InstantCommons
InstantCommons je funkce MediaWiki, která dovoluje použití jakéhokoli mediálního souboru nahraného na servery Wikimedia Commons v jakémkoliv projektu MediaWiki na celém světě. Wikiprojekty, které mají funkci InstantCommons povolenou, ukládají soubory z Commons do cache, takže je stačí stáhnout jen jednou a při opakovaném načtení stránky už načítají kopii souboru z místního úložiště.
Zdůvodnění
V dubnu 2019 obsahovalo centrální mediální úložiště Nadace Wikimedia - Wikimedia Commons - přes 52 milionů souborů. Každý z těchto souborů je dostupný pod svobodnou licencí nebo jako zcela volné dílo; další omezení použití (s výjimkou zobrazení oficiálních log či obchodních značek) tedy neexistují. Licence, které omezují komerční využití souboru, nelze považovat za svobodné.
Jak roste všeobecné povědomí o Commons, roste i žádostivost cizích subjektů používat jeho obsah a přispívat také svými materiály. Technicky vzato je dnes možné načítat obrázky přímo ze server Wikimedia v kontextu jakékoliv webové stránky. Takovýto "hotlinking" není zakázaný, nicméně z mnoha důvodů může přinášet problémy:
- Nerespektuje licenční podmínky uvedené u obrázku a nepřenáší ani jeho metadata.
- Ztrácí se informace o autorství souboru a jeho umístění na serveru Wikimedia.
- Při každém zobrazení stránky dochází k použití datového toku ze serveru Wikimedia (platí v případě, že obrázek nezůstane uložený v cache klienta nebo proxy).
- It does not facilitate useful image operations such as thumbnail generation and captioning and is difficult to use in the context of a wiki, particularly for standard layout operations
- It is tied to URLs as resource identifiers, which complicates mirroring
- It creates an untrackable external usage web, where any change on Wikimedia's side necessarily affects these external users
- It does not permit offline viewing, which is crucial in countries which have only intermittent network access.
InstantCommons seeks to address all this by providing an easy method for cached loading of images and metadata from Wikimedia's servers. The first implementation of InstantCommons will be within MediaWiki, allowing for all MediaWiki image operations (thumbnailing, captioning, galleries, etc.) to be performed transparently. However, other wiki engines can implement InstantCommons-like functionality using the API operations described below.
Základní funkce
During the installation, the site administrator can choose whether to enable InstantCommons. Ideally, however, the feature should be enabled by default (provided a writable upload directory is specified) to allow the largest possible number of users to use Wikimedia Commons content.
If the feature is enabled, the wiki behaves like a Wikimedia project, that is, if an image or other media file is referred to which exists on Commons, it can be included in a wiki page like a locally uploaded file by specifying its name. Local filenames take precedence over Commons filenames.
Konfigurace
Pro povolení InstantCommons v MediaWiki (verze 1.16 či pozdější) stačí přidat do Vašeho LocalSettings.php tento řádek (pro další informace vizte $wgUseInstantCommons):
$wgUseInstantCommons = true;
Pro povolení v MediaWiki verze 1.13-1.15 si přečtěte Manual:$wgForeignFileRepos#Using files from Wikimedia Commons : ForeignAPIRepo.
Funkce by měla běžet okamžitě. Pokud se tak nestalo, zkontrolujte, zda na svém webovém serveru nemáte vypnutou PHP funkci curl_exec().
HTTPS
Starting June 2015, Wikimedia Commons can only be accessed using HTTPS. Some installs may be missing their root certificate store which prevents MediaWiki from contacting Commons over HTTPS. If InstantCommons stopped working, try:
- Installing the php curl extension. (It is generally more reliable, and more likely to have proper certificates already installed.) On Debian/Ubuntu:
sudo apt-get install php-curl - Verify you have an up-to-date certificate store. If you have the php curl extension installed, follow the instructions webaware or Talk:InstantCommons#Stop_working.
SElinux
If your server OS implements SElinux, please take a look at the dedicated section on the SELinux settings page, and make sure HTTPD scripts and modules can access the network successfully. If SElinux prevents HTTPD scripts and modules from connecting to WikiMedia Commons repository, the InstantCommons feature will simply not work.
Behind a firewall
If the server on which the wiki runs is behind a firewall, the wiki server must be granted outgoing http/https requests to commons.wikimedia.org and upload.wikimedia.org, for Instant Commons to work. The IP address ranges are found at wikitech:IP addresses.
Using files via InstantCommons
With InstantCommons enabled, you can choose any image from Wikimedia Commons (e.g. this one), click the "Use this file" button (the button with the wiki icon 
next to) and paste the markup in your wiki.
In our example, pasting
[[File:Wikipedia-Marker-commons.svg|thumb|A picture from Wikimedia Commons embedded in this Wiki]]
will render the thumbnail (as can be seen on the right side of this page).
Note that when using files in this way you will still need to respect any licensing and other file use legal requirements - see Commons:Reusing content outside Wikimedia.
Scalability considerations
Because the InstantCommons feature allows a wiki user to download resources from the Wikimedia servers, it is crucial that there is no possibility of a Denial of Service attack against either the using wiki, or the Wikimedia Commons, for example, by pasting 30K of links to the largest files on Wikimedia Commons into a wiki page and pressing "preview". Therefore, every successful InstantCommons request will have to be logged by the InstantCommons-enabled wiki together with the originating user or IP address and the time of the request. If an individual user overrides a generous internal bandwidth limitation (could be as high as 1 GB by default, but should be user-configurable), future images will not be downloaded within a 24 hour period. This limitation should not exist for wiki administrators (if a wiki admin wants to conduct a denial of service attack against their own wiki, they do not need to be stopped from doing so; if they want to conduct an attack against Wikimedia, they cannot be stopped from doing so except on Wikimedia's end). In addition to the per-user bandwidth limit, there could be a limit on the size of files which should be downloaded transparently. This would primarily be because files above a certain size would delay pageviews significantly and might even cause the page request to time out. It might be desirable to use an external application for the purpose of downloading these files, so that it can be done in the background without causing the page request to continue. Finally, there could be a total maximum size for the InstantCommons cache; if this size is exceeded, no further files would be downloaded.
While it is unlikely that individual wikis using the InstantCommons feature would cause a significant increase in cost for the Wikimedia Foundation (since every file only has to be downloaded once, and there are per-user bandwidth limitations), it would nevertheless be fair and reasonable for projects using the feature to include a notice on InstantCommons description pages such as: "This file comes from Wikimedia Commons, a media archive hosted by the Wikimedia Foundation. If you would like to support the Wikimedia Foundation, you can donate here ..."
Future potential
In the future, it may be desirable to offer a publisher/subscribe model of changes, which will require wiki-to-wiki authentication and a database of images which are used in subscribing wikis. This would also open up the threat of cross-wiki vandalism, which could be addressed using a delay phase of 24 hours or more for changes to take effect. Two-way functionality is another possibility, that is, to allow uploading free media directly to Commons from any wiki installation. However, this will require federated authentication as a minimum. It may also necessitate cross-wiki communication facilities to notify users from other wikis about Commons policies, which could be part of a larger project like LiquidThreads.
See also
- Manual:$wgForeignFileRepos - for the same functionality as InstantCommons but with other wikis
- PhotoCommons: Wordpress plug-in to provide the same functionality
- Examples of sites which are using InstantCommons