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// 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 array but always
// returns 16-byte addresses.
package net
// IP address lengths (bytes).
const (
IPv4len = 4
IPv6len = 16
)
// An IP is a single IP address, an array of bytes.
// Functions in this package accept either 4-byte (IP v4)
// or 16-byte (IP v6) arrays as input. Unless otherwise
// specified, functions in this package always return
// IP addresses in 16-byte form using the canonical
// embedding.
//
// 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 array: a 16-byte array can still
// be an IPv4 address.
type IP []byte
// An IP mask is an IP address.
type IPMask []byte
// 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)
for i := 0; i < 10; i++ {
p[i] = 0
}
p[10] = 0xff
p[11] = 0xff
p[12] = a
p[13] = b
p[14] = c
p[15] = d
return p
}
// IPv4Mask returns the IP mask (in 16-byte form) of the
// IPv4 mask a.b.c.d.
func IPv4Mask(a, b, c, d byte) IPMask {
p := make(IPMask, IPv6len)
for i := 0; i < 12; i++ {
p[i] = 0xff
}
p[12] = a
p[13] = b
p[14] = c
p[15] = d
return p
}
// Well-known IPv4 addresses
var (
IPv4bcast = IPv4(255, 255, 255, 255) // broadcast
IPv4allsys = IPv4(224, 0, 0, 1) // all systems
IPv4allrouter = IPv4(224, 0, 0, 2) // all routers
IPv4zero = IPv4(0, 0, 0, 0) // all zeros
)
// Well-known IPv6 addresses
var (
IPzero = make(IP, IPv6len) // all zeros
)
// 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
}
return nil // not reached
}
// Mask returns the result of masking the IP address ip with mask.
func (ip IP) Mask(mask IPMask) IP {
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
}
// Convert i to decimal string.
func itod(i uint) string {
if i == 0 {
return "0"
}
// Assemble decimal in reverse order.
var b [32]byte
bp := len(b)
for ; i > 0; i /= 10 {
bp--
b[bp] = byte(i%10) + '0'
}
return string(b[bp:])
}
// Convert i to hexadecimal string.
func itox(i uint) string {
if i == 0 {
return "0"
}
// Assemble hexadecimal in reverse order.
var b [32]byte
bp := len(b)
for ; i > 0; i /= 16 {
bp--
b[bp] = "0123456789abcdef"[byte(i%16)]
}
return string(b[bp:])
}
// String returns the string form of the IP address ip.
// If the address is an IPv4 address, the string representation
// is dotted decimal ("74.125.19.99"). Otherwise the representation
// is IPv6 ("2001:4860:0:2001::68").
func (ip IP) String() string {
p := ip
if len(ip) == 0 {
return ""
}
// If IPv4, use dotted notation.
if p4 := p.To4(); len(p4) == 4 {
return itod(uint(p4[0])) + "." +
itod(uint(p4[1])) + "." +
itod(uint(p4[2])) + "." +
itod(uint(p4[3]))
}
if len(p) != IPv6len {
return "?"
}
// Find longest run of zeros.
e0 := -1
e1 := -1
for i := 0; i < 16; i += 2 {
j := i
for j < 16 && p[j] == 0 && p[j+1] == 0 {
j += 2
}
if j > i && j-i > e1-e0 {
e0 = i
e1 = j
}
}
// The symbol "::" MUST NOT be used to shorten just one 16 bit 0 field.
if e1-e0 <= 2 {
e0 = -1
e1 = -1
}
// Print with possible :: in place of run of zeros
var s string
for i := 0; i < 16; i += 2 {
if i == e0 {
s += "::"
i = e1
if i >= 16 {
break
}
} else if i > 0 {
s += ":"
}
s += itox((uint(p[i]) << 8) | uint(p[i+1]))
}
return s
}
// 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
}
// String returns the string representation of mask.
// If the mask is in the canonical form--ones followed by zeros--the
// string representation is just the decimal number of ones.
// If the mask is in a non-canonical form, it is formatted
// as an IP address.
func (mask IPMask) String() string {
switch len(mask) {
case 4:
n := simpleMaskLength(mask)
if n >= 0 {
return itod(uint(n + (IPv6len-IPv4len)*8))
}
case 16:
n := simpleMaskLength(mask)
if n >= 12*8 {
return itod(uint(n - 12*8))
}
}
return IP(mask).String()
}
// Parse IPv4 address (d.d.d.d).
func parseIPv4(s string) IP {
var p [IPv4len]byte
i := 0
for j := 0; j < IPv4len; j++ {
if i >= len(s) {
// Missing octets.
return nil
}
if j > 0 {
if s[i] != '.' {
return nil
}
i++
}
var (
n int
ok bool
)
n, i, ok = dtoi(s, i)
if !ok || n > 0xFF {
return nil
}
p[j] = byte(n)
}
if i != len(s) {
return nil
}
return IPv4(p[0], p[1], p[2], p[3])
}
// Parse IPv6 address. Many forms.
// The basic form is a sequence of eight colon-separated
// 16-bit hex numbers separated by colons,
// as in 0123:4567:89ab:cdef:0123:4567:89ab:cdef.
// Two exceptions:
// * A run of zeros can be replaced with "::".
// * The last 32 bits can be in IPv4 form.
// Thus, ::ffff:1.2.3.4 is the IPv4 address 1.2.3.4.
func parseIPv6(s string) IP {
p := make(IP, 16)
ellipsis := -1 // position of ellipsis in p
i := 0 // index in string s
// Might have leading ellipsis
if len(s) >= 2 && s[0] == ':' && s[1] == ':' {
ellipsis = 0
i = 2
// Might be only ellipsis
if i == len(s) {
return p
}
}
// Loop, parsing hex numbers followed by colon.
j := 0
L:
for j < IPv6len {
// Hex number.
n, i1, ok := xtoi(s, i)
if !ok || n > 0xFFFF {
return nil
}
// If followed by dot, might be in trailing IPv4.
if i1 < len(s) && s[i1] == '.' {
if ellipsis < 0 && j != IPv6len-IPv4len {
// Not the right place.
return nil
}
if j+IPv4len > IPv6len {
// Not enough room.
return nil
}
p4 := parseIPv4(s[i:])
if p4 == nil {
return nil
}
p[j] = p4[12]
p[j+1] = p4[13]
p[j+2] = p4[14]
p[j+3] = p4[15]
i = len(s)
j += 4
break
}
// Save this 16-bit chunk.
p[j] = byte(n >> 8)
p[j+1] = byte(n)
j += 2
// Stop at end of string.
i = i1
if i == len(s) {
break
}
// Otherwise must be followed by colon and more.
if s[i] != ':' && i+1 == len(s) {
return nil
}
i++
// Look for ellipsis.
if s[i] == ':' {
if ellipsis >= 0 { // already have one
return nil
}
ellipsis = j
if i++; i == len(s) { // can be at end
break
}
}
}
// Must have used entire string.
if i != len(s) {
return nil
}
// If didn't parse enough, expand ellipsis.
if j < IPv6len {
if ellipsis < 0 {
return nil
}
n := IPv6len - j
for k := j - 1; k >= ellipsis; k-- {
p[k+n] = p[k]
}
for k := ellipsis + n - 1; k >= ellipsis; k-- {
p[k] = 0
}
}
return p
}
// ParseIP parses s as an IP address, returning the result.
// The string s can be in dotted decimal ("74.125.19.99")
// or IPv6 ("2001:4860:0:2001::68") form.
// If s is not a valid textual representation of an IP address,
// ParseIP returns nil.
func ParseIP(s string) IP {
p := parseIPv4(s)
if p != nil {
return p
}
return parseIPv6(s)
}