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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 main
import (
"fmt"
"math/big"
"net"
)
// 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))
}
//NoOverlap 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 NoOverlap(subnets []*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 {
for j := range subnets {
if i == j {
continue
}
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
}