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<?php
/**
* GIF frame counter.
*
* Originally written in Perl by Steve Sanbeg.
* Ported to PHP by Andrew Garrett
* Deliberately not using MWExceptions to avoid external dependencies, encouraging
* redistribution.
*
* 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
* @ingroup Media
*/
/**
* GIF frame counter.
*
* @ingroup Media
*/
class GIFMetadataExtractor {
/** @var string */
private static $gifFrameSep;
/** @var string */
private static $gifExtensionSep;
/** @var string */
private static $gifTerm;
const VERSION = 1;
// Each sub-block is less than or equal to 255 bytes.
// Most of the time its 255 bytes, except for in XMP
// blocks, where it's usually between 32-127 bytes each.
const MAX_SUBBLOCKS = 262144; // 5mb divided by 20.
/**
* @throws Exception
* @param string $filename
* @return array
*/
static function getMetadata( $filename ) {
self::$gifFrameSep = pack( "C", ord( "," ) );
self::$gifExtensionSep = pack( "C", ord( "!" ) );
self::$gifTerm = pack( "C", ord( ";" ) );
$frameCount = 0;
$duration = 0.0;
$isLooped = false;
$xmp = "";
$comment = [];
if ( !$filename ) {
throw new Exception( "No file name specified" );
} elseif ( !file_exists( $filename ) || is_dir( $filename ) ) {
throw new Exception( "File $filename does not exist" );
}
$fh = fopen( $filename, 'rb' );
if ( !$fh ) {
throw new Exception( "Unable to open file $filename" );
}
// Check for the GIF header
$buf = fread( $fh, 6 );
if ( !( $buf == 'GIF87a' || $buf == 'GIF89a' ) ) {
throw new Exception( "Not a valid GIF file; header: $buf" );
}
// Skip over width and height.
fread( $fh, 4 );
// Read BPP
$buf = fread( $fh, 1 );
$bpp = self::decodeBPP( $buf );
// Skip over background and aspect ratio
fread( $fh, 2 );
// Skip over the GCT
self::readGCT( $fh, $bpp );
while ( !feof( $fh ) ) {
$buf = fread( $fh, 1 );
if ( $buf == self::$gifFrameSep ) {
// Found a frame
$frameCount++;
# # Skip bounding box
fread( $fh, 8 );
# # Read BPP
$buf = fread( $fh, 1 );
$bpp = self::decodeBPP( $buf );
# # Read GCT
self::readGCT( $fh, $bpp );
fread( $fh, 1 );
self::skipBlock( $fh );
} elseif ( $buf == self::$gifExtensionSep ) {
$buf = fread( $fh, 1 );
if ( strlen( $buf ) < 1 ) {
throw new Exception( "Ran out of input" );
}
$extension_code = unpack( 'C', $buf )[1];
if ( $extension_code == 0xF9 ) {
// Graphics Control Extension.
fread( $fh, 1 ); // Block size
fread( $fh, 1 ); // Transparency, disposal method, user input
$buf = fread( $fh, 2 ); // Delay, in hundredths of seconds.
if ( strlen( $buf ) < 2 ) {
throw new Exception( "Ran out of input" );
}
$delay = unpack( 'v', $buf )[1];
$duration += $delay * 0.01;
fread( $fh, 1 ); // Transparent colour index
$term = fread( $fh, 1 ); // Should be a terminator
if ( strlen( $term ) < 1 ) {
throw new Exception( "Ran out of input" );
}
$term = unpack( 'C', $term )[1];
if ( $term != 0 ) {
throw new Exception( "Malformed Graphics Control Extension block" );
}
} elseif ( $extension_code == 0xFE ) {
// Comment block(s).
$data = self::readBlock( $fh );
if ( $data === "" ) {
throw new Exception( 'Read error, zero-length comment block' );
}
// The standard says this should be ASCII, however its unclear if
// thats true in practise. Check to see if its valid utf-8, if so
// assume its that, otherwise assume its windows-1252 (iso-8859-1)
$dataCopy = $data;
// quickIsNFCVerify has the side effect of replacing any invalid characters
UtfNormal\Validator::quickIsNFCVerify( $dataCopy );
if ( $dataCopy !== $data ) {
MediaWiki\suppressWarnings();
$data = iconv( 'windows-1252', 'UTF-8', $data );
MediaWiki\restoreWarnings();
}
$commentCount = count( $comment );
if ( $commentCount === 0
|| $comment[$commentCount - 1] !== $data
) {
// Some applications repeat the same comment on each
// frame of an animated GIF image, so if this comment
// is identical to the last, only extract once.
$comment[] = $data;
}
} elseif ( $extension_code == 0xFF ) {
// Application extension (Netscape info about the animated gif)
// or XMP (or theoretically any other type of extension block)
$blockLength = fread( $fh, 1 );
if ( strlen( $blockLength ) < 1 ) {
throw new Exception( "Ran out of input" );
}
$blockLength = unpack( 'C', $blockLength )[1];
$data = fread( $fh, $blockLength );
if ( $blockLength != 11 ) {
wfDebug( __METHOD__ . " GIF application block with wrong length\n" );
fseek( $fh, -( $blockLength + 1 ), SEEK_CUR );
self::skipBlock( $fh );
continue;
}
// NETSCAPE2.0 (application name for animated gif)
if ( $data == 'NETSCAPE2.0' ) {
$data = fread( $fh, 2 ); // Block length and introduction, should be 03 01
if ( $data != "\x03\x01" ) {
throw new Exception( "Expected \x03\x01, got $data" );
}
// Unsigned little-endian integer, loop count or zero for "forever"
$loopData = fread( $fh, 2 );
if ( strlen( $loopData ) < 2 ) {
throw new Exception( "Ran out of input" );
}
$loopCount = unpack( 'v', $loopData )[1];
if ( $loopCount != 1 ) {
$isLooped = true;
}
// Read out terminator byte
fread( $fh, 1 );
} elseif ( $data == 'XMP DataXMP' ) {
// application name for XMP data.
// see pg 18 of XMP spec part 3.
$xmp = self::readBlock( $fh, true );
if ( substr( $xmp, -257, 3 ) !== "\x01\xFF\xFE"
|| substr( $xmp, -4 ) !== "\x03\x02\x01\x00"
) {
// this is just a sanity check.
throw new Exception( "XMP does not have magic trailer!" );
}
// strip out trailer.
$xmp = substr( $xmp, 0, -257 );
} else {
// unrecognized extension block
fseek( $fh, -( $blockLength + 1 ), SEEK_CUR );
self::skipBlock( $fh );
continue;
}
} else {
self::skipBlock( $fh );
}
} elseif ( $buf == self::$gifTerm ) {
break;
} else {
if ( strlen( $buf ) < 1 ) {
throw new Exception( "Ran out of input" );
}
$byte = unpack( 'C', $buf )[1];
throw new Exception( "At position: " . ftell( $fh ) . ", Unknown byte " . $byte );
}
}
return [
'frameCount' => $frameCount,
'looped' => $isLooped,
'duration' => $duration,
'xmp' => $xmp,
'comment' => $comment,
];
}
/**
* @param resource $fh
* @param int $bpp
* @return void
*/
static function readGCT( $fh, $bpp ) {
if ( $bpp > 0 ) {
$max = pow( 2, $bpp );
for ( $i = 1; $i <= $max; ++$i ) {
fread( $fh, 3 );
}
}
}
/**
* @param string $data
* @throws Exception
* @return int
*/
static function decodeBPP( $data ) {
if ( strlen( $data ) < 1 ) {
throw new Exception( "Ran out of input" );
}
$buf = unpack( 'C', $data )[1];
$bpp = ( $buf & 7 ) + 1;
$buf >>= 7;
$have_map = $buf & 1;
return $have_map ? $bpp : 0;
}
/**
* @param resource $fh
* @throws Exception
*/
static function skipBlock( $fh ) {
while ( !feof( $fh ) ) {
$buf = fread( $fh, 1 );
if ( strlen( $buf ) < 1 ) {
throw new Exception( "Ran out of input" );
}
$block_len = unpack( 'C', $buf )[1];
if ( $block_len == 0 ) {
return;
}
fread( $fh, $block_len );
}
}
/**
* Read a block. In the GIF format, a block is made up of
* several sub-blocks. Each sub block starts with one byte
* saying how long the sub-block is, followed by the sub-block.
* The entire block is terminated by a sub-block of length
* 0.
* @param resource $fh File handle
* @param bool $includeLengths Include the length bytes of the
* sub-blocks in the returned value. Normally this is false,
* except XMP is weird and does a hack where you need to keep
* these length bytes.
* @throws Exception
* @return string The data.
*/
static function readBlock( $fh, $includeLengths = false ) {
$data = '';
$subLength = fread( $fh, 1 );
$blocks = 0;
while ( $subLength !== "\0" ) {
$blocks++;
if ( $blocks > self::MAX_SUBBLOCKS ) {
throw new Exception( "MAX_SUBBLOCKS exceeded (over $blocks sub-blocks)" );
}
if ( feof( $fh ) ) {
throw new Exception( "Read error: Unexpected EOF." );
}
if ( $includeLengths ) {
$data .= $subLength;
}
$data .= fread( $fh, ord( $subLength ) );
$subLength = fread( $fh, 1 );
}
return $data;
}
}