Go/GoLang check IP address in range

In Go/GoLang, what is the fastest way to check if an IP address is in a specific range?

For example, given range 216.14.49.184 to 216.14.49.191, how would I check if a given input IP address is in that range?

IP addresses are represented as bigendian []byte slices in go (the IP type) so will compare correctly using bytes.Compare.

Eg (play)

package main

import (
	"bytes"
	"fmt"
	"net"
)

var (
	ip1 = net.ParseIP("216.14.49.184")
	ip2 = net.ParseIP("216.14.49.191")
)

func check(ip string) bool {
	trial := net.ParseIP(ip)
	if trial.To4() == nil {
		fmt.Printf("%v is not an IPv4 address\n", trial)
		return false
	}
	if bytes.Compare(trial, ip1) >= 0 && bytes.Compare(trial, ip2) <= 0 {
		fmt.Printf("%v is between %v and %v\n", trial, ip1, ip2)
		return true
	}
	fmt.Printf("%v is NOT between %v and %v\n", trial, ip1, ip2)
	return false
}

func main() {
	check("1.2.3.4")
	check("216.14.49.185")
	check("1::16")
}

Which produces

1.2.3.4 is NOT between 216.14.49.184 and 216.14.49.191
216.14.49.185 is between 216.14.49.184 and 216.14.49.191
1::16 is not an IPv4 address

This is already in the stdlib in the "net" package as a function called net.Contains. You dont need to rewrite code that already exists!

See documentation here.

To use it you just have to parse the desired subnets

network := "192.168.5.0/24"
clientips := []string{
	"192.168.5.1",
	"192.168.6.0",
}
_, subnet, _ := net.ParseCIDR(network)
for _, clientip := range clientips {
	ip := net.ParseIP(clientip)
	if subnet.Contains(ip) {
		fmt.Println("IP in subnet", clientip)
	}
}

In case the above code doesn't make sense here is a golang play link

The generic version for ipv4/ipv6.

ip.go:

package ip

import (
	"bytes"
	"net"

	"github.com/golang/glog"
)

//test to determine if a given ip is between two others (inclusive)
func IpBetween(from net.IP, to net.IP, test net.IP) bool {
	if from == nil || to == nil || test == nil {
		glog.Warning("An ip input is nil") // or return an error!?
		return false
	}

	from16 := from.To16()
	to16 := to.To16()
	test16 := test.To16()
	if from16 == nil || to16 == nil || test16 == nil {
		glog.Warning("An ip did not convert to a 16 byte") // or return an error!?
		return false
	}

	if bytes.Compare(test16, from16) >= 0 && bytes.Compare(test16, to16) <= 0 {
		return true
	}
	return false
}

and ip_test.go:

package ip

import (
	"net"
	"testing"
)

func TestIPBetween(t *testing.T) {
	HandleIpBetween(t, "0.0.0.0", "255.255.255.255", "128.128.128.128", true)
	HandleIpBetween(t, "0.0.0.0", "128.128.128.128", "255.255.255.255", false)
	HandleIpBetween(t, "74.50.153.0", "74.50.153.4", "74.50.153.0", true)
	HandleIpBetween(t, "74.50.153.0", "74.50.153.4", "74.50.153.4", true)
	HandleIpBetween(t, "74.50.153.0", "74.50.153.4", "74.50.153.5", false)
	HandleIpBetween(t, "2001:0db8:85a3:0000:0000:8a2e:0370:7334", "74.50.153.4", "74.50.153.2", false)
	HandleIpBetween(t, "2001:0db8:85a3:0000:0000:8a2e:0370:7334", "2001:0db8:85a3:0000:0000:8a2e:0370:8334", "2001:0db8:85a3:0000:0000:8a2e:0370:7334", true)
	HandleIpBetween(t, "2001:0db8:85a3:0000:0000:8a2e:0370:7334", "2001:0db8:85a3:0000:0000:8a2e:0370:8334", "2001:0db8:85a3:0000:0000:8a2e:0370:7350", true)
	HandleIpBetween(t, "2001:0db8:85a3:0000:0000:8a2e:0370:7334", "2001:0db8:85a3:0000:0000:8a2e:0370:8334", "2001:0db8:85a3:0000:0000:8a2e:0370:8334", true)
	HandleIpBetween(t, "2001:0db8:85a3:0000:0000:8a2e:0370:7334", "2001:0db8:85a3:0000:0000:8a2e:0370:8334", "2001:0db8:85a3:0000:0000:8a2e:0370:8335", false)
	HandleIpBetween(t, "::ffff:192.0.2.128", "::ffff:192.0.2.250", "::ffff:192.0.2.127", false)
	HandleIpBetween(t, "::ffff:192.0.2.128", "::ffff:192.0.2.250", "::ffff:192.0.2.128", true)
	HandleIpBetween(t, "::ffff:192.0.2.128", "::ffff:192.0.2.250", "::ffff:192.0.2.129", true)
	HandleIpBetween(t, "::ffff:192.0.2.128", "::ffff:192.0.2.250", "::ffff:192.0.2.250", true)
	HandleIpBetween(t, "::ffff:192.0.2.128", "::ffff:192.0.2.250", "::ffff:192.0.2.251", false)
	HandleIpBetween(t, "::ffff:192.0.2.128", "::ffff:192.0.2.250", "192.0.2.130", true)
	HandleIpBetween(t, "192.0.2.128", "192.0.2.250", "::ffff:192.0.2.130", true)
	HandleIpBetween(t, "idonotparse", "192.0.2.250", "::ffff:192.0.2.130", false)

}

func HandleIpBetween(t *testing.T, from string, to string, test string, assert bool) {
	res := IpBetween(net.ParseIP(from), net.ParseIP(to), net.ParseIP(test))
	if res != assert {
		t.Errorf("Assertion (have: %s should be: %s) failed on range %s-%s with test %s", res, assert, from, to, test)
	}
}

I ported over the code from a C# example found here: https://stackoverflow.com/a/2138724/1655418

And for some reason it ends up being 1ms faster than Nick's solution.

My question was for the "fastest" way, so I figured I'd post mine and see what the community thinks.

package iptesting
import (
"fmt"
"testing"
"net"
"time"
"bytes"
)
func TestIPRangeTime(t *testing.T) {
lowerBytes := net.ParseIP("216.14.49.184").To4()
upperBytes := net.ParseIP("216.14.49.191").To4()
inputBytes := net.ParseIP("216.14.49.184").To4()
startTime := time.Now()
for i := 0; i < 27000; i++ {
IsInRange(inputBytes, lowerBytes, upperBytes)
}
endTime := time.Now()
fmt.Println("ELAPSED time port: ", endTime.Sub(startTime))
lower := net.ParseIP("216.14.49.184")
upper := net.ParseIP("216.14.49.191")
trial := net.ParseIP("216.14.49.184")
startTime = time.Now()
for i := 0; i < 27000; i++ {
IsInRange2(trial, lower, upper)
}
endTime = time.Now()
fmt.Println("ELAPSED time bytescompare: ", endTime.Sub(startTime))
}
func IsInRange2(trial net.IP, lower net.IP, upper net.IP) bool {
if bytes.Compare(trial, lower) >= 0 && bytes.Compare(trial, upper) <= 0 {
return true
}
return false
}
func IsInRange(ip []byte, lower []byte, upper []byte) bool {
//fmt.Printf("given ip len: %d\n", len(ip))
lowerBoundary := true
upperBoundary := true
for i := 0; i < len(lower) && (lowerBoundary || upperBoundary); i++ {
if lowerBoundary && ip[i] < lower[i] || upperBoundary && ip[i] > upper[i] {
return false
}
if ip[i] == lower[i] {
if lowerBoundary {
lowerBoundary = true
} else {
lowerBoundary = false
}
//lowerBoundary &= true
} else {
lowerBoundary = false
//lowerBoundary &= false
}
if ip[i] == upper[i] {
//fmt.Printf("matched upper\n")
if upperBoundary {
upperBoundary = true
} else {
upperBoundary = false
}
//upperBoundary &= true
} else {
upperBoundary = false
//upperBoundary &= false
}
}
return true
}

My results:

=== RUN TestIPRangeTime
ELAPSED time port:  1.0001ms
ELAPSED time bytescompare:  2.0001ms
--- PASS: TestIPRangeTime (0.00 seconds)
=== RUN TestIPRangeTime
ELAPSED time port:  1ms
ELAPSED time bytescompare:  2.0002ms
--- PASS: TestIPRangeTime (0.00 seconds)
=== RUN TestIPRangeTime
ELAPSED time port:  1.0001ms
ELAPSED time bytescompare:  2.0001ms
--- PASS: TestIPRangeTime (0.00 seconds)
=== RUN TestIPRangeTime
ELAPSED time port:  1.0001ms
ELAPSED time bytescompare:  2.0001ms
--- PASS: TestIPRangeTime (0.00 seconds)

How about some implementation like inet_pton? The result is easy to be stored.

func IP2Integer(ip *net.IP) (int64, error) {
ip4 := ip.To4()
if ip4 == nil {
return 0, fmt.Errorf("illegal: %v", ip)
}
bin := make([]string, len(ip4))
for i, v := range ip4 {
bin[i] = fmt.Sprintf("%08b", v)
}
return strconv.ParseInt(strings.Join(bin, ""), 2, 64)
}

Go 1.18

You can use the new package net/netip. The package defines the type netip.Addr:

> Compared to the net.IP type, this package's Addr type takes less memory, is immutable, and is comparable (supports == and being a map key).

You can compare IPs with the method Compare:

> Compare returns an integer comparing two IPs. The result will be:
> - 0 if ip == ip2
> - -1 if ip < ip2
> - +1 if ip > ip2.
>
> The definition of "less than" is the same as the Less method.

Assuming that you're dealing with IPv4 addresses, a simple in-range comparison might look like the following:

package main
import (
"fmt"
"net/netip"
)
func main() {
ip1, _ := netip.ParseAddr("216.14.49.184")
ip2, _ := netip.ParseAddr("216.14.49.191")
myIP, _ := netip.ParseAddr("192.168.8.1")
fmt.Println(inRange(ip1, ip2, myIP)) // false
myIP, _ = netip.ParseAddr("216.14.49.185")
fmt.Println(inRange(ip1, ip2, myIP)) // true
}
func inRange(ipLow, ipHigh, ip netip.Addr) bool {
return ipLow.Compare(ip) <= 0 && ipHigh.Compare(ip) > 0
}

Note: In real-world code don't actually ignore errors from parsing the IP strings.

see in gist

ipmatcher.go

type IPMatcher struct {
IP net.IP
SubNet *net.IPNet
}
type IPMatchers []*IPMatcher
func NewIPMatcher(ipStr string) (*IPMatcher, error) {
ip, subNet, err := net.ParseCIDR(ipStr)
if err != nil {
ip = net.ParseIP(ipStr)
if ip == nil {
return nil, errors.New("invalid IP: "+ipStr)
}
}
return &IPMatcher{ip, subNet}, nil
}
func (m IPMatcher) Match(ipStr string) bool {
ip := net.ParseIP(ipStr)
if ip == nil {
return false
}
return m.IP.Equal(ip) || m.SubNet != nil && m.SubNet.Contains(ip)
}
func NewIPMatchers(ips []string) (list IPMatchers, err error) {
for _, ipStr := range ips {
var m *IPMatcher
m, err = NewIPMatcher(ipStr)
if err != nil {
return
}
list = append(list, m)
}
return
}
func IPContains(ipMatchers []*IPMatcher, ip string) bool {
for _, m := range ipMatchers {
if m.Match(ip) {
return true
}
}
return false
}
func (ms IPMatchers) Match(ip string) bool {
return IPContains(ms, ip)
}

ipmatcher_test.go

import "testing"
func TestIPMatcher(t *testing.T)  {
a, errA := NewIPMatcher("127.0.0.1")
if errA != nil {
t.Error(errA)
}
if a.IP.String() != "127.0.0.1" || a.SubNet != nil {
t.Error("ip parse error")
}
b, errB := NewIPMatcher("192.168.1.1/24")
if errB != nil {
t.Error(errB)
}
if b.IP.String() != "192.168.1.1" || b.SubNet == nil {
t.Errorf("ip match error: %s, %v", b.IP.String(), b.SubNet)
}
if !b.Match("192.168.1.1") || !b.Match("192.168.1.2") {
t.Error("ip match error")
}
}
func TestIPMatchers(t *testing.T)  {
var WhiteListIPs = []string{"127.0.0.1", "192.168.1.0/24", "10.1.0.0/16"}
M, err := NewIPMatchers(WhiteListIPs)
if err != nil {
t.Error(err)
}
if !M.Match("127.0.0.1") || !M.Match("192.168.1.1") || !M.Match("192.168.1.199") ||
!M.Match("10.1.0.1") || !M.Match("10.1.3.1") {
t.Error("ip match error")
}
if M.Match("127.0.0.2") || M.Match("192.168.2.1") || M.Match("10.2.0.1") {
t.Error("ip match error 2")
}
}

see in gist

The IPAddress Go library can do this quickly in a polymorphic manner with both IPv4 and IPv6 addresses. Repository here. Disclaimer: I am the project manager.

import (
	"fmt"
	"github.com/seancfoley/ipaddress-go/ipaddr"
)

func main() {
	isInRange("216.14.49.184", "216.14.49.191", "216.14.49.190")
	isInRange("2001:db8:85a3::8a2e:0370:7334",
		"2001:db8:85a3::8a00:ff:ffff", "2001:db8:85a3::8a03:a:b")
}

func getAddress(str string) *ipaddr.IPAddress {
	return ipaddr.NewIPAddressString(str).GetAddress()
}

func isInRange(range1Str, range2Str, addrStr string) {
	range1, range2 := getAddress(range1Str), getAddress(range2Str)
	addr := getAddress(addrStr)
	rng := range1.SpanWithRange(range2)
	fmt.Printf("%v contains %v %t\n", rng, addr, rng.Contains(addr))
}

Output:

216.14.49.184 -> 216.14.49.191 contains 216.14.49.190 true
2001:db8:85a3::8a00:ff:ffff -> 2001:db8:85a3::8a2e:370:7334 contains 2001:db8:85a3::8a03:a:b true