Source file src/net/ip.go

Documentation: net

  // 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 _ "unsafe" // for go:linkname
  
  // IP address lengths (bytes).
  const (
  	IPv4len = 4
  	IPv6len = 16
  )
  
  // An IP is a single IP address, a slice of bytes.
  // Functions in this package accept either 4-byte (IPv4)
  // or 16-byte (IPv6) slices as input.
  //
  // Note that in this documentation, referring to an
  // IP address as an IPv4 address or an IPv6 address
  // is a semantic property of the address, not just the
  // length of the byte slice: a 16-byte slice can still
  // be an IPv4 address.
  type IP []byte
  
  // An IP mask is an IP address.
  type IPMask []byte
  
  // An IPNet represents an IP network.
  type IPNet struct {
  	IP   IP     // network number
  	Mask IPMask // network mask
  }
  
  // IPv4 returns the IP address (in 16-byte form) of the
  // IPv4 address a.b.c.d.
  func IPv4(a, b, c, d byte) IP {
  	p := make(IP, IPv6len)
  	copy(p, v4InV6Prefix)
  	p[12] = a
  	p[13] = b
  	p[14] = c
  	p[15] = d
  	return p
  }
  
  var v4InV6Prefix = []byte{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0xff, 0xff}
  
  // IPv4Mask returns the IP mask (in 4-byte form) of the
  // IPv4 mask a.b.c.d.
  func IPv4Mask(a, b, c, d byte) IPMask {
  	p := make(IPMask, IPv4len)
  	p[0] = a
  	p[1] = b
  	p[2] = c
  	p[3] = d
  	return p
  }
  
  // CIDRMask returns an IPMask consisting of `ones' 1 bits
  // followed by 0s up to a total length of `bits' bits.
  // For a mask of this form, CIDRMask is the inverse of IPMask.Size.
  func CIDRMask(ones, bits int) IPMask {
  	if bits != 8*IPv4len && bits != 8*IPv6len {
  		return nil
  	}
  	if ones < 0 || ones > bits {
  		return nil
  	}
  	l := bits / 8
  	m := make(IPMask, l)
  	n := uint(ones)
  	for i := 0; i < l; i++ {
  		if n >= 8 {
  			m[i] = 0xff
  			n -= 8
  			continue
  		}
  		m[i] = ^byte(0xff >> n)
  		n = 0
  	}
  	return m
  }
  
  // Well-known IPv4 addresses
  var (
  	IPv4bcast     = IPv4(255, 255, 255, 255) // 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)
  }
  
  // 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 true {
  	case ip[0] < 0x80:
  		return classAMask
  	case ip[0] < 0xC0:
  		return classBMask
  	default:
  		return classCMask
  	}
  }
  
  func allFF(b []byte) bool {
  	for _, c := range b {
  		if c != 0xff {
  			return false
  		}
  	}
  	return true
  }
  
  // Mask returns the result of masking the IP address ip with mask.
  func (ip IP) Mask(mask IPMask) IP {
  	if len(mask) == IPv6len && len(ip) == IPv4len && allFF(mask[:12]) {
  		mask = mask[12:]
  	}
  	if len(mask) == IPv4len && len(ip) == IPv6len && bytesEqual(ip[:12], v4InV6Prefix) {
  		ip = ip[12:]
  	}
  	n := len(ip)
  	if n != len(mask) {
  		return nil
  	}
  	out := make(IP, n)
  	for i := 0; i < n; i++ {
  		out[i] = ip[i] & mask[i]
  	}
  	return out
  }
  
  // ubtoa encodes the string form of the integer v to dst[start:] and
  // returns the number of bytes written to dst. The caller must ensure
  // that dst has sufficient length.
  func ubtoa(dst []byte, start int, v byte) int {
  	if v < 10 {
  		dst[start] = v + '0'
  		return 1
  	} else if v < 100 {
  		dst[start+1] = v%10 + '0'
  		dst[start] = v/10 + '0'
  		return 2
  	}
  
  	dst[start+2] = v%10 + '0'
  	dst[start+1] = (v/10)%10 + '0'
  	dst[start] = v/100 + '0'
  	return 3
  }
  
  // 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 ("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 {
  	p := ip
  
  	if len(ip) == 0 {
  		return "<nil>"
  	}
  
  	// If IPv4, use dotted notation.
  	if p4 := p.To4(); len(p4) == IPv4len {
  		const maxIPv4StringLen = len("255.255.255.255")
  		b := make([]byte, maxIPv4StringLen)
  
  		n := ubtoa(b, 0, p4[0])
  		b[n] = '.'
  		n++
  
  		n += ubtoa(b, n, p4[1])
  		b[n] = '.'
  		n++
  
  		n += ubtoa(b, n, p4[2])
  		b[n] = '.'
  		n++
  
  		n += ubtoa(b, n, p4[3])
  		return string(b[:n])
  	}
  	if len(p) != IPv6len {
  		return "?" + hexString(ip)
  	}
  
  	// Find longest run of zeros.
  	e0 := -1
  	e1 := -1
  	for i := 0; i < IPv6len; i += 2 {
  		j := i
  		for j < IPv6len && p[j] == 0 && p[j+1] == 0 {
  			j += 2
  		}
  		if j > i && j-i > e1-e0 {
  			e0 = i
  			e1 = j
  			i = j
  		}
  	}
  	// The symbol "::" MUST NOT be used to shorten just one 16 bit 0 field.
  	if e1-e0 <= 2 {
  		e0 = -1
  		e1 = -1
  	}
  
  	const maxLen = len("ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff")
  	b := make([]byte, 0, maxLen)
  
  	// Print with possible :: in place of run of zeros
  	for i := 0; i < IPv6len; i += 2 {
  		if i == e0 {
  			b = append(b, ':', ':')
  			i = e1
  			if i >= IPv6len {
  				break
  			}
  		} else if i > 0 {
  			b = append(b, ':')
  		}
  		b = appendHex(b, (uint32(p[i])<<8)|uint32(p[i+1]))
  	}
  	return string(b)
  }
  
  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 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 bytesEqual(ip, x)
  	}
  	if len(ip) == IPv4len && len(x) == IPv6len {
  		return bytesEqual(x[0:12], v4InV6Prefix) && bytesEqual(ip, x[12:])
  	}
  	if len(ip) == IPv6len && len(x) == IPv4len {
  		return bytesEqual(ip[0:12], v4InV6Prefix) && bytesEqual(ip[12:], x)
  	}
  	return false
  }
  
  // bytes.Equal is implemented in runtime/asm_$goarch.s
  //go:linkname bytesEqual bytes.Equal
  func bytesEqual(x, y []byte) bool
  
  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 "192.0.2.1/24"
  // or "2001:db8::/48" as defined in RFC 4632 and RFC 4291.
  // If the mask is not in the canonical form, it returns the
  // string which consists of an IP address, followed by a slash
  // character and a mask expressed as hexadecimal form with no
  // punctuation like "198.51.100.1/c000ff00".
  func (n *IPNet) String() string {
  	nn, m := networkNumberAndMask(n)
  	if nn == nil || m == nil {
  		return "<nil>"
  	}
  	l := simpleMaskLength(m)
  	if l == -1 {
  		return nn.String() + "/" + m.String()
  	}
  	return nn.String() + "/" + uitoa(uint(l))
  }
  
  // Parse IPv4 address (d.d.d.d).
  func parseIPv4(s string) IP {
  	var p [IPv4len]byte
  	for i := 0; i < IPv4len; i++ {
  		if len(s) == 0 {
  			// Missing octets.
  			return nil
  		}
  		if i > 0 {
  			if s[0] != '.' {
  				return nil
  			}
  			s = s[1:]
  		}
  		n, c, ok := dtoi(s)
  		if !ok || n > 0xFF {
  			return nil
  		}
  		s = s[c:]
  		p[i] = byte(n)
  	}
  	if len(s) != 0 {
  		return nil
  	}
  	return IPv4(p[0], p[1], p[2], p[3])
  }
  
  // parseIPv6Zone parses s as a literal IPv6 address and its associated zone
  // identifier which is described in RFC 4007.
  func parseIPv6Zone(s string) (IP, string) {
  	s, zone := splitHostZone(s)
  	return parseIPv6(s), zone
  }
  
  // parseIPv6Zone parses s as a literal IPv6 address described in RFC 4291
  // and RFC 5952.
  func parseIPv6(s string) (ip IP) {
  	ip = make(IP, IPv6len)
  	ellipsis := -1 // position of ellipsis in ip
  
  	// Might have leading ellipsis
  	if len(s) >= 2 && s[0] == ':' && s[1] == ':' {
  		ellipsis = 0
  		s = s[2:]
  		// Might be only ellipsis
  		if len(s) == 0 {
  			return ip
  		}
  	}
  
  	// Loop, parsing hex numbers followed by colon.
  	i := 0
  	for i < IPv6len {
  		// Hex number.
  		n, c, ok := xtoi(s)
  		if !ok || n > 0xFFFF {
  			return nil
  		}
  
  		// If followed by dot, might be in trailing IPv4.
  		if c < len(s) && s[c] == '.' {
  			if ellipsis < 0 && i != IPv6len-IPv4len {
  				// Not the right place.
  				return nil
  			}
  			if i+IPv4len > IPv6len {
  				// Not enough room.
  				return nil
  			}
  			ip4 := parseIPv4(s)
  			if ip4 == nil {
  				return nil
  			}
  			ip[i] = ip4[12]
  			ip[i+1] = ip4[13]
  			ip[i+2] = ip4[14]
  			ip[i+3] = ip4[15]
  			s = ""
  			i += IPv4len
  			break
  		}
  
  		// Save this 16-bit chunk.
  		ip[i] = byte(n >> 8)
  		ip[i+1] = byte(n)
  		i += 2
  
  		// Stop at end of string.
  		s = s[c:]
  		if len(s) == 0 {
  			break
  		}
  
  		// Otherwise must be followed by colon and more.
  		if s[0] != ':' || len(s) == 1 {
  			return nil
  		}
  		s = s[1:]
  
  		// Look for ellipsis.
  		if s[0] == ':' {
  			if ellipsis >= 0 { // already have one
  				return nil
  			}
  			ellipsis = i
  			s = s[1:]
  			if len(s) == 0 { // can be at end
  				break
  			}
  		}
  	}
  
  	// Must have used entire string.
  	if len(s) != 0 {
  		return nil
  	}
  
  	// If didn't parse enough, expand ellipsis.
  	if i < IPv6len {
  		if ellipsis < 0 {
  			return nil
  		}
  		n := IPv6len - i
  		for j := i - 1; j >= ellipsis; j-- {
  			ip[j+n] = ip[j]
  		}
  		for j := ellipsis + n - 1; j >= ellipsis; j-- {
  			ip[j] = 0
  		}
  	} else if ellipsis >= 0 {
  		// Ellipsis must represent at least one 0 group.
  		return nil
  	}
  	return ip
  }
  
  // ParseIP parses s as an IP address, returning the result.
  // The string s can be in dotted decimal ("192.0.2.1")
  // or IPv6 ("2001:db8::68") form.
  // If s is not a valid textual representation of an IP address,
  // ParseIP returns nil.
  func ParseIP(s string) IP {
  	for i := 0; i < len(s); i++ {
  		switch s[i] {
  		case '.':
  			return parseIPv4(s)
  		case ':':
  			return parseIPv6(s)
  		}
  	}
  	return nil
  }
  
  // parseIPZone parses s as an IP address, return it and its associated zone
  // identifier (IPv6 only).
  func parseIPZone(s string) (IP, string) {
  	for i := 0; i < len(s); i++ {
  		switch s[i] {
  		case '.':
  			return parseIPv4(s), ""
  		case ':':
  			return parseIPv6Zone(s)
  		}
  	}
  	return nil, ""
  }
  
  // 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 := byteIndex(s, '/')
  	if i < 0 {
  		return nil, nil, &ParseError{Type: "CIDR address", Text: s}
  	}
  	addr, mask := s[:i], s[i+1:]
  	iplen := IPv4len
  	ip := parseIPv4(addr)
  	if ip == nil {
  		iplen = IPv6len
  		ip = parseIPv6(addr)
  	}
  	n, i, ok := dtoi(mask)
  	if ip == nil || !ok || i != len(mask) || n < 0 || n > 8*iplen {
  		return nil, nil, &ParseError{Type: "CIDR address", Text: s}
  	}
  	m := CIDRMask(n, 8*iplen)
  	return ip, &IPNet{IP: ip.Mask(m), Mask: m}, nil
  }
  

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