Last modified: 2009-08-23 23:27:57 UTC

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Bug 20364 - GIFMetadataExtractor.php throws "Unexpected non-MediaWiki exception encountered, of type 'Exception'", halts if metadata in user-provided image not accepted
GIFMetadataExtractor.php throws "Unexpected non-MediaWiki exception encounter...
Status: RESOLVED FIXED
Product: MediaWiki
Classification: Unclassified
File management (Other open bugs)
1.16.x
PC Linux
: Normal normal (vote)
: ---
Assigned To: Brion Vibber
http://jpe.gs/wiki/File:Sucrose_b.gif
:
Depends on:
Blocks:
  Show dependency treegraph
 
Reported: 2009-08-23 14:49 UTC by Carl Austin Bennett
Modified: 2009-08-23 23:27 UTC (History)
1 user (show)

See Also:
Web browser: ---
Mobile Platform: ---
Assignee Huggle Beta Tester: ---


Attachments

Description Carl Austin Bennett 2009-08-23 14:49:41 UTC
The error handling in GIFMetadataExtractor.php appears to create more problems than it solves. If the script finds the smallest bit of the metadata objectionable in a user-supplied image, it does not allow any part of the page on which the image appears to display.

Errors which could be safely ignored (for instance, the http://jpe.gs/wiki/File:Sucrose_b.gif file triggering an error at GIFMetadataExtractor.php:133) instead now prevent the display of the entire page, for every page in every wiki on which the image appears.

This issue appeared on 'upgrade' from MediaWiki 1.14 to the August 15, 2009 SVN version 1.16alpha - header in the metadata extractor file claims to be avoiding use of the MWException class for portability reasons, but even no displayed metadata at all would be better than entire wiki pages turned into:


Unexpected non-MediaWiki exception encountered, of type "Exception"
exception 'Exception' with message 'At position: 208, Unknown byte 11' in ...mw116a/includes/media/GIFMetadataExtractor.php:133
Stack trace:
#0 ...mw116a/includes/media/GIF.php(16): GIFMetadataExtractor::getMetadata('/var/im...')
#1 ...mw116a/includes/filerepo/UnregisteredLocalFile.php(89): GIFHandler->getMetadata(Object(UnregisteredLocalFile), '/var/im...')
#2 ...mw116a/includes/filerepo/File.php(899): UnregisteredLocalFile->getMetadata()
#3 ...mw116a/includes/ImagePage.php(90): File->formatMetadata()
#4 ...mw116a/includes/Wiki.php(463): ImagePage->view()
#5 ...mw116a/includes/Wiki.php(67): MediaWiki->performAction(Object(OutputPage), Object(ImagePage), Object(Title), Object(User), Object(WebRequest))
#6 ...mw116a/index.php(116): MediaWiki->performRequestForTitle(Object(Title), Object(ImagePage), Object(OutputPage), Object(User), Object(WebRequest))
#7 {main}

#0 ...mw116a/includes/media/GIF.php(16): GIFMetadataExtractor::getMetadata('/var/im...')
#1 ...mw116a/includes/filerepo/UnregisteredLocalFile.php(89): GIFHandler->getMetadata(Object(UnregisteredLocalFile), '/var/im...')
#2 ...mw116a/includes/filerepo/File.php(899): UnregisteredLocalFile->getMetadata()
#3 ...mw116a/includes/ImagePage.php(90): File->formatMetadata()
#4 ...mw116a/includes/Wiki.php(463): ImagePage->view()
#5 ...mw116a/includes/Wiki.php(67): MediaWiki->performAction(Object(OutputPage), Object(ImagePage), Object(Title), Object(User), Object(WebRequest))
#6 ...mw116a/index.php(116): MediaWiki->performRequestForTitle(Object(Title), Object(ImagePage), Object(OutputPage), Object(User), Object(WebRequest))
#7 {main}


Disabling the one "throw new Exception" line of code throwing the error (includes/media/GIFMetadataExtractor.php:133) allows the image to display normally:

                        } else {
                                $byte = unpack( 'C', $buf );
                                $byte = $byte[1];
                                #throw new Exception( "At position: ".ftell($fh). ", Unknown byte ".$byte );
                        }

Oddly, the image itself looks fine in the browser. Whatever supposed 'error' exists in this animated .gif file is not valid enough that is should be used to justify MediaWiki 1.16a refusing to display the entire page, for every page where the image appears.

Any chance the code could be changed to recover just a wee bit more gracefully?
Comment 1 Chad H. 2009-08-23 14:52:48 UTC
Assigning to Andrew.
Comment 2 Brion Vibber 2009-08-23 23:20:29 UTC
Assigning to myself since I was poking at it. :)
Comment 3 Brion Vibber 2009-08-23 23:27:57 UTC
Fixed in r55541.

There was a missing parameter in GIFMetadataExtractor's skipBlock() call for 'netscape 2.0' data blocks, which threw a monkey in the works. Now also checking for exceptions thrown by the metadata load and stubbing out null metadata for files which can't be read, rather than letting the exception bubble up and kill MediaWiki. :)

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