InstantCommons/zh



即时共享资源是MediaWiki的一个特性，允许在全世界任何一个MediaWiki实体能够使用维基共享资源的任何已上传的媒体文件. 启用即时共享资源特性的wiki站点，可以在第一次请求该文件后自动缓存在本地，并且之后会使用该本地复本来显示.

原理
截至2017年7月，由维基媒体基金会主持的中央媒体资料库维基共享资源包含超过4千万个文件. 这些文件中的每一个都可以在自由内容许可下或公共域中获得，除使用官方徽章或商标之外，没有其他限制使用. 限制商业用途的许可证被视为非自由.

随着对维基共享资源的认识不断提高，外部各方也希望使用其中包含的内容，并提供新材料. 目前技术上可以在任何网页的上下文中直接从维基媒体的服务器加载图像. 允许这样的热链接，但由于多种原因它存在问题： 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.
 * 它不尊重图像的许可条款，也不允许可靠地传输其他元数据
 * Besides failing to properly credit the author of the media file, it also does not give credit to Wikimedia
 * It consumes Wikimedia bandwidth on every pageview (unless the image has been cached on the client side or through a 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.

基本功能设置
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.

This feature relies on php curl extension. If you do not have this extension installed, maybe InstantCommons cannot work.

配置
For enabling InstantCommons in MediaWiki version 1.16 or later, it is sufficient to add this line to your LocalSettings.php (see for details):

For enabling in MediaWiki versions 1.13-1.15, see here.

This feature should work immediately. If it's not, check if the PHP function  is disabled in your web server.

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:
 * Verify you have an up-to-date certificate store. If you have the php curl extension installed, follow the instructions here.

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 IP addresses.

通过InstantCommons使用文件
With InstantCommons enabled, you can choose any image from Wikimedia Commons (e.g. ), 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

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 his 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.

参见

 * - 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