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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 (IPv4)
// or 16-byte (IPv6) arrays 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 array: a 16-byte array 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) // 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 returns true if ip is an unspecified address.
func (ip IP) IsUnspecified() bool {
        if ip.Equal(IPv4zero) || ip.Equal(IPv6unspecified) {
                return true
        }
        return false
}

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

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

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

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

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

// IsGlobalUnicast returns true if ip is a global unicast
// address.
func (ip IP) IsGlobalUnicast() bool {
        return !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
        }
        return nil // not reached
}

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
}

// 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 "<nil>"
        }

        // If IPv4, use dotted notation.
        if p4 := p.To4(); len(p4) == IPv4len {
                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 < 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
                }
        }
        // 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 < IPv6len; i += 2 {
                if i == e0 {
                        s += "::"
                        i = e1
                        if i >= IPv6len {
                                break
                        }
                } else if i > 0 {
                        s += ":"
                }
                s += itox((uint(p[i])<<8)|uint(p[i+1]), 1)
        }
        return s
}

// Equal returns true if 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
}

func bytesEqual(x, y []byte) bool {
        if len(x) != len(y) {
                return false
        }
        for i, b := range x {
                if y[i] != b {
                        return false
                }
        }
        return true
}

// 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 {
        s := ""
        for _, b := range m {
                s += itox(uint(b), 2)
        }
        if len(s) == 0 {
                return "<nil>"
        }
        return s
}

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
}

// String returns the CIDR notation of n like "192.168.100.1/24"
// 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 "192.168.100.1/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() + "/" + itod(uint(l))
}

// Network returns the address's network name, "ip+net".
func (n *IPNet) Network() string { return "ip+net" }

// 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, IPv6len)
        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
        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 += IPv4len
                        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
}

// A ParseError represents a malformed text string and the type of string that was expected.
type ParseError struct {
        Type string
        Text string
}

func (e *ParseError) Error() string {
        return "invalid " + e.Type + ": " + e.Text
}

func parseIP(s string) IP {
        if p := parseIPv4(s); p != nil {
                return p
        }
        if p := parseIPv6(s); p != nil {
                return p
        }
        return nil
}

// 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 {
        if p := parseIPv4(s); p != nil {
                return p
        }
        return parseIPv6(s)
}

// ParseCIDR parses s as a CIDR notation IP address and mask,
// like "192.168.100.1/24" or "2001:DB8::/48", as defined in
// RFC 4632 and RFC 4291.
//
// It returns the IP address and the network implied by the IP
// and mask.  For example, ParseCIDR("192.168.100.1/16") returns
// the IP address 192.168.100.1 and the network 192.168.0.0/16.
func ParseCIDR(s string) (IP, *IPNet, error) {
        i := byteIndex(s, '/')
        if i < 0 {
                return nil, nil, &ParseError{"CIDR address", s}
        }
        ipstr, maskstr := s[:i], s[i+1:]
        iplen := IPv4len
        ip := parseIPv4(ipstr)
        if ip == nil {
                iplen = IPv6len
                ip = parseIPv6(ipstr)
        }
        n, i, ok := dtoi(maskstr, 0)
        if ip == nil || !ok || i != len(maskstr) || n < 0 || n > 8*iplen {
                return nil, nil, &ParseError{"CIDR address", s}
        }
        m := CIDRMask(n, 8*iplen)
        return ip, &IPNet{ip.Mask(m), m}, nil
}