includes/utils/UIDGenerator.php

   1 <?php
   2 /**
   3  * This file deals with UID generation.
   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 Aaron Schulz
  22  */
  23
  24 /**
  25  * Class for getting statistically unique IDs
  26  *
  27  * @since 1.21
  28  */
  29 class UIDGenerator {
  30         /** @var UIDGenerator */
  31         protected static $instance = null;
  32
  33         protected $nodeId32; // string; node ID in binary (32 bits)
  34         protected $nodeId48; // string; node ID in binary (48 bits)
  35
  36         protected $lockFile88; // string; local file path
  37         protected $lockFile128; // string; local file path
  38
  39         /** @var Array */
  40         protected $fileHandles = array(); // cache file handles
  41
  42         const QUICK_RAND = 1; // get randomness from fast and insecure sources
  43
  44         protected function __construct() {
  45                 $idFile = wfTempDir() . '/mw-' . __CLASS__ . '-UID-nodeid';
  46                 $nodeId = is_file( $idFile ) ? file_get_contents( $idFile ) : '';
  47                 // Try to get some ID that uniquely identifies this machine (RFC 4122)...
  48                 if ( !preg_match( '/^[0-9a-f]{12}$/i', $nodeId ) ) {
  49                         wfSuppressWarnings();
  50                         if ( wfIsWindows() ) {
  51                                 // http://technet.microsoft.com/en-us/library/bb490913.aspx
  52                                 $csv = trim( wfShellExec( 'getmac /NH /FO CSV' ) );
  53                                 $line = substr( $csv, 0, strcspn( $csv, "\n" ) );
  54                                 $info = str_getcsv( $line );
  55                                 $nodeId = isset( $info[0] ) ? str_replace( '-', '', $info[0] ) : '';
  56                         } elseif ( is_executable( '/sbin/ifconfig' ) ) { // Linux/BSD/Solaris/OS X
  57                                 // See http://linux.die.net/man/8/ifconfig
  58                                 $m = array();
  59                                 preg_match( '/\s([0-9a-f]{2}(:[0-9a-f]{2}){5})\s/',
  60                                         wfShellExec( '/sbin/ifconfig -a' ), $m );
  61                                 $nodeId = isset( $m[1] ) ? str_replace( ':', '', $m[1] ) : '';
  62                         }
  63                         wfRestoreWarnings();
  64                         if ( !preg_match( '/^[0-9a-f]{12}$/i', $nodeId ) ) {
  65                                 $nodeId = MWCryptRand::generateHex( 12, true );
  66                                 $nodeId[1] = dechex( hexdec( $nodeId[1] ) | 0x1 ); // set multicast bit
  67                         }
  68                         file_put_contents( $idFile, $nodeId ); // cache
  69                 }
  70                 $this->nodeId32 = wfBaseConvert( substr( sha1( $nodeId ), 0, 8 ), 16, 2, 32 );
  71                 $this->nodeId48 = wfBaseConvert( $nodeId, 16, 2, 48 );
  72                 // If different processes run as different users, they may have different temp dirs.
  73                 // This is dealt with by initializing the clock sequence number and counters randomly.
  74                 $this->lockFile88 = wfTempDir() . '/mw-' . __CLASS__ . '-UID-88';
  75                 $this->lockFile128 = wfTempDir() . '/mw-' . __CLASS__ . '-UID-128';
  76         }
  77
  78         /**
  79          * @return UIDGenerator
  80          */
  81         protected static function singleton() {
  82                 if ( self::$instance === null ) {
  83                         self::$instance = new self();
  84                 }
  85
  86                 return self::$instance;
  87         }
  88
  89         /**
  90          * Get a statistically unique 88-bit unsigned integer ID string.
  91          * The bits of the UID are prefixed with the time (down to the millisecond).
  92          *
  93          * These IDs are suitable as values for the shard key of distributed data.
  94          * If a column uses these as values, it should be declared UNIQUE to handle collisions.
  95          * New rows almost always have higher UIDs, which makes B-TREE updates on INSERT fast.
  96          * They can also be stored "DECIMAL(27) UNSIGNED" or BINARY(11) in MySQL.
  97          *
  98          * UID generation is serialized on each server (as the node ID is for the whole machine).
  99          *
 100          * @param $base integer Specifies a base other than 10
 101          * @return string Number
 102          * @throws MWException
 103          */
 104         public static function newTimestampedUID88( $base = 10 ) {
 105                 if ( !is_integer( $base ) || $base > 36 || $base < 2 ) {
 106                         throw new MWException( "Base must an integer be between 2 and 36" );
 107                 }
 108                 $gen = self::singleton();
 109                 $time = $gen->getTimestampAndDelay( 'lockFile88', 1, 1024 );
 110
 111                 return wfBaseConvert( $gen->getTimestampedID88( $time ), 2, $base );
 112         }
 113
 114         /**
 115          * @param array $time (UIDGenerator::millitime(), clock sequence)
 116          * @return string 88 bits
 117          */
 118         protected function getTimestampedID88( array $info ) {
 119                 list( $time, $counter ) = $info;
 120                 // Take the 46 MSBs of "milliseconds since epoch"
 121                 $id_bin = $this->millisecondsSinceEpochBinary( $time );
 122                 // Add a 10 bit counter resulting in 56 bits total
 123                 $id_bin .= str_pad( decbin( $counter ), 10, '0', STR_PAD_LEFT );
 124                 // Add the 32 bit node ID resulting in 88 bits total
 125                 $id_bin .= $this->nodeId32;
 126                 // Convert to a 1-27 digit integer string
 127                 if ( strlen( $id_bin ) !== 88 ) {
 128                         throw new MWException( "Detected overflow for millisecond timestamp." );
 129                 }
 130
 131                 return $id_bin;
 132         }
 133
 134         /**
 135          * Get a statistically unique 128-bit unsigned integer ID string.
 136          * The bits of the UID are prefixed with the time (down to the millisecond).
 137          *
 138          * These IDs are suitable as globally unique IDs, without any enforced uniqueness.
 139          * New rows almost always have higher UIDs, which makes B-TREE updates on INSERT fast.
 140          * They can also be stored as "DECIMAL(39) UNSIGNED" or BINARY(16) in MySQL.
 141          *
 142          * UID generation is serialized on each server (as the node ID is for the whole machine).
 143          *
 144          * @param $base integer Specifies a base other than 10
 145          * @return string Number
 146          * @throws MWException
 147          */
 148         public static function newTimestampedUID128( $base = 10 ) {
 149                 if ( !is_integer( $base ) || $base > 36 || $base < 2 ) {
 150                         throw new MWException( "Base must be an integer between 2 and 36" );
 151                 }
 152                 $gen = self::singleton();
 153                 $time = $gen->getTimestampAndDelay( 'lockFile128', 16384, 1048576 );
 154
 155                 return wfBaseConvert( $gen->getTimestampedID128( $time ), 2, $base );
 156         }
 157
 158         /**
 159          * @param array $info (UIDGenerator::millitime(), counter, clock sequence)
 160          * @return string 128 bits
 161          */
 162         protected function getTimestampedID128( array $info ) {
 163                 list( $time, $counter, $clkSeq ) = $info;
 164                 // Take the 46 MSBs of "milliseconds since epoch"
 165                 $id_bin = $this->millisecondsSinceEpochBinary( $time );
 166                 // Add a 20 bit counter resulting in 66 bits total
 167                 $id_bin .= str_pad( decbin( $counter ), 20, '0', STR_PAD_LEFT );
 168                 // Add a 14 bit clock sequence number resulting in 80 bits total
 169                 $id_bin .= str_pad( decbin( $clkSeq ), 14, '0', STR_PAD_LEFT );
 170                 // Add the 48 bit node ID resulting in 128 bits total
 171                 $id_bin .= $this->nodeId48;
 172                 // Convert to a 1-39 digit integer string
 173                 if ( strlen( $id_bin ) !== 128 ) {
 174                         throw new MWException( "Detected overflow for millisecond timestamp." );
 175                 }
 176
 177                 return $id_bin;
 178         }
 179
 180         /**
 181          * Return an RFC4122 compliant v4 UUID
 182          *
 183          * @param $flags integer Bitfield (supports UIDGenerator::QUICK_RAND)
 184          * @return string
 185          * @throws MWException
 186          */
 187         public static function newUUIDv4( $flags = 0 ) {
 188                 $hex = ( $flags & self::QUICK_RAND )
 189                         ? wfRandomString( 31 )
 190                         : MWCryptRand::generateHex( 31 );
 191
 192                 return sprintf( '%s-%s-%s-%s-%s',
 193                         // "time_low" (32 bits)
 194                         substr( $hex, 0, 8 ),
 195                         // "time_mid" (16 bits)
 196                         substr( $hex, 8, 4 ),
 197                         // "time_hi_and_version" (16 bits)
 198                         '4' . substr( $hex, 12, 3 ),
 199                         // "clk_seq_hi_res (8 bits, variant is binary 10x) and "clk_seq_low" (8 bits)
 200                         dechex( 0x8 | ( hexdec( $hex[15] ) & 0x3 ) ) . $hex[16] . substr( $hex, 17, 2 ),
 201                         // "node" (48 bits)
 202                         substr( $hex, 19, 12 )
 203                 );
 204         }
 205
 206         /**
 207          * Return an RFC4122 compliant v4 UUID
 208          *
 209          * @param $flags integer Bitfield (supports UIDGenerator::QUICK_RAND)
 210          * @return string 32 hex characters with no hyphens
 211          * @throws MWException
 212          */
 213         public static function newRawUUIDv4( $flags = 0 ) {
 214                 return str_replace( '-', '', self::newUUIDv4( $flags ) );
 215         }
 216
 217         /**
 218          * Get a (time,counter,clock sequence) where (time,counter) is higher
 219          * than any previous (time,counter) value for the given clock sequence.
 220          * This is useful for making UIDs sequential on a per-node bases.
 221          *
 222          * @param string $lockFile Name of a local lock file
 223          * @param $clockSeqSize integer The number of possible clock sequence values
 224          * @param $counterSize integer The number of possible counter values
 225          * @return Array (result of UIDGenerator::millitime(), counter, clock sequence)
 226          * @throws MWException
 227          */
 228         protected function getTimestampAndDelay( $lockFile, $clockSeqSize, $counterSize ) {
 229                 // Get the UID lock file handle
 230                 if ( isset( $this->fileHandles[$lockFile] ) ) {
 231                         $handle = $this->fileHandles[$lockFile];
 232                 } else {
 233                         $handle = fopen( $this->$lockFile, 'cb+' );
 234                         $this->fileHandles[$lockFile] = $handle ?: null; // cache
 235                 }
 236                 // Acquire the UID lock file
 237                 if ( $handle === false ) {
 238                         throw new MWException( "Could not open '{$this->$lockFile}'." );
 239                 } elseif ( !flock( $handle, LOCK_EX ) ) {
 240                         throw new MWException( "Could not acquire '{$this->$lockFile}'." );
 241                 }
 242                 // Get the current timestamp, clock sequence number, last time, and counter
 243                 rewind( $handle );
 244                 $data = explode( ' ', fgets( $handle ) ); // "<clk seq> <sec> <msec> <counter> <offset>"
 245                 $clockChanged = false; // clock set back significantly?
 246                 if ( count( $data ) == 5 ) { // last UID info already initialized
 247                         $clkSeq = (int)$data[0] % $clockSeqSize;
 248                         $prevTime = array( (int)$data[1], (int)$data[2] );
 249                         $offset = (int)$data[4] % $counterSize; // random counter offset
 250                         $counter = 0; // counter for UIDs with the same timestamp
 251                         // Delay until the clock reaches the time of the last ID.
 252                         // This detects any microtime() drift among processes.
 253                         $time = $this->timeWaitUntil( $prevTime );
 254                         if ( !$time ) { // too long to delay?
 255                                 $clockChanged = true; // bump clock sequence number
 256                                 $time = self::millitime();
 257                         } elseif ( $time == $prevTime ) {
 258                                 // Bump the counter if there are timestamp collisions
 259                                 $counter = (int)$data[3] % $counterSize;
 260                                 if ( ++$counter >= $counterSize ) { // sanity (starts at 0)
 261                                         flock( $handle, LOCK_UN ); // abort
 262                                         throw new MWException( "Counter overflow for timestamp value." );
 263                                 }
 264                         }
 265                 } else { // last UID info not initialized
 266                         $clkSeq = mt_rand( 0, $clockSeqSize - 1 );
 267                         $counter = 0;
 268                         $offset = mt_rand( 0, $counterSize - 1 );
 269                         $time = self::millitime();
 270                 }
 271                 // microtime() and gettimeofday() can drift from time() at least on Windows.
 272                 // The drift is immediate for processes running while the system clock changes.
 273                 // time() does not have this problem. See https://bugs.php.net/bug.php?id=42659.
 274                 if ( abs( time() - $time[0] ) >= 2 ) {
 275                         // We don't want processes using too high or low timestamps to avoid duplicate
 276                         // UIDs and clock sequence number churn. This process should just be restarted.
 277                         flock( $handle, LOCK_UN ); // abort
 278                         throw new MWException( "Process clock is outdated or drifted." );
 279                 }
 280                 // If microtime() is synced and a clock change was detected, then the clock went back
 281                 if ( $clockChanged ) {
 282                         // Bump the clock sequence number and also randomize the counter offset,
 283                         // which is useful for UIDs that do not include the clock sequence number.
 284                         $clkSeq = ( $clkSeq + 1 ) % $clockSeqSize;
 285                         $offset = mt_rand( 0, $counterSize - 1 );
 286                         trigger_error( "Clock was set back; sequence number incremented." );
 287                 }
 288                 // Update the (clock sequence number, timestamp, counter)
 289                 ftruncate( $handle, 0 );
 290                 rewind( $handle );
 291                 fwrite( $handle, "{$clkSeq} {$time[0]} {$time[1]} {$counter} {$offset}" );
 292                 fflush( $handle );
 293                 // Release the UID lock file
 294                 flock( $handle, LOCK_UN );
 295
 296                 return array( $time, ( $counter + $offset ) % $counterSize, $clkSeq );
 297         }
 298
 299         /**
 300          * Wait till the current timestamp reaches $time and return the current
 301          * timestamp. This returns false if it would have to wait more than 10ms.
 302          *
 303          * @param array $time Result of UIDGenerator::millitime()
 304          * @return Array|bool UIDGenerator::millitime() result or false
 305          */
 306         protected function timeWaitUntil( array $time ) {
 307                 do {
 308                         $ct = self::millitime();
 309                         if ( $ct >= $time ) { // http://php.net/manual/en/language.operators.comparison.php
 310                                 return $ct; // current timestamp is higher than $time
 311                         }
 312                 } while ( ( ( $time[0] - $ct[0] ) * 1000 + ( $time[1] - $ct[1] ) ) <= 10 );
 313
 314                 return false;
 315         }
 316
 317         /**
 318          * @param array $time Result of UIDGenerator::millitime()
 319          * @return string 46 MSBs of "milliseconds since epoch" in binary (rolls over in 4201)
 320          */
 321         protected function millisecondsSinceEpochBinary( array $time ) {
 322                 list( $sec, $msec ) = $time;
 323                 $ts = 1000 * $sec + $msec;
 324                 if ( $ts > pow( 2, 52 ) ) {
 325                         throw new MWException( __METHOD__ .
 326                                 ': sorry, this function doesn\'t work after the year 144680' );
 327                 }
 328
 329                 return substr( wfBaseConvert( $ts, 10, 2, 46 ), -46 );
 330         }
 331
 332         /**
 333          * @return Array (current time in seconds, milliseconds since then)
 334          */
 335         protected static function millitime() {
 336                 list( $msec, $sec ) = explode( ' ', microtime() );
 337
 338                 return array( (int)$sec, (int)( $msec * 1000 ) );
 339         }
 340
 341         function __destruct() {
 342                 array_map( 'fclose', $this->fileHandles );
 343         }
 344 }