Source file src/net/netip/netip.go

Documentation: net/netip

     1  // Copyright 2020 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // Package netip defines an IP address type that's a small value type.
     6  // Building on that [Addr] type, the package also defines [AddrPort] (an
     7  // IP address and a port) and [Prefix] (an IP address and a bit length
     8  // prefix).
     9  //
    10  // Compared to the [net.IP] type, [Addr] type takes less memory, is immutable,
    11  // and is comparable (supports == and being a map key).
    12  package netip
    13  
    14  import (
    15  	"cmp"
    16  	"errors"
    17  	"internal/bytealg"
    18  	"internal/byteorder"
    19  	"internal/itoa"
    20  	"math"
    21  	"strconv"
    22  	"unique"
    23  )
    24  
    25  // Sizes: (64-bit)
    26  //   net.IP:     24 byte slice header + {4, 16} = 28 to 40 bytes
    27  //   net.IPAddr: 40 byte slice header + {4, 16} = 44 to 56 bytes + zone length
    28  //   netip.Addr: 24 bytes (zone is per-name singleton, shared across all users)
    29  
    30  // Addr represents an IPv4 or IPv6 address (with or without a scoped
    31  // addressing zone), similar to [net.IP] or [net.IPAddr].
    32  //
    33  // Unlike [net.IP] or [net.IPAddr], Addr is a comparable value
    34  // type (it supports == and can be a map key) and is immutable.
    35  //
    36  // The zero Addr is not a valid IP address.
    37  // Addr{} is distinct from both 0.0.0.0 and ::.
    38  type Addr struct {
    39  	// addr is the hi and lo bits of an IPv6 address. If z==z4,
    40  	// hi and lo contain the IPv4-mapped IPv6 address.
    41  	//
    42  	// hi and lo are constructed by interpreting a 16-byte IPv6
    43  	// address as a big-endian 128-bit number. The most significant
    44  	// bits of that number go into hi, the rest into lo.
    45  	//
    46  	// For example, 0011:2233:4455:6677:8899:aabb:ccdd:eeff is stored as:
    47  	//  addr.hi = 0x0011223344556677
    48  	//  addr.lo = 0x8899aabbccddeeff
    49  	//
    50  	// We store IPs like this, rather than as [16]byte, because it
    51  	// turns most operations on IPs into arithmetic and bit-twiddling
    52  	// operations on 64-bit registers, which is much faster than
    53  	// bytewise processing.
    54  	addr uint128
    55  
    56  	// Details about the address, wrapped up together and canonicalized.
    57  	z unique.Handle[addrDetail]
    58  }
    59  
    60  // addrDetail represents the details of an Addr, like address family and IPv6 zone.
    61  type addrDetail struct {
    62  	isV6   bool   // IPv4 is false, IPv6 is true.
    63  	zoneV6 string // != "" only if IsV6 is true.
    64  }
    65  
    66  // z0, z4, and z6noz are sentinel Addr.z values.
    67  // See the Addr type's field docs.
    68  var (
    69  	z0    unique.Handle[addrDetail]
    70  	z4    = unique.Make(addrDetail{})
    71  	z6noz = unique.Make(addrDetail{isV6: true})
    72  )
    73  
    74  // IPv6LinkLocalAllNodes returns the IPv6 link-local all nodes multicast
    75  // address ff02::1.
    76  func IPv6LinkLocalAllNodes() Addr { return AddrFrom16([16]byte{0: 0xff, 1: 0x02, 15: 0x01}) }
    77  
    78  // IPv6LinkLocalAllRouters returns the IPv6 link-local all routers multicast
    79  // address ff02::2.
    80  func IPv6LinkLocalAllRouters() Addr { return AddrFrom16([16]byte{0: 0xff, 1: 0x02, 15: 0x02}) }
    81  
    82  // IPv6Loopback returns the IPv6 loopback address ::1.
    83  func IPv6Loopback() Addr { return AddrFrom16([16]byte{15: 0x01}) }
    84  
    85  // IPv6Unspecified returns the IPv6 unspecified address "::".
    86  func IPv6Unspecified() Addr { return Addr{z: z6noz} }
    87  
    88  // IPv4Unspecified returns the IPv4 unspecified address "0.0.0.0".
    89  func IPv4Unspecified() Addr { return AddrFrom4([4]byte{}) }
    90  
    91  // AddrFrom4 returns the address of the IPv4 address given by the bytes in addr.
    92  func AddrFrom4(addr [4]byte) Addr {
    93  	return Addr{
    94  		addr: uint128{0, 0xffff00000000 | uint64(addr[0])<<24 | uint64(addr[1])<<16 | uint64(addr[2])<<8 | uint64(addr[3])},
    95  		z:    z4,
    96  	}
    97  }
    98  
    99  // AddrFrom16 returns the IPv6 address given by the bytes in addr.
   100  // An IPv4-mapped IPv6 address is left as an IPv6 address.
   101  // (Use Unmap to convert them if needed.)
   102  func AddrFrom16(addr [16]byte) Addr {
   103  	return Addr{
   104  		addr: uint128{
   105  			byteorder.BeUint64(addr[:8]),
   106  			byteorder.BeUint64(addr[8:]),
   107  		},
   108  		z: z6noz,
   109  	}
   110  }
   111  
   112  // ParseAddr parses s as an IP address, returning the result. The string
   113  // s can be in dotted decimal ("192.0.2.1"), IPv6 ("2001:db8::68"),
   114  // or IPv6 with a scoped addressing zone ("fe80::1cc0:3e8c:119f:c2e1%ens18").
   115  func ParseAddr(s string) (Addr, error) {
   116  	for i := 0; i < len(s); i++ {
   117  		switch s[i] {
   118  		case '.':
   119  			return parseIPv4(s)
   120  		case ':':
   121  			return parseIPv6(s)
   122  		case '%':
   123  			// Assume that this was trying to be an IPv6 address with
   124  			// a zone specifier, but the address is missing.
   125  			return Addr{}, parseAddrError{in: s, msg: "missing IPv6 address"}
   126  		}
   127  	}
   128  	return Addr{}, parseAddrError{in: s, msg: "unable to parse IP"}
   129  }
   130  
   131  // MustParseAddr calls [ParseAddr](s) and panics on error.
   132  // It is intended for use in tests with hard-coded strings.
   133  func MustParseAddr(s string) Addr {
   134  	ip, err := ParseAddr(s)
   135  	if err != nil {
   136  		panic(err)
   137  	}
   138  	return ip
   139  }
   140  
   141  type parseAddrError struct {
   142  	in  string // the string given to ParseAddr
   143  	msg string // an explanation of the parse failure
   144  	at  string // optionally, the unparsed portion of in at which the error occurred.
   145  }
   146  
   147  func (err parseAddrError) Error() string {
   148  	q := strconv.Quote
   149  	if err.at != "" {
   150  		return "ParseAddr(" + q(err.in) + "): " + err.msg + " (at " + q(err.at) + ")"
   151  	}
   152  	return "ParseAddr(" + q(err.in) + "): " + err.msg
   153  }
   154  
   155  func parseIPv4Fields(in string, off, end int, fields []uint8) error {
   156  	var val, pos int
   157  	var digLen int // number of digits in current octet
   158  	s := in[off:end]
   159  	for i := 0; i < len(s); i++ {
   160  		if s[i] >= '0' && s[i] <= '9' {
   161  			if digLen == 1 && val == 0 {
   162  				return parseAddrError{in: in, msg: "IPv4 field has octet with leading zero"}
   163  			}
   164  			val = val*10 + int(s[i]) - '0'
   165  			digLen++
   166  			if val > 255 {
   167  				return parseAddrError{in: in, msg: "IPv4 field has value >255"}
   168  			}
   169  		} else if s[i] == '.' {
   170  			// .1.2.3
   171  			// 1.2.3.
   172  			// 1..2.3
   173  			if i == 0 || i == len(s)-1 || s[i-1] == '.' {
   174  				return parseAddrError{in: in, msg: "IPv4 field must have at least one digit", at: s[i:]}
   175  			}
   176  			// 1.2.3.4.5
   177  			if pos == 3 {
   178  				return parseAddrError{in: in, msg: "IPv4 address too long"}
   179  			}
   180  			fields[pos] = uint8(val)
   181  			pos++
   182  			val = 0
   183  			digLen = 0
   184  		} else {
   185  			return parseAddrError{in: in, msg: "unexpected character", at: s[i:]}
   186  		}
   187  	}
   188  	if pos < 3 {
   189  		return parseAddrError{in: in, msg: "IPv4 address too short"}
   190  	}
   191  	fields[3] = uint8(val)
   192  	return nil
   193  }
   194  
   195  // parseIPv4 parses s as an IPv4 address (in form "192.168.0.1").
   196  func parseIPv4(s string) (ip Addr, err error) {
   197  	var fields [4]uint8
   198  	err = parseIPv4Fields(s, 0, len(s), fields[:])
   199  	if err != nil {
   200  		return Addr{}, err
   201  	}
   202  	return AddrFrom4(fields), nil
   203  }
   204  
   205  // parseIPv6 parses s as an IPv6 address (in form "2001:db8::68").
   206  func parseIPv6(in string) (Addr, error) {
   207  	s := in
   208  
   209  	// Split off the zone right from the start. Yes it's a second scan
   210  	// of the string, but trying to handle it inline makes a bunch of
   211  	// other inner loop conditionals more expensive, and it ends up
   212  	// being slower.
   213  	zone := ""
   214  	i := bytealg.IndexByteString(s, '%')
   215  	if i != -1 {
   216  		s, zone = s[:i], s[i+1:]
   217  		if zone == "" {
   218  			// Not allowed to have an empty zone if explicitly specified.
   219  			return Addr{}, parseAddrError{in: in, msg: "zone must be a non-empty string"}
   220  		}
   221  	}
   222  
   223  	var ip [16]byte
   224  	ellipsis := -1 // position of ellipsis in ip
   225  
   226  	// Might have leading ellipsis
   227  	if len(s) >= 2 && s[0] == ':' && s[1] == ':' {
   228  		ellipsis = 0
   229  		s = s[2:]
   230  		// Might be only ellipsis
   231  		if len(s) == 0 {
   232  			return IPv6Unspecified().WithZone(zone), nil
   233  		}
   234  	}
   235  
   236  	// Loop, parsing hex numbers followed by colon.
   237  	i = 0
   238  	for i < 16 {
   239  		// Hex number. Similar to parseIPv4, inlining the hex number
   240  		// parsing yields a significant performance increase.
   241  		off := 0
   242  		acc := uint32(0)
   243  		for ; off < len(s); off++ {
   244  			c := s[off]
   245  			if c >= '0' && c <= '9' {
   246  				acc = (acc << 4) + uint32(c-'0')
   247  			} else if c >= 'a' && c <= 'f' {
   248  				acc = (acc << 4) + uint32(c-'a'+10)
   249  			} else if c >= 'A' && c <= 'F' {
   250  				acc = (acc << 4) + uint32(c-'A'+10)
   251  			} else {
   252  				break
   253  			}
   254  			if off > 3 {
   255  				//more than 4 digits in group, fail.
   256  				return Addr{}, parseAddrError{in: in, msg: "each group must have 4 or less digits", at: s}
   257  			}
   258  			if acc > math.MaxUint16 {
   259  				// Overflow, fail.
   260  				return Addr{}, parseAddrError{in: in, msg: "IPv6 field has value >=2^16", at: s}
   261  			}
   262  		}
   263  		if off == 0 {
   264  			// No digits found, fail.
   265  			return Addr{}, parseAddrError{in: in, msg: "each colon-separated field must have at least one digit", at: s}
   266  		}
   267  
   268  		// If followed by dot, might be in trailing IPv4.
   269  		if off < len(s) && s[off] == '.' {
   270  			if ellipsis < 0 && i != 12 {
   271  				// Not the right place.
   272  				return Addr{}, parseAddrError{in: in, msg: "embedded IPv4 address must replace the final 2 fields of the address", at: s}
   273  			}
   274  			if i+4 > 16 {
   275  				// Not enough room.
   276  				return Addr{}, parseAddrError{in: in, msg: "too many hex fields to fit an embedded IPv4 at the end of the address", at: s}
   277  			}
   278  
   279  			end := len(in)
   280  			if len(zone) > 0 {
   281  				end -= len(zone) + 1
   282  			}
   283  			err := parseIPv4Fields(in, end-len(s), end, ip[i:i+4])
   284  			if err != nil {
   285  				return Addr{}, err
   286  			}
   287  			s = ""
   288  			i += 4
   289  			break
   290  		}
   291  
   292  		// Save this 16-bit chunk.
   293  		ip[i] = byte(acc >> 8)
   294  		ip[i+1] = byte(acc)
   295  		i += 2
   296  
   297  		// Stop at end of string.
   298  		s = s[off:]
   299  		if len(s) == 0 {
   300  			break
   301  		}
   302  
   303  		// Otherwise must be followed by colon and more.
   304  		if s[0] != ':' {
   305  			return Addr{}, parseAddrError{in: in, msg: "unexpected character, want colon", at: s}
   306  		} else if len(s) == 1 {
   307  			return Addr{}, parseAddrError{in: in, msg: "colon must be followed by more characters", at: s}
   308  		}
   309  		s = s[1:]
   310  
   311  		// Look for ellipsis.
   312  		if s[0] == ':' {
   313  			if ellipsis >= 0 { // already have one
   314  				return Addr{}, parseAddrError{in: in, msg: "multiple :: in address", at: s}
   315  			}
   316  			ellipsis = i
   317  			s = s[1:]
   318  			if len(s) == 0 { // can be at end
   319  				break
   320  			}
   321  		}
   322  	}
   323  
   324  	// Must have used entire string.
   325  	if len(s) != 0 {
   326  		return Addr{}, parseAddrError{in: in, msg: "trailing garbage after address", at: s}
   327  	}
   328  
   329  	// If didn't parse enough, expand ellipsis.
   330  	if i < 16 {
   331  		if ellipsis < 0 {
   332  			return Addr{}, parseAddrError{in: in, msg: "address string too short"}
   333  		}
   334  		n := 16 - i
   335  		for j := i - 1; j >= ellipsis; j-- {
   336  			ip[j+n] = ip[j]
   337  		}
   338  		clear(ip[ellipsis : ellipsis+n])
   339  	} else if ellipsis >= 0 {
   340  		// Ellipsis must represent at least one 0 group.
   341  		return Addr{}, parseAddrError{in: in, msg: "the :: must expand to at least one field of zeros"}
   342  	}
   343  	return AddrFrom16(ip).WithZone(zone), nil
   344  }
   345  
   346  // AddrFromSlice parses the 4- or 16-byte byte slice as an IPv4 or IPv6 address.
   347  // Note that a [net.IP] can be passed directly as the []byte argument.
   348  // If slice's length is not 4 or 16, AddrFromSlice returns [Addr]{}, false.
   349  func AddrFromSlice(slice []byte) (ip Addr, ok bool) {
   350  	switch len(slice) {
   351  	case 4:
   352  		return AddrFrom4([4]byte(slice)), true
   353  	case 16:
   354  		return AddrFrom16([16]byte(slice)), true
   355  	}
   356  	return Addr{}, false
   357  }
   358  
   359  // v4 returns the i'th byte of ip. If ip is not an IPv4, v4 returns
   360  // unspecified garbage.
   361  func (ip Addr) v4(i uint8) uint8 {
   362  	return uint8(ip.addr.lo >> ((3 - i) * 8))
   363  }
   364  
   365  // v6 returns the i'th byte of ip. If ip is an IPv4 address, this
   366  // accesses the IPv4-mapped IPv6 address form of the IP.
   367  func (ip Addr) v6(i uint8) uint8 {
   368  	return uint8(*(ip.addr.halves()[(i/8)%2]) >> ((7 - i%8) * 8))
   369  }
   370  
   371  // v6u16 returns the i'th 16-bit word of ip. If ip is an IPv4 address,
   372  // this accesses the IPv4-mapped IPv6 address form of the IP.
   373  func (ip Addr) v6u16(i uint8) uint16 {
   374  	return uint16(*(ip.addr.halves()[(i/4)%2]) >> ((3 - i%4) * 16))
   375  }
   376  
   377  // isZero reports whether ip is the zero value of the IP type.
   378  // The zero value is not a valid IP address of any type.
   379  //
   380  // Note that "0.0.0.0" and "::" are not the zero value. Use IsUnspecified to
   381  // check for these values instead.
   382  func (ip Addr) isZero() bool {
   383  	// Faster than comparing ip == Addr{}, but effectively equivalent,
   384  	// as there's no way to make an IP with a nil z from this package.
   385  	return ip.z == z0
   386  }
   387  
   388  // IsValid reports whether the [Addr] is an initialized address (not the zero Addr).
   389  //
   390  // Note that "0.0.0.0" and "::" are both valid values.
   391  func (ip Addr) IsValid() bool { return ip.z != z0 }
   392  
   393  // BitLen returns the number of bits in the IP address:
   394  // 128 for IPv6, 32 for IPv4, and 0 for the zero [Addr].
   395  //
   396  // Note that IPv4-mapped IPv6 addresses are considered IPv6 addresses
   397  // and therefore have bit length 128.
   398  func (ip Addr) BitLen() int {
   399  	switch ip.z {
   400  	case z0:
   401  		return 0
   402  	case z4:
   403  		return 32
   404  	}
   405  	return 128
   406  }
   407  
   408  // Zone returns ip's IPv6 scoped addressing zone, if any.
   409  func (ip Addr) Zone() string {
   410  	if ip.z == z0 {
   411  		return ""
   412  	}
   413  	return ip.z.Value().zoneV6
   414  }
   415  
   416  // Compare returns an integer comparing two IPs.
   417  // The result will be 0 if ip == ip2, -1 if ip < ip2, and +1 if ip > ip2.
   418  // The definition of "less than" is the same as the [Addr.Less] method.
   419  func (ip Addr) Compare(ip2 Addr) int {
   420  	f1, f2 := ip.BitLen(), ip2.BitLen()
   421  	if f1 < f2 {
   422  		return -1
   423  	}
   424  	if f1 > f2 {
   425  		return 1
   426  	}
   427  	hi1, hi2 := ip.addr.hi, ip2.addr.hi
   428  	if hi1 < hi2 {
   429  		return -1
   430  	}
   431  	if hi1 > hi2 {
   432  		return 1
   433  	}
   434  	lo1, lo2 := ip.addr.lo, ip2.addr.lo
   435  	if lo1 < lo2 {
   436  		return -1
   437  	}
   438  	if lo1 > lo2 {
   439  		return 1
   440  	}
   441  	if ip.Is6() {
   442  		za, zb := ip.Zone(), ip2.Zone()
   443  		if za < zb {
   444  			return -1
   445  		}
   446  		if za > zb {
   447  			return 1
   448  		}
   449  	}
   450  	return 0
   451  }
   452  
   453  // Less reports whether ip sorts before ip2.
   454  // IP addresses sort first by length, then their address.
   455  // IPv6 addresses with zones sort just after the same address without a zone.
   456  func (ip Addr) Less(ip2 Addr) bool { return ip.Compare(ip2) == -1 }
   457  
   458  // Is4 reports whether ip is an IPv4 address.
   459  //
   460  // It returns false for IPv4-mapped IPv6 addresses. See [Addr.Unmap].
   461  func (ip Addr) Is4() bool {
   462  	return ip.z == z4
   463  }
   464  
   465  // Is4In6 reports whether ip is an IPv4-mapped IPv6 address.
   466  func (ip Addr) Is4In6() bool {
   467  	return ip.Is6() && ip.addr.hi == 0 && ip.addr.lo>>32 == 0xffff
   468  }
   469  
   470  // Is6 reports whether ip is an IPv6 address, including IPv4-mapped
   471  // IPv6 addresses.
   472  func (ip Addr) Is6() bool {
   473  	return ip.z != z0 && ip.z != z4
   474  }
   475  
   476  // Unmap returns ip with any IPv4-mapped IPv6 address prefix removed.
   477  //
   478  // That is, if ip is an IPv6 address wrapping an IPv4 address, it
   479  // returns the wrapped IPv4 address. Otherwise it returns ip unmodified.
   480  func (ip Addr) Unmap() Addr {
   481  	if ip.Is4In6() {
   482  		ip.z = z4
   483  	}
   484  	return ip
   485  }
   486  
   487  // WithZone returns an IP that's the same as ip but with the provided
   488  // zone. If zone is empty, the zone is removed. If ip is an IPv4
   489  // address, WithZone is a no-op and returns ip unchanged.
   490  func (ip Addr) WithZone(zone string) Addr {
   491  	if !ip.Is6() {
   492  		return ip
   493  	}
   494  	if zone == "" {
   495  		ip.z = z6noz
   496  		return ip
   497  	}
   498  	ip.z = unique.Make(addrDetail{isV6: true, zoneV6: zone})
   499  	return ip
   500  }
   501  
   502  // withoutZone unconditionally strips the zone from ip.
   503  // It's similar to WithZone, but small enough to be inlinable.
   504  func (ip Addr) withoutZone() Addr {
   505  	if !ip.Is6() {
   506  		return ip
   507  	}
   508  	ip.z = z6noz
   509  	return ip
   510  }
   511  
   512  // hasZone reports whether ip has an IPv6 zone.
   513  func (ip Addr) hasZone() bool {
   514  	return ip.z != z0 && ip.z != z4 && ip.z != z6noz
   515  }
   516  
   517  // IsLinkLocalUnicast reports whether ip is a link-local unicast address.
   518  func (ip Addr) IsLinkLocalUnicast() bool {
   519  	if ip.Is4In6() {
   520  		ip = ip.Unmap()
   521  	}
   522  
   523  	// Dynamic Configuration of IPv4 Link-Local Addresses
   524  	// https://datatracker.ietf.org/doc/html/rfc3927#section-2.1
   525  	if ip.Is4() {
   526  		return ip.v4(0) == 169 && ip.v4(1) == 254
   527  	}
   528  	// IP Version 6 Addressing Architecture (2.4 Address Type Identification)
   529  	// https://datatracker.ietf.org/doc/html/rfc4291#section-2.4
   530  	if ip.Is6() {
   531  		return ip.v6u16(0)&0xffc0 == 0xfe80
   532  	}
   533  	return false // zero value
   534  }
   535  
   536  // IsLoopback reports whether ip is a loopback address.
   537  func (ip Addr) IsLoopback() bool {
   538  	if ip.Is4In6() {
   539  		ip = ip.Unmap()
   540  	}
   541  
   542  	// Requirements for Internet Hosts -- Communication Layers (3.2.1.3 Addressing)
   543  	// https://datatracker.ietf.org/doc/html/rfc1122#section-3.2.1.3
   544  	if ip.Is4() {
   545  		return ip.v4(0) == 127
   546  	}
   547  	// IP Version 6 Addressing Architecture (2.4 Address Type Identification)
   548  	// https://datatracker.ietf.org/doc/html/rfc4291#section-2.4
   549  	if ip.Is6() {
   550  		return ip.addr.hi == 0 && ip.addr.lo == 1
   551  	}
   552  	return false // zero value
   553  }
   554  
   555  // IsMulticast reports whether ip is a multicast address.
   556  func (ip Addr) IsMulticast() bool {
   557  	if ip.Is4In6() {
   558  		ip = ip.Unmap()
   559  	}
   560  
   561  	// Host Extensions for IP Multicasting (4. HOST GROUP ADDRESSES)
   562  	// https://datatracker.ietf.org/doc/html/rfc1112#section-4
   563  	if ip.Is4() {
   564  		return ip.v4(0)&0xf0 == 0xe0
   565  	}
   566  	// IP Version 6 Addressing Architecture (2.4 Address Type Identification)
   567  	// https://datatracker.ietf.org/doc/html/rfc4291#section-2.4
   568  	if ip.Is6() {
   569  		return ip.addr.hi>>(64-8) == 0xff // ip.v6(0) == 0xff
   570  	}
   571  	return false // zero value
   572  }
   573  
   574  // IsInterfaceLocalMulticast reports whether ip is an IPv6 interface-local
   575  // multicast address.
   576  func (ip Addr) IsInterfaceLocalMulticast() bool {
   577  	// IPv6 Addressing Architecture (2.7.1. Pre-Defined Multicast Addresses)
   578  	// https://datatracker.ietf.org/doc/html/rfc4291#section-2.7.1
   579  	if ip.Is6() && !ip.Is4In6() {
   580  		return ip.v6u16(0)&0xff0f == 0xff01
   581  	}
   582  	return false // zero value
   583  }
   584  
   585  // IsLinkLocalMulticast reports whether ip is a link-local multicast address.
   586  func (ip Addr) IsLinkLocalMulticast() bool {
   587  	if ip.Is4In6() {
   588  		ip = ip.Unmap()
   589  	}
   590  
   591  	// IPv4 Multicast Guidelines (4. Local Network Control Block (224.0.0/24))
   592  	// https://datatracker.ietf.org/doc/html/rfc5771#section-4
   593  	if ip.Is4() {
   594  		return ip.v4(0) == 224 && ip.v4(1) == 0 && ip.v4(2) == 0
   595  	}
   596  	// IPv6 Addressing Architecture (2.7.1. Pre-Defined Multicast Addresses)
   597  	// https://datatracker.ietf.org/doc/html/rfc4291#section-2.7.1
   598  	if ip.Is6() {
   599  		return ip.v6u16(0)&0xff0f == 0xff02
   600  	}
   601  	return false // zero value
   602  }
   603  
   604  // IsGlobalUnicast reports whether ip is a global unicast address.
   605  //
   606  // It returns true for IPv6 addresses which fall outside of the current
   607  // IANA-allocated 2000::/3 global unicast space, with the exception of the
   608  // link-local address space. It also returns true even if ip is in the IPv4
   609  // private address space or IPv6 unique local address space.
   610  // It returns false for the zero [Addr].
   611  //
   612  // For reference, see RFC 1122, RFC 4291, and RFC 4632.
   613  func (ip Addr) IsGlobalUnicast() bool {
   614  	if ip.z == z0 {
   615  		// Invalid or zero-value.
   616  		return false
   617  	}
   618  
   619  	if ip.Is4In6() {
   620  		ip = ip.Unmap()
   621  	}
   622  
   623  	// Match package net's IsGlobalUnicast logic. Notably private IPv4 addresses
   624  	// and ULA IPv6 addresses are still considered "global unicast".
   625  	if ip.Is4() && (ip == IPv4Unspecified() || ip == AddrFrom4([4]byte{255, 255, 255, 255})) {
   626  		return false
   627  	}
   628  
   629  	return ip != IPv6Unspecified() &&
   630  		!ip.IsLoopback() &&
   631  		!ip.IsMulticast() &&
   632  		!ip.IsLinkLocalUnicast()
   633  }
   634  
   635  // IsPrivate reports whether ip is a private address, according to RFC 1918
   636  // (IPv4 addresses) and RFC 4193 (IPv6 addresses). That is, it reports whether
   637  // ip is in 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16, or fc00::/7. This is the
   638  // same as [net.IP.IsPrivate].
   639  func (ip Addr) IsPrivate() bool {
   640  	if ip.Is4In6() {
   641  		ip = ip.Unmap()
   642  	}
   643  
   644  	// Match the stdlib's IsPrivate logic.
   645  	if ip.Is4() {
   646  		// RFC 1918 allocates 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16 as
   647  		// private IPv4 address subnets.
   648  		return ip.v4(0) == 10 ||
   649  			(ip.v4(0) == 172 && ip.v4(1)&0xf0 == 16) ||
   650  			(ip.v4(0) == 192 && ip.v4(1) == 168)
   651  	}
   652  
   653  	if ip.Is6() {
   654  		// RFC 4193 allocates fc00::/7 as the unique local unicast IPv6 address
   655  		// subnet.
   656  		return ip.v6(0)&0xfe == 0xfc
   657  	}
   658  
   659  	return false // zero value
   660  }
   661  
   662  // IsUnspecified reports whether ip is an unspecified address, either the IPv4
   663  // address "0.0.0.0" or the IPv6 address "::".
   664  //
   665  // Note that the zero [Addr] is not an unspecified address.
   666  func (ip Addr) IsUnspecified() bool {
   667  	return ip == IPv4Unspecified() || ip == IPv6Unspecified()
   668  }
   669  
   670  // Prefix keeps only the top b bits of IP, producing a Prefix
   671  // of the specified length.
   672  // If ip is a zero [Addr], Prefix always returns a zero Prefix and a nil error.
   673  // Otherwise, if bits is less than zero or greater than ip.BitLen(),
   674  // Prefix returns an error.
   675  func (ip Addr) Prefix(b int) (Prefix, error) {
   676  	if b < 0 {
   677  		return Prefix{}, errors.New("negative Prefix bits")
   678  	}
   679  	effectiveBits := b
   680  	switch ip.z {
   681  	case z0:
   682  		return Prefix{}, nil
   683  	case z4:
   684  		if b > 32 {
   685  			return Prefix{}, errors.New("prefix length " + itoa.Itoa(b) + " too large for IPv4")
   686  		}
   687  		effectiveBits += 96
   688  	default:
   689  		if b > 128 {
   690  			return Prefix{}, errors.New("prefix length " + itoa.Itoa(b) + " too large for IPv6")
   691  		}
   692  	}
   693  	ip.addr = ip.addr.and(mask6(effectiveBits))
   694  	return PrefixFrom(ip, b), nil
   695  }
   696  
   697  // As16 returns the IP address in its 16-byte representation.
   698  // IPv4 addresses are returned as IPv4-mapped IPv6 addresses.
   699  // IPv6 addresses with zones are returned without their zone (use the
   700  // [Addr.Zone] method to get it).
   701  // The ip zero value returns all zeroes.
   702  func (ip Addr) As16() (a16 [16]byte) {
   703  	byteorder.BePutUint64(a16[:8], ip.addr.hi)
   704  	byteorder.BePutUint64(a16[8:], ip.addr.lo)
   705  	return a16
   706  }
   707  
   708  // As4 returns an IPv4 or IPv4-in-IPv6 address in its 4-byte representation.
   709  // If ip is the zero [Addr] or an IPv6 address, As4 panics.
   710  // Note that 0.0.0.0 is not the zero Addr.
   711  func (ip Addr) As4() (a4 [4]byte) {
   712  	if ip.z == z4 || ip.Is4In6() {
   713  		byteorder.BePutUint32(a4[:], uint32(ip.addr.lo))
   714  		return a4
   715  	}
   716  	if ip.z == z0 {
   717  		panic("As4 called on IP zero value")
   718  	}
   719  	panic("As4 called on IPv6 address")
   720  }
   721  
   722  // AsSlice returns an IPv4 or IPv6 address in its respective 4-byte or 16-byte representation.
   723  func (ip Addr) AsSlice() []byte {
   724  	switch ip.z {
   725  	case z0:
   726  		return nil
   727  	case z4:
   728  		var ret [4]byte
   729  		byteorder.BePutUint32(ret[:], uint32(ip.addr.lo))
   730  		return ret[:]
   731  	default:
   732  		var ret [16]byte
   733  		byteorder.BePutUint64(ret[:8], ip.addr.hi)
   734  		byteorder.BePutUint64(ret[8:], ip.addr.lo)
   735  		return ret[:]
   736  	}
   737  }
   738  
   739  // Next returns the address following ip.
   740  // If there is none, it returns the zero [Addr].
   741  func (ip Addr) Next() Addr {
   742  	ip.addr = ip.addr.addOne()
   743  	if ip.Is4() {
   744  		if uint32(ip.addr.lo) == 0 {
   745  			// Overflowed.
   746  			return Addr{}
   747  		}
   748  	} else {
   749  		if ip.addr.isZero() {
   750  			// Overflowed
   751  			return Addr{}
   752  		}
   753  	}
   754  	return ip
   755  }
   756  
   757  // Prev returns the IP before ip.
   758  // If there is none, it returns the IP zero value.
   759  func (ip Addr) Prev() Addr {
   760  	if ip.Is4() {
   761  		if uint32(ip.addr.lo) == 0 {
   762  			return Addr{}
   763  		}
   764  	} else if ip.addr.isZero() {
   765  		return Addr{}
   766  	}
   767  	ip.addr = ip.addr.subOne()
   768  	return ip
   769  }
   770  
   771  // String returns the string form of the IP address ip.
   772  // It returns one of 5 forms:
   773  //
   774  //   - "invalid IP", if ip is the zero [Addr]
   775  //   - IPv4 dotted decimal ("192.0.2.1")
   776  //   - IPv6 ("2001:db8::1")
   777  //   - "::ffff:1.2.3.4" (if [Addr.Is4In6])
   778  //   - IPv6 with zone ("fe80:db8::1%eth0")
   779  //
   780  // Note that unlike package net's IP.String method,
   781  // IPv4-mapped IPv6 addresses format with a "::ffff:"
   782  // prefix before the dotted quad.
   783  func (ip Addr) String() string {
   784  	switch ip.z {
   785  	case z0:
   786  		return "invalid IP"
   787  	case z4:
   788  		return ip.string4()
   789  	default:
   790  		if ip.Is4In6() {
   791  			return ip.string4In6()
   792  		}
   793  		return ip.string6()
   794  	}
   795  }
   796  
   797  // AppendTo appends a text encoding of ip,
   798  // as generated by [Addr.MarshalText],
   799  // to b and returns the extended buffer.
   800  func (ip Addr) AppendTo(b []byte) []byte {
   801  	switch ip.z {
   802  	case z0:
   803  		return b
   804  	case z4:
   805  		return ip.appendTo4(b)
   806  	default:
   807  		if ip.Is4In6() {
   808  			return ip.appendTo4In6(b)
   809  		}
   810  		return ip.appendTo6(b)
   811  	}
   812  }
   813  
   814  // digits is a string of the hex digits from 0 to f. It's used in
   815  // appendDecimal and appendHex to format IP addresses.
   816  const digits = "0123456789abcdef"
   817  
   818  // appendDecimal appends the decimal string representation of x to b.
   819  func appendDecimal(b []byte, x uint8) []byte {
   820  	// Using this function rather than strconv.AppendUint makes IPv4
   821  	// string building 2x faster.
   822  
   823  	if x >= 100 {
   824  		b = append(b, digits[x/100])
   825  	}
   826  	if x >= 10 {
   827  		b = append(b, digits[x/10%10])
   828  	}
   829  	return append(b, digits[x%10])
   830  }
   831  
   832  // appendHex appends the hex string representation of x to b.
   833  func appendHex(b []byte, x uint16) []byte {
   834  	// Using this function rather than strconv.AppendUint makes IPv6
   835  	// string building 2x faster.
   836  
   837  	if x >= 0x1000 {
   838  		b = append(b, digits[x>>12])
   839  	}
   840  	if x >= 0x100 {
   841  		b = append(b, digits[x>>8&0xf])
   842  	}
   843  	if x >= 0x10 {
   844  		b = append(b, digits[x>>4&0xf])
   845  	}
   846  	return append(b, digits[x&0xf])
   847  }
   848  
   849  // appendHexPad appends the fully padded hex string representation of x to b.
   850  func appendHexPad(b []byte, x uint16) []byte {
   851  	return append(b, digits[x>>12], digits[x>>8&0xf], digits[x>>4&0xf], digits[x&0xf])
   852  }
   853  
   854  func (ip Addr) string4() string {
   855  	const max = len("255.255.255.255")
   856  	ret := make([]byte, 0, max)
   857  	ret = ip.appendTo4(ret)
   858  	return string(ret)
   859  }
   860  
   861  func (ip Addr) appendTo4(ret []byte) []byte {
   862  	ret = appendDecimal(ret, ip.v4(0))
   863  	ret = append(ret, '.')
   864  	ret = appendDecimal(ret, ip.v4(1))
   865  	ret = append(ret, '.')
   866  	ret = appendDecimal(ret, ip.v4(2))
   867  	ret = append(ret, '.')
   868  	ret = appendDecimal(ret, ip.v4(3))
   869  	return ret
   870  }
   871  
   872  func (ip Addr) string4In6() string {
   873  	const max = len("::ffff:255.255.255.255%enp5s0")
   874  	ret := make([]byte, 0, max)
   875  	ret = ip.appendTo4In6(ret)
   876  	return string(ret)
   877  }
   878  
   879  func (ip Addr) appendTo4In6(ret []byte) []byte {
   880  	ret = append(ret, "::ffff:"...)
   881  	ret = ip.Unmap().appendTo4(ret)
   882  	if ip.z != z6noz {
   883  		ret = append(ret, '%')
   884  		ret = append(ret, ip.Zone()...)
   885  	}
   886  	return ret
   887  }
   888  
   889  // string6 formats ip in IPv6 textual representation. It follows the
   890  // guidelines in section 4 of RFC 5952
   891  // (https://tools.ietf.org/html/rfc5952#section-4): no unnecessary
   892  // zeros, use :: to elide the longest run of zeros, and don't use ::
   893  // to compact a single zero field.
   894  func (ip Addr) string6() string {
   895  	// Use a zone with a "plausibly long" name, so that most zone-ful
   896  	// IP addresses won't require additional allocation.
   897  	//
   898  	// The compiler does a cool optimization here, where ret ends up
   899  	// stack-allocated and so the only allocation this function does
   900  	// is to construct the returned string. As such, it's okay to be a
   901  	// bit greedy here, size-wise.
   902  	const max = len("ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff%enp5s0")
   903  	ret := make([]byte, 0, max)
   904  	ret = ip.appendTo6(ret)
   905  	return string(ret)
   906  }
   907  
   908  func (ip Addr) appendTo6(ret []byte) []byte {
   909  	zeroStart, zeroEnd := uint8(255), uint8(255)
   910  	for i := uint8(0); i < 8; i++ {
   911  		j := i
   912  		for j < 8 && ip.v6u16(j) == 0 {
   913  			j++
   914  		}
   915  		if l := j - i; l >= 2 && l > zeroEnd-zeroStart {
   916  			zeroStart, zeroEnd = i, j
   917  		}
   918  	}
   919  
   920  	for i := uint8(0); i < 8; i++ {
   921  		if i == zeroStart {
   922  			ret = append(ret, ':', ':')
   923  			i = zeroEnd
   924  			if i >= 8 {
   925  				break
   926  			}
   927  		} else if i > 0 {
   928  			ret = append(ret, ':')
   929  		}
   930  
   931  		ret = appendHex(ret, ip.v6u16(i))
   932  	}
   933  
   934  	if ip.z != z6noz {
   935  		ret = append(ret, '%')
   936  		ret = append(ret, ip.Zone()...)
   937  	}
   938  	return ret
   939  }
   940  
   941  // StringExpanded is like [Addr.String] but IPv6 addresses are expanded with leading
   942  // zeroes and no "::" compression. For example, "2001:db8::1" becomes
   943  // "2001:0db8:0000:0000:0000:0000:0000:0001".
   944  func (ip Addr) StringExpanded() string {
   945  	switch ip.z {
   946  	case z0, z4:
   947  		return ip.String()
   948  	}
   949  
   950  	const size = len("ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff")
   951  	ret := make([]byte, 0, size)
   952  	for i := uint8(0); i < 8; i++ {
   953  		if i > 0 {
   954  			ret = append(ret, ':')
   955  		}
   956  
   957  		ret = appendHexPad(ret, ip.v6u16(i))
   958  	}
   959  
   960  	if ip.z != z6noz {
   961  		// The addition of a zone will cause a second allocation, but when there
   962  		// is no zone the ret slice will be stack allocated.
   963  		ret = append(ret, '%')
   964  		ret = append(ret, ip.Zone()...)
   965  	}
   966  	return string(ret)
   967  }
   968  
   969  // MarshalText implements the [encoding.TextMarshaler] interface,
   970  // The encoding is the same as returned by [Addr.String], with one exception:
   971  // If ip is the zero [Addr], the encoding is the empty string.
   972  func (ip Addr) MarshalText() ([]byte, error) {
   973  	switch ip.z {
   974  	case z0:
   975  		return []byte(""), nil
   976  	case z4:
   977  		max := len("255.255.255.255")
   978  		b := make([]byte, 0, max)
   979  		return ip.appendTo4(b), nil
   980  	default:
   981  		if ip.Is4In6() {
   982  			max := len("::ffff:255.255.255.255%enp5s0")
   983  			b := make([]byte, 0, max)
   984  			return ip.appendTo4In6(b), nil
   985  		}
   986  		max := len("ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff%enp5s0")
   987  		b := make([]byte, 0, max)
   988  		return ip.appendTo6(b), nil
   989  	}
   990  }
   991  
   992  // UnmarshalText implements the encoding.TextUnmarshaler interface.
   993  // The IP address is expected in a form accepted by [ParseAddr].
   994  //
   995  // If text is empty, UnmarshalText sets *ip to the zero [Addr] and
   996  // returns no error.
   997  func (ip *Addr) UnmarshalText(text []byte) error {
   998  	if len(text) == 0 {
   999  		*ip = Addr{}
  1000  		return nil
  1001  	}
  1002  	var err error
  1003  	*ip, err = ParseAddr(string(text))
  1004  	return err
  1005  }
  1006  
  1007  func (ip Addr) marshalBinaryWithTrailingBytes(trailingBytes int) []byte {
  1008  	var b []byte
  1009  	switch ip.z {
  1010  	case z0:
  1011  		b = make([]byte, trailingBytes)
  1012  	case z4:
  1013  		b = make([]byte, 4+trailingBytes)
  1014  		byteorder.BePutUint32(b, uint32(ip.addr.lo))
  1015  	default:
  1016  		z := ip.Zone()
  1017  		b = make([]byte, 16+len(z)+trailingBytes)
  1018  		byteorder.BePutUint64(b[:8], ip.addr.hi)
  1019  		byteorder.BePutUint64(b[8:], ip.addr.lo)
  1020  		copy(b[16:], z)
  1021  	}
  1022  	return b
  1023  }
  1024  
  1025  // MarshalBinary implements the [encoding.BinaryMarshaler] interface.
  1026  // It returns a zero-length slice for the zero [Addr],
  1027  // the 4-byte form for an IPv4 address,
  1028  // and the 16-byte form with zone appended for an IPv6 address.
  1029  func (ip Addr) MarshalBinary() ([]byte, error) {
  1030  	return ip.marshalBinaryWithTrailingBytes(0), nil
  1031  }
  1032  
  1033  // UnmarshalBinary implements the [encoding.BinaryUnmarshaler] interface.
  1034  // It expects data in the form generated by MarshalBinary.
  1035  func (ip *Addr) UnmarshalBinary(b []byte) error {
  1036  	n := len(b)
  1037  	switch {
  1038  	case n == 0:
  1039  		*ip = Addr{}
  1040  		return nil
  1041  	case n == 4:
  1042  		*ip = AddrFrom4([4]byte(b))
  1043  		return nil
  1044  	case n == 16:
  1045  		*ip = AddrFrom16([16]byte(b))
  1046  		return nil
  1047  	case n > 16:
  1048  		*ip = AddrFrom16([16]byte(b[:16])).WithZone(string(b[16:]))
  1049  		return nil
  1050  	}
  1051  	return errors.New("unexpected slice size")
  1052  }
  1053  
  1054  // AddrPort is an IP and a port number.
  1055  type AddrPort struct {
  1056  	ip   Addr
  1057  	port uint16
  1058  }
  1059  
  1060  // AddrPortFrom returns an [AddrPort] with the provided IP and port.
  1061  // It does not allocate.
  1062  func AddrPortFrom(ip Addr, port uint16) AddrPort { return AddrPort{ip: ip, port: port} }
  1063  
  1064  // Addr returns p's IP address.
  1065  func (p AddrPort) Addr() Addr { return p.ip }
  1066  
  1067  // Port returns p's port.
  1068  func (p AddrPort) Port() uint16 { return p.port }
  1069  
  1070  // splitAddrPort splits s into an IP address string and a port
  1071  // string. It splits strings shaped like "foo:bar" or "[foo]:bar",
  1072  // without further validating the substrings. v6 indicates whether the
  1073  // ip string should parse as an IPv6 address or an IPv4 address, in
  1074  // order for s to be a valid ip:port string.
  1075  func splitAddrPort(s string) (ip, port string, v6 bool, err error) {
  1076  	i := bytealg.LastIndexByteString(s, ':')
  1077  	if i == -1 {
  1078  		return "", "", false, errors.New("not an ip:port")
  1079  	}
  1080  
  1081  	ip, port = s[:i], s[i+1:]
  1082  	if len(ip) == 0 {
  1083  		return "", "", false, errors.New("no IP")
  1084  	}
  1085  	if len(port) == 0 {
  1086  		return "", "", false, errors.New("no port")
  1087  	}
  1088  	if ip[0] == '[' {
  1089  		if len(ip) < 2 || ip[len(ip)-1] != ']' {
  1090  			return "", "", false, errors.New("missing ]")
  1091  		}
  1092  		ip = ip[1 : len(ip)-1]
  1093  		v6 = true
  1094  	}
  1095  
  1096  	return ip, port, v6, nil
  1097  }
  1098  
  1099  // ParseAddrPort parses s as an [AddrPort].
  1100  //
  1101  // It doesn't do any name resolution: both the address and the port
  1102  // must be numeric.
  1103  func ParseAddrPort(s string) (AddrPort, error) {
  1104  	var ipp AddrPort
  1105  	ip, port, v6, err := splitAddrPort(s)
  1106  	if err != nil {
  1107  		return ipp, err
  1108  	}
  1109  	port16, err := strconv.ParseUint(port, 10, 16)
  1110  	if err != nil {
  1111  		return ipp, errors.New("invalid port " + strconv.Quote(port) + " parsing " + strconv.Quote(s))
  1112  	}
  1113  	ipp.port = uint16(port16)
  1114  	ipp.ip, err = ParseAddr(ip)
  1115  	if err != nil {
  1116  		return AddrPort{}, err
  1117  	}
  1118  	if v6 && ipp.ip.Is4() {
  1119  		return AddrPort{}, errors.New("invalid ip:port " + strconv.Quote(s) + ", square brackets can only be used with IPv6 addresses")
  1120  	} else if !v6 && ipp.ip.Is6() {
  1121  		return AddrPort{}, errors.New("invalid ip:port " + strconv.Quote(s) + ", IPv6 addresses must be surrounded by square brackets")
  1122  	}
  1123  	return ipp, nil
  1124  }
  1125  
  1126  // MustParseAddrPort calls [ParseAddrPort](s) and panics on error.
  1127  // It is intended for use in tests with hard-coded strings.
  1128  func MustParseAddrPort(s string) AddrPort {
  1129  	ip, err := ParseAddrPort(s)
  1130  	if err != nil {
  1131  		panic(err)
  1132  	}
  1133  	return ip
  1134  }
  1135  
  1136  // IsValid reports whether p.Addr() is valid.
  1137  // All ports are valid, including zero.
  1138  func (p AddrPort) IsValid() bool { return p.ip.IsValid() }
  1139  
  1140  // Compare returns an integer comparing two AddrPorts.
  1141  // The result will be 0 if p == p2, -1 if p < p2, and +1 if p > p2.
  1142  // AddrPorts sort first by IP address, then port.
  1143  func (p AddrPort) Compare(p2 AddrPort) int {
  1144  	if c := p.Addr().Compare(p2.Addr()); c != 0 {
  1145  		return c
  1146  	}
  1147  	return cmp.Compare(p.Port(), p2.Port())
  1148  }
  1149  
  1150  func (p AddrPort) String() string {
  1151  	var b []byte
  1152  	switch p.ip.z {
  1153  	case z0:
  1154  		return "invalid AddrPort"
  1155  	case z4:
  1156  		const max = len("255.255.255.255:65535")
  1157  		b = make([]byte, 0, max)
  1158  		b = p.ip.appendTo4(b)
  1159  	default:
  1160  		if p.ip.Is4In6() {
  1161  			const max = len("[::ffff:255.255.255.255%enp5s0]:65535")
  1162  			b = make([]byte, 0, max)
  1163  			b = append(b, '[')
  1164  			b = p.ip.appendTo4In6(b)
  1165  		} else {
  1166  			const max = len("[ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff%enp5s0]:65535")
  1167  			b = make([]byte, 0, max)
  1168  			b = append(b, '[')
  1169  			b = p.ip.appendTo6(b)
  1170  		}
  1171  		b = append(b, ']')
  1172  	}
  1173  	b = append(b, ':')
  1174  	b = strconv.AppendUint(b, uint64(p.port), 10)
  1175  	return string(b)
  1176  }
  1177  
  1178  // AppendTo appends a text encoding of p,
  1179  // as generated by [AddrPort.MarshalText],
  1180  // to b and returns the extended buffer.
  1181  func (p AddrPort) AppendTo(b []byte) []byte {
  1182  	switch p.ip.z {
  1183  	case z0:
  1184  		return b
  1185  	case z4:
  1186  		b = p.ip.appendTo4(b)
  1187  	default:
  1188  		b = append(b, '[')
  1189  		if p.ip.Is4In6() {
  1190  			b = p.ip.appendTo4In6(b)
  1191  		} else {
  1192  			b = p.ip.appendTo6(b)
  1193  		}
  1194  		b = append(b, ']')
  1195  	}
  1196  	b = append(b, ':')
  1197  	b = strconv.AppendUint(b, uint64(p.port), 10)
  1198  	return b
  1199  }
  1200  
  1201  // MarshalText implements the [encoding.TextMarshaler] interface. The
  1202  // encoding is the same as returned by [AddrPort.String], with one exception: if
  1203  // p.Addr() is the zero [Addr], the encoding is the empty string.
  1204  func (p AddrPort) MarshalText() ([]byte, error) {
  1205  	var max int
  1206  	switch p.ip.z {
  1207  	case z0:
  1208  	case z4:
  1209  		max = len("255.255.255.255:65535")
  1210  	default:
  1211  		max = len("[ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff%enp5s0]:65535")
  1212  	}
  1213  	b := make([]byte, 0, max)
  1214  	b = p.AppendTo(b)
  1215  	return b, nil
  1216  }
  1217  
  1218  // UnmarshalText implements the encoding.TextUnmarshaler
  1219  // interface. The [AddrPort] is expected in a form
  1220  // generated by [AddrPort.MarshalText] or accepted by [ParseAddrPort].
  1221  func (p *AddrPort) UnmarshalText(text []byte) error {
  1222  	if len(text) == 0 {
  1223  		*p = AddrPort{}
  1224  		return nil
  1225  	}
  1226  	var err error
  1227  	*p, err = ParseAddrPort(string(text))
  1228  	return err
  1229  }
  1230  
  1231  // MarshalBinary implements the [encoding.BinaryMarshaler] interface.
  1232  // It returns [Addr.MarshalBinary] with an additional two bytes appended
  1233  // containing the port in little-endian.
  1234  func (p AddrPort) MarshalBinary() ([]byte, error) {
  1235  	b := p.Addr().marshalBinaryWithTrailingBytes(2)
  1236  	byteorder.LePutUint16(b[len(b)-2:], p.Port())
  1237  	return b, nil
  1238  }
  1239  
  1240  // UnmarshalBinary implements the [encoding.BinaryUnmarshaler] interface.
  1241  // It expects data in the form generated by [AddrPort.MarshalBinary].
  1242  func (p *AddrPort) UnmarshalBinary(b []byte) error {
  1243  	if len(b) < 2 {
  1244  		return errors.New("unexpected slice size")
  1245  	}
  1246  	var addr Addr
  1247  	err := addr.UnmarshalBinary(b[:len(b)-2])
  1248  	if err != nil {
  1249  		return err
  1250  	}
  1251  	*p = AddrPortFrom(addr, byteorder.LeUint16(b[len(b)-2:]))
  1252  	return nil
  1253  }
  1254  
  1255  // Prefix is an IP address prefix (CIDR) representing an IP network.
  1256  //
  1257  // The first [Prefix.Bits]() of [Addr]() are specified. The remaining bits match any address.
  1258  // The range of Bits() is [0,32] for IPv4 or [0,128] for IPv6.
  1259  type Prefix struct {
  1260  	ip Addr
  1261  
  1262  	// bitsPlusOne stores the prefix bit length plus one.
  1263  	// A Prefix is valid if and only if bitsPlusOne is non-zero.
  1264  	bitsPlusOne uint8
  1265  }
  1266  
  1267  // PrefixFrom returns a [Prefix] with the provided IP address and bit
  1268  // prefix length.
  1269  //
  1270  // It does not allocate. Unlike [Addr.Prefix], [PrefixFrom] does not mask
  1271  // off the host bits of ip.
  1272  //
  1273  // If bits is less than zero or greater than ip.BitLen, [Prefix.Bits]
  1274  // will return an invalid value -1.
  1275  func PrefixFrom(ip Addr, bits int) Prefix {
  1276  	var bitsPlusOne uint8
  1277  	if !ip.isZero() && bits >= 0 && bits <= ip.BitLen() {
  1278  		bitsPlusOne = uint8(bits) + 1
  1279  	}
  1280  	return Prefix{
  1281  		ip:          ip.withoutZone(),
  1282  		bitsPlusOne: bitsPlusOne,
  1283  	}
  1284  }
  1285  
  1286  // Addr returns p's IP address.
  1287  func (p Prefix) Addr() Addr { return p.ip }
  1288  
  1289  // Bits returns p's prefix length.
  1290  //
  1291  // It reports -1 if invalid.
  1292  func (p Prefix) Bits() int { return int(p.bitsPlusOne) - 1 }
  1293  
  1294  // IsValid reports whether p.Bits() has a valid range for p.Addr().
  1295  // If p.Addr() is the zero [Addr], IsValid returns false.
  1296  // Note that if p is the zero [Prefix], then p.IsValid() == false.
  1297  func (p Prefix) IsValid() bool { return p.bitsPlusOne > 0 }
  1298  
  1299  func (p Prefix) isZero() bool { return p == Prefix{} }
  1300  
  1301  // IsSingleIP reports whether p contains exactly one IP.
  1302  func (p Prefix) IsSingleIP() bool { return p.IsValid() && p.Bits() == p.ip.BitLen() }
  1303  
  1304  // compare returns an integer comparing two prefixes.
  1305  // The result will be 0 if p == p2, -1 if p < p2, and +1 if p > p2.
  1306  // Prefixes sort first by validity (invalid before valid), then
  1307  // address family (IPv4 before IPv6), then prefix length, then
  1308  // address.
  1309  //
  1310  // Unexported for Go 1.22 because we may want to compare by p.Addr first.
  1311  // See post-acceptance discussion on go.dev/issue/61642.
  1312  func (p Prefix) compare(p2 Prefix) int {
  1313  	if c := cmp.Compare(p.Addr().BitLen(), p2.Addr().BitLen()); c != 0 {
  1314  		return c
  1315  	}
  1316  	if c := cmp.Compare(p.Bits(), p2.Bits()); c != 0 {
  1317  		return c
  1318  	}
  1319  	return p.Addr().Compare(p2.Addr())
  1320  }
  1321  
  1322  type parsePrefixError struct {
  1323  	in  string // the string given to ParsePrefix
  1324  	msg string // an explanation of the parse failure
  1325  }
  1326  
  1327  func (err parsePrefixError) Error() string {
  1328  	return "netip.ParsePrefix(" + strconv.Quote(err.in) + "): " + err.msg
  1329  }
  1330  
  1331  // ParsePrefix parses s as an IP address prefix.
  1332  // The string can be in the form "192.168.1.0/24" or "2001:db8::/32",
  1333  // the CIDR notation defined in RFC 4632 and RFC 4291.
  1334  // IPv6 zones are not permitted in prefixes, and an error will be returned if a
  1335  // zone is present.
  1336  //
  1337  // Note that masked address bits are not zeroed. Use Masked for that.
  1338  func ParsePrefix(s string) (Prefix, error) {
  1339  	i := bytealg.LastIndexByteString(s, '/')
  1340  	if i < 0 {
  1341  		return Prefix{}, parsePrefixError{in: s, msg: "no '/'"}
  1342  	}
  1343  	ip, err := ParseAddr(s[:i])
  1344  	if err != nil {
  1345  		return Prefix{}, parsePrefixError{in: s, msg: err.Error()}
  1346  	}
  1347  	// IPv6 zones are not allowed: https://go.dev/issue/51899
  1348  	if ip.Is6() && ip.z != z6noz {
  1349  		return Prefix{}, parsePrefixError{in: s, msg: "IPv6 zones cannot be present in a prefix"}
  1350  	}
  1351  
  1352  	bitsStr := s[i+1:]
  1353  
  1354  	// strconv.Atoi accepts a leading sign and leading zeroes, but we don't want that.
  1355  	if len(bitsStr) > 1 && (bitsStr[0] < '1' || bitsStr[0] > '9') {
  1356  		return Prefix{}, parsePrefixError{in: s, msg: "bad bits after slash: " + strconv.Quote(bitsStr)}
  1357  	}
  1358  
  1359  	bits, err := strconv.Atoi(bitsStr)
  1360  	if err != nil {
  1361  		return Prefix{}, parsePrefixError{in: s, msg: "bad bits after slash: " + strconv.Quote(bitsStr)}
  1362  	}
  1363  	maxBits := 32
  1364  	if ip.Is6() {
  1365  		maxBits = 128
  1366  	}
  1367  	if bits < 0 || bits > maxBits {
  1368  		return Prefix{}, parsePrefixError{in: s, msg: "prefix length out of range"}
  1369  	}
  1370  	return PrefixFrom(ip, bits), nil
  1371  }
  1372  
  1373  // MustParsePrefix calls [ParsePrefix](s) and panics on error.
  1374  // It is intended for use in tests with hard-coded strings.
  1375  func MustParsePrefix(s string) Prefix {
  1376  	ip, err := ParsePrefix(s)
  1377  	if err != nil {
  1378  		panic(err)
  1379  	}
  1380  	return ip
  1381  }
  1382  
  1383  // Masked returns p in its canonical form, with all but the high
  1384  // p.Bits() bits of p.Addr() masked off.
  1385  //
  1386  // If p is zero or otherwise invalid, Masked returns the zero [Prefix].
  1387  func (p Prefix) Masked() Prefix {
  1388  	m, _ := p.ip.Prefix(p.Bits())
  1389  	return m
  1390  }
  1391  
  1392  // Contains reports whether the network p includes ip.
  1393  //
  1394  // An IPv4 address will not match an IPv6 prefix.
  1395  // An IPv4-mapped IPv6 address will not match an IPv4 prefix.
  1396  // A zero-value IP will not match any prefix.
  1397  // If ip has an IPv6 zone, Contains returns false,
  1398  // because Prefixes strip zones.
  1399  func (p Prefix) Contains(ip Addr) bool {
  1400  	if !p.IsValid() || ip.hasZone() {
  1401  		return false
  1402  	}
  1403  	if f1, f2 := p.ip.BitLen(), ip.BitLen(); f1 == 0 || f2 == 0 || f1 != f2 {
  1404  		return false
  1405  	}
  1406  	if ip.Is4() {
  1407  		// xor the IP addresses together; mismatched bits are now ones.
  1408  		// Shift away the number of bits we don't care about.
  1409  		// Shifts in Go are more efficient if the compiler can prove
  1410  		// that the shift amount is smaller than the width of the shifted type (64 here).
  1411  		// We know that p.bits is in the range 0..32 because p is Valid;
  1412  		// the compiler doesn't know that, so mask with 63 to help it.
  1413  		// Now truncate to 32 bits, because this is IPv4.
  1414  		// If all the bits we care about are equal, the result will be zero.
  1415  		return uint32((ip.addr.lo^p.ip.addr.lo)>>((32-p.Bits())&63)) == 0
  1416  	} else {
  1417  		// xor the IP addresses together.
  1418  		// Mask away the bits we don't care about.
  1419  		// If all the bits we care about are equal, the result will be zero.
  1420  		return ip.addr.xor(p.ip.addr).and(mask6(p.Bits())).isZero()
  1421  	}
  1422  }
  1423  
  1424  // Overlaps reports whether p and o contain any IP addresses in common.
  1425  //
  1426  // If p and o are of different address families or either have a zero
  1427  // IP, it reports false. Like the Contains method, a prefix with an
  1428  // IPv4-mapped IPv6 address is still treated as an IPv6 mask.
  1429  func (p Prefix) Overlaps(o Prefix) bool {
  1430  	if !p.IsValid() || !o.IsValid() {
  1431  		return false
  1432  	}
  1433  	if p == o {
  1434  		return true
  1435  	}
  1436  	if p.ip.Is4() != o.ip.Is4() {
  1437  		return false
  1438  	}
  1439  	var minBits int
  1440  	if pb, ob := p.Bits(), o.Bits(); pb < ob {
  1441  		minBits = pb
  1442  	} else {
  1443  		minBits = ob
  1444  	}
  1445  	if minBits == 0 {
  1446  		return true
  1447  	}
  1448  	// One of these Prefix calls might look redundant, but we don't require
  1449  	// that p and o values are normalized (via Prefix.Masked) first,
  1450  	// so the Prefix call on the one that's already minBits serves to zero
  1451  	// out any remaining bits in IP.
  1452  	var err error
  1453  	if p, err = p.ip.Prefix(minBits); err != nil {
  1454  		return false
  1455  	}
  1456  	if o, err = o.ip.Prefix(minBits); err != nil {
  1457  		return false
  1458  	}
  1459  	return p.ip == o.ip
  1460  }
  1461  
  1462  // AppendTo appends a text encoding of p,
  1463  // as generated by [Prefix.MarshalText],
  1464  // to b and returns the extended buffer.
  1465  func (p Prefix) AppendTo(b []byte) []byte {
  1466  	if p.isZero() {
  1467  		return b
  1468  	}
  1469  	if !p.IsValid() {
  1470  		return append(b, "invalid Prefix"...)
  1471  	}
  1472  
  1473  	// p.ip is non-nil, because p is valid.
  1474  	if p.ip.z == z4 {
  1475  		b = p.ip.appendTo4(b)
  1476  	} else {
  1477  		if p.ip.Is4In6() {
  1478  			b = append(b, "::ffff:"...)
  1479  			b = p.ip.Unmap().appendTo4(b)
  1480  		} else {
  1481  			b = p.ip.appendTo6(b)
  1482  		}
  1483  	}
  1484  
  1485  	b = append(b, '/')
  1486  	b = appendDecimal(b, uint8(p.Bits()))
  1487  	return b
  1488  }
  1489  
  1490  // MarshalText implements the [encoding.TextMarshaler] interface,
  1491  // The encoding is the same as returned by [Prefix.String], with one exception:
  1492  // If p is the zero value, the encoding is the empty string.
  1493  func (p Prefix) MarshalText() ([]byte, error) {
  1494  	var max int
  1495  	switch p.ip.z {
  1496  	case z0:
  1497  	case z4:
  1498  		max = len("255.255.255.255/32")
  1499  	default:
  1500  		max = len("ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff%enp5s0/128")
  1501  	}
  1502  	b := make([]byte, 0, max)
  1503  	b = p.AppendTo(b)
  1504  	return b, nil
  1505  }
  1506  
  1507  // UnmarshalText implements the encoding.TextUnmarshaler interface.
  1508  // The IP address is expected in a form accepted by [ParsePrefix]
  1509  // or generated by [Prefix.MarshalText].
  1510  func (p *Prefix) UnmarshalText(text []byte) error {
  1511  	if len(text) == 0 {
  1512  		*p = Prefix{}
  1513  		return nil
  1514  	}
  1515  	var err error
  1516  	*p, err = ParsePrefix(string(text))
  1517  	return err
  1518  }
  1519  
  1520  // MarshalBinary implements the [encoding.BinaryMarshaler] interface.
  1521  // It returns [Addr.MarshalBinary] with an additional byte appended
  1522  // containing the prefix bits.
  1523  func (p Prefix) MarshalBinary() ([]byte, error) {
  1524  	b := p.Addr().withoutZone().marshalBinaryWithTrailingBytes(1)
  1525  	b[len(b)-1] = uint8(p.Bits())
  1526  	return b, nil
  1527  }
  1528  
  1529  // UnmarshalBinary implements the [encoding.BinaryUnmarshaler] interface.
  1530  // It expects data in the form generated by [Prefix.MarshalBinary].
  1531  func (p *Prefix) UnmarshalBinary(b []byte) error {
  1532  	if len(b) < 1 {
  1533  		return errors.New("unexpected slice size")
  1534  	}
  1535  	var addr Addr
  1536  	err := addr.UnmarshalBinary(b[:len(b)-1])
  1537  	if err != nil {
  1538  		return err
  1539  	}
  1540  	*p = PrefixFrom(addr, int(b[len(b)-1]))
  1541  	return nil
  1542  }
  1543  
  1544  // String returns the CIDR notation of p: "<ip>/<bits>".
  1545  func (p Prefix) String() string {
  1546  	if !p.IsValid() {
  1547  		return "invalid Prefix"
  1548  	}
  1549  	return p.ip.String() + "/" + itoa.Itoa(p.Bits())
  1550  }
  1551  

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