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<?php /** * Efficient concatenated text storage. * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation; either version 2 of the License, or * (at your option) any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License along * with this program; if not, write to the Free Software Foundation, Inc., * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. * http://www.gnu.org/copyleft/gpl.html * * @file */ /** * Diff-based history compression * Requires xdiff and zlib * * WARNING: Objects of this class are serialized and permanently stored in the DB. * Do not change the name or visibility of any property! */ class DiffHistoryBlob implements HistoryBlob { /** @var string[] Uncompressed item cache */ public $mItems = []; /** @var int Total uncompressed size */ public $mSize = 0; /** * @var array|null Array of diffs. If a diff D from A to B is notated D = B - A, * and Z is an empty string: * * { item[map[i]] - item[map[i-1]] where i > 0 * diff[i] = { * { item[map[i]] - Z where i = 0 */ public $mDiffs; /** @var array The diff map, see above */ public $mDiffMap; /** @var string The key for getText() */ public $mDefaultKey; /** @var string|null Compressed storage */ public $mCompressed; /** @var bool True if the object is locked against further writes */ public $mFrozen = false; /** * @var int The maximum uncompressed size before the object becomes sad * Should be less than max_allowed_packet */ public $mMaxSize = 10_000_000; /** @var int The maximum number of text items before the object becomes sad */ public $mMaxCount = 100; /** Constants from xdiff.h */ private const XDL_BDOP_INS = 1; private const XDL_BDOP_CPY = 2; private const XDL_BDOP_INSB = 3; public function __construct() { if ( !function_exists( 'gzdeflate' ) ) { throw new RuntimeException( "Need zlib support to read or write DiffHistoryBlob\n" ); } } /** * @param string $text * @return string */ public function addItem( $text ) { if ( $this->mFrozen ) { throw new BadMethodCallException( __METHOD__ . ": Cannot add more items after sleep/wakeup" ); } $this->mItems[] = $text; $this->mSize += strlen( $text ); $this->mDiffs = null; // later return (string)( count( $this->mItems ) - 1 ); } /** * @param string $key * @return string */ public function getItem( $key ) { return $this->mItems[(int)$key]; } /** * @param string $text */ public function setText( $text ) { $this->mDefaultKey = $this->addItem( $text ); } /** * @return string */ public function getText() { return $this->getItem( $this->mDefaultKey ); } private function compress() { if ( !function_exists( 'xdiff_string_rabdiff' ) ) { throw new RuntimeException( "Need xdiff support to write DiffHistoryBlob\n" ); } if ( isset( $this->mDiffs ) ) { // Already compressed return; } if ( $this->mItems === [] ) { return; } // Create two diff sequences: one for main text and one for small text $sequences = [ 'small' => [ 'tail' => '', 'diffs' => [], 'map' => [], ], 'main' => [ 'tail' => '', 'diffs' => [], 'map' => [], ], ]; $smallFactor = 0.5; $mItemsCount = count( $this->mItems ); for ( $i = 0; $i < $mItemsCount; $i++ ) { $text = $this->mItems[$i]; if ( $i == 0 ) { $seqName = 'main'; } else { $mainTail = $sequences['main']['tail']; if ( strlen( $text ) < strlen( $mainTail ) * $smallFactor ) { $seqName = 'small'; } else { $seqName = 'main'; } } $tail = $sequences[$seqName]['tail']; $diff = $this->diff( $tail, $text ); $sequences[$seqName]['diffs'][] = $diff; $sequences[$seqName]['map'][] = $i; $sequences[$seqName]['tail'] = $text; } // Knit the sequences together $tail = ''; $this->mDiffs = []; $this->mDiffMap = []; foreach ( $sequences as $seq ) { if ( $seq['diffs'] === [] ) { continue; } if ( $tail === '' ) { $this->mDiffs[] = $seq['diffs'][0]; } else { $head = $this->patch( '', $seq['diffs'][0] ); $this->mDiffs[] = $this->diff( $tail, $head ); } $this->mDiffMap[] = $seq['map'][0]; $diffsCount = count( $seq['diffs'] ); for ( $i = 1; $i < $diffsCount; $i++ ) { $this->mDiffs[] = $seq['diffs'][$i]; $this->mDiffMap[] = $seq['map'][$i]; } $tail = $seq['tail']; } } /** * @param string $t1 * @param string $t2 * @return string */ private function diff( $t1, $t2 ) { return xdiff_string_rabdiff( $t1, $t2 ); } /** * @param string $base * @param string $diff * @return bool|string */ private function patch( $base, $diff ) { if ( function_exists( 'xdiff_string_bpatch' ) ) { return xdiff_string_bpatch( $base, $diff ); } # Pure PHP implementation $header = unpack( 'Vofp/Vcsize', substr( $diff, 0, 8 ) ); # Check the checksum $ofp = $this->xdiffAdler32( $base ); if ( $ofp !== substr( $diff, 0, 4 ) ) { wfDebug( __METHOD__ . ": incorrect base checksum" ); return false; } if ( $header['csize'] != strlen( $base ) ) { wfDebug( __METHOD__ . ": incorrect base length" ); return false; } $p = 8; $out = ''; while ( $p < strlen( $diff ) ) { $x = unpack( 'Cop', substr( $diff, $p, 1 ) ); $op = $x['op']; ++$p; switch ( $op ) { case self::XDL_BDOP_INS: $x = unpack( 'Csize', substr( $diff, $p, 1 ) ); $p++; $out .= substr( $diff, $p, $x['size'] ); $p += $x['size']; break; case self::XDL_BDOP_INSB: $x = unpack( 'Vcsize', substr( $diff, $p, 4 ) ); $p += 4; $out .= substr( $diff, $p, $x['csize'] ); $p += $x['csize']; break; case self::XDL_BDOP_CPY: $x = unpack( 'Voff/Vcsize', substr( $diff, $p, 8 ) ); $p += 8; $out .= substr( $base, $x['off'], $x['csize'] ); break; default: wfDebug( __METHOD__ . ": invalid op" ); return false; } } return $out; } /** * Compute a binary "Adler-32" checksum as defined by LibXDiff, i.e. with * the bytes backwards and initialised with 0 instead of 1. See T36428. * * @param string $s * @return string */ public function xdiffAdler32( $s ) { static $init = null; $init ??= str_repeat( "\xf0", 205 ) . "\xee" . str_repeat( "\xf0", 67 ) . "\x02"; // The real Adler-32 checksum of $init is zero, so it initialises the // state to zero, as it is at the start of LibXDiff's checksum // algorithm. Appending the subject string then simulates LibXDiff. return strrev( hash( 'adler32', $init . $s, true ) ); } private function uncompress() { if ( !$this->mDiffs ) { return; } $tail = ''; $mDiffsCount = count( $this->mDiffs ); for ( $diffKey = 0; $diffKey < $mDiffsCount; $diffKey++ ) { $textKey = $this->mDiffMap[$diffKey]; $text = $this->patch( $tail, $this->mDiffs[$diffKey] ); $this->mItems[$textKey] = $text; $tail = $text; } } /** * @return array */ public function __sleep() { $this->compress(); if ( $this->mItems === [] ) { $info = false; } else { // Take forward differences to improve the compression ratio for sequences $map = ''; $prev = 0; foreach ( $this->mDiffMap as $i ) { if ( $map !== '' ) { $map .= ','; } $map .= $i - $prev; $prev = $i; } $info = [ 'diffs' => $this->mDiffs, 'map' => $map ]; } if ( isset( $this->mDefaultKey ) ) { $info['default'] = $this->mDefaultKey; } $this->mCompressed = gzdeflate( serialize( $info ) ); return [ 'mCompressed' ]; } public function __wakeup() { // addItem() doesn't work if mItems is partially filled from mDiffs $this->mFrozen = true; $info = HistoryBlobUtils::unserializeArray( gzinflate( $this->mCompressed ) ); $this->mCompressed = null; if ( !$info ) { // Empty object return; } if ( isset( $info['default'] ) ) { $this->mDefaultKey = $info['default']; } $this->mDiffs = $info['diffs']; if ( isset( $info['base'] ) ) { // Old format $this->mDiffMap = range( 0, count( $this->mDiffs ) - 1 ); array_unshift( $this->mDiffs, pack( 'VVCV', 0, 0, self::XDL_BDOP_INSB, strlen( $info['base'] ) ) . $info['base'] ); } else { // New format $map = explode( ',', $info['map'] ); $cur = 0; $this->mDiffMap = []; foreach ( $map as $i ) { $cur += $i; $this->mDiffMap[] = $cur; } } $this->uncompress(); } /** * Helper function for compression jobs * Returns true until the object is "full" and ready to be committed * * @return bool */ public function isHappy() { return $this->mSize < $this->mMaxSize && count( $this->mItems ) < $this->mMaxCount; } }
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