== Current URL format
There are four "API endpoints" for MediaWiki which can be used to request thumbnails:
* `thumb.php`: used mostly when [[https://www.mediawiki.org/wiki/Manual:$wgGenerateThumbnailOnParse|`$wgGenerateThumbnailOnParse`]] and [[https://www.mediawiki.org/wiki/Manual:$wgLocalFileRepo|`transformVia404`]] are both false. Endpoint is at [[https://www.mediawiki.org/wiki/Manual:$wgThumbnailScriptPath|`$wgThumbnailScriptPath`]] (e.g. [[https://commons.wikimedia.org/w/thumb.php|: https://commons.wikimedia.org/w/thumb.php]]).
* direct/404 handler: this typically reflects how images are stored on disk, and MediaWiki relies on the web server (or something else like Varnish) to map URLs to files. With `$wgGenerateThumbnailOnParse` set to true, files will be pre-generated and this is not really an API. With that false and `transformVia404` true, these URLs are mapped (again by the web server or some other external thing) to `thumb_handler.php` which is a wrapper around `thumb.php` that takes a nice URL and converts it into a parameter array. The URL format is `<zone prefix>/[archive/|temp/][<first few characters of sha1>/]<filename>` for originals, `<zone prefix>/[archive/|temp/][<first few characters of sha1>/]<filename>/<param-string><maybe-filename><maybe-extension>` for thumbnails. For example https://upload.wikimedia.org/wikipedia/commons/thumb/6/66/Camera2_mgx.svg/100px-Camera2_mgx.svg.png
** `<maybe-filename>` is the filename, or just `thumbnail` if that would be too long; `<maybe-extension>` is the extension if it is different from the original; `<zone prefix>` is whatever is returned by `FileRepo::getZoneUrl($zone)` (which can be configured via [[https://www.mediawiki.org/wiki/Manual:$wgLocalFileRepo|`$wgLocalFileRepo`]] / [[https://www.mediawiki.org/wiki/Manual:$wgForeignFileRepos|`$wgForeignFileRepos`]]). For Wikimedia wikis this is `https://upload.wikimedia.org/<project>/<language>/` for originals and `https://upload.wikimedia.org/<project>/<language>/<zone>` for most other stuff (most notably zone is ``https://upload.wikimedia.org/<project>/<language>/thumb` for thumbnails). The number of sha1 characters to put in the path is also configurable via the repos.
** for old versions of files (which are under `/archive`, or `/temp` if they are also temp files) the file name takes the form of `<YYYYMMDDHHMMSS timestamp>!<original filename>`. The timestamp is included in the sha1 calculation for normal files, but nor for temp files.
* `img_auth.php`: used by private wikis to check for permissions. It will return thumbnails if they exist but will not render them. URLs are more or less in the form `<$wgScriptPath>/img_auth.php/<filename>` or `<$wgScriptPath>/img_auth.php/<thumbname>` but can be extended via [[https://www.mediawiki.org/wiki/Manual:$wgImgAuthUrlPathMap|`$wgImgAuthUrlPathMap`]] or the [[https://www.mediawiki.org/wiki/Manual:Hooks/ImgAuthBeforeStream|ImgAuthBeforeStream]] hook.
* upload stash: shows uploaded-but-not-yet-published files of the current user. Available via the special page `Special:UploadStash/file/<stash key>` for originals, `Special:UploadStash/file/<stash key>/<thumb name>` for thumbs. Stash key is returned by the upload API; thumb name is the last path segment for the normal (404 handler) thumb URL. Depending on [[https://www.mediawiki.org/wiki/Manual:$wgUploadStashScalerBaseUrl|`$wgUploadStashScalerBaseUrl`]] might actually render thumbnails or just proxy to the 404 handler.
== Parameter handli
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Processing of 404 handler ULRs (the other endpoints do some subset of this):
- for the 404 handler, convert the URL into parameters (`thumb.php` just uses the query params):
- f => the filename (penultimate path segment)
- thumbName => the thumbnail name, with parameters (the last path segment)
- archive/temp => flags for this being the thumbnail of an old version or temporary file
- rel404 => the whole path, more or less
- normalize some params (BC): w => width, h => height, p => page
- add params from ExtractThumbParameters hook (deprecated)
- PagedTiffHandler (BC only): lossy, page, width
- OggHandler (discontiued in MW 1.24): seek
- unset thumbName, add params from `MediaHandler::parseParamString(<param-string>)`
- ImageHandler: width
- BitmapHandler: interlace
- JpegHandler: quality
- SvgHandler: lang, width
- DjVuHandler: page, width
- PdfHandler: page, width
- PagedTiffHandler: lossy => [lossy|lossless], page, width
- PdfHandler: page, width
- MP3MediaHandler: does not take any params
- TimedMediaHandler: width, seek
- unset thumbName/archived/temp/f/rel404/r (but use them to select the right repo/file)
- handle 'download' parameter
- call `File::transform` with the collected parameters