summaryrefslogtreecommitdiff
path: root/includes/HistoryBlob.php
blob: 69f1120d43f6df9bedb4349478228fb0454e1d11 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
<?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
 */

/**
 * Base class for general text storage via the "object" flag in old_flags, or
 * two-part external storage URLs. Used for represent efficient concatenated
 * storage, and migration-related pointer objects.
 */
interface HistoryBlob {
	/**
	 * Adds an item of text, returns a stub object which points to the item.
	 * You must call setLocation() on the stub object before storing it to the
	 * database
	 *
	 * @param string $text
	 *
	 * @return string The key for getItem()
	 */
	function addItem( $text );

	/**
	 * Get item by key, or false if the key is not present
	 *
	 * @param string $key
	 *
	 * @return string|bool
	 */
	function getItem( $key );

	/**
	 * Set the "default text"
	 * This concept is an odd property of the current DB schema, whereby each text item has a revision
	 * associated with it. The default text is the text of the associated revision. There may, however,
	 * be other revisions in the same object.
	 *
	 * Default text is not required for two-part external storage URLs.
	 *
	 * @param string $text
	 */
	function setText( $text );

	/**
	 * Get default text. This is called from Revision::getRevisionText()
	 *
	 * @return string
	 */
	function getText();
}

/**
 * Concatenated gzip (CGZ) storage
 * Improves compression ratio by concatenating like objects before gzipping
 */
class ConcatenatedGzipHistoryBlob implements HistoryBlob {
	public $mVersion = 0, $mCompressed = false, $mItems = array(), $mDefaultHash = '';
	public $mSize = 0;
	public $mMaxSize = 10000000;
	public $mMaxCount = 100;

	/**
	 * Constructor
	 */
	public function __construct() {
		if ( !function_exists( 'gzdeflate' ) ) {
			throw new MWException( "Need zlib support to read or write this "
				. "kind of history object (ConcatenatedGzipHistoryBlob)\n" );
		}
	}

	/**
	 * @param string $text
	 * @return string
	 */
	public function addItem( $text ) {
		$this->uncompress();
		$hash = md5( $text );
		if ( !isset( $this->mItems[$hash] ) ) {
			$this->mItems[$hash] = $text;
			$this->mSize += strlen( $text );
		}
		return $hash;
	}

	/**
	 * @param string $hash
	 * @return array|bool
	 */
	public function getItem( $hash ) {
		$this->uncompress();
		if ( array_key_exists( $hash, $this->mItems ) ) {
			return $this->mItems[$hash];
		} else {
			return false;
		}
	}

	/**
	 * @param string $text
	 * @return void
	 */
	public function setText( $text ) {
		$this->uncompress();
		$this->mDefaultHash = $this->addItem( $text );
	}

	/**
	 * @return array|bool
	 */
	public function getText() {
		$this->uncompress();
		return $this->getItem( $this->mDefaultHash );
	}

	/**
	 * Remove an item
	 *
	 * @param string $hash
	 */
	public function removeItem( $hash ) {
		$this->mSize -= strlen( $this->mItems[$hash] );
		unset( $this->mItems[$hash] );
	}

	/**
	 * Compress the bulk data in the object
	 */
	public function compress() {
		if ( !$this->mCompressed ) {
			$this->mItems = gzdeflate( serialize( $this->mItems ) );
			$this->mCompressed = true;
		}
	}

	/**
	 * Uncompress bulk data
	 */
	public function uncompress() {
		if ( $this->mCompressed ) {
			$this->mItems = unserialize( gzinflate( $this->mItems ) );
			$this->mCompressed = false;
		}
	}

	/**
	 * @return array
	 */
	function __sleep() {
		$this->compress();
		return array( 'mVersion', 'mCompressed', 'mItems', 'mDefaultHash' );
	}

	function __wakeup() {
		$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;
	}
}

/**
 * Pointer object for an item within a CGZ blob stored in the text table.
 */
class HistoryBlobStub {
	/**
	 * @var array One-step cache variable to hold base blobs; operations that
	 * pull multiple revisions may often pull multiple times from the same
	 * blob. By keeping the last-used one open, we avoid redundant
	 * unserialization and decompression overhead.
	 */
	protected static $blobCache = array();

	/** @var int */
	public $mOldId;

	/** @var string */
	public $mHash;

	/** @var string */
	public $mRef;

	/**
	 * @param string $hash The content hash of the text
	 * @param int $oldid The old_id for the CGZ object
	 */
	function __construct( $hash = '', $oldid = 0 ) {
		$this->mHash = $hash;
	}

	/**
	 * Sets the location (old_id) of the main object to which this object
	 * points
	 * @param int $id
	 */
	function setLocation( $id ) {
		$this->mOldId = $id;
	}

	/**
	 * Sets the location (old_id) of the referring object
	 * @param string $id
	 */
	function setReferrer( $id ) {
		$this->mRef = $id;
	}

	/**
	 * Gets the location of the referring object
	 * @return string
	 */
	function getReferrer() {
		return $this->mRef;
	}

	/**
	 * @return string
	 */
	function getText() {
		if ( isset( self::$blobCache[$this->mOldId] ) ) {
			$obj = self::$blobCache[$this->mOldId];
		} else {
			$dbr = wfGetDB( DB_SLAVE );
			$row = $dbr->selectRow(
				'text',
				array( 'old_flags', 'old_text' ),
				array( 'old_id' => $this->mOldId )
			);

			if ( !$row ) {
				return false;
			}

			$flags = explode( ',', $row->old_flags );
			if ( in_array( 'external', $flags ) ) {
				$url = $row->old_text;
				$parts = explode( '://', $url, 2 );
				if ( !isset( $parts[1] ) || $parts[1] == '' ) {
					return false;
				}
				$row->old_text = ExternalStore::fetchFromUrl( $url );

			}

			if ( !in_array( 'object', $flags ) ) {
				return false;
			}

			if ( in_array( 'gzip', $flags ) ) {
				// This shouldn't happen, but a bug in the compress script
				// may at times gzip-compress a HistoryBlob object row.
				$obj = unserialize( gzinflate( $row->old_text ) );
			} else {
				$obj = unserialize( $row->old_text );
			}

			if ( !is_object( $obj ) ) {
				// Correct for old double-serialization bug.
				$obj = unserialize( $obj );
			}

			// Save this item for reference; if pulling many
			// items in a row we'll likely use it again.
			$obj->uncompress();
			self::$blobCache = array( $this->mOldId => $obj );
		}

		return $obj->getItem( $this->mHash );
	}

	/**
	 * Get the content hash
	 *
	 * @return string
	 */
	function getHash() {
		return $this->mHash;
	}
}

/**
 * To speed up conversion from 1.4 to 1.5 schema, text rows can refer to the
 * leftover cur table as the backend. This avoids expensively copying hundreds
 * of megabytes of data during the conversion downtime.
 *
 * Serialized HistoryBlobCurStub objects will be inserted into the text table
 * on conversion if $wgLegacySchemaConversion is set to true.
 */
class HistoryBlobCurStub {
	/** @var int */
	public $mCurId;

	/**
	 * @param int $curid The cur_id pointed to
	 */
	function __construct( $curid = 0 ) {
		$this->mCurId = $curid;
	}

	/**
	 * Sets the location (cur_id) of the main object to which this object
	 * points
	 *
	 * @param int $id
	 */
	function setLocation( $id ) {
		$this->mCurId = $id;
	}

	/**
	 * @return string|bool
	 */
	function getText() {
		$dbr = wfGetDB( DB_SLAVE );
		$row = $dbr->selectRow( 'cur', array( 'cur_text' ), array( 'cur_id' => $this->mCurId ) );
		if ( !$row ) {
			return false;
		}
		return $row->cur_text;
	}
}

/**
 * Diff-based history compression
 * Requires xdiff 1.5+ and zlib
 */
class DiffHistoryBlob implements HistoryBlob {
	/** @var array Uncompressed item cache */
	public $mItems = array();

	/** @var int Total uncompressed size */
	public $mSize = 0;

	/**
	 * @var array 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 int The key for getText()
	 */
	public $mDefaultKey;

	/** @var string 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 = 10000000;

	/** @var int The maximum number of text items before the object becomes sad */
	public $mMaxCount = 100;

	/** Constants from xdiff.h */
	const XDL_BDOP_INS = 1;
	const XDL_BDOP_CPY = 2;
	const XDL_BDOP_INSB = 3;

	function __construct() {
		if ( !function_exists( 'gzdeflate' ) ) {
			throw new MWException( "Need zlib support to read or write DiffHistoryBlob\n" );
		}
	}

	/**
	 * @throws MWException
	 * @param string $text
	 * @return int
	 */
	function addItem( $text ) {
		if ( $this->mFrozen ) {
			throw new MWException( __METHOD__ . ": Cannot add more items after sleep/wakeup" );
		}

		$this->mItems[] = $text;
		$this->mSize += strlen( $text );
		$this->mDiffs = null; // later
		return count( $this->mItems ) - 1;
	}

	/**
	 * @param string $key
	 * @return string
	 */
	function getItem( $key ) {
		return $this->mItems[$key];
	}

	/**
	 * @param string $text
	 */
	function setText( $text ) {
		$this->mDefaultKey = $this->addItem( $text );
	}

	/**
	 * @return string
	 */
	function getText() {
		return $this->getItem( $this->mDefaultKey );
	}

	/**
	 * @throws MWException
	 */
	function compress() {
		if ( !function_exists( 'xdiff_string_rabdiff' ) ) {
			throw new MWException( "Need xdiff 1.5+ support to write DiffHistoryBlob\n" );
		}
		if ( isset( $this->mDiffs ) ) {
			// Already compressed
			return;
		}
		if ( !count( $this->mItems ) ) {
			// Empty
			return;
		}

		// Create two diff sequences: one for main text and one for small text
		$sequences = array(
			'small' => array(
				'tail' => '',
				'diffs' => array(),
				'map' => array(),
			),
			'main' => array(
				'tail' => '',
				'diffs' => array(),
				'map' => array(),
			),
		);
		$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';
				}
			}
			$seq =& $sequences[$seqName];
			$tail = $seq['tail'];
			$diff = $this->diff( $tail, $text );
			$seq['diffs'][] = $diff;
			$seq['map'][] = $i;
			$seq['tail'] = $text;
		}
		unset( $seq ); // unlink dangerous alias

		// Knit the sequences together
		$tail = '';
		$this->mDiffs = array();
		$this->mDiffMap = array();
		foreach ( $sequences as $seq ) {
			if ( !count( $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
	 */
	function diff( $t1, $t2 ) {
		# Need to do a null concatenation with warnings off, due to bugs in the current version of xdiff
		# "String is not zero-terminated"
		wfSuppressWarnings();
		$diff = xdiff_string_rabdiff( $t1, $t2 ) . '';
		wfRestoreWarnings();
		return $diff;
	}

	/**
	 * @param string $base
	 * @param string $diff
	 * @return bool|string
	 */
	function patch( $base, $diff ) {
		if ( function_exists( 'xdiff_string_bpatch' ) ) {
			wfSuppressWarnings();
			$text = xdiff_string_bpatch( $base, $diff ) . '';
			wfRestoreWarnings();
			return $text;
		}

		# Pure PHP implementation

		$header = unpack( 'Vofp/Vcsize', substr( $diff, 0, 8 ) );

		# Check the checksum if hash extension is available
		$ofp = $this->xdiffAdler32( $base );
		if ( $ofp !== false && $ofp !== substr( $diff, 0, 4 ) ) {
			wfDebug( __METHOD__ . ": incorrect base checksum\n" );
			return false;
		}
		if ( $header['csize'] != strlen( $base ) ) {
			wfDebug( __METHOD__ . ": incorrect base length\n" );
			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\n" );
				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 bug 34428.
	 *
	 * @param string $s
	 * @return string|bool False if the hash extension is not available
	 */
	function xdiffAdler32( $s ) {
		if ( !function_exists( 'hash' ) ) {
			return false;
		}

		static $init;
		if ( $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 ) );
	}

	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
	 */
	function __sleep() {
		$this->compress();
		if ( !count( $this->mItems ) ) {
			// Empty object
			$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 = array(
				'diffs' => $this->mDiffs,
				'map' => $map
			);
		}
		if ( isset( $this->mDefaultKey ) ) {
			$info['default'] = $this->mDefaultKey;
		}
		$this->mCompressed = gzdeflate( serialize( $info ) );
		return array( 'mCompressed' );
	}

	function __wakeup() {
		// addItem() doesn't work if mItems is partially filled from mDiffs
		$this->mFrozen = true;
		$info = unserialize( gzinflate( $this->mCompressed ) );
		unset( $this->mCompressed );

		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 = array();
			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
	 */
	function isHappy() {
		return $this->mSize < $this->mMaxSize
			&& count( $this->mItems ) < $this->mMaxCount;
	}

}