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Name	Size	Permission
http	[ DIR ]	drwxr-xr-x
internal	[ DIR ]	drwxr-xr-x
mail	[ DIR ]	drwxr-xr-x
netip	[ DIR ]	drwxr-xr-x
rpc	[ DIR ]	drwxr-xr-x
smtp	[ DIR ]	drwxr-xr-x
testdata	[ DIR ]	drwxr-xr-x
textproto	[ DIR ]	drwxr-xr-x
url	[ DIR ]	drwxr-xr-x
addrselect.go	9.69 KB	-rw-r--r--
addrselect_test.go	8.5 KB	-rw-r--r--
cgo_aix.go	582 B	-rw-r--r--
cgo_android.go	272 B	-rw-r--r--
cgo_bsd.go	343 B	-rw-r--r--
cgo_darwin.go	298 B	-rw-r--r--
cgo_linux.go	642 B	-rw-r--r--
cgo_netbsd.go	276 B	-rw-r--r--
cgo_openbsd.go	276 B	-rw-r--r--
cgo_resnew.go	580 B	-rw-r--r--
cgo_resold.go	579 B	-rw-r--r--
cgo_socknew.go	753 B	-rw-r--r--
cgo_sockold.go	842 B	-rw-r--r--
cgo_solaris.go	343 B	-rw-r--r--
cgo_stub.go	1.33 KB	-rw-r--r--
cgo_unix.go	11.42 KB	-rw-r--r--
cgo_unix_cgo.go	2.24 KB	-rw-r--r--
cgo_unix_cgo_res.go	892 B	-rw-r--r--
cgo_unix_cgo_resn.go	979 B	-rw-r--r--
cgo_unix_syscall.go	3 KB	-rw-r--r--
cgo_unix_test.go	1.44 KB	-rw-r--r--
conf.go	15.48 KB	-rw-r--r--
conf_test.go	12.29 KB	-rw-r--r--
conn_test.go	1.82 KB	-rw-r--r--
dial.go	26.85 KB	-rw-r--r--
dial_test.go	30.28 KB	-rw-r--r--
dial_unix_test.go	2.77 KB	-rw-r--r--
dnsclient.go	5.67 KB	-rw-r--r--
dnsclient_test.go	1.51 KB	-rw-r--r--
dnsclient_unix.go	24.66 KB	-rw-r--r--
dnsclient_unix_test.go	72.77 KB	-rw-r--r--
dnsconfig.go	2.19 KB	-rw-r--r--
dnsconfig_unix.go	4.12 KB	-rw-r--r--
dnsconfig_unix_test.go	7.07 KB	-rw-r--r--
dnsconfig_windows.go	1.61 KB	-rw-r--r--
dnsname_test.go	1.96 KB	-rw-r--r--
error_plan9.go	224 B	-rw-r--r--
error_plan9_test.go	437 B	-rw-r--r--
error_posix.go	543 B	-rw-r--r--
error_posix_test.go	981 B	-rw-r--r--
error_test.go	20.32 KB	-rw-r--r--
error_unix.go	382 B	-rw-r--r--
error_unix_test.go	723 B	-rw-r--r--
error_windows.go	355 B	-rw-r--r--
error_windows_test.go	757 B	-rw-r--r--
example_test.go	8.45 KB	-rw-r--r--
external_test.go	4.05 KB	-rw-r--r--
fd_fake.go	3.79 KB	-rw-r--r--
fd_js.go	627 B	-rw-r--r--
fd_plan9.go	3.56 KB	-rw-r--r--
fd_posix.go	4.29 KB	-rw-r--r--
fd_unix.go	5.43 KB	-rw-r--r--
fd_wasip1.go	496 B	-rw-r--r--
fd_windows.go	6.21 KB	-rw-r--r--
file.go	1.69 KB	-rw-r--r--
file_plan9.go	2.77 KB	-rw-r--r--
file_stub.go	481 B	-rw-r--r--
file_test.go	6.43 KB	-rw-r--r--
file_unix.go	2.55 KB	-rw-r--r--
file_unix_test.go	2.07 KB	-rw-r--r--
file_wasip1.go	2.2 KB	-rw-r--r--
file_wasip1_test.go	3.76 KB	-rw-r--r--
file_windows.go	521 B	-rw-r--r--
hook.go	934 B	-rw-r--r--
hook_plan9.go	211 B	-rw-r--r--
hook_unix.go	658 B	-rw-r--r--
hook_windows.go	720 B	-rw-r--r--
hosts.go	3.48 KB	-rw-r--r--
hosts_test.go	5.6 KB	-rw-r--r--
interface.go	7.57 KB	-rw-r--r--
interface_aix.go	4.46 KB	-rw-r--r--
interface_bsd.go	2.82 KB	-rw-r--r--
interface_bsd_test.go	1.44 KB	-rw-r--r--
interface_bsdvar.go	718 B	-rw-r--r--
interface_darwin.go	1.29 KB	-rw-r--r--
interface_freebsd.go	1.29 KB	-rw-r--r--
interface_linux.go	6.96 KB	-rw-r--r--
interface_linux_test.go	3.65 KB	-rw-r--r--
interface_plan9.go	4.74 KB	-rw-r--r--
interface_solaris.go	2.13 KB	-rw-r--r--
interface_stub.go	814 B	-rw-r--r--
interface_test.go	9.76 KB	-rw-r--r--
interface_unix_test.go	4.85 KB	-rw-r--r--
interface_windows.go	5.49 KB	-rw-r--r--
ip.go	13.97 KB	-rw-r--r--
ip_test.go	25.69 KB	-rw-r--r--
iprawsock.go	7.11 KB	-rw-r--r--
iprawsock_plan9.go	874 B	-rw-r--r--
iprawsock_posix.go	3.89 KB	-rw-r--r--
iprawsock_test.go	5.98 KB	-rw-r--r--
ipsock.go	9.43 KB	-rw-r--r--
ipsock_plan9.go	7.48 KB	-rw-r--r--
ipsock_plan9_test.go	645 B	-rw-r--r--
ipsock_posix.go	8.62 KB	-rw-r--r--
ipsock_test.go	6.81 KB	-rw-r--r--
listen_test.go	20.5 KB	-rw-r--r--
lookup.go	28.6 KB	-rw-r--r--
lookup_plan9.go	9.89 KB	-rw-r--r--
lookup_test.go	41.45 KB	-rw-r--r--
lookup_unix.go	3.35 KB	-rw-r--r--
lookup_windows.go	14.19 KB	-rw-r--r--
lookup_windows_test.go	8.7 KB	-rw-r--r--
mac.go	1.88 KB	-rw-r--r--
mac_test.go	3.26 KB	-rw-r--r--
main_cloexec_test.go	693 B	-rw-r--r--
main_conf_test.go	2.45 KB	-rw-r--r--
main_plan9_test.go	392 B	-rw-r--r--
main_posix_test.go	1.37 KB	-rw-r--r--
main_test.go	7.53 KB	-rw-r--r--
main_unix_test.go	1.19 KB	-rw-r--r--
main_wasm_test.go	284 B	-rw-r--r--
main_windows_test.go	1 KB	-rw-r--r--
mockserver_test.go	13.28 KB	-rw-r--r--
mptcpsock_linux.go	3.96 KB	-rw-r--r--
mptcpsock_linux_test.go	4.06 KB	-rw-r--r--
mptcpsock_stub.go	542 B	-rw-r--r--
net.go	27.12 KB	-rw-r--r--
net_fake.go	26.45 KB	-rw-r--r--
net_fake_test.go	2.79 KB	-rw-r--r--
net_test.go	13.3 KB	-rw-r--r--
net_windows_test.go	16.28 KB	-rw-r--r--
netcgo_off.go	222 B	-rw-r--r--
netcgo_on.go	220 B	-rw-r--r--
netgo_netcgo.go	453 B	-rw-r--r--
netgo_off.go	220 B	-rw-r--r--
netgo_on.go	218 B	-rw-r--r--
nss.go	5.48 KB	-rw-r--r--
nss_test.go	3.4 KB	-rw-r--r--
packetconn_test.go	3.02 KB	-rw-r--r--
parse.go	5.66 KB	-rw-r--r--
parse_test.go	1.65 KB	-rw-r--r--
pipe.go	5.43 KB	-rw-r--r--
pipe_test.go	1.2 KB	-rw-r--r--
platform_test.go	4.33 KB	-rw-r--r--
port.go	1.46 KB	-rw-r--r--
port_test.go	1.34 KB	-rw-r--r--
port_unix.go	1.24 KB	-rw-r--r--
protoconn_test.go	7.44 KB	-rw-r--r--
rawconn.go	2.7 KB	-rw-r--r--
rawconn_stub_test.go	631 B	-rw-r--r--
rawconn_test.go	4.33 KB	-rw-r--r--
rawconn_unix_test.go	2.96 KB	-rw-r--r--
rawconn_windows_test.go	3.12 KB	-rw-r--r--
resolverdialfunc_test.go	8.25 KB	-rw-r--r--
rlimit_js.go	346 B	-rw-r--r--
rlimit_unix.go	1.1 KB	-rw-r--r--
sendfile_linux.go	1.15 KB	-rw-r--r--
sendfile_stub.go	403 B	-rw-r--r--
sendfile_test.go	12.06 KB	-rw-r--r--
sendfile_unix_alt.go	2.27 KB	-rw-r--r--
sendfile_windows.go	1.05 KB	-rw-r--r--
server_test.go	11.67 KB	-rw-r--r--
sock_bsd.go	918 B	-rw-r--r--
sock_cloexec.go	730 B	-rw-r--r--
sock_cloexec_solaris.go	1.43 KB	-rw-r--r--
sock_linux.go	993 B	-rw-r--r--
sock_linux_test.go	575 B	-rw-r--r--
sock_plan9.go	262 B	-rw-r--r--
sock_posix.go	6.29 KB	-rw-r--r--
sock_stub.go	390 B	-rw-r--r--
sock_windows.go	802 B	-rw-r--r--
sockaddr_posix.go	1.45 KB	-rw-r--r--
sockopt_aix.go	1.43 KB	-rw-r--r--
sockopt_bsd.go	2.21 KB	-rw-r--r--
sockopt_fake.go	955 B	-rw-r--r--
sockopt_linux.go	1.25 KB	-rw-r--r--
sockopt_plan9.go	406 B	-rw-r--r--
sockopt_posix.go	2.13 KB	-rw-r--r--
sockopt_solaris.go	1.25 KB	-rw-r--r--
sockopt_windows.go	1.51 KB	-rw-r--r--
sockoptip_bsdvar.go	867 B	-rw-r--r--
sockoptip_linux.go	735 B	-rw-r--r--
sockoptip_posix.go	1.38 KB	-rw-r--r--
sockoptip_stub.go	769 B	-rw-r--r--
sockoptip_windows.go	786 B	-rw-r--r--
splice_linux.go	1.71 KB	-rw-r--r--
splice_linux_test.go	14.49 KB	-rw-r--r--
splice_stub.go	376 B	-rw-r--r--
sys_cloexec.go	962 B	-rw-r--r--
tcpconn_keepalive_conf_darwin_...	430 B	-rw-r--r--
tcpconn_keepalive_conf_posix_t...	1.55 KB	-rw-r--r--
tcpconn_keepalive_conf_solaris...	1.77 KB	-rw-r--r--
tcpconn_keepalive_conf_unix_te...	490 B	-rw-r--r--
tcpconn_keepalive_conf_windows...	987 B	-rw-r--r--
tcpconn_keepalive_illumos_test...	3.98 KB	-rw-r--r--
tcpconn_keepalive_posix_test.g...	2.52 KB	-rw-r--r--
tcpconn_keepalive_solaris_test...	5.67 KB	-rw-r--r--
tcpconn_keepalive_test.go	4.15 KB	-rw-r--r--
tcpsock.go	13.67 KB	-rw-r--r--
tcpsock_plan9.go	2.3 KB	-rw-r--r--
tcpsock_posix.go	6.27 KB	-rw-r--r--
tcpsock_solaris.go	1.32 KB	-rw-r--r--
tcpsock_test.go	17.68 KB	-rw-r--r--
tcpsock_unix.go	1.05 KB	-rw-r--r--
tcpsock_unix_test.go	2.34 KB	-rw-r--r--
tcpsock_windows.go	1.31 KB	-rw-r--r--
tcpsockopt_darwin.go	1.4 KB	-rw-r--r--
tcpsockopt_openbsd.go	759 B	-rw-r--r--
tcpsockopt_plan9.go	762 B	-rw-r--r--
tcpsockopt_posix.go	442 B	-rw-r--r--
tcpsockopt_solaris.go	3.35 KB	-rw-r--r--
tcpsockopt_stub.go	570 B	-rw-r--r--
tcpsockopt_unix.go	1.32 KB	-rw-r--r--
tcpsockopt_windows.go	3.76 KB	-rw-r--r--
timeout_test.go	30.01 KB	-rw-r--r--
udpsock.go	11.83 KB	-rw-r--r--
udpsock_plan9.go	4.64 KB	-rw-r--r--
udpsock_plan9_test.go	1.31 KB	-rw-r--r--
udpsock_posix.go	7.53 KB	-rw-r--r--
udpsock_test.go	17.24 KB	-rw-r--r--
unixsock.go	10.12 KB	-rw-r--r--
unixsock_linux_test.go	2.29 KB	-rw-r--r--
unixsock_plan9.go	1.24 KB	-rw-r--r--
unixsock_posix.go	6.64 KB	-rw-r--r--
unixsock_readmsg_cloexec.go	654 B	-rw-r--r--
unixsock_readmsg_cmsg_cloexec....	332 B	-rw-r--r--
unixsock_readmsg_other.go	275 B	-rw-r--r--
unixsock_readmsg_test.go	2.51 KB	-rw-r--r--
unixsock_test.go	10.64 KB	-rw-r--r--
unixsock_windows_test.go	1.83 KB	-rw-r--r--
write_unix_test.go	1.61 KB	-rw-r--r--
writev_test.go	5.03 KB	-rw-r--r--
writev_unix.go	666 B	-rw-r--r--

Code Editor : ip.go

// 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 (
	"internal/bytealg"
	"internal/itoa"
	"internal/stringslite"
	"net/netip"
)

// 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 IPMask is a bitmask that can be used to manipulate
// IP addresses for IP addressing and routing.
//
// See type [IPNet] and func [ParseCIDR] for details.
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)
}

// IsPrivate reports whether ip is a private address, according to
// RFC 1918 (IPv4 addresses) and RFC 4193 (IPv6 addresses).
func (ip IP) IsPrivate() bool {
	if ip4 := ip.To4(); ip4 != nil {
		// Following RFC 1918, Section 3. Private Address Space which says:
		//   The Internet Assigned Numbers Authority (IANA) has reserved the
		//   following three blocks of the IP address space for private internets:
		//     10.0.0.0        -   10.255.255.255  (10/8 prefix)
		//     172.16.0.0      -   172.31.255.255  (172.16/12 prefix)
		//     192.168.0.0     -   192.168.255.255 (192.168/16 prefix)
		return ip4[0] == 10 ||
			(ip4[0] == 172 && ip4[1]&0xf0 == 16) ||
			(ip4[0] == 192 && ip4[1] == 168)
	}
	// Following RFC 4193, Section 8. IANA Considerations which says:
	//   The IANA has assigned the FC00::/7 prefix to "Unique Local Unicast".
	return len(ip) == IPv6len && ip[0]&0xfe == 0xfc
}

// 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 {
	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 && bytealg.Equal(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.
// 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 conforming to RFC 5952 ("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 {
	if len(ip) == 0 {
		return "<nil>"
	}

if len(ip) != IPv4len && len(ip) != IPv6len {
		return "?" + hexString(ip)
	}
	// If IPv4, use dotted notation.
	if p4 := ip.To4(); len(p4) == IPv4len {
		return netip.AddrFrom4([4]byte(p4)).String()
	}
	return netip.AddrFrom16([16]byte(ip)).String()
}

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 [IP.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 bytealg.Equal(ip, x)
	}
	if len(ip) == IPv4len && len(x) == IPv6len {
		return bytealg.Equal(x[0:12], v4InV6Prefix) && bytealg.Equal(ip, x[12:])
	}
	if len(ip) == IPv6len && len(x) == IPv4len {
		return bytealg.Equal(ip[0:12], v4InV6Prefix) && bytealg.Equal(ip[12:], x)
	}
	return false
}

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 "192.0.2.0/24"
// 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 "198.51.100.0/c000ff00".
func (n *IPNet) String() string {
	if n == nil {
		return "<nil>"
	}
	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() + "/" + itoa.Uitoa(uint(l))
}

// ParseIP parses s as an IP address, returning the result.
// The string s can be in IPv4 dotted decimal ("192.0.2.1"), IPv6
// ("2001:db8::68"), or IPv4-mapped IPv6 ("::ffff:192.0.2.1") form.
// If s is not a valid textual representation of an IP address,
// ParseIP returns nil. The returned address is always 16 bytes,
// IPv4 addresses are returned in IPv4-mapped IPv6 form.
func ParseIP(s string) IP {
	if addr, valid := parseIP(s); valid {
		return IP(addr[:])
	}
	return nil
}

func parseIP(s string) ([16]byte, bool) {
	ip, err := netip.ParseAddr(s)
	if err != nil || ip.Zone() != "" {
		return [16]byte{}, false
	}
	return ip.As16(), true
}

// 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) {
	addr, mask, found := stringslite.Cut(s, "/")
	if !found {
		return nil, nil, &ParseError{Type: "CIDR address", Text: s}
	}

ipAddr, err := netip.ParseAddr(addr)
	if err != nil || ipAddr.Zone() != "" {
		return nil, nil, &ParseError{Type: "CIDR address", Text: s}
	}

n, i, ok := dtoi(mask)
	if !ok || i != len(mask) || n < 0 || n > ipAddr.BitLen() {
		return nil, nil, &ParseError{Type: "CIDR address", Text: s}
	}
	m := CIDRMask(n, ipAddr.BitLen())
	addr16 := ipAddr.As16()
	return IP(addr16[:]), &IPNet{IP: IP(addr16[:]).Mask(m), Mask: m}, nil
}

func copyIP(x IP) IP {
	y := make(IP, len(x))
	copy(y, x)
	return y
}

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Code Editor : ip.go