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// Package cidr is a collection of assorted utilities for computing
// network and host addresses within network ranges.
//
// It expects a CIDR-type address structure where addresses are divided into
// some number of prefix bits representing the network and then the remaining
// suffix bits represent the host.
//
// For example, it can help to calculate addresses for sub-networks of a
// parent network, or to calculate host addresses within a particular prefix.
//
// At present this package is prioritizing simplicity of implementation and
// de-prioritizing speed and memory usage. Thus caution is advised before
// using this package in performance-critical applications or hot codepaths.
// Patches to improve the speed and memory usage may be accepted as long as
// they do not result in a significant increase in code complexity.
package cidr
import (
"fmt"
"math/big"
"net"
)
// Subnet takes a parent CIDR range and creates a subnet within it
// with the given number of additional prefix bits and the given
// network number.
//
// For example, 10.3.0.0/16, extended by 8 bits, with a network number
// of 5, becomes 10.3.5.0/24 .
func Subnet(base *net.IPNet, newBits int, num int) (*net.IPNet, error) {
ip := base.IP
mask := base.Mask
parentLen, addrLen := mask.Size()
newPrefixLen := parentLen + newBits
if newPrefixLen > addrLen {
return nil, fmt.Errorf("insufficient address space to extend prefix of %d by %d", parentLen, newBits)
}
maxNetNum := uint64(1<<uint64(newBits)) - 1
if uint64(num) > maxNetNum {
return nil, fmt.Errorf("prefix extension of %d does not accommodate a subnet numbered %d", newBits, num)
}
return &net.IPNet{
IP: insertNumIntoIP(ip, num, newPrefixLen),
Mask: net.CIDRMask(newPrefixLen, addrLen),
}, nil
}
// Host takes a parent CIDR range and turns it into a host IP address with
// the given host number.
//
// For example, 10.3.0.0/16 with a host number of 2 gives 10.3.0.2.
func Host(base *net.IPNet, num int) (net.IP, error) {
ip := base.IP
mask := base.Mask
parentLen, addrLen := mask.Size()
hostLen := addrLen - parentLen
maxHostNum := uint64(1<<uint64(hostLen)) - 1
numUint64 := uint64(num)
if num < 0 {
numUint64 = uint64(-num) - 1
num = int(maxHostNum - numUint64)
}
if numUint64 > maxHostNum {
return nil, fmt.Errorf("prefix of %d does not accommodate a host numbered %d", parentLen, num)
}
var bitlength int
if ip.To4() != nil {
bitlength = 32
} else {
bitlength = 128
}
return insertNumIntoIP(ip, num, bitlength), nil
}
// AddressRange returns the first and last addresses in the given CIDR range.
func AddressRange(network *net.IPNet) (net.IP, net.IP) {
// the first IP is easy
firstIP := network.IP
// the last IP is the network address OR NOT the mask address
prefixLen, bits := network.Mask.Size()
if prefixLen == bits {
// Easy!
// But make sure that our two slices are distinct, since they
// would be in all other cases.
lastIP := make([]byte, len(firstIP))
copy(lastIP, firstIP)
return firstIP, lastIP
}
firstIPInt, bits := ipToInt(firstIP)
hostLen := uint(bits) - uint(prefixLen)
lastIPInt := big.NewInt(1)
lastIPInt.Lsh(lastIPInt, hostLen)
lastIPInt.Sub(lastIPInt, big.NewInt(1))
lastIPInt.Or(lastIPInt, firstIPInt)
return firstIP, intToIP(lastIPInt, bits)
}
// AddressCount returns the number of distinct host addresses within the given
// CIDR range.
//
// Since the result is a uint64, this function returns meaningful information
// only for IPv4 ranges and IPv6 ranges with a prefix size of at least 65.
func AddressCount(network *net.IPNet) uint64 {
prefixLen, bits := network.Mask.Size()
return 1 << (uint64(bits) - uint64(prefixLen))
}
//VerifyNoOverlap takes a list subnets and supernet (CIDRBlock) and verifies
//none of the subnets overlap and all subnets are in the supernet
//it returns an error if any of those conditions are not satisfied
func VerifyNoOverlap(subnets []*net.IPNet, CIDRBlock *net.IPNet) error {
firstLastIP := make([][]net.IP, len(subnets))
for i, s := range subnets {
first, last := AddressRange(s)
firstLastIP[i] = []net.IP{first, last}
}
for i, s := range subnets {
if !CIDRBlock.Contains(firstLastIP[i][0]) || !CIDRBlock.Contains(firstLastIP[i][1]) {
return fmt.Errorf("%s does not fully contain %s", CIDRBlock.String(), s.String())
}
for j := i + 1; j < len(subnets); j++ {
first := firstLastIP[j][0]
last := firstLastIP[j][1]
if s.Contains(first) || s.Contains(last) {
return fmt.Errorf("%s overlaps with %s", subnets[j].String(), s.String())
}
}
}
return nil
}
// PreviousSubnet returns the subnet of the desired mask in the IP space
// just lower than the start of IPNet provided. If the IP space rolls over
// then the second return value is true
func PreviousSubnet(network *net.IPNet, prefixLen int) (*net.IPNet, bool) {
startIP := checkIPv4(network.IP)
previousIP := make(net.IP, len(startIP))
copy(previousIP, startIP)
cMask := net.CIDRMask(prefixLen, 8*len(previousIP))
previousIP = Dec(previousIP)
previous := &net.IPNet{IP: previousIP.Mask(cMask), Mask: cMask}
if startIP.Equal(net.IPv4zero) || startIP.Equal(net.IPv6zero) {
return previous, true
}
return previous, false
}
// NextSubnet returns the next available subnet of the desired mask size
// starting for the maximum IP of the offset subnet
// If the IP exceeds the maxium IP then the second return value is true
func NextSubnet(network *net.IPNet, prefixLen int) (*net.IPNet, bool) {
_, currentLast := AddressRange(network)
mask := net.CIDRMask(prefixLen, 8*len(currentLast))
currentSubnet := &net.IPNet{IP: currentLast.Mask(mask), Mask: mask}
_, last := AddressRange(currentSubnet)
last = Inc(last)
next := &net.IPNet{IP: last.Mask(mask), Mask: mask}
if last.Equal(net.IPv4zero) || last.Equal(net.IPv6zero) {
return next, true
}
return next, false
}
//Inc increases the IP by one this returns a new []byte for the IP
func Inc(IP net.IP) net.IP {
IP = checkIPv4(IP)
incIP := make([]byte, len(IP))
copy(incIP, IP)
for j := len(incIP) - 1; j >= 0; j-- {
incIP[j]++
if incIP[j] > 0 {
break
}
}
return incIP
}
//Dec decreases the IP by one this returns a new []byte for the IP
func Dec(IP net.IP) net.IP {
IP = checkIPv4(IP)
decIP := make([]byte, len(IP))
copy(decIP, IP)
decIP = checkIPv4(decIP)
for j := len(decIP) - 1; j >= 0; j-- {
decIP[j]--
if decIP[j] < 255 {
break
}
}
return decIP
}
func checkIPv4(ip net.IP) net.IP {
// Go for some reason allocs IPv6len for IPv4 so we have to correct it
if v4 := ip.To4(); v4 != nil {
return v4
}
return ip
}
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