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1 | <?php |
2 | /** |
3 | * Efficient concatenated text storage. |
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 | */ |
22 | |
23 | /** |
24 | * Diff-based history compression |
25 | * Requires xdiff and zlib |
26 | * |
27 | * WARNING: Objects of this class are serialized and permanently stored in the DB. |
28 | * Do not change the name or visibility of any property! |
29 | */ |
30 | class DiffHistoryBlob implements HistoryBlob { |
31 | /** @var string[] Uncompressed item cache */ |
32 | public $mItems = []; |
33 | |
34 | /** @var int Total uncompressed size */ |
35 | public $mSize = 0; |
36 | |
37 | /** |
38 | * @var array|null Array of diffs. If a diff D from A to B is notated D = B - A, |
39 | * and Z is an empty string: |
40 | * |
41 | * { item[map[i]] - item[map[i-1]] where i > 0 |
42 | * diff[i] = { |
43 | * { item[map[i]] - Z where i = 0 |
44 | */ |
45 | public $mDiffs; |
46 | |
47 | /** @var array The diff map, see above */ |
48 | public $mDiffMap; |
49 | |
50 | /** @var string The key for getText() |
51 | */ |
52 | public $mDefaultKey; |
53 | |
54 | /** @var string|null Compressed storage */ |
55 | public $mCompressed; |
56 | |
57 | /** @var bool True if the object is locked against further writes */ |
58 | public $mFrozen = false; |
59 | |
60 | /** |
61 | * @var int The maximum uncompressed size before the object becomes sad |
62 | * Should be less than max_allowed_packet |
63 | */ |
64 | public $mMaxSize = 10_000_000; |
65 | |
66 | /** @var int The maximum number of text items before the object becomes sad */ |
67 | public $mMaxCount = 100; |
68 | |
69 | /** Constants from xdiff.h */ |
70 | private const XDL_BDOP_INS = 1; |
71 | private const XDL_BDOP_CPY = 2; |
72 | private const XDL_BDOP_INSB = 3; |
73 | |
74 | public function __construct() { |
75 | if ( !function_exists( 'gzdeflate' ) ) { |
76 | throw new RuntimeException( "Need zlib support to read or write DiffHistoryBlob\n" ); |
77 | } |
78 | } |
79 | |
80 | /** |
81 | * @param string $text |
82 | * @return string |
83 | */ |
84 | public function addItem( $text ) { |
85 | if ( $this->mFrozen ) { |
86 | throw new BadMethodCallException( __METHOD__ . ": Cannot add more items after sleep/wakeup" ); |
87 | } |
88 | |
89 | $this->mItems[] = $text; |
90 | $this->mSize += strlen( $text ); |
91 | $this->mDiffs = null; // later |
92 | return (string)( count( $this->mItems ) - 1 ); |
93 | } |
94 | |
95 | /** |
96 | * @param string $key |
97 | * @return string |
98 | */ |
99 | public function getItem( $key ) { |
100 | return $this->mItems[(int)$key]; |
101 | } |
102 | |
103 | /** |
104 | * @param string $text |
105 | */ |
106 | public function setText( $text ) { |
107 | $this->mDefaultKey = $this->addItem( $text ); |
108 | } |
109 | |
110 | /** |
111 | * @return string |
112 | */ |
113 | public function getText() { |
114 | return $this->getItem( $this->mDefaultKey ); |
115 | } |
116 | |
117 | private function compress() { |
118 | if ( !function_exists( 'xdiff_string_rabdiff' ) ) { |
119 | throw new RuntimeException( "Need xdiff support to write DiffHistoryBlob\n" ); |
120 | } |
121 | if ( isset( $this->mDiffs ) ) { |
122 | // Already compressed |
123 | return; |
124 | } |
125 | if ( $this->mItems === [] ) { |
126 | return; |
127 | } |
128 | |
129 | // Create two diff sequences: one for main text and one for small text |
130 | $sequences = [ |
131 | 'small' => [ |
132 | 'tail' => '', |
133 | 'diffs' => [], |
134 | 'map' => [], |
135 | ], |
136 | 'main' => [ |
137 | 'tail' => '', |
138 | 'diffs' => [], |
139 | 'map' => [], |
140 | ], |
141 | ]; |
142 | $smallFactor = 0.5; |
143 | |
144 | $mItemsCount = count( $this->mItems ); |
145 | for ( $i = 0; $i < $mItemsCount; $i++ ) { |
146 | $text = $this->mItems[$i]; |
147 | if ( $i == 0 ) { |
148 | $seqName = 'main'; |
149 | } else { |
150 | $mainTail = $sequences['main']['tail']; |
151 | if ( strlen( $text ) < strlen( $mainTail ) * $smallFactor ) { |
152 | $seqName = 'small'; |
153 | } else { |
154 | $seqName = 'main'; |
155 | } |
156 | } |
157 | |
158 | $tail = $sequences[$seqName]['tail']; |
159 | $diff = $this->diff( $tail, $text ); |
160 | $sequences[$seqName]['diffs'][] = $diff; |
161 | $sequences[$seqName]['map'][] = $i; |
162 | $sequences[$seqName]['tail'] = $text; |
163 | } |
164 | |
165 | // Knit the sequences together |
166 | $tail = ''; |
167 | $this->mDiffs = []; |
168 | $this->mDiffMap = []; |
169 | foreach ( $sequences as $seq ) { |
170 | if ( $seq['diffs'] === [] ) { |
171 | continue; |
172 | } |
173 | if ( $tail === '' ) { |
174 | $this->mDiffs[] = $seq['diffs'][0]; |
175 | } else { |
176 | $head = $this->patch( '', $seq['diffs'][0] ); |
177 | $this->mDiffs[] = $this->diff( $tail, $head ); |
178 | } |
179 | $this->mDiffMap[] = $seq['map'][0]; |
180 | $diffsCount = count( $seq['diffs'] ); |
181 | for ( $i = 1; $i < $diffsCount; $i++ ) { |
182 | $this->mDiffs[] = $seq['diffs'][$i]; |
183 | $this->mDiffMap[] = $seq['map'][$i]; |
184 | } |
185 | $tail = $seq['tail']; |
186 | } |
187 | } |
188 | |
189 | /** |
190 | * @param string $t1 |
191 | * @param string $t2 |
192 | * @return string |
193 | */ |
194 | private function diff( $t1, $t2 ) { |
195 | return xdiff_string_rabdiff( $t1, $t2 ); |
196 | } |
197 | |
198 | /** |
199 | * @param string $base |
200 | * @param string $diff |
201 | * @return bool|string |
202 | */ |
203 | private function patch( $base, $diff ) { |
204 | if ( function_exists( 'xdiff_string_bpatch' ) ) { |
205 | return xdiff_string_bpatch( $base, $diff ); |
206 | } |
207 | |
208 | # Pure PHP implementation |
209 | |
210 | $header = unpack( 'Vofp/Vcsize', substr( $diff, 0, 8 ) ); |
211 | |
212 | # Check the checksum |
213 | $ofp = $this->xdiffAdler32( $base ); |
214 | if ( $ofp !== substr( $diff, 0, 4 ) ) { |
215 | wfDebug( __METHOD__ . ": incorrect base checksum" ); |
216 | return false; |
217 | } |
218 | if ( $header['csize'] != strlen( $base ) ) { |
219 | wfDebug( __METHOD__ . ": incorrect base length" ); |
220 | return false; |
221 | } |
222 | |
223 | $p = 8; |
224 | $out = ''; |
225 | while ( $p < strlen( $diff ) ) { |
226 | $x = unpack( 'Cop', substr( $diff, $p, 1 ) ); |
227 | $op = $x['op']; |
228 | ++$p; |
229 | switch ( $op ) { |
230 | case self::XDL_BDOP_INS: |
231 | $x = unpack( 'Csize', substr( $diff, $p, 1 ) ); |
232 | $p++; |
233 | $out .= substr( $diff, $p, $x['size'] ); |
234 | $p += $x['size']; |
235 | break; |
236 | case self::XDL_BDOP_INSB: |
237 | $x = unpack( 'Vcsize', substr( $diff, $p, 4 ) ); |
238 | $p += 4; |
239 | $out .= substr( $diff, $p, $x['csize'] ); |
240 | $p += $x['csize']; |
241 | break; |
242 | case self::XDL_BDOP_CPY: |
243 | $x = unpack( 'Voff/Vcsize', substr( $diff, $p, 8 ) ); |
244 | $p += 8; |
245 | $out .= substr( $base, $x['off'], $x['csize'] ); |
246 | break; |
247 | default: |
248 | wfDebug( __METHOD__ . ": invalid op" ); |
249 | return false; |
250 | } |
251 | } |
252 | return $out; |
253 | } |
254 | |
255 | /** |
256 | * Compute a binary "Adler-32" checksum as defined by LibXDiff, i.e. with |
257 | * the bytes backwards and initialised with 0 instead of 1. See T36428. |
258 | * |
259 | * @param string $s |
260 | * @return string |
261 | */ |
262 | public function xdiffAdler32( $s ) { |
263 | static $init; |
264 | if ( $init === null ) { |
265 | $init = str_repeat( "\xf0", 205 ) . "\xee" . str_repeat( "\xf0", 67 ) . "\x02"; |
266 | } |
267 | |
268 | // The real Adler-32 checksum of $init is zero, so it initialises the |
269 | // state to zero, as it is at the start of LibXDiff's checksum |
270 | // algorithm. Appending the subject string then simulates LibXDiff. |
271 | return strrev( hash( 'adler32', $init . $s, true ) ); |
272 | } |
273 | |
274 | private function uncompress() { |
275 | if ( !$this->mDiffs ) { |
276 | return; |
277 | } |
278 | $tail = ''; |
279 | $mDiffsCount = count( $this->mDiffs ); |
280 | for ( $diffKey = 0; $diffKey < $mDiffsCount; $diffKey++ ) { |
281 | $textKey = $this->mDiffMap[$diffKey]; |
282 | $text = $this->patch( $tail, $this->mDiffs[$diffKey] ); |
283 | $this->mItems[$textKey] = $text; |
284 | $tail = $text; |
285 | } |
286 | } |
287 | |
288 | /** |
289 | * @return array |
290 | */ |
291 | public function __sleep() { |
292 | $this->compress(); |
293 | if ( $this->mItems === [] ) { |
294 | $info = false; |
295 | } else { |
296 | // Take forward differences to improve the compression ratio for sequences |
297 | $map = ''; |
298 | $prev = 0; |
299 | foreach ( $this->mDiffMap as $i ) { |
300 | if ( $map !== '' ) { |
301 | $map .= ','; |
302 | } |
303 | $map .= $i - $prev; |
304 | $prev = $i; |
305 | } |
306 | $info = [ |
307 | 'diffs' => $this->mDiffs, |
308 | 'map' => $map |
309 | ]; |
310 | } |
311 | if ( isset( $this->mDefaultKey ) ) { |
312 | $info['default'] = $this->mDefaultKey; |
313 | } |
314 | $this->mCompressed = gzdeflate( serialize( $info ) ); |
315 | return [ 'mCompressed' ]; |
316 | } |
317 | |
318 | public function __wakeup() { |
319 | // addItem() doesn't work if mItems is partially filled from mDiffs |
320 | $this->mFrozen = true; |
321 | $info = HistoryBlobUtils::unserializeArray( gzinflate( $this->mCompressed ) ); |
322 | $this->mCompressed = null; |
323 | |
324 | if ( !$info ) { |
325 | // Empty object |
326 | return; |
327 | } |
328 | |
329 | if ( isset( $info['default'] ) ) { |
330 | $this->mDefaultKey = $info['default']; |
331 | } |
332 | $this->mDiffs = $info['diffs']; |
333 | if ( isset( $info['base'] ) ) { |
334 | // Old format |
335 | $this->mDiffMap = range( 0, count( $this->mDiffs ) - 1 ); |
336 | array_unshift( $this->mDiffs, |
337 | pack( 'VVCV', 0, 0, self::XDL_BDOP_INSB, strlen( $info['base'] ) ) . |
338 | $info['base'] ); |
339 | } else { |
340 | // New format |
341 | $map = explode( ',', $info['map'] ); |
342 | $cur = 0; |
343 | $this->mDiffMap = []; |
344 | foreach ( $map as $i ) { |
345 | $cur += $i; |
346 | $this->mDiffMap[] = $cur; |
347 | } |
348 | } |
349 | $this->uncompress(); |
350 | } |
351 | |
352 | /** |
353 | * Helper function for compression jobs |
354 | * Returns true until the object is "full" and ready to be committed |
355 | * |
356 | * @return bool |
357 | */ |
358 | public function isHappy() { |
359 | return $this->mSize < $this->mMaxSize |
360 | && count( $this->mItems ) < $this->mMaxCount; |
361 | } |
362 | |
363 | } |