MediaWiki  master
DiffHistoryBlob.php
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1 <?php
27 class DiffHistoryBlob implements HistoryBlob {
29  public $mItems = [];
30 
32  public $mSize = 0;
33 
42  public $mDiffs;
43 
45  public $mDiffMap;
46 
49  public $mDefaultKey;
50 
52  public $mCompressed;
53 
55  public $mFrozen = false;
56 
61  public $mMaxSize = 10000000;
62 
64  public $mMaxCount = 100;
65 
67  const XDL_BDOP_INS = 1;
68  const XDL_BDOP_CPY = 2;
69  const XDL_BDOP_INSB = 3;
70 
71  function __construct() {
72  if ( !function_exists( 'gzdeflate' ) ) {
73  throw new MWException( "Need zlib support to read or write DiffHistoryBlob\n" );
74  }
75  }
76 
82  function addItem( $text ) {
83  if ( $this->mFrozen ) {
84  throw new MWException( __METHOD__ . ": Cannot add more items after sleep/wakeup" );
85  }
86 
87  $this->mItems[] = $text;
88  $this->mSize += strlen( $text );
89  $this->mDiffs = null; // later
90  return count( $this->mItems ) - 1;
91  }
92 
97  function getItem( $key ) {
98  return $this->mItems[$key];
99  }
100 
104  function setText( $text ) {
105  $this->mDefaultKey = $this->addItem( $text );
106  }
107 
111  function getText() {
112  return $this->getItem( $this->mDefaultKey );
113  }
114 
118  function compress() {
119  if ( !function_exists( 'xdiff_string_rabdiff' ) ) {
120  throw new MWException( "Need xdiff 1.5+ support to write DiffHistoryBlob\n" );
121  }
122  if ( isset( $this->mDiffs ) ) {
123  // Already compressed
124  return;
125  }
126  if ( $this->mItems === [] ) {
127  return;
128  }
129 
130  // Create two diff sequences: one for main text and one for small text
131  $sequences = [
132  'small' => [
133  'tail' => '',
134  'diffs' => [],
135  'map' => [],
136  ],
137  'main' => [
138  'tail' => '',
139  'diffs' => [],
140  'map' => [],
141  ],
142  ];
143  $smallFactor = 0.5;
144 
145  $mItemsCount = count( $this->mItems );
146  for ( $i = 0; $i < $mItemsCount; $i++ ) {
147  $text = $this->mItems[$i];
148  if ( $i == 0 ) {
149  $seqName = 'main';
150  } else {
151  $mainTail = $sequences['main']['tail'];
152  if ( strlen( $text ) < strlen( $mainTail ) * $smallFactor ) {
153  $seqName = 'small';
154  } else {
155  $seqName = 'main';
156  }
157  }
158  $seq =& $sequences[$seqName];
159  $tail = $seq['tail'];
160  $diff = $this->diff( $tail, $text );
161  $seq['diffs'][] = $diff;
162  $seq['map'][] = $i;
163  $seq['tail'] = $text;
164  }
165  unset( $seq ); // unlink dangerous alias
166 
167  // Knit the sequences together
168  $tail = '';
169  $this->mDiffs = [];
170  $this->mDiffMap = [];
171  foreach ( $sequences as $seq ) {
172  if ( $seq['diffs'] === [] ) {
173  continue;
174  }
175  if ( $tail === '' ) {
176  $this->mDiffs[] = $seq['diffs'][0];
177  } else {
178  $head = $this->patch( '', $seq['diffs'][0] );
179  $this->mDiffs[] = $this->diff( $tail, $head );
180  }
181  $this->mDiffMap[] = $seq['map'][0];
182  $diffsCount = count( $seq['diffs'] );
183  for ( $i = 1; $i < $diffsCount; $i++ ) {
184  $this->mDiffs[] = $seq['diffs'][$i];
185  $this->mDiffMap[] = $seq['map'][$i];
186  }
187  $tail = $seq['tail'];
188  }
189  }
190 
196  function diff( $t1, $t2 ) {
197  # Need to do a null concatenation with warnings off, due to bugs in the current version of xdiff
198  # "String is not zero-terminated"
199  Wikimedia\suppressWarnings();
200  $diff = xdiff_string_rabdiff( $t1, $t2 ) . '';
201  Wikimedia\restoreWarnings();
202  return $diff;
203  }
204 
210  function patch( $base, $diff ) {
211  if ( function_exists( 'xdiff_string_bpatch' ) ) {
212  Wikimedia\suppressWarnings();
213  $text = xdiff_string_bpatch( $base, $diff ) . '';
214  Wikimedia\restoreWarnings();
215  return $text;
216  }
217 
218  # Pure PHP implementation
219 
220  $header = unpack( 'Vofp/Vcsize', substr( $diff, 0, 8 ) );
221 
222  # Check the checksum if hash extension is available
223  $ofp = $this->xdiffAdler32( $base );
224  if ( $ofp !== false && $ofp !== substr( $diff, 0, 4 ) ) {
225  wfDebug( __METHOD__ . ": incorrect base checksum\n" );
226  return false;
227  }
228  if ( $header['csize'] != strlen( $base ) ) {
229  wfDebug( __METHOD__ . ": incorrect base length\n" );
230  return false;
231  }
232 
233  $p = 8;
234  $out = '';
235  while ( $p < strlen( $diff ) ) {
236  $x = unpack( 'Cop', substr( $diff, $p, 1 ) );
237  $op = $x['op'];
238  ++$p;
239  switch ( $op ) {
240  case self::XDL_BDOP_INS:
241  $x = unpack( 'Csize', substr( $diff, $p, 1 ) );
242  $p++;
243  $out .= substr( $diff, $p, $x['size'] );
244  $p += $x['size'];
245  break;
246  case self::XDL_BDOP_INSB:
247  $x = unpack( 'Vcsize', substr( $diff, $p, 4 ) );
248  $p += 4;
249  $out .= substr( $diff, $p, $x['csize'] );
250  $p += $x['csize'];
251  break;
252  case self::XDL_BDOP_CPY:
253  $x = unpack( 'Voff/Vcsize', substr( $diff, $p, 8 ) );
254  $p += 8;
255  $out .= substr( $base, $x['off'], $x['csize'] );
256  break;
257  default:
258  wfDebug( __METHOD__ . ": invalid op\n" );
259  return false;
260  }
261  }
262  return $out;
263  }
264 
272  function xdiffAdler32( $s ) {
273  if ( !function_exists( 'hash' ) ) {
274  return false;
275  }
276 
277  static $init;
278  if ( $init === null ) {
279  $init = str_repeat( "\xf0", 205 ) . "\xee" . str_repeat( "\xf0", 67 ) . "\x02";
280  }
281 
282  // The real Adler-32 checksum of $init is zero, so it initialises the
283  // state to zero, as it is at the start of LibXDiff's checksum
284  // algorithm. Appending the subject string then simulates LibXDiff.
285  return strrev( hash( 'adler32', $init . $s, true ) );
286  }
287 
288  function uncompress() {
289  if ( !$this->mDiffs ) {
290  return;
291  }
292  $tail = '';
293  $mDiffsCount = count( $this->mDiffs );
294  for ( $diffKey = 0; $diffKey < $mDiffsCount; $diffKey++ ) {
295  $textKey = $this->mDiffMap[$diffKey];
296  $text = $this->patch( $tail, $this->mDiffs[$diffKey] );
297  $this->mItems[$textKey] = $text;
298  $tail = $text;
299  }
300  }
301 
305  function __sleep() {
306  $this->compress();
307  if ( $this->mItems === [] ) {
308  $info = false;
309  } else {
310  // Take forward differences to improve the compression ratio for sequences
311  $map = '';
312  $prev = 0;
313  foreach ( $this->mDiffMap as $i ) {
314  if ( $map !== '' ) {
315  $map .= ',';
316  }
317  $map .= $i - $prev;
318  $prev = $i;
319  }
320  $info = [
321  'diffs' => $this->mDiffs,
322  'map' => $map
323  ];
324  }
325  if ( isset( $this->mDefaultKey ) ) {
326  $info['default'] = $this->mDefaultKey;
327  }
328  $this->mCompressed = gzdeflate( serialize( $info ) );
329  return [ 'mCompressed' ];
330  }
331 
332  function __wakeup() {
333  // addItem() doesn't work if mItems is partially filled from mDiffs
334  $this->mFrozen = true;
335  $info = unserialize( gzinflate( $this->mCompressed ) );
336  unset( $this->mCompressed );
337 
338  if ( !$info ) {
339  // Empty object
340  return;
341  }
342 
343  if ( isset( $info['default'] ) ) {
344  $this->mDefaultKey = $info['default'];
345  }
346  $this->mDiffs = $info['diffs'];
347  if ( isset( $info['base'] ) ) {
348  // Old format
349  $this->mDiffMap = range( 0, count( $this->mDiffs ) - 1 );
350  array_unshift( $this->mDiffs,
351  pack( 'VVCV', 0, 0, self::XDL_BDOP_INSB, strlen( $info['base'] ) ) .
352  $info['base'] );
353  } else {
354  // New format
355  $map = explode( ',', $info['map'] );
356  $cur = 0;
357  $this->mDiffMap = [];
358  foreach ( $map as $i ) {
359  $cur += $i;
360  $this->mDiffMap[] = $cur;
361  }
362  }
363  $this->uncompress();
364  }
365 
372  function isHappy() {
373  return $this->mSize < $this->mMaxSize
374  && count( $this->mItems ) < $this->mMaxCount;
375  }
376 
377 }
int $mMaxSize
The maximum uncompressed size before the object becomes sad Should be less than max_allowed_packet.
int $mSize
Total uncompressed size.
serialize()
array $mItems
Uncompressed item cache.
const XDL_BDOP_INS
Constants from xdiff.h.
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Definition: hooks.txt:767
array $mDiffMap
The diff map, see above.
xdiffAdler32( $s)
Compute a binary "Adler-32" checksum as defined by LibXDiff, i.e.
wfDebug( $text, $dest='all', array $context=[])
Sends a line to the debug log if enabled or, optionally, to a comment in output.
unserialize( $serialized)
isHappy()
Helper function for compression jobs Returns true until the object is "full" and ready to be committe...
this hook is for auditing only or null if authentication failed before getting that far or null if we can t even determine that When $user is not null
Definition: hooks.txt:767
$header
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Definition: distributors.txt:9
injection txt This is an overview of how MediaWiki makes use of dependency injection The design described here grew from the discussion of RFC T384 The term dependency this means that anything an object needs to operate should be injected from the the object itself should only know narrow no concrete implementation of the logic it relies on The requirement to inject everything typically results in an architecture that based on two main types of and essentially stateless service objects that use other service objects to operate on the value objects As of the beginning MediaWiki is only starting to use the DI approach Much of the code still relies on global state or direct resulting in a highly cyclical dependency which acts as the top level factory for services in MediaWiki which can be used to gain access to default instances of various services MediaWikiServices however also allows new services to be defined and default services to be redefined Services are defined or redefined by providing a callback the instantiator that will return a new instance of the service When it will create an instance of MediaWikiServices and populate it with the services defined in the files listed by thereby bootstrapping the DI framework Per $wgServiceWiringFiles lists includes ServiceWiring php
Definition: injection.txt:35
Diff-based history compression Requires xdiff 1.5+ and zlib.
bool $mFrozen
True if the object is locked against further writes.
patch( $base, $diff)
array $mDiffs
Array of diffs.
string $mCompressed
Compressed storage.
int $mDefaultKey
The key for getText()
int $mMaxCount
The maximum number of text items before the object becomes sad.
Base class for general text storage via the "object" flag in old_flags, or two-part external storage ...
Definition: HistoryBlob.php:28