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