dca4931b42
This touches various production classes and maintenance scripts. The code should do the exact same as before. The main benefit is that the syntax avoids any repetition. Change-Id: I5c552125469f4d7fb5b0fe494d198951b05eb35f
361 lines
8.9 KiB
PHP
361 lines
8.9 KiB
PHP
<?php
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/**
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* Efficient concatenated text storage.
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License along
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* with this program; if not, write to the Free Software Foundation, Inc.,
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* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
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* http://www.gnu.org/copyleft/gpl.html
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*
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* @file
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*/
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/**
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* Diff-based history compression
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* Requires xdiff and zlib
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*
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* WARNING: Objects of this class are serialized and permanently stored in the DB.
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* Do not change the name or visibility of any property!
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*/
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class DiffHistoryBlob implements HistoryBlob {
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/** @var string[] Uncompressed item cache */
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public $mItems = [];
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/** @var int Total uncompressed size */
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public $mSize = 0;
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/**
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* @var array|null Array of diffs. If a diff D from A to B is notated D = B - A,
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* and Z is an empty string:
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*
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* { item[map[i]] - item[map[i-1]] where i > 0
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* diff[i] = {
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* { item[map[i]] - Z where i = 0
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*/
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public $mDiffs;
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/** @var array The diff map, see above */
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public $mDiffMap;
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/** @var string The key for getText()
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*/
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public $mDefaultKey;
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/** @var string|null Compressed storage */
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public $mCompressed;
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/** @var bool True if the object is locked against further writes */
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public $mFrozen = false;
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/**
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* @var int The maximum uncompressed size before the object becomes sad
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* Should be less than max_allowed_packet
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*/
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public $mMaxSize = 10_000_000;
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/** @var int The maximum number of text items before the object becomes sad */
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public $mMaxCount = 100;
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/** Constants from xdiff.h */
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private const XDL_BDOP_INS = 1;
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private const XDL_BDOP_CPY = 2;
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private const XDL_BDOP_INSB = 3;
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public function __construct() {
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if ( !function_exists( 'gzdeflate' ) ) {
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throw new RuntimeException( "Need zlib support to read or write DiffHistoryBlob\n" );
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}
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}
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/**
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* @param string $text
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* @return string
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*/
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public function addItem( $text ) {
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if ( $this->mFrozen ) {
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throw new BadMethodCallException( __METHOD__ . ": Cannot add more items after sleep/wakeup" );
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}
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$this->mItems[] = $text;
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$this->mSize += strlen( $text );
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$this->mDiffs = null; // later
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return (string)( count( $this->mItems ) - 1 );
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}
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/**
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* @param string $key
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* @return string
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*/
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public function getItem( $key ) {
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return $this->mItems[(int)$key];
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}
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/**
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* @param string $text
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*/
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public function setText( $text ) {
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$this->mDefaultKey = $this->addItem( $text );
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}
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/**
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* @return string
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*/
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public function getText() {
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return $this->getItem( $this->mDefaultKey );
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}
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private function compress() {
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if ( !function_exists( 'xdiff_string_rabdiff' ) ) {
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throw new RuntimeException( "Need xdiff support to write DiffHistoryBlob\n" );
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}
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if ( isset( $this->mDiffs ) ) {
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// Already compressed
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return;
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}
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if ( $this->mItems === [] ) {
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return;
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}
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// Create two diff sequences: one for main text and one for small text
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$sequences = [
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'small' => [
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'tail' => '',
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'diffs' => [],
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'map' => [],
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],
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'main' => [
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'tail' => '',
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'diffs' => [],
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'map' => [],
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],
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];
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$smallFactor = 0.5;
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$mItemsCount = count( $this->mItems );
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for ( $i = 0; $i < $mItemsCount; $i++ ) {
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$text = $this->mItems[$i];
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if ( $i == 0 ) {
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$seqName = 'main';
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} else {
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$mainTail = $sequences['main']['tail'];
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if ( strlen( $text ) < strlen( $mainTail ) * $smallFactor ) {
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$seqName = 'small';
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} else {
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$seqName = 'main';
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}
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}
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$tail = $sequences[$seqName]['tail'];
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$diff = $this->diff( $tail, $text );
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$sequences[$seqName]['diffs'][] = $diff;
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$sequences[$seqName]['map'][] = $i;
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$sequences[$seqName]['tail'] = $text;
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}
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// Knit the sequences together
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$tail = '';
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$this->mDiffs = [];
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$this->mDiffMap = [];
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foreach ( $sequences as $seq ) {
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if ( $seq['diffs'] === [] ) {
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continue;
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}
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if ( $tail === '' ) {
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$this->mDiffs[] = $seq['diffs'][0];
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} else {
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$head = $this->patch( '', $seq['diffs'][0] );
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$this->mDiffs[] = $this->diff( $tail, $head );
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}
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$this->mDiffMap[] = $seq['map'][0];
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$diffsCount = count( $seq['diffs'] );
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for ( $i = 1; $i < $diffsCount; $i++ ) {
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$this->mDiffs[] = $seq['diffs'][$i];
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$this->mDiffMap[] = $seq['map'][$i];
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}
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$tail = $seq['tail'];
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}
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}
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/**
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* @param string $t1
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* @param string $t2
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* @return string
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*/
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private function diff( $t1, $t2 ) {
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return xdiff_string_rabdiff( $t1, $t2 );
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}
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/**
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* @param string $base
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* @param string $diff
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* @return bool|string
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*/
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private function patch( $base, $diff ) {
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if ( function_exists( 'xdiff_string_bpatch' ) ) {
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return xdiff_string_bpatch( $base, $diff );
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}
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# Pure PHP implementation
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$header = unpack( 'Vofp/Vcsize', substr( $diff, 0, 8 ) );
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# Check the checksum
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$ofp = $this->xdiffAdler32( $base );
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if ( $ofp !== substr( $diff, 0, 4 ) ) {
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wfDebug( __METHOD__ . ": incorrect base checksum" );
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return false;
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}
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if ( $header['csize'] != strlen( $base ) ) {
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wfDebug( __METHOD__ . ": incorrect base length" );
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return false;
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}
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$p = 8;
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$out = '';
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while ( $p < strlen( $diff ) ) {
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$x = unpack( 'Cop', substr( $diff, $p, 1 ) );
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$op = $x['op'];
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++$p;
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switch ( $op ) {
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case self::XDL_BDOP_INS:
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$x = unpack( 'Csize', substr( $diff, $p, 1 ) );
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$p++;
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$out .= substr( $diff, $p, $x['size'] );
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$p += $x['size'];
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break;
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case self::XDL_BDOP_INSB:
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$x = unpack( 'Vcsize', substr( $diff, $p, 4 ) );
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$p += 4;
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$out .= substr( $diff, $p, $x['csize'] );
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$p += $x['csize'];
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break;
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case self::XDL_BDOP_CPY:
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$x = unpack( 'Voff/Vcsize', substr( $diff, $p, 8 ) );
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$p += 8;
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$out .= substr( $base, $x['off'], $x['csize'] );
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break;
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default:
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wfDebug( __METHOD__ . ": invalid op" );
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return false;
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}
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}
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return $out;
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}
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/**
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* Compute a binary "Adler-32" checksum as defined by LibXDiff, i.e. with
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* the bytes backwards and initialised with 0 instead of 1. See T36428.
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*
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* @param string $s
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* @return string
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*/
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public function xdiffAdler32( $s ) {
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static $init = null;
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$init ??= str_repeat( "\xf0", 205 ) . "\xee" . str_repeat( "\xf0", 67 ) . "\x02";
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// The real Adler-32 checksum of $init is zero, so it initialises the
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// state to zero, as it is at the start of LibXDiff's checksum
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// algorithm. Appending the subject string then simulates LibXDiff.
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return strrev( hash( 'adler32', $init . $s, true ) );
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}
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private function uncompress() {
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if ( !$this->mDiffs ) {
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return;
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}
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$tail = '';
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$mDiffsCount = count( $this->mDiffs );
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for ( $diffKey = 0; $diffKey < $mDiffsCount; $diffKey++ ) {
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$textKey = $this->mDiffMap[$diffKey];
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$text = $this->patch( $tail, $this->mDiffs[$diffKey] );
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$this->mItems[$textKey] = $text;
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$tail = $text;
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}
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}
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/**
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* @return array
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*/
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public function __sleep() {
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$this->compress();
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if ( $this->mItems === [] ) {
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$info = false;
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} else {
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// Take forward differences to improve the compression ratio for sequences
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$map = '';
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$prev = 0;
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foreach ( $this->mDiffMap as $i ) {
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if ( $map !== '' ) {
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$map .= ',';
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}
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$map .= $i - $prev;
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$prev = $i;
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}
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$info = [
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'diffs' => $this->mDiffs,
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'map' => $map
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];
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}
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if ( isset( $this->mDefaultKey ) ) {
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$info['default'] = $this->mDefaultKey;
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}
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$this->mCompressed = gzdeflate( serialize( $info ) );
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return [ 'mCompressed' ];
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}
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public function __wakeup() {
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// addItem() doesn't work if mItems is partially filled from mDiffs
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$this->mFrozen = true;
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$info = HistoryBlobUtils::unserializeArray( gzinflate( $this->mCompressed ) );
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$this->mCompressed = null;
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if ( !$info ) {
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// Empty object
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return;
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}
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if ( isset( $info['default'] ) ) {
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$this->mDefaultKey = $info['default'];
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}
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$this->mDiffs = $info['diffs'];
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if ( isset( $info['base'] ) ) {
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// Old format
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$this->mDiffMap = range( 0, count( $this->mDiffs ) - 1 );
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array_unshift( $this->mDiffs,
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pack( 'VVCV', 0, 0, self::XDL_BDOP_INSB, strlen( $info['base'] ) ) .
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$info['base'] );
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} else {
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// New format
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$map = explode( ',', $info['map'] );
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$cur = 0;
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$this->mDiffMap = [];
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foreach ( $map as $i ) {
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$cur += $i;
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$this->mDiffMap[] = $cur;
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}
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}
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$this->uncompress();
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}
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/**
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* Helper function for compression jobs
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* Returns true until the object is "full" and ready to be committed
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*
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* @return bool
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*/
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public function isHappy() {
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return $this->mSize < $this->mMaxSize
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&& count( $this->mItems ) < $this->mMaxCount;
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}
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}
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