Testing if a network in cidr notation overlaps another network

Question

I'm searching for a php algorithm that efficiently test if one cidr notated network overlaps another.

Basically I have the following situation:

Array of cidr adresses:

$cidrNetworks = array(
    '192.168.10.0/24',
    '10.10.0.30/20',
    etc.
);

I have a method that adds networks to the array, but this method should throw an exception when a network is added that overlaps with a network allready in the array.

So ie. if 192.168.10.0/25 is added an exception should be thrown.

Does anyone have/know/"can think of" an method to test this efficiently?

Answer 1

Here is an updated version of the class previously discussed in chat. It can do what you require, as well as many other useful things.

<?php

    class IPv4Subnet implements ArrayAccess, Iterator {

        /*
         * Address format constants
         */
        const ADDRESS_BINARY = 0x01;
        const ADDRESS_INT = 0x02;
        const ADDRESS_DOTDEC = 0x04;
        const ADDRESS_SUBNET = 0x08;

        /*
         * Constants to control whether getHosts() returns the network/broadcast addresses
         */
        const HOSTS_WITH_NETWORK = 0x10;
        const HOSTS_WITH_BROADCAST = 0x20;
        const HOSTS_ALL = 0x30;

        /*
         * Properties to store base address and subnet mask as binary strings
         */
        protected $address;
        protected $mask;

        /*
         * Counter to track the current iteration offset
         */
        private $iteratorOffset = 0;

        /*
         * Array to hold values retrieved via ArrayAccess
         */
        private $arrayAccessObjects = array();

        /*
         * Helper methods
         */
        private function longToBinary ($long) {
            return pack('N', $long);
        }
        private function longToDottedDecimal ($long) {
            return ($long >> 24 & 0xFF).'.'.($long >> 16 & 0xFF).'.'.($long >> 8 & 0xFF).'.'.($long & 0xFF);
        }
        private function longToByteArray ($long) {
            return array(
                $long >> 24 & 0xFF,
                $long >> 16 & 0xFF,
                $long >> 8 & 0xFF,
                $long & 0xFF
            );
        }
        private function longToSubnet ($long) {
            if (!isset($this->arrayAccessObjects[$long])) {
                $this->arrayAccessObjects[$long] = new self($long);
            }
            return $this->arrayAccessObjects[$long];
        }
        private function binaryToLong ($binary) {
            return current(unpack('N', $binary));
        }
        private function binaryToDottedDecimal ($binary) {
            return implode('.', unpack('C*', $binary));
        }
        private function binaryToX ($binary, $mode) {
            if ($mode & self::ADDRESS_BINARY) {
                $result = $binary;
            } else if ($mode & self::ADDRESS_INT) {
                $result = $this->binaryToLong($binary);
            } else if ($mode & self::ADDRESS_DOTDEC) {
                $result = $this->binaryToDottedDecimal($binary);
            } else {
                $result = $this->longToSubnet($this->binaryToLong($binary));
            }
            return $result;
        }
        private function byteArrayToLong($bytes) {
            return ($bytes[0] << 24) | ($bytes[1] << 16) | ($bytes[2] << 8) | $bytes[3];
        }
        private function byteArrayToBinary($bytes) {
            return pack('C*', $bytes[0], $bytes[1], $bytes[2], $bytes[3]);
        }

        private function normaliseComparisonSubject (&$subject) {
            if (!is_object($subject)) {
                $subject = new self($subject);
            }
            if (!($subject instanceof self)) {
                throw new InvalidArgumentException('Subject must be an instance of IPv4Subnet');
            }
        }

        private function validateOctetArray (&$octets) {
            foreach ($octets as &$octet) {
                $octet = (int) $octet;
                if ($octet < 0 || $octet > 255) {
                    return FALSE;
                }
            }
            return TRUE;
        }

        /*
         * Constructor
         */
        public function __construct ($address = NULL, $mask = NULL) {
            if ($address === NULL || (is_string($address) && trim($address) === '')) {
                $address = array(0, 0, 0, 0);
            } else if (is_int($address)) {
                $address = $this->longToByteArray($address);
            } else if (is_string($address)) {
                $parts = preg_split('#\s*/\s*#', trim($address), -1, PREG_SPLIT_NO_EMPTY);
                if (count($parts) > 2) {
                    throw new InvalidArgumentException('No usable IP address supplied: Syntax error');
                } else if ($parts[0] === '') {
                    throw new InvalidArgumentException('No usable IP address supplied: IP address empty');
                }
                if (!empty($parts[1]) && !isset($mask)) {
                    $mask = $parts[1];
                }
                $address = preg_split('#\s*\.\s*#', $parts[0], -1, PREG_SPLIT_NO_EMPTY);
            } else if (is_array($address)) {
                $address = array_values($address);
            } else {
                throw new InvalidArgumentException('No usable IP address supplied: Value must be a string or an integer');
            }

            $suppliedAddressOctets = count($address);
            $address += array(0, 0, 0, 0);
            if ($suppliedAddressOctets > 4) {
                throw new InvalidArgumentException('No usable IP address supplied: IP address has more than 4 octets');
            } else if (!$this->validateOctetArray($address)) {
                throw new InvalidArgumentException('No usable IP address supplied: At least one octet value outside acceptable range 0 - 255');
            }

            if ($mask === NULL) {
                $mask = array_pad(array(), $suppliedAddressOctets, 255) + array(0, 0, 0, 0);
            } else if (is_int($mask)) {
                $mask = $this->longToByteArray($mask);
            } else if (is_string($mask)) {
                $mask = preg_split('#\s*\.\s*#', trim($mask), -1, PREG_SPLIT_NO_EMPTY);

                switch (count($mask)) {
                    case 1: // CIDR
                        $cidr = (int) $mask[0];
                        if ($cidr === 0) {
                            // Shifting 32 bits on a 32 bit system doesn't work, so treat this as a special case
                            $mask = array(0, 0, 0, 0);
                        } else if ($cidr <= 32) {
                            // This looks odd, but it's the nicest way I have found to get the 32 least significant bits set in a
                            // way that works on both 32 and 64 bit platforms
                            $base = ~((~0 << 16) << 16);
                            $mask = $this->longToByteArray($base << (32 - $cidr));
                        } else {
                            throw new InvalidArgumentException('Supplied mask invalid: CIDR outside acceptable range 0 - 32');
                        }
                        break;
                    case 4: break; // Dotted decimal
                    default: throw new InvalidArgumentException('Supplied mask invalid: Must be either a full dotted-decimal or a CIDR');
                }
            } else if (is_array($mask)) {
                $mask = array_values($mask);
            } else {
                throw new InvalidArgumentException('Supplied mask invalid: Type invalid');
            }

            if (!$this->validateOctetArray($mask)) {
                throw new InvalidArgumentException('Supplied mask invalid: At least one octet value outside acceptable range 0 - 255');
            }
            // Check bits are contiguous from left
            // TODO: Improve this mechanism
            $asciiBits = sprintf('%032b', $this->byteArrayToLong($mask));
            if (strpos(rtrim($asciiBits, '0'), '0') !== FALSE) {
                throw new InvalidArgumentException('Supplied mask invalid: Set bits are not contiguous from the most significant bit');
            }

            $this->mask = $this->byteArrayToBinary($mask);
            $this->address = $this->byteArrayToBinary($address) & $this->mask;
        }

        /*
         * ArrayAccess interface methods (read only)
         */
        public function offsetExists ($offset) {
            if ($offset === 'network' || $offset === 'broadcast') {
                return TRUE;
            }

            $offset = filter_var($offset, FILTER_VALIDATE_INT);
            if ($offset === FALSE || $offset < 0) {
                return FALSE;
            }

            return $offset < $this->getHostsCount();
        }
        public function offsetGet ($offset) {
            if (!$this->offsetExists($offset)) {
                return NULL;
            }

            if ($offset === 'network') {
                $address = $this->getNetworkAddress(self::ADDRESS_INT);
            } else if ($offset === 'broadcast') {
                $address = $this->getBroadcastAddress(self::ADDRESS_INT);
            } else {
                // How much the address needs to be adjusted by to account for network address
                $adjustment = (int) ($this->getHostsCount() > 2);
                $address = $this->binaryToLong($this->address) + $offset + $adjustment;
            }

            return $this->longToSubnet($address);
        }
        public function offsetSet ($offset, $value) {}
        public function offsetUnset ($offset) {}

        /*
         * Iterator interface methods
         */
        public function current () {
            return $this->offsetGet($this->iteratorOffset);
        }
        public function key () {
            return $this->iteratorOffset;
        }
        public function next () {
            $this->iteratorOffset++;
        }
        public function rewind () {
            $this->iteratorOffset = 0;
        }
        public function valid () {
            return $this->iteratorOffset < $this->getHostsCount();
        }

        /*
         * Data access methods
         */
        public function getHosts ($mode = self::ADDRESS_SUBNET) {
            // Parse flags and initialise vars
            $bin = (bool) ($mode & self::ADDRESS_BINARY);
            $int = (bool) ($mode & self::ADDRESS_INT);
            $dd = (bool) ($mode & self::ADDRESS_DOTDEC);
            $base = $this->binaryToLong($this->address);
            $mask = $this->binaryToLong($this->mask);
            $hasNwBc = !($mask & 0x03);
            $result = array();

            // Get network address if requested
            if (($mode & self::HOSTS_WITH_NETWORK) && $hasNwBc) {
                $result[] = $base;
            }

            // Get hosts
            for ($current = $hasNwBc ? $base + 1 : $base; ($current & $mask) === $base; $current++) {
                $result[] = $current;
            }

            // Remove broadcast address if present and not requested
            if ($hasNwBc && !($mode & self::HOSTS_WITH_BROADCAST)) {
                array_pop($result);
            }

            // Convert to the correct type
            if ($bin) {
                $result = array_map(array($this, 'longToBinary'), $result);
            } else if ($dd) {
                $result = array_map(array($this, 'longToDottedDecimal'), $result);
            } else if (!$int) {
                $result = array_map(array($this, 'longToSubnet'), $result);
            }

            return $result;
        }
        public function getHostsCount () {
            $count = $this->getBroadcastAddress(self::ADDRESS_INT) - $this->getNetworkAddress(self::ADDRESS_INT);
            return $count > 2 ? $count - 1 : $count + 1; // Adjust return value to exclude network/broadcast addresses
        }
        public function getNetworkAddress ($mode = self::ADDRESS_SUBNET) {
            return $this->binaryToX($this->address, $mode);
        }
        public function getBroadcastAddress ($mode = self::ADDRESS_SUBNET) {
            return $this->binaryToX($this->address | ~$this->mask, $mode);
        }
        public function getMask ($mode = self::ADDRESS_DOTDEC) {
            return $this->binaryToX($this->mask, $mode);
        }

        /*
         * Stringify methods
         */
        public function __toString () {
            if ($this->getHostsCount() === 1) {
                $result = $this->toDottedDecimal();
            } else {
                $result = $this->toCIDR();
            }
            return $result;
        }
        public function toDottedDecimal () {
            $result = $this->getNetworkAddress(self::ADDRESS_DOTDEC);
            if ($this->mask !== "\xFF\xFF\xFF\xFF") {
                $result .= '/'.$this->getMask(self::ADDRESS_DOTDEC);
            }
            return $result;
        }
        public function toCIDR () {
            $address = $this->getNetworkAddress(self::ADDRESS_DOTDEC);
            $cidr = strlen(trim(sprintf('%b', $this->getMask(self::ADDRESS_INT)), '0')); // TODO: Improve this mechanism
            return $address.'/'.$cidr;
        }

        /*
         * Comparison methods
         */
        public function contains ($subject) {
            $this->normaliseComparisonSubject($subject);

            $subjectAddress = $subject->getNetworkAddress(self::ADDRESS_BINARY);
            $subjectMask = $subject->getMask(self::ADDRESS_BINARY);

            return $this->mask !== $subjectMask && ($this->mask | ($this->mask ^ $subjectMask)) !== $this->mask && ($subjectAddress & $this->mask) === $this->address;
        }

        public function within ($subject) {
            $this->normaliseComparisonSubject($subject);

            $subjectAddress = $subject->getNetworkAddress(self::ADDRESS_BINARY);
            $subjectMask = $subject->getMask(self::ADDRESS_BINARY);

            return $this->mask !== $subjectMask && ($this->mask | ($this->mask ^ $subjectMask)) === $this->mask && ($this->address & $subjectMask) === $subjectAddress;
        }
        public function equalTo ($subject) {
            $this->normaliseComparisonSubject($subject);

            return $this->address === $subject->getNetworkAddress(self::ADDRESS_BINARY) && $this->mask === $subject->getMask(self::ADDRESS_BINARY);
        }
        public function intersect ($subject) {
            $this->normaliseComparisonSubject($subject);

            return $this->equalTo($subject) || $this->contains($subject) || $this->within($subject);
        }

    }

In order to do what you desire, the class provides 4 methods:

contains()
within()
equalTo()
intersect()

Example usage of these:

// Also accepts dotted decimal mask. The mask may also be passed to the second
// argument. Any valid combination of dotted decimal, CIDR and integers will be
// accepted
$subnet = new IPv4Subnet('192.168.0.0/24');

// These methods will accept a string or another instance
var_dump($subnet->contains('192.168.0.1')); //TRUE
var_dump($subnet->contains('192.168.1.1')); //FALSE
var_dump($subnet->contains('192.168.0.0/16')); //FALSE
var_dump($subnet->within('192.168.0.0/16')); //TRUE
// ...hopefully you get the picture. intersect() returns TRUE if any of the
// other three match.

The class also implements the Iterator interface, allowing you to iterate over all the addresses in a subnet. The iterator excludes the network and broadcast addresses, which can be retrieved separately.

Example:

$subnet = new IPv4Subnet('192.168.0.0/28');
echo "Network: ", $subnet->getNetworkAddress(),
     "; Broadcast: ", $subnet->getBroadcastAddress(),
     "\nHosts:\n";
foreach ($subnet as $host) {
    echo $host, "\n";
}

The class also implements ArrayAccess, allowing you to treat it as an array:

$subnet = new IPv4Subnet('192.168.0.0/28');
echo $subnet['network'], "\n"; // 192.168.0.0
echo $subnet[0], "\n"; // 192.168.0.1
// ...
echo $subnet[13], "\n"; // 192.168.0.14
echo $subnet['broadcast'], "\n"; // 192.168.0.15

NB: The iterator/array methods of accessing the subnet's host addresses will return another IPv4Subnet object. The class implements __toString(), which will return the IP address as a dotted decimal if it represents a single address, or the CIDR if it represents more than one. The data can be accessed directly as a string or an integer by calling the relevant get*() method and passing the desired flag(s) (see constants defined at the top of the class).

All operations are 32- and 64-bit safe. Compatibility should be (although not thoroughly tested) 5.2+

See it working

---

For completeness, I imagine your use case would be implemented something along these lines:

public function addSubnet ($newSubnet) {
    $newSubnet = new IPv4Subnet($newSubnet);
    foreach ($this->subnets as &$existingSubnet) {
        if ($existingSubnet->contains($newSubnet)) {
            throw new Exception('Subnet already added');
        } else if ($existingSubnet->within($newSubnet)) {
            $existingSubnet = $newSubnet;
            return;
        }
    }
    $this->subnets[] = $newSubnet;
}

See it working