ip.go

     1  // Copyright 2009 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  // IP address manipulations
     6  //
     7  // IPv4 addresses are 4 bytes; IPv6 addresses are 16 bytes.
     8  // An IPv4 address can be converted to an IPv6 address by
     9  // adding a canonical prefix (10 zeros, 2 0xFFs).
    10  // This library accepts either size of byte slice but always
    11  // returns 16-byte addresses.
    12  
    13  package net
    14  
    15  import (
    16  	"internal/bytealg"
    17  	"internal/itoa"
    18  	"internal/stringslite"
    19  	"net/netip"
    20  )
    21  
    22  // IP address lengths (bytes).
    23  const (
    24  	IPv4len = 4
    25  	IPv6len = 16
    26  )
    27  
    28  // An IP is a single IP address, a slice of bytes.
    29  // Functions in this package accept either 4-byte (IPv4)
    30  // or 16-byte (IPv6) slices as input.
    31  //
    32  // Note that in this documentation, referring to an
    33  // IP address as an IPv4 address or an IPv6 address
    34  // is a semantic property of the address, not just the
    35  // length of the byte slice: a 16-byte slice can still
    36  // be an IPv4 address.
    37  type IP []byte
    38  
    39  // An IPMask is a bitmask that can be used to manipulate
    40  // IP addresses for IP addressing and routing.
    41  //
    42  // See type [IPNet] and func [ParseCIDR] for details.
    43  type IPMask []byte
    44  
    45  // An IPNet represents an IP network.
    46  type IPNet struct {
    47  	IP   IP     // network number
    48  	Mask IPMask // network mask
    49  }
    50  
    51  // IPv4 returns the IP address (in 16-byte form) of the
    52  // IPv4 address a.b.c.d.
    53  func IPv4(a, b, c, d byte) IP {
    54  	p := make(IP, IPv6len)
    55  	copy(p, v4InV6Prefix)
    56  	p[12] = a
    57  	p[13] = b
    58  	p[14] = c
    59  	p[15] = d
    60  	return p
    61  }
    62  
    63  var v4InV6Prefix = []byte{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0xff, 0xff}
    64  
    65  // IPv4Mask returns the IP mask (in 4-byte form) of the
    66  // IPv4 mask a.b.c.d.
    67  func IPv4Mask(a, b, c, d byte) IPMask {
    68  	p := make(IPMask, IPv4len)
    69  	p[0] = a
    70  	p[1] = b
    71  	p[2] = c
    72  	p[3] = d
    73  	return p
    74  }
    75  
    76  // CIDRMask returns an [IPMask] consisting of 'ones' 1 bits
    77  // followed by 0s up to a total length of 'bits' bits.
    78  // For a mask of this form, CIDRMask is the inverse of [IPMask.Size].
    79  func CIDRMask(ones, bits int) IPMask {
    80  	if bits != 8*IPv4len && bits != 8*IPv6len {
    81  		return nil
    82  	}
    83  	if ones < 0 || ones > bits {
    84  		return nil
    85  	}
    86  	l := bits / 8
    87  	m := make(IPMask, l)
    88  	n := uint(ones)
    89  	for i := 0; i < l; i++ {
    90  		if n >= 8 {
    91  			m[i] = 0xff
    92  			n -= 8
    93  			continue
    94  		}
    95  		m[i] = ^byte(0xff >> n)
    96  		n = 0
    97  	}
    98  	return m
    99  }
   100  
   101  // Well-known IPv4 addresses
   102  var (
   103  	IPv4bcast     = IPv4(255, 255, 255, 255) // limited broadcast
   104  	IPv4allsys    = IPv4(224, 0, 0, 1)       // all systems
   105  	IPv4allrouter = IPv4(224, 0, 0, 2)       // all routers
   106  	IPv4zero      = IPv4(0, 0, 0, 0)         // all zeros
   107  )
   108  
   109  // Well-known IPv6 addresses
   110  var (
   111  	IPv6zero                   = IP{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}
   112  	IPv6unspecified            = IP{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}
   113  	IPv6loopback               = IP{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1}
   114  	IPv6interfacelocalallnodes = IP{0xff, 0x01, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0x01}
   115  	IPv6linklocalallnodes      = IP{0xff, 0x02, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0x01}
   116  	IPv6linklocalallrouters    = IP{0xff, 0x02, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0x02}
   117  )
   118  
   119  // IsUnspecified reports whether ip is an unspecified address, either
   120  // the IPv4 address "0.0.0.0" or the IPv6 address "::".
   121  func (ip IP) IsUnspecified() bool {
   122  	return ip.Equal(IPv4zero) || ip.Equal(IPv6unspecified)
   123  }
   124  
   125  // IsLoopback reports whether ip is a loopback address.
   126  func (ip IP) IsLoopback() bool {
   127  	if ip4 := ip.To4(); ip4 != nil {
   128  		return ip4[0] == 127
   129  	}
   130  	return ip.Equal(IPv6loopback)
   131  }
   132  
   133  // IsPrivate reports whether ip is a private address, according to
   134  // RFC 1918 (IPv4 addresses) and RFC 4193 (IPv6 addresses).
   135  func (ip IP) IsPrivate() bool {
   136  	if ip4 := ip.To4(); ip4 != nil {
   137  		// Following RFC 1918, Section 3. Private Address Space which says:
   138  		//   The Internet Assigned Numbers Authority (IANA) has reserved the
   139  		//   following three blocks of the IP address space for private internets:
   140  		//     10.0.0.0        -   10.255.255.255  (10/8 prefix)
   141  		//     172.16.0.0      -   172.31.255.255  (172.16/12 prefix)
   142  		//     192.168.0.0     -   192.168.255.255 (192.168/16 prefix)
   143  		return ip4[0] == 10 ||
   144  			(ip4[0] == 172 && ip4[1]&0xf0 == 16) ||
   145  			(ip4[0] == 192 && ip4[1] == 168)
   146  	}
   147  	// Following RFC 4193, Section 8. IANA Considerations which says:
   148  	//   The IANA has assigned the FC00::/7 prefix to "Unique Local Unicast".
   149  	return len(ip) == IPv6len && ip[0]&0xfe == 0xfc
   150  }
   151  
   152  // IsMulticast reports whether ip is a multicast address.
   153  func (ip IP) IsMulticast() bool {
   154  	if ip4 := ip.To4(); ip4 != nil {
   155  		return ip4[0]&0xf0 == 0xe0
   156  	}
   157  	return len(ip) == IPv6len && ip[0] == 0xff
   158  }
   159  
   160  // IsInterfaceLocalMulticast reports whether ip is
   161  // an interface-local multicast address.
   162  func (ip IP) IsInterfaceLocalMulticast() bool {
   163  	return len(ip) == IPv6len && ip[0] == 0xff && ip[1]&0x0f == 0x01
   164  }
   165  
   166  // IsLinkLocalMulticast reports whether ip is a link-local
   167  // multicast address.
   168  func (ip IP) IsLinkLocalMulticast() bool {
   169  	if ip4 := ip.To4(); ip4 != nil {
   170  		return ip4[0] == 224 && ip4[1] == 0 && ip4[2] == 0
   171  	}
   172  	return len(ip) == IPv6len && ip[0] == 0xff && ip[1]&0x0f == 0x02
   173  }
   174  
   175  // IsLinkLocalUnicast reports whether ip is a link-local
   176  // unicast address.
   177  func (ip IP) IsLinkLocalUnicast() bool {
   178  	if ip4 := ip.To4(); ip4 != nil {
   179  		return ip4[0] == 169 && ip4[1] == 254
   180  	}
   181  	return len(ip) == IPv6len && ip[0] == 0xfe && ip[1]&0xc0 == 0x80
   182  }
   183  
   184  // IsGlobalUnicast reports whether ip is a global unicast
   185  // address.
   186  //
   187  // The identification of global unicast addresses uses address type
   188  // identification as defined in RFC 1122, RFC 4632 and RFC 4291 with
   189  // the exception of IPv4 directed broadcast addresses.
   190  // It returns true even if ip is in IPv4 private address space or
   191  // local IPv6 unicast address space.
   192  func (ip IP) IsGlobalUnicast() bool {
   193  	return (len(ip) == IPv4len || len(ip) == IPv6len) &&
   194  		!ip.Equal(IPv4bcast) &&
   195  		!ip.IsUnspecified() &&
   196  		!ip.IsLoopback() &&
   197  		!ip.IsMulticast() &&
   198  		!ip.IsLinkLocalUnicast()
   199  }
   200  
   201  // Is p all zeros?
   202  func isZeros(p IP) bool {
   203  	for i := 0; i < len(p); i++ {
   204  		if p[i] != 0 {
   205  			return false
   206  		}
   207  	}
   208  	return true
   209  }
   210  
   211  // To4 converts the IPv4 address ip to a 4-byte representation.
   212  // If ip is not an IPv4 address, To4 returns nil.
   213  func (ip IP) To4() IP {
   214  	if len(ip) == IPv4len {
   215  		return ip
   216  	}
   217  	if len(ip) == IPv6len &&
   218  		isZeros(ip[0:10]) &&
   219  		ip[10] == 0xff &&
   220  		ip[11] == 0xff {
   221  		return ip[12:16]
   222  	}
   223  	return nil
   224  }
   225  
   226  // To16 converts the IP address ip to a 16-byte representation.
   227  // If ip is not an IP address (it is the wrong length), To16 returns nil.
   228  func (ip IP) To16() IP {
   229  	if len(ip) == IPv4len {
   230  		return IPv4(ip[0], ip[1], ip[2], ip[3])
   231  	}
   232  	if len(ip) == IPv6len {
   233  		return ip
   234  	}
   235  	return nil
   236  }
   237  
   238  // Default route masks for IPv4.
   239  var (
   240  	classAMask = IPv4Mask(0xff, 0, 0, 0)
   241  	classBMask = IPv4Mask(0xff, 0xff, 0, 0)
   242  	classCMask = IPv4Mask(0xff, 0xff, 0xff, 0)
   243  )
   244  
   245  // DefaultMask returns the default IP mask for the IP address ip.
   246  // Only IPv4 addresses have default masks; DefaultMask returns
   247  // nil if ip is not a valid IPv4 address.
   248  func (ip IP) DefaultMask() IPMask {
   249  	if ip = ip.To4(); ip == nil {
   250  		return nil
   251  	}
   252  	switch {
   253  	case ip[0] < 0x80:
   254  		return classAMask
   255  	case ip[0] < 0xC0:
   256  		return classBMask
   257  	default:
   258  		return classCMask
   259  	}
   260  }
   261  
   262  func allFF(b []byte) bool {
   263  	for _, c := range b {
   264  		if c != 0xff {
   265  			return false
   266  		}
   267  	}
   268  	return true
   269  }
   270  
   271  // Mask returns the result of masking the IP address ip with mask.
   272  func (ip IP) Mask(mask IPMask) IP {
   273  	if len(mask) == IPv6len && len(ip) == IPv4len && allFF(mask[:12]) {
   274  		mask = mask[12:]
   275  	}
   276  	if len(mask) == IPv4len && len(ip) == IPv6len && bytealg.Equal(ip[:12], v4InV6Prefix) {
   277  		ip = ip[12:]
   278  	}
   279  	n := len(ip)
   280  	if n != len(mask) {
   281  		return nil
   282  	}
   283  	out := make(IP, n)
   284  	for i := 0; i < n; i++ {
   285  		out[i] = ip[i] & mask[i]
   286  	}
   287  	return out
   288  }
   289  
   290  // String returns the string form of the IP address ip.
   291  // It returns one of 4 forms:
   292  //   - "<nil>", if ip has length 0
   293  //   - dotted decimal ("192.0.2.1"), if ip is an IPv4 or IP4-mapped IPv6 address
   294  //   - IPv6 conforming to RFC 5952 ("2001:db8::1"), if ip is a valid IPv6 address
   295  //   - the hexadecimal form of ip, without punctuation, if no other cases apply
   296  func (ip IP) String() string {
   297  	if len(ip) == 0 {
   298  		return "<nil>"
   299  	}
   300  
   301  	if len(ip) != IPv4len && len(ip) != IPv6len {
   302  		return "?" + hexString(ip)
   303  	}
   304  	// If IPv4, use dotted notation.
   305  	if p4 := ip.To4(); len(p4) == IPv4len {
   306  		return netip.AddrFrom4([4]byte(p4)).String()
   307  	}
   308  	return netip.AddrFrom16([16]byte(ip)).String()
   309  }
   310  
   311  func hexString(b []byte) string {
   312  	s := make([]byte, len(b)*2)
   313  	for i, tn := range b {
   314  		s[i*2], s[i*2+1] = hexDigit[tn>>4], hexDigit[tn&0xf]
   315  	}
   316  	return string(s)
   317  }
   318  
   319  // ipEmptyString is like ip.String except that it returns
   320  // an empty string when ip is unset.
   321  func ipEmptyString(ip IP) string {
   322  	if len(ip) == 0 {
   323  		return ""
   324  	}
   325  	return ip.String()
   326  }
   327  
   328  // MarshalText implements the [encoding.TextMarshaler] interface.
   329  // The encoding is the same as returned by [IP.String], with one exception:
   330  // When len(ip) is zero, it returns an empty slice.
   331  func (ip IP) MarshalText() ([]byte, error) {
   332  	if len(ip) == 0 {
   333  		return []byte(""), nil
   334  	}
   335  	if len(ip) != IPv4len && len(ip) != IPv6len {
   336  		return nil, &AddrError{Err: "invalid IP address", Addr: hexString(ip)}
   337  	}
   338  	return []byte(ip.String()), nil
   339  }
   340  
   341  // UnmarshalText implements the [encoding.TextUnmarshaler] interface.
   342  // The IP address is expected in a form accepted by [ParseIP].
   343  func (ip *IP) UnmarshalText(text []byte) error {
   344  	if len(text) == 0 {
   345  		*ip = nil
   346  		return nil
   347  	}
   348  	s := string(text)
   349  	x := ParseIP(s)
   350  	if x == nil {
   351  		return &ParseError{Type: "IP address", Text: s}
   352  	}
   353  	*ip = x
   354  	return nil
   355  }
   356  
   357  // Equal reports whether ip and x are the same IP address.
   358  // An IPv4 address and that same address in IPv6 form are
   359  // considered to be equal.
   360  func (ip IP) Equal(x IP) bool {
   361  	if len(ip) == len(x) {
   362  		return bytealg.Equal(ip, x)
   363  	}
   364  	if len(ip) == IPv4len && len(x) == IPv6len {
   365  		return bytealg.Equal(x[0:12], v4InV6Prefix) && bytealg.Equal(ip, x[12:])
   366  	}
   367  	if len(ip) == IPv6len && len(x) == IPv4len {
   368  		return bytealg.Equal(ip[0:12], v4InV6Prefix) && bytealg.Equal(ip[12:], x)
   369  	}
   370  	return false
   371  }
   372  
   373  func (ip IP) matchAddrFamily(x IP) bool {
   374  	return ip.To4() != nil && x.To4() != nil || ip.To16() != nil && ip.To4() == nil && x.To16() != nil && x.To4() == nil
   375  }
   376  
   377  // If mask is a sequence of 1 bits followed by 0 bits,
   378  // return the number of 1 bits.
   379  func simpleMaskLength(mask IPMask) int {
   380  	var n int
   381  	for i, v := range mask {
   382  		if v == 0xff {
   383  			n += 8
   384  			continue
   385  		}
   386  		// found non-ff byte
   387  		// count 1 bits
   388  		for v&0x80 != 0 {
   389  			n++
   390  			v <<= 1
   391  		}
   392  		// rest must be 0 bits
   393  		if v != 0 {
   394  			return -1
   395  		}
   396  		for i++; i < len(mask); i++ {
   397  			if mask[i] != 0 {
   398  				return -1
   399  			}
   400  		}
   401  		break
   402  	}
   403  	return n
   404  }
   405  
   406  // Size returns the number of leading ones and total bits in the mask.
   407  // If the mask is not in the canonical form--ones followed by zeros--then
   408  // Size returns 0, 0.
   409  func (m IPMask) Size() (ones, bits int) {
   410  	ones, bits = simpleMaskLength(m), len(m)*8
   411  	if ones == -1 {
   412  		return 0, 0
   413  	}
   414  	return
   415  }
   416  
   417  // String returns the hexadecimal form of m, with no punctuation.
   418  func (m IPMask) String() string {
   419  	if len(m) == 0 {
   420  		return "<nil>"
   421  	}
   422  	return hexString(m)
   423  }
   424  
   425  func networkNumberAndMask(n *IPNet) (ip IP, m IPMask) {
   426  	if ip = n.IP.To4(); ip == nil {
   427  		ip = n.IP
   428  		if len(ip) != IPv6len {
   429  			return nil, nil
   430  		}
   431  	}
   432  	m = n.Mask
   433  	switch len(m) {
   434  	case IPv4len:
   435  		if len(ip) != IPv4len {
   436  			return nil, nil
   437  		}
   438  	case IPv6len:
   439  		if len(ip) == IPv4len {
   440  			m = m[12:]
   441  		}
   442  	default:
   443  		return nil, nil
   444  	}
   445  	return
   446  }
   447  
   448  // Contains reports whether the network includes ip.
   449  func (n *IPNet) Contains(ip IP) bool {
   450  	nn, m := networkNumberAndMask(n)
   451  	if x := ip.To4(); x != nil {
   452  		ip = x
   453  	}
   454  	l := len(ip)
   455  	if l != len(nn) {
   456  		return false
   457  	}
   458  	for i := 0; i < l; i++ {
   459  		if nn[i]&m[i] != ip[i]&m[i] {
   460  			return false
   461  		}
   462  	}
   463  	return true
   464  }
   465  
   466  // Network returns the address's network name, "ip+net".
   467  func (n *IPNet) Network() string { return "ip+net" }
   468  
   469  // String returns the CIDR notation of n like "192.0.2.0/24"
   470  // or "2001:db8::/48" as defined in RFC 4632 and RFC 4291.
   471  // If the mask is not in the canonical form, it returns the
   472  // string which consists of an IP address, followed by a slash
   473  // character and a mask expressed as hexadecimal form with no
   474  // punctuation like "198.51.100.0/c000ff00".
   475  func (n *IPNet) String() string {
   476  	if n == nil {
   477  		return "<nil>"
   478  	}
   479  	nn, m := networkNumberAndMask(n)
   480  	if nn == nil || m == nil {
   481  		return "<nil>"
   482  	}
   483  	l := simpleMaskLength(m)
   484  	if l == -1 {
   485  		return nn.String() + "/" + m.String()
   486  	}
   487  	return nn.String() + "/" + itoa.Uitoa(uint(l))
   488  }
   489  
   490  // ParseIP parses s as an IP address, returning the result.
   491  // The string s can be in IPv4 dotted decimal ("192.0.2.1"), IPv6
   492  // ("2001:db8::68"), or IPv4-mapped IPv6 ("::ffff:192.0.2.1") form.
   493  // If s is not a valid textual representation of an IP address,
   494  // ParseIP returns nil. The returned address is always 16 bytes,
   495  // IPv4 addresses are returned in IPv4-mapped IPv6 form.
   496  func ParseIP(s string) IP {
   497  	if addr, valid := parseIP(s); valid {
   498  		return IP(addr[:])
   499  	}
   500  	return nil
   501  }
   502  
   503  func parseIP(s string) ([16]byte, bool) {
   504  	ip, err := netip.ParseAddr(s)
   505  	if err != nil || ip.Zone() != "" {
   506  		return [16]byte{}, false
   507  	}
   508  	return ip.As16(), true
   509  }
   510  
   511  // ParseCIDR parses s as a CIDR notation IP address and prefix length,
   512  // like "192.0.2.0/24" or "2001:db8::/32", as defined in
   513  // RFC 4632 and RFC 4291.
   514  //
   515  // It returns the IP address and the network implied by the IP and
   516  // prefix length.
   517  // For example, ParseCIDR("192.0.2.1/24") returns the IP address
   518  // 192.0.2.1 and the network 192.0.2.0/24.
   519  func ParseCIDR(s string) (IP, *IPNet, error) {
   520  	addr, mask, found := stringslite.Cut(s, "/")
   521  	if !found {
   522  		return nil, nil, &ParseError{Type: "CIDR address", Text: s}
   523  	}
   524  
   525  	ipAddr, err := netip.ParseAddr(addr)
   526  	if err != nil || ipAddr.Zone() != "" {
   527  		return nil, nil, &ParseError{Type: "CIDR address", Text: s}
   528  	}
   529  
   530  	n, i, ok := dtoi(mask)
   531  	if !ok || i != len(mask) || n < 0 || n > ipAddr.BitLen() {
   532  		return nil, nil, &ParseError{Type: "CIDR address", Text: s}
   533  	}
   534  	m := CIDRMask(n, ipAddr.BitLen())
   535  	addr16 := ipAddr.As16()
   536  	return IP(addr16[:]), &IPNet{IP: IP(addr16[:]).Mask(m), Mask: m}, nil
   537  }
   538  
   539  func copyIP(x IP) IP {
   540  	y := make(IP, len(x))
   541  	copy(y, x)
   542  	return y
   543  }
   544
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