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GIFMetadataExtractor.php
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1 <?php
36  private static $gifFrameSep;
37 
39  private static $gifExtensionSep;
40 
42  private static $gifTerm;
43 
44  const VERSION = 1;
45 
46  // Each sub-block is less than or equal to 255 bytes.
47  // Most of the time its 255 bytes, except for in XMP
48  // blocks, where it's usually between 32-127 bytes each.
49  const MAX_SUBBLOCKS = 262144; // 5mb divided by 20.
50 
56  static function getMetadata( $filename ) {
57  self::$gifFrameSep = pack( "C", ord( "," ) ); // 2C
58  self::$gifExtensionSep = pack( "C", ord( "!" ) ); // 21
59  self::$gifTerm = pack( "C", ord( ";" ) ); // 3B
60 
61  $frameCount = 0;
62  $duration = 0.0;
63  $isLooped = false;
64  $xmp = "";
65  $comment = [];
66 
67  if ( !$filename ) {
68  throw new Exception( "No file name specified" );
69  } elseif ( !file_exists( $filename ) || is_dir( $filename ) ) {
70  throw new Exception( "File $filename does not exist" );
71  }
72 
73  $fh = fopen( $filename, 'rb' );
74 
75  if ( !$fh ) {
76  throw new Exception( "Unable to open file $filename" );
77  }
78 
79  // Check for the GIF header
80  $buf = fread( $fh, 6 );
81  if ( !( $buf == 'GIF87a' || $buf == 'GIF89a' ) ) {
82  throw new Exception( "Not a valid GIF file; header: $buf" );
83  }
84 
85  // Read width and height.
86  $buf = fread( $fh, 2 );
87  $width = unpack( 'v', $buf )[1];
88  $buf = fread( $fh, 2 );
89  $height = unpack( 'v', $buf )[1];
90 
91  // Read BPP
92  $buf = fread( $fh, 1 );
93  $bpp = self::decodeBPP( $buf );
94 
95  // Skip over background and aspect ratio
96  fread( $fh, 2 );
97 
98  // Skip over the GCT
99  self::readGCT( $fh, $bpp );
100 
101  while ( !feof( $fh ) ) {
102  $buf = fread( $fh, 1 );
103 
104  if ( $buf == self::$gifFrameSep ) {
105  // Found a frame
106  $frameCount++;
107 
108  # # Skip bounding box
109  fread( $fh, 8 );
110 
111  # # Read BPP
112  $buf = fread( $fh, 1 );
113  $bpp = self::decodeBPP( $buf );
114 
115  # # Read GCT
116  self::readGCT( $fh, $bpp );
117  fread( $fh, 1 );
118  self::skipBlock( $fh );
119  } elseif ( $buf == self::$gifExtensionSep ) {
120  $buf = fread( $fh, 1 );
121  if ( strlen( $buf ) < 1 ) {
122  throw new Exception( "Ran out of input" );
123  }
124  $extension_code = unpack( 'C', $buf )[1];
125 
126  if ( $extension_code == 0xF9 ) {
127  // Graphics Control Extension.
128  fread( $fh, 1 ); // Block size
129 
130  fread( $fh, 1 ); // Transparency, disposal method, user input
131 
132  $buf = fread( $fh, 2 ); // Delay, in hundredths of seconds.
133  if ( strlen( $buf ) < 2 ) {
134  throw new Exception( "Ran out of input" );
135  }
136  $delay = unpack( 'v', $buf )[1];
137  $duration += $delay * 0.01;
138 
139  fread( $fh, 1 ); // Transparent colour index
140 
141  $term = fread( $fh, 1 ); // Should be a terminator
142  if ( strlen( $term ) < 1 ) {
143  throw new Exception( "Ran out of input" );
144  }
145  $term = unpack( 'C', $term )[1];
146  if ( $term != 0 ) {
147  throw new Exception( "Malformed Graphics Control Extension block" );
148  }
149  } elseif ( $extension_code == 0xFE ) {
150  // Comment block(s).
151  $data = self::readBlock( $fh );
152  if ( $data === "" ) {
153  throw new Exception( 'Read error, zero-length comment block' );
154  }
155 
156  // The standard says this should be ASCII, however its unclear if
157  // thats true in practise. Check to see if its valid utf-8, if so
158  // assume its that, otherwise assume its windows-1252 (iso-8859-1)
159  $dataCopy = $data;
160  // quickIsNFCVerify has the side effect of replacing any invalid characters
161  UtfNormal\Validator::quickIsNFCVerify( $dataCopy );
162 
163  if ( $dataCopy !== $data ) {
164  Wikimedia\suppressWarnings();
165  $data = iconv( 'windows-1252', 'UTF-8', $data );
166  Wikimedia\restoreWarnings();
167  }
168 
169  $commentCount = count( $comment );
170  if ( $commentCount === 0
171  || $comment[$commentCount - 1] !== $data
172  ) {
173  // Some applications repeat the same comment on each
174  // frame of an animated GIF image, so if this comment
175  // is identical to the last, only extract once.
176  $comment[] = $data;
177  }
178  } elseif ( $extension_code == 0xFF ) {
179  // Application extension (Netscape info about the animated gif)
180  // or XMP (or theoretically any other type of extension block)
181  $blockLength = fread( $fh, 1 );
182  if ( strlen( $blockLength ) < 1 ) {
183  throw new Exception( "Ran out of input" );
184  }
185  $blockLength = unpack( 'C', $blockLength )[1];
186  $data = fread( $fh, $blockLength );
187 
188  if ( $blockLength != 11 ) {
189  wfDebug( __METHOD__ . " GIF application block with wrong length\n" );
190  fseek( $fh, -( $blockLength + 1 ), SEEK_CUR );
191  self::skipBlock( $fh );
192  continue;
193  }
194 
195  // NETSCAPE2.0 (application name for animated gif)
196  if ( $data == 'NETSCAPE2.0' ) {
197  $data = fread( $fh, 2 ); // Block length and introduction, should be 03 01
198 
199  if ( $data != "\x03\x01" ) {
200  throw new Exception( "Expected \x03\x01, got $data" );
201  }
202 
203  // Unsigned little-endian integer, loop count or zero for "forever"
204  $loopData = fread( $fh, 2 );
205  if ( strlen( $loopData ) < 2 ) {
206  throw new Exception( "Ran out of input" );
207  }
208  $loopCount = unpack( 'v', $loopData )[1];
209 
210  if ( $loopCount != 1 ) {
211  $isLooped = true;
212  }
213 
214  // Read out terminator byte
215  fread( $fh, 1 );
216  } elseif ( $data == 'XMP DataXMP' ) {
217  // application name for XMP data.
218  // see pg 18 of XMP spec part 3.
219 
220  $xmp = self::readBlock( $fh, true );
221 
222  if ( substr( $xmp, -257, 3 ) !== "\x01\xFF\xFE"
223  || substr( $xmp, -4 ) !== "\x03\x02\x01\x00"
224  ) {
225  // this is just a sanity check.
226  throw new Exception( "XMP does not have magic trailer!" );
227  }
228 
229  // strip out trailer.
230  $xmp = substr( $xmp, 0, -257 );
231  } else {
232  // unrecognized extension block
233  fseek( $fh, -( $blockLength + 1 ), SEEK_CUR );
234  self::skipBlock( $fh );
235  continue;
236  }
237  } else {
238  self::skipBlock( $fh );
239  }
240  } elseif ( $buf == self::$gifTerm ) {
241  break;
242  } else {
243  if ( strlen( $buf ) < 1 ) {
244  throw new Exception( "Ran out of input" );
245  }
246  $byte = unpack( 'C', $buf )[1];
247  throw new Exception( "At position: " . ftell( $fh ) . ", Unknown byte " . $byte );
248  }
249  }
250 
251  return [
252  'frameCount' => $frameCount,
253  'looped' => $isLooped,
254  'duration' => $duration,
255  'xmp' => $xmp,
256  'comment' => $comment,
257  ];
258  }
259 
265  static function readGCT( $fh, $bpp ) {
266  if ( $bpp > 0 ) {
267  $max = 2 ** $bpp;
268  for ( $i = 1; $i <= $max; ++$i ) {
269  fread( $fh, 3 );
270  }
271  }
272  }
273 
279  static function decodeBPP( $data ) {
280  if ( strlen( $data ) < 1 ) {
281  throw new Exception( "Ran out of input" );
282  }
283  $buf = unpack( 'C', $data )[1];
284  $bpp = ( $buf & 7 ) + 1;
285  // @phan-suppress-next-line PhanTypeInvalidLeftOperandOfIntegerOp
286  $buf >>= 7;
287 
288  $have_map = $buf & 1;
289 
290  return $have_map ? $bpp : 0;
291  }
292 
297  static function skipBlock( $fh ) {
298  while ( !feof( $fh ) ) {
299  $buf = fread( $fh, 1 );
300  if ( strlen( $buf ) < 1 ) {
301  throw new Exception( "Ran out of input" );
302  }
303  $block_len = unpack( 'C', $buf )[1];
304  if ( $block_len == 0 ) {
305  return;
306  }
307  fread( $fh, $block_len );
308  }
309  }
310 
325  static function readBlock( $fh, $includeLengths = false ) {
326  $data = '';
327  $subLength = fread( $fh, 1 );
328  $blocks = 0;
329 
330  while ( $subLength !== "\0" ) {
331  $blocks++;
332  if ( $blocks > self::MAX_SUBBLOCKS ) {
333  throw new Exception( "MAX_SUBBLOCKS exceeded (over $blocks sub-blocks)" );
334  }
335  if ( feof( $fh ) ) {
336  throw new Exception( "Read error: Unexpected EOF." );
337  }
338  if ( $includeLengths ) {
339  $data .= $subLength;
340  }
341 
342  $data .= fread( $fh, ord( $subLength ) );
343  $subLength = fread( $fh, 1 );
344  }
345 
346  return $data;
347  }
348 }
static readGCT( $fh, $bpp)
wfDebug( $text, $dest='all', array $context=[])
Sends a line to the debug log if enabled or, optionally, to a comment in output.
static getMetadata( $filename)
static readBlock( $fh, $includeLengths=false)
Read a block.