Semanticmediawiki: Fatal error in SpecialOWLExport

[Nikerabbit]

Setup and configuration

• SMW version: 2.5.6
• MW version: 1.32.0-alpha
• PHP version: 7.1.17-1+ubuntu16.04.1+deb.sury.org+1 (fpm-fcgi)
• DB system (MySQL, Blazegraph, etc.) and version: 10.0.34-MariaDB-0ubuntu0.16.04.1

Issue

Fatal error in PHP log:

2018-06-01 13:20:36 web1.translatewiki.net translatewiki_net-bw_: [8f5dd3644f907828fa90fe94] https://translatewiki.net/w/i.php?title=Special:ExportRDF/Thread:User_talk:Movses/%C3%83%C2%90%C3%82%C2%BE%C3%83%C2%91%C3%82%C2%88%C3%83%C2%90%C3%82%C2%B8%C3%83%C2%90%C3%82%C2%B1%C3%83%C2%90%C3%82%C2%BA%C3%83%C2%90%C3%82%C2%B8_%C3%83%C2%91%C3%82%C2%81_%C3%83%C2%90%C3%82%C2%BF%C3%83%C2%91%C3%82?%C3%83%C2%90%C3%82%C2%B5%C3%83%C2%91%C3%82%C2%84%C3%83%C2%90%C3%82%C2%B8%C3%83%C2%90%C3%82%C2%BA%C3%83%C2%91%C3%82%C2%81%C3%83%C2%90%C3%82%C2%B0%C3%83%C2%90%C3%82%C2%BC%C3%83%C2%90%C3%82%C2%B8_%C3%83%C2%90%C3%82%C2%BF%C3%83%C2%91%C3%82?%C3%83%C2%90%C3%82%C2%B8_%C3%83%C2%90%C3%82%C2%BF%C3%83%C2%90%C3%82%C2%B5%C3%83%C2%91%C3%82?%C3%83%C2%90%C3%82%C2%B5%C3%83%C2%90%C3%82%C2%B2%C3%83%C2%90%C3%82%C2%BE%C3%83%C2%90%C3%82%C2%B4%C3%83%C2%90%C3%82%C2%B0%C3%83%C2%91%C3%82%C2%85/reply&xmlmime=rdf Error from line 184 of /srv/mediawiki/tags/2018-05-23_19:00:54/extensions/SemanticMediaWiki/includes/specials/SMW_SpecialOWLExport.php: Call to a member function isRedirect() on null

No stracktrace available.

Steps to reproduce

When visiting the above URL. It's unclear what causes such url in the first place.
Happens in sandbox too: https://sandbox.semantic-mediawiki.org/w/index.php?title=Sp%C3%A9cial:Export_RDF/Thread:User_talk:Movses/%C3%83%C2%90%C3%82%C2%BE%C3%83%C2%91%C3%82%C2%88%C3%83%C2%90%C3%82%C2%B8%C3%83%C2%90%C3%82%C2%B1%C3%83%C2%90%C3%82%C2%BA%C3%83%C2%90%C3%82%C2%B8_%C3%83%C2%91%C3%82%C2%81_%C3%83%C2%90%C3%82%C2%BF%C3%83%C2%91%C3%82%3F%C3%83%C2%90%C3%82%C2%B5%C3%83%C2%91%C3%82%C2%84%C3%83%C2%90%C3%82%C2%B8%C3%83%C2%90%C3%82%C2%BA%C3%83%C2%91%C3%82%C2%81%C3%83%C2%90%C3%82%C2%B0%C3%83%C2%90%C3%82%C2%BC%C3%83%C2%90%C3%82%C2%B8_%C3%83%C2%90%C3%82%C2%BF%C3%83%C2%91%C3%82%3F%C3%83%C2%90%C3%82%C2%B8_%C3%83%C2%90%C3%82%C2%BF%C3%83%C2%90%C3%82%C2%B5%C3%83%C2%91%C3%82%3F%C3%83%C2%90%C3%82%C2%B5%C3%83%C2%90%C3%82%C2%B2%C3%83%C2%90%C3%82%C2%BE%C3%83%C2%90%C3%82%C2%B4%C3%83%C2%90%C3%82%C2%B0%C3%83%C2%91%C3%82%C2%85/reply&xmlmime=rdf

[mwjames]

Error from line 184 of /srv/mediawiki/tags/2018-05-23_19:00:54/extensions/SemanticMediaWiki/includes/specials/SMW_SpecialOWLExport.php: Call to a member function isRedirect() on null

Most likely the title contains some "illegal" characters the Title class cannot handle and I'm guessing that a simple check should cover the NULL case.

-       if ( isset( $pages[0] ) && Title::newFromText( $pages[0] )->isRedirect() ) {
+       if ( isset( $pages[0] ) && ( $title = Title::newFromText( $pages[0] ) ) !== null && $title->isRedirect() ) {
            $backlinks = false;
        }

[kghbln]

This fix could probably be back-ported to 2.5.x, too.

[mwjames]

The cause is a length issue that hits the 255 restriction and produces a NULL on a title longer than 255, as for comparison:

• Special:ExportRDF/Foo/ошибки_с_пÑÂ%3Fефиксами_пÑÂ%3Fи_пеÑÂ%3FеводаÑÂ/reply&xmlmime=rdf passes (253) while
• Special:ExportRDF/Foo/ошибки_с_пÑÂ%3Fефиксами_пÑÂ%3Fи_пеÑÂ%3FеводаÑÂ---/reply&xmlmime=rdf doesn't (256)

The proposed change should prevent the failure even though the length issue isn't addressed which itself cannot be solved by SMW.

[kghbln]

@mwjames I will do a pull tomorrow.

The proposed change should prevent the failure even though the length issue isn't addressed which itself cannot be solved by SMW.

@Nikerabbit Worth creating a task for MW at Phabricator?

[mwjames]

@Nikerabbit Worth creating a task for MW at Phabricator?

No, I think MW has a fixed length of 255 for a title and anything above will just blow.

[mwjames]

I'd say merge it and once on the sandbox test that the link (sandbox
link) from above no longer fails.

On 7/16/18, Karsten Hoffmeyer [e-mail] wrote:

Assigned #3173 to @mwjames.

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You are receiving this because you were assigned.
Reply to this email directly or view it on GitHub:
https://github.com/SemanticMediaWiki/SemanticMediaWiki/issues/3173#event-1734672337

[kghbln]

I'd say merge it and once on the sandbox test that the link (sandbox link) from above no longer fails.

Affirmative. We now get an RDF as expected.