includes/IP.php

   1 <?php
   2 /**
   3  * Functions and constants to play with IP addresses and ranges
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License along
  16  * with this program; if not, write to the Free Software Foundation, Inc.,
  17  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  18  * http://www.gnu.org/copyleft/gpl.html
  19  *
  20  * @file
  21  * @author Ashar Voultoiz <hashar at free dot fr>, Aaron Schulz
  22  */
  23
  24 // Some regex definition to "play" with IP address and IP address blocks
  25
  26 // An IPv4 address is made of 4 bytes from x00 to xFF which is d0 to d255
  27 define( 'RE_IP_BYTE', '(25[0-5]|2[0-4][0-9]|1[0-9][0-9]|0?[0-9]?[0-9])' );
  28 define( 'RE_IP_ADD' , RE_IP_BYTE . '\.' . RE_IP_BYTE . '\.' . RE_IP_BYTE . '\.' . RE_IP_BYTE );
  29 // An IPv4 block is an IP address and a prefix (d1 to d32)
  30 define( 'RE_IP_PREFIX', '(3[0-2]|[12]?\d)' );
  31 define( 'RE_IP_BLOCK', RE_IP_ADD . '\/' . RE_IP_PREFIX );
  32
  33 // An IPv6 address is made up of 8 words (each x0000 to xFFFF).
  34 // However, the "::" abbreviation can be used on consecutive x0000 words.
  35 define( 'RE_IPV6_WORD', '([0-9A-Fa-f]{1,4})' );
  36 define( 'RE_IPV6_PREFIX', '(12[0-8]|1[01][0-9]|[1-9]?\d)');
  37 define( 'RE_IPV6_ADD',
  38         '(' . // starts with "::" (includes the address "::")
  39                 '(::|:(:' . RE_IPV6_WORD . '){1,7})' .
  40         '|' . // ends with "::" (not including the address "::")
  41                 RE_IPV6_WORD . '(:' . RE_IPV6_WORD . '){0,6}::' .
  42         '|' . // has no "::"
  43                 RE_IPV6_WORD . '(:' . RE_IPV6_WORD . '){7}' .
  44         '|' . // contains one "::" in the middle ("^" check always fails if no "::" found)
  45                 RE_IPV6_WORD . '(:(?P<abbr>(?(abbr)|:))?' . RE_IPV6_WORD . '){1,6}(?(abbr)|^)' .
  46         ')'
  47 );
  48 // An IPv6 block is an IP address and a prefix (d1 to d128)
  49 define( 'RE_IPV6_BLOCK', RE_IPV6_ADD . '\/' . RE_IPV6_PREFIX );
  50 // For IPv6 canonicalization (NOT for strict validation; these are quite lax!)
  51 define( 'RE_IPV6_GAP', ':(?:0+:)*(?::(?:0+:)*)?' );
  52 define( 'RE_IPV6_V4_PREFIX', '0*' . RE_IPV6_GAP . '(?:ffff:)?' );
  53
  54 // This might be useful for regexps used elsewhere, matches any IPv6 or IPv6 address or network
  55 define( 'IP_ADDRESS_STRING',
  56         '(?:' .
  57                 RE_IP_ADD . '(\/' . RE_IP_PREFIX . '|)' . // IPv4
  58         '|' .
  59                 RE_IPV6_ADD . '(\/' . RE_IPV6_PREFIX . '|)' . // IPv6
  60         ')'
  61 );
  62
  63 /**
  64  * A collection of public static functions to play with IP address
  65  * and IP blocks.
  66  */
  67 class IP {
  68         /**
  69          * Determine if a string is as valid IP address or network (CIDR prefix).
  70          * SIIT IPv4-translated addresses are rejected.
  71          * Note: canonicalize() tries to convert translated addresses to IPv4.
  72          *
  73          * @param $ip String: possible IP address
  74          * @return Boolean
  75          */
  76         public static function isIPAddress( $ip ) {
  77                 return (bool)preg_match( '/^' . IP_ADDRESS_STRING . '$/', $ip );
  78         }
  79
  80         /**
  81          * Given a string, determine if it as valid IP in IPv6 only.
  82          * Note: Unlike isValid(), this looks for networks too.
  83          *
  84          * @param $ip String: possible IP address
  85          * @return Boolean
  86          */
  87         public static function isIPv6( $ip ) {
  88                 return (bool)preg_match( '/^' . RE_IPV6_ADD . '(\/' . RE_IPV6_PREFIX . '|)$/', $ip );
  89         }
  90
  91         /**
  92          * Given a string, determine if it as valid IP in IPv4 only.
  93          * Note: Unlike isValid(), this looks for networks too.
  94          *
  95          * @param $ip String: possible IP address
  96          * @return Boolean
  97          */
  98         public static function isIPv4( $ip ) {
  99                 return (bool)preg_match( '/^' . RE_IP_ADD . '(\/' . RE_IP_PREFIX . '|)$/', $ip );
 100         }
 101
 102         /**
 103          * Validate an IP address. Ranges are NOT considered valid.
 104          * SIIT IPv4-translated addresses are rejected.
 105          * Note: canonicalize() tries to convert translated addresses to IPv4.
 106          *
 107          * @param $ip String
 108          * @return Boolean: True if it is valid.
 109          */
 110         public static function isValid( $ip ) {
 111                 return ( preg_match( '/^' . RE_IP_ADD . '$/', $ip )
 112                         || preg_match( '/^' . RE_IPV6_ADD . '$/', $ip ) );
 113         }
 114
 115         /**
 116          * Validate an IP Block (valid address WITH a valid prefix).
 117          * SIIT IPv4-translated addresses are rejected.
 118          * Note: canonicalize() tries to convert translated addresses to IPv4.
 119          *
 120          * @param $ipblock String
 121          * @return Boolean: True if it is valid.
 122          */
 123         public static function isValidBlock( $ipblock ) {
 124                 return ( preg_match( '/^' . RE_IPV6_BLOCK . '$/', $ipblock )
 125                         || preg_match( '/^' . RE_IP_BLOCK . '$/', $ipblock ) );
 126         }
 127
 128         /**
 129          * Convert an IP into a nice standard form.
 130          * IPv6 addresses in octet notation are expanded to 8 words.
 131          * IPv4 addresses are just trimmed.
 132          *
 133          * @param $ip String: IP address in quad or octet form (CIDR or not).
 134          * @return String
 135          */
 136         public static function sanitizeIP( $ip ) {
 137                 $ip = trim( $ip );
 138                 if ( $ip === '' ) {
 139                         return null;
 140                 }
 141                 if ( self::isIPv4( $ip ) || !self::isIPv6( $ip ) ) {
 142                         return $ip; // nothing else to do for IPv4 addresses or invalid ones
 143                 }
 144                 // Remove any whitespaces, convert to upper case
 145                 $ip = strtoupper( $ip );
 146                 // Expand zero abbreviations
 147                 $abbrevPos = strpos( $ip, '::' );
 148                 if ( $abbrevPos !== false ) {
 149                         // We know this is valid IPv6. Find the last index of the
 150                         // address before any CIDR number (e.g. "a:b:c::/24").
 151                         $CIDRStart = strpos( $ip, "/" );
 152                         $addressEnd = ( $CIDRStart !== false )
 153                                 ? $CIDRStart - 1
 154                                 : strlen( $ip ) - 1;
 155                         // If the '::' is at the beginning...
 156                         if ( $abbrevPos == 0 ) {
 157                                 $repeat = '0:';
 158                                 $extra = ( $ip == '::' ) ? '0' : ''; // for the address '::'
 159                                 $pad = 9; // 7+2 (due to '::')
 160                         // If the '::' is at the end...
 161                         } elseif ( $abbrevPos == ( $addressEnd - 1 ) ) {
 162                                 $repeat = ':0';
 163                                 $extra = '';
 164                                 $pad = 9; // 7+2 (due to '::')
 165                         // If the '::' is in the middle...
 166                         } else {
 167                                 $repeat = ':0';
 168                                 $extra = ':';
 169                                 $pad = 8; // 6+2 (due to '::')
 170                         }
 171                         $ip = str_replace( '::',
 172                                 str_repeat( $repeat, $pad - substr_count( $ip, ':' ) ) . $extra,
 173                                 $ip
 174                         );
 175                 }
 176                 // Remove leading zereos from each bloc as needed
 177                 $ip = preg_replace( '/(^|:)0+' . RE_IPV6_WORD . '/', '$1$2', $ip );
 178                 return $ip;
 179         }
 180
 181         /**
 182          * Given an unsigned integer, returns an IPv6 address in octet notation
 183          *
 184          * @param $ip_int String: IP address.
 185          * @return String
 186          */
 187         public static function toOctet( $ip_int ) {
 188                 return self::hexToOctet( wfBaseConvert( $ip_int, 10, 16, 32, false ) );
 189         }
 190
 191         /**
 192          * Convert an IPv4 or IPv6 hexadecimal representation back to readable format
 193          *
 194          * @param $hex String: number, with "v6-" prefix if it is IPv6
 195          * @return String: quad-dotted (IPv4) or octet notation (IPv6)
 196          */
 197         public static function formatHex( $hex ) {
 198                 if ( substr( $hex, 0, 3 ) == 'v6-' ) { // IPv6
 199                         return self::hexToOctet( substr( $hex, 3 ) );
 200                 } else { // IPv4
 201                         return self::hexToQuad( $hex );
 202                 }
 203         }
 204
 205         /**
 206          * Converts a hexadecimal number to an IPv6 address in octet notation
 207          *
 208          * @param $ip_hex String: pure hex (no v6- prefix)
 209          * @return String (of format a:b:c:d:e:f:g:h)
 210          */
 211         public static function hexToOctet( $ip_hex ) {
 212                 // Pad hex to 32 chars (128 bits)
 213                 $ip_hex = str_pad( strtoupper( $ip_hex ), 32, '0', STR_PAD_LEFT );
 214                 // Separate into 8 words
 215                 $ip_oct = substr( $ip_hex, 0, 4 );
 216                 for ( $n = 1; $n < 8; $n++ ) {
 217                         $ip_oct .= ':' . substr( $ip_hex, 4 * $n, 4 );
 218                 }
 219                 // NO leading zeroes
 220                 $ip_oct = preg_replace( '/(^|:)0+' . RE_IPV6_WORD . '/', '$1$2', $ip_oct );
 221                 return $ip_oct;
 222         }
 223
 224         /**
 225          * Converts a hexadecimal number to an IPv4 address in quad-dotted notation
 226          *
 227          * @param $ip_hex String: pure hex
 228          * @return String (of format a.b.c.d)
 229          */
 230         public static function hexToQuad( $ip_hex ) {
 231                 // Pad hex to 8 chars (32 bits)
 232                 $ip_hex = str_pad( strtoupper( $ip_hex ), 8, '0', STR_PAD_LEFT );
 233                 // Separate into four quads
 234                 $s = '';
 235                 for ( $i = 0; $i < 4; $i++ ) {
 236                         if ( $s !== '' ) {
 237                                 $s .= '.';
 238                         }
 239                         $s .= base_convert( substr( $ip_hex, $i * 2, 2 ), 16, 10 );
 240                 }
 241                 return $s;
 242         }
 243
 244         /**
 245          * Determine if an IP address really is an IP address, and if it is public,
 246          * i.e. not RFC 1918 or similar
 247          * Comes from ProxyTools.php
 248          *
 249          * @param $ip String
 250          * @return Boolean
 251          */
 252         public static function isPublic( $ip ) {
 253                 if ( self::isIPv6( $ip ) ) {
 254                         return self::isPublic6( $ip );
 255                 }
 256                 $n = self::toUnsigned( $ip );
 257                 if ( !$n ) {
 258                         return false;
 259                 }
 260
 261                 // ip2long accepts incomplete addresses, as well as some addresses
 262                 // followed by garbage characters. Check that it's really valid.
 263                 if ( $ip != long2ip( $n ) ) {
 264                         return false;
 265                 }
 266
 267                 static $privateRanges = false;
 268                 if ( !$privateRanges ) {
 269                         $privateRanges = array(
 270                                 array( '10.0.0.0',    '10.255.255.255' ),   # RFC 1918 (private)
 271                                 array( '172.16.0.0',  '172.31.255.255' ),   #     "
 272                                 array( '192.168.0.0', '192.168.255.255' ),  #     "
 273                                 array( '0.0.0.0',     '0.255.255.255' ),    # this network
 274                                 array( '127.0.0.0',   '127.255.255.255' ),  # loopback
 275                         );
 276                 }
 277
 278                 foreach ( $privateRanges as $r ) {
 279                         $start = self::toUnsigned( $r[0] );
 280                         $end = self::toUnsigned( $r[1] );
 281                         if ( $n >= $start && $n <= $end ) {
 282                                 return false;
 283                         }
 284                 }
 285                 return true;
 286         }
 287
 288         /**
 289          * Determine if an IPv6 address really is an IP address, and if it is public,
 290          * i.e. not RFC 4193 or similar
 291          *
 292          * @param $ip String
 293          * @return Boolean
 294          */
 295         private static function isPublic6( $ip ) {
 296                 static $privateRanges = false;
 297                 if ( !$privateRanges ) {
 298                         $privateRanges = array(
 299                                 array( 'fc::', 'fdff:ffff:ffff:ffff:ffff:ffff:ffff:ffff' ), # RFC 4193 (local)
 300                                 array( '0:0:0:0:0:0:0:1', '0:0:0:0:0:0:0:1' ), # loopback
 301                         );
 302                 }
 303                 $n = self::toHex( $ip );
 304                 foreach ( $privateRanges as $r ) {
 305                         $start = self::toHex( $r[0] );
 306                         $end = self::toHex( $r[1] );
 307                         if ( $n >= $start && $n <= $end ) {
 308                                 return false;
 309                         }
 310                 }
 311                 return true;
 312         }
 313
 314         /**
 315          * Return a zero-padded upper case hexadecimal representation of an IP address.
 316          *
 317          * Hexadecimal addresses are used because they can easily be extended to
 318          * IPv6 support. To separate the ranges, the return value from this
 319          * function for an IPv6 address will be prefixed with "v6-", a non-
 320          * hexadecimal string which sorts after the IPv4 addresses.
 321          *
 322          * @param $ip String: quad dotted/octet IP address.
 323          * @return String
 324          */
 325         public static function toHex( $ip ) {
 326                 if ( self::isIPv6( $ip ) ) {
 327                         $n = 'v6-' . self::IPv6ToRawHex( $ip );
 328                 } else {
 329                         $n = self::toUnsigned( $ip );
 330                         if ( $n !== false ) {
 331                                 $n = wfBaseConvert( $n, 10, 16, 8, false );
 332                         }
 333                 }
 334                 return $n;
 335         }
 336
 337         /**
 338          * Given an IPv6 address in octet notation, returns a pure hex string.
 339          *
 340          * @param $ip String: octet ipv6 IP address.
 341          * @return String: pure hex (uppercase)
 342          */
 343         private static function IPv6ToRawHex( $ip ) {
 344                 $ip = self::sanitizeIP( $ip );
 345                 if ( !$ip ) {
 346                         return null;
 347                 }
 348                 $r_ip = '';
 349                 foreach ( explode( ':', $ip ) as $v ) {
 350                         $r_ip .= str_pad( $v, 4, 0, STR_PAD_LEFT );
 351                 }
 352                 return $r_ip;
 353         }
 354
 355         /**
 356          * Given an IP address in dotted-quad/octet notation, returns an unsigned integer.
 357          * Like ip2long() except that it actually works and has a consistent error return value.
 358          * Comes from ProxyTools.php
 359          *
 360          * @param $ip String: quad dotted IP address.
 361          * @return Mixed: string/int/false
 362          */
 363         public static function toUnsigned( $ip ) {
 364                 if ( self::isIPv6( $ip ) ) {
 365                         $n = self::toUnsigned6( $ip );
 366                 } else {
 367                         $n = ip2long( $ip );
 368                         if ( $n < 0 ) {
 369                                 $n += pow( 2, 32 );
 370                         }
 371                 }
 372                 return $n;
 373         }
 374
 375         private static function toUnsigned6( $ip ) {
 376                 return wfBaseConvert( self::IPv6ToRawHex( $ip ), 16, 10 );
 377         }
 378
 379         /**
 380          * Convert a network specification in CIDR notation
 381          * to an integer network and a number of bits
 382          *
 383          * @param $range String: IP with CIDR prefix
 384          * @return array(int or string, int)
 385          */
 386         public static function parseCIDR( $range ) {
 387                 if ( self::isIPv6( $range ) ) {
 388                         return self::parseCIDR6( $range );
 389                 }
 390                 $parts = explode( '/', $range, 2 );
 391                 if ( count( $parts ) != 2 ) {
 392                         return array( false, false );
 393                 }
 394                 list( $network, $bits ) = $parts;
 395                 $network = ip2long( $network );
 396                 if ( $network !== false && is_numeric( $bits ) && $bits >= 0 && $bits <= 32 ) {
 397                         if ( $bits == 0 ) {
 398                                 $network = 0;
 399                         } else {
 400                                 $network &= ~( ( 1 << ( 32 - $bits ) ) - 1);
 401                         }
 402                         # Convert to unsigned
 403                         if ( $network < 0 ) {
 404                                 $network += pow( 2, 32 );
 405                         }
 406                 } else {
 407                         $network = false;
 408                         $bits = false;
 409                 }
 410                 return array( $network, $bits );
 411         }
 412
 413         /**
 414          * Given a string range in a number of formats,
 415          * return the start and end of the range in hexadecimal.
 416          *
 417          * Formats are:
 418          *     1.2.3.4/24          CIDR
 419          *     1.2.3.4 - 1.2.3.5   Explicit range
 420          *     1.2.3.4             Single IP
 421          *
 422          *     2001:0db8:85a3::7344/96                                   CIDR
 423          *     2001:0db8:85a3::7344 - 2001:0db8:85a3::7344   Explicit range
 424          *     2001:0db8:85a3::7344                                      Single IP
 425          * @param $range String: IP range
 426          * @return array(string, string)
 427          */
 428         public static function parseRange( $range ) {
 429                 // CIDR notation
 430                 if ( strpos( $range, '/' ) !== false ) {
 431                         if ( self::isIPv6( $range ) ) {
 432                                 return self::parseRange6( $range );
 433                         }
 434                         list( $network, $bits ) = self::parseCIDR( $range );
 435                         if ( $network === false ) {
 436                                 $start = $end = false;
 437                         } else {
 438                                 $start = sprintf( '%08X', $network );
 439                                 $end = sprintf( '%08X', $network + pow( 2, ( 32 - $bits ) ) - 1 );
 440                         }
 441                 // Explicit range
 442                 } elseif ( strpos( $range, '-' ) !== false ) {
 443                         list( $start, $end ) = array_map( 'trim', explode( '-', $range, 2 ) );
 444                         if ( self::isIPv6( $start ) && self::isIPv6( $end ) ) {
 445                                 return self::parseRange6( $range );
 446                         }
 447                         if ( self::isIPv4( $start ) && self::isIPv4( $end ) ) {
 448                                 $start = self::toUnsigned( $start );
 449                                 $end = self::toUnsigned( $end );
 450                                 if ( $start > $end ) {
 451                                         $start = $end = false;
 452                                 } else {
 453                                         $start = sprintf( '%08X', $start );
 454                                         $end = sprintf( '%08X', $end );
 455                                 }
 456                         } else {
 457                                 $start = $end = false;
 458                         }
 459                 } else {
 460                         # Single IP
 461                         $start = $end = self::toHex( $range );
 462                 }
 463                 if ( $start === false || $end === false ) {
 464                         return array( false, false );
 465                 } else {
 466                         return array( $start, $end );
 467                 }
 468         }
 469
 470         /**
 471          * Convert a network specification in IPv6 CIDR notation to an
 472          * integer network and a number of bits
 473          *
 474          * @return array(string, int)
 475          */
 476         private static function parseCIDR6( $range ) {
 477                 # Explode into <expanded IP,range>
 478                 $parts = explode( '/', IP::sanitizeIP( $range ), 2 );
 479                 if ( count( $parts ) != 2 ) {
 480                         return array( false, false );
 481                 }
 482                 list( $network, $bits ) = $parts;
 483                 $network = self::IPv6ToRawHex( $network );
 484                 if ( $network !== false && is_numeric( $bits ) && $bits >= 0 && $bits <= 128 ) {
 485                         if ( $bits == 0 ) {
 486                                 $network = "0";
 487                         } else {
 488                                 # Native 32 bit functions WONT work here!!!
 489                                 # Convert to a padded binary number
 490                                 $network = wfBaseConvert( $network, 16, 2, 128 );
 491                                 # Truncate the last (128-$bits) bits and replace them with zeros
 492                                 $network = str_pad( substr( $network, 0, $bits ), 128, 0, STR_PAD_RIGHT );
 493                                 # Convert back to an integer
 494                                 $network = wfBaseConvert( $network, 2, 10 );
 495                         }
 496                 } else {
 497                         $network = false;
 498                         $bits = false;
 499                 }
 500                 return array( $network, (int)$bits );
 501         }
 502
 503         /**
 504          * Given a string range in a number of formats, return the
 505          * start and end of the range in hexadecimal. For IPv6.
 506          *
 507          * Formats are:
 508          *     2001:0db8:85a3::7344/96                                   CIDR
 509          *     2001:0db8:85a3::7344 - 2001:0db8:85a3::7344   Explicit range
 510          *     2001:0db8:85a3::7344/96                                   Single IP
 511          * @return array(string, string)
 512          */
 513         private static function parseRange6( $range ) {
 514                 # Expand any IPv6 IP
 515                 $range = IP::sanitizeIP( $range );
 516                 // CIDR notation...
 517                 if ( strpos( $range, '/' ) !== false ) {
 518                         list( $network, $bits ) = self::parseCIDR6( $range );
 519                         if ( $network === false ) {
 520                                 $start = $end = false;
 521                         } else {
 522                                 $start = wfBaseConvert( $network, 10, 16, 32, false );
 523                                 # Turn network to binary (again)
 524                                 $end = wfBaseConvert( $network, 10, 2, 128 );
 525                                 # Truncate the last (128-$bits) bits and replace them with ones
 526                                 $end = str_pad( substr( $end, 0, $bits ), 128, 1, STR_PAD_RIGHT );
 527                                 # Convert to hex
 528                                 $end = wfBaseConvert( $end, 2, 16, 32, false );
 529                                 # see toHex() comment
 530                                 $start = "v6-$start";
 531                                 $end = "v6-$end";
 532                         }
 533                 // Explicit range notation...
 534                 } elseif ( strpos( $range, '-' ) !== false ) {
 535                         list( $start, $end ) = array_map( 'trim', explode( '-', $range, 2 ) );
 536                         $start = self::toUnsigned6( $start );
 537                         $end = self::toUnsigned6( $end );
 538                         if ( $start > $end ) {
 539                                 $start = $end = false;
 540                         } else {
 541                                 $start = wfBaseConvert( $start, 10, 16, 32, false );
 542                                 $end = wfBaseConvert( $end, 10, 16, 32, false );
 543                         }
 544                         # see toHex() comment
 545                         $start = "v6-$start";
 546                         $end = "v6-$end";
 547                 } else {
 548                         # Single IP
 549                         $start = $end = self::toHex( $range );
 550                 }
 551                 if ( $start === false || $end === false ) {
 552                         return array( false, false );
 553                 } else {
 554                         return array( $start, $end );
 555                 }
 556         }
 557
 558         /**
 559          * Determine if a given IPv4/IPv6 address is in a given CIDR network
 560          *
 561          * @param $addr String: the address to check against the given range.
 562          * @param $range String: the range to check the given address against.
 563          * @return Boolean: whether or not the given address is in the given range.
 564          */
 565         public static function isInRange( $addr, $range ) {
 566                 $hexIP = self::toHex( $addr );
 567                 list( $start, $end ) = self::parseRange( $range );
 568                 return ( strcmp( $hexIP, $start ) >= 0 &&
 569                         strcmp( $hexIP, $end ) <= 0 );
 570         }
 571
 572         /**
 573          * Convert some unusual representations of IPv4 addresses to their
 574          * canonical dotted quad representation.
 575          *
 576          * This currently only checks a few IPV4-to-IPv6 related cases.  More
 577          * unusual representations may be added later.
 578          *
 579          * @param $addr String: something that might be an IP address
 580          * @return String: valid dotted quad IPv4 address or null
 581          */
 582         public static function canonicalize( $addr ) {
 583                 if ( self::isValid( $addr ) ) {
 584                         return $addr;
 585                 }
 586                 // Turn mapped addresses from ::ce:ffff:1.2.3.4 to 1.2.3.4
 587                 if ( strpos( $addr, ':' ) !== false && strpos( $addr, '.' ) !== false ) {
 588                         $addr = substr( $addr, strrpos( $addr, ':' ) + 1 );
 589                         if ( self::isIPv4( $addr ) ) {
 590                                 return $addr;
 591                         }
 592                 }
 593                 // IPv6 loopback address
 594                 $m = array();
 595                 if ( preg_match( '/^0*' . RE_IPV6_GAP . '1$/', $addr, $m ) ) {
 596                         return '127.0.0.1';
 597                 }
 598                 // IPv4-mapped and IPv4-compatible IPv6 addresses
 599                 if ( preg_match( '/^' . RE_IPV6_V4_PREFIX . '(' . RE_IP_ADD . ')$/i', $addr, $m ) ) {
 600                         return $m[1];
 601                 }
 602                 if ( preg_match( '/^' . RE_IPV6_V4_PREFIX . RE_IPV6_WORD .
 603                         ':' . RE_IPV6_WORD . '$/i', $addr, $m ) )
 604                 {
 605                         return long2ip( ( hexdec( $m[1] ) << 16 ) + hexdec( $m[2] ) );
 606                 }
 607
 608                 return null;  // give up
 609         }
 610 }