for i, tn := range b {
 		s[i*2], s[i*2+1] = hexDigit[tn>>4], hexDigit[tn&0xf]
 	}
 	return string(s)
 }

 // 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 [IP.String], with one exception:
 // When len(ip) is zero, it returns an empty slice.
 func (ip IP) MarshalText() ([]byte, error) {
 	if len(ip) == 0 {
 		return []byte(""), nil
 	}
 	if len(ip) != IPv4len && len(ip) != IPv6len {
 		return nil, &AddrError{Err: "invalid IP address", Addr: hexString(ip)}
 	}
 	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{Type: "IP address", Text: s}
 	}
 	*ip = x
 	return nil
 }

 // Equal reports whether 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 bytealg.Equal(ip, x)
 	}
 	if len(ip) == IPv4len && len(x) == IPv6len {
 		return bytealg.Equal(x[0:12], v4InV6Prefix) && bytealg.Equal(ip, x[12:])
 	}
 	if len(ip) == IPv6len && len(x) == IPv4len {
 		return bytealg.Equal(ip[0:12], v4InV6Prefix) && bytealg.Equal(ip[12:], x)
 	}
 	return false
 }

 func (ip IP) matchAddrFamily(x IP) bool {
 	return ip.To4() != nil && x.To4() != nil || ip.To16() != nil && ip.To4() == nil && x.To16() != nil && x.To4() == nil
 }

 // 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>"
 	}
 	return hexString(m)
 }

 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 "192.0.2.0/24"
 // 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 "198.51.100.0/c000ff00".
 func (n *IPNet) String() string {
 	if n == nil {
 		return "<nil>"
 	}
 	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() + "/" + itoa.Uitoa(uint(l))
 }

 // ParseIP parses s as an IP address, returning the result.
 // The string s can be in IPv4 dotted decimal ("192.0.2.1"), IPv6
 // ("2001:db8::68"), or IPv4-mapped IPv6 ("::ffff:192.0.2.1") form.
 // If s is not a valid textual representation of an IP address,
 // ParseIP returns nil.
 func ParseIP(s string) IP {
 	if addr, valid := parseIP(s); valid {
 		return IP(addr[:])
 	}
 	return nil
 }

 func parseIP(s string) ([16]byte, bool) {
 	ip, err := netip.ParseAddr(s)
 	if err != nil || ip.Zone() != "" {
 		return [16]byte{}, false
 	}
 	return ip.As16(), true
 }

 // ParseCIDR parses s as a CIDR notation IP address and prefix length,
 // like "192.0.2.0/24" or "2001:db8::/32", as defined in
 // RFC 4632 and RFC 4291.
 //
 // It returns the IP address and the network implied by the IP and
 // prefix length.
 // For example, ParseCIDR("192.0.2.1/24") returns the IP address
 // 192.0.2.1 and the network 192.0.2.0/24.
 func ParseCIDR(s string) (IP, *IPNet, error) {
 	i := bytealg.IndexByteString(s, '/')
 	if i < 0 {
 		return nil, nil, &ParseError{Type: "CIDR address", Text: s}
 	}
 	addr, mask := s[:i], s[i+1:]

 	ipAddr, err := netip.ParseAddr(addr)
 	if err != nil || ipAddr.Zone() != "" {
 		return nil, nil, &ParseError{Type: "CIDR address", Text: s}
 	}

 	n, i, ok := dtoi(mask)
 	if !ok || i != len(mask) || n < 0 || n > ipAddr.BitLen() {
 		return nil, nil, &ParseError{Type: "CIDR address", Text: s}
 	}
 	m := CIDRMask(n, ipAddr.BitLen())
 	addr16 := ipAddr.As16()
 	return IP(addr16[:]), &IPNet{IP: IP(addr16[:]).Mask(m), Mask: m}, nil
 }

 func copyIP(x IP) IP {
 	y := make(IP, len(x))
 	copy(y, x)
 	return y
 }
	// 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 (
	"internal/bytealg"
	"internal/itoa"
	"net/netip"
	)

	// 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 IPMask is a bitmask that can be used to manipulate
	// IP addresses for IP addressing and routing.
	//
	// See type [IPNet] and func [ParseCIDR] for details.
	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) // limited 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 reports whether ip is an unspecified address, either
	// the IPv4 address "0.0.0.0" or the IPv6 address "::".
	func (ip IP) IsUnspecified() bool {
	return ip.Equal(IPv4zero) \|\| ip.Equal(IPv6unspecified)
	}

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

	// IsPrivate reports whether ip is a private address, according to
	// RFC 1918 (IPv4 addresses) and RFC 4193 (IPv6 addresses).
	func (ip IP) IsPrivate() bool {
	if ip4 := ip.To4(); ip4 != nil {
	// Following RFC 1918, Section 3. Private Address Space which says:
	// The Internet Assigned Numbers Authority (IANA) has reserved the
	// following three blocks of the IP address space for private internets:
	// 10.0.0.0 - 10.255.255.255 (10/8 prefix)
	// 172.16.0.0 - 172.31.255.255 (172.16/12 prefix)
	// 192.168.0.0 - 192.168.255.255 (192.168/16 prefix)
	return ip4[0] == 10 \|\|
	(ip4[0] == 172 && ip4[1]&0xf0 == 16) \|\|
	(ip4[0] == 192 && ip4[1] == 168)
	}
	// Following RFC 4193, Section 8. IANA Considerations which says:
	// The IANA has assigned the FC00::/7 prefix to "Unique Local Unicast".
	return len(ip) == IPv6len && ip[0]&0xfe == 0xfc
	}

	// IsMulticast reports whether ip is a multicast address.
	func (ip IP) IsMulticast() bool {
	if ip4 := ip.To4(); ip4 != nil {
	return ip4[0]&0xf0 == 0xe0
	}
	return len(ip) == IPv6len && ip[0] == 0xff
	}

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

	// IsLinkLocalMulticast reports whether ip is a link-local
	// multicast address.
	func (ip IP) IsLinkLocalMulticast() bool {
	if ip4 := ip.To4(); ip4 != nil {
	return ip4[0] == 224 && ip4[1] == 0 && ip4[2] == 0
	}
	return len(ip) == IPv6len && ip[0] == 0xff && ip[1]&0x0f == 0x02
	}

	// IsLinkLocalUnicast reports whether ip is a link-local
	// unicast address.
	func (ip IP) IsLinkLocalUnicast() bool {
	if ip4 := ip.To4(); ip4 != nil {
	return ip4[0] == 169 && ip4[1] == 254
	}
	return len(ip) == IPv6len && ip[0] == 0xfe && ip[1]&0xc0 == 0x80
	}

	// IsGlobalUnicast reports whether ip is a global unicast
	// address.
	//
	// The identification of global unicast addresses uses address type
	// identification as defined in RFC 1122, RFC 4632 and RFC 4291 with
	// the exception of IPv4 directed broadcast addresses.
	// It returns true even if ip is in IPv4 private address space or
	// local IPv6 unicast address space.
	func (ip IP) IsGlobalUnicast() bool {
	return (len(ip) == IPv4len \|\| len(ip) == IPv6len) &&
	!ip.Equal(IPv4bcast) &&
	!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 {
	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 && bytealg.Equal(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.
	// It returns one of 4 forms:
	// - "<nil>", if ip has length 0
	// - dotted decimal ("192.0.2.1"), if ip is an IPv4 or IP4-mapped IPv6 address
	// - IPv6 conforming to RFC 5952 ("2001:db8::1"), if ip is a valid IPv6 address
	// - the hexadecimal form of ip, without punctuation, if no other cases apply
	func (ip IP) String() string {
	if len(ip) == 0 {
	return "<nil>"
	}

	if len(ip) != IPv4len && len(ip) != IPv6len {
	return "?" + hexString(ip)
	}
	// If IPv4, use dotted notation.
	if p4 := ip.To4(); len(p4) == IPv4len {
	return netip.AddrFrom4([4]byte(p4)).String()
	}
	return netip.AddrFrom16([16]byte(ip)).String()
	}

	func hexString(b []byte) string {
	s := make([]byte, len(b)*2)
	for i, tn := range b {
	s[i2], s[i2+1] = hexDigit[tn>>4], hexDigit[tn&0xf]
	}
	return string(s)
	}

	// 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 [IP.String], with one exception:
	// When len(ip) is zero, it returns an empty slice.
	func (ip IP) MarshalText() ([]byte, error) {
	if len(ip) == 0 {
	return []byte(""), nil
	}
	if len(ip) != IPv4len && len(ip) != IPv6len {
	return nil, &AddrError{Err: "invalid IP address", Addr: hexString(ip)}
	}
	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{Type: "IP address", Text: s}
	}
	*ip = x
	return nil
	}

	// Equal reports whether 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 bytealg.Equal(ip, x)
	}
	if len(ip) == IPv4len && len(x) == IPv6len {
	return bytealg.Equal(x[0:12], v4InV6Prefix) && bytealg.Equal(ip, x[12:])
	}
	if len(ip) == IPv6len && len(x) == IPv4len {
	return bytealg.Equal(ip[0:12], v4InV6Prefix) && bytealg.Equal(ip[12:], x)
	}
	return false
	}

	func (ip IP) matchAddrFamily(x IP) bool {
	return ip.To4() != nil && x.To4() != nil \|\| ip.To16() != nil && ip.To4() == nil && x.To16() != nil && x.To4() == nil
	}

	// 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>"
	}
	return hexString(m)
	}

	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 "192.0.2.0/24"
	// 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 "198.51.100.0/c000ff00".
	func (n *IPNet) String() string {
	if n == nil {
	return "<nil>"
	}
	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() + "/" + itoa.Uitoa(uint(l))
	}

	// ParseIP parses s as an IP address, returning the result.
	// The string s can be in IPv4 dotted decimal ("192.0.2.1"), IPv6
	// ("2001:db8::68"), or IPv4-mapped IPv6 ("::ffff:192.0.2.1") form.
	// If s is not a valid textual representation of an IP address,
	// ParseIP returns nil.
	func ParseIP(s string) IP {
	if addr, valid := parseIP(s); valid {
	return IP(addr[:])
	}
	return nil
	}

	func parseIP(s string) ([16]byte, bool) {
	ip, err := netip.ParseAddr(s)
	if err != nil \|\| ip.Zone() != "" {
	return [16]byte{}, false
	}
	return ip.As16(), true
	}

	// ParseCIDR parses s as a CIDR notation IP address and prefix length,
	// like "192.0.2.0/24" or "2001:db8::/32", as defined in
	// RFC 4632 and RFC 4291.
	//
	// It returns the IP address and the network implied by the IP and
	// prefix length.
	// For example, ParseCIDR("192.0.2.1/24") returns the IP address
	// 192.0.2.1 and the network 192.0.2.0/24.
	func ParseCIDR(s string) (IP, *IPNet, error) {
	i := bytealg.IndexByteString(s, '/')
	if i < 0 {
	return nil, nil, &ParseError{Type: "CIDR address", Text: s}
	}
	addr, mask := s[:i], s[i+1:]

	ipAddr, err := netip.ParseAddr(addr)
	if err != nil \|\| ipAddr.Zone() != "" {
	return nil, nil, &ParseError{Type: "CIDR address", Text: s}
	}

	n, i, ok := dtoi(mask)
	if !ok \|\| i != len(mask) \|\| n < 0 \|\| n > ipAddr.BitLen() {
	return nil, nil, &ParseError{Type: "CIDR address", Text: s}
	}
	m := CIDRMask(n, ipAddr.BitLen())
	addr16 := ipAddr.As16()
	return IP(addr16[:]), &IPNet{IP: IP(addr16[:]).Mask(m), Mask: m}, nil
	}

	func copyIP(x IP) IP {
	y := make(IP, len(x))
	copy(y, x)
	return y
	}