Limit thumbnail generation

* This fixes a denial-of-service exploit that would allow the client to
generate an infinite number of thumbnails and fill up the storage completely.
Since the client had control over the requested thumbnail sizes, it could make arbitrary requests for thumbnails, and every time the backend did not find an already generated thumbnail with the specified sizes, it would happily generate a new one.
* Remove the ability of the client to decide thumbnail dimensions and
only let the back-end do this by reading the configuration.
* Limit the number of generated thumbnails per file to only one, with
"landscape" dimensions (4/3).
* Use CSS "object-fit" property to adjust displaying of landscape thumbnails into squares. Ref: https://developer.mozilla.org/en-US/docs/Web/CSS/object-fit

src/_h5ai/private/conf/options.json

@@ -355,7 +355,7 @@
     - mov: array of strings
     - doc: array of strings
     - delay: number, delay in milliseconds after "dom-ready" before thumb-requesting starts
-    - size: number, size in pixel of the generated thumbnails
+    - size: number, height in pixel of the generated thumbnails
     - seek: number, percentage of total video duration to seek into
     - exif: boolean, use included EXIF thumbs if possible
     - chunksize: int, number of thumbs per request

src/_h5ai/private/php/core/class-context.php

@@ -23,6 +23,9 @@ public function __construct($session, $request, $setup) {
 
         $this->options = Json::load($this->setup->get('CONF_PATH') . '/options.json');
 
+        $this->thumbnail_height = $this->options['thumbnails']['size'] ?? 240;
+        $this->thumbnail_width = floor($this->thumbnail_height * (4 / 3));
+
         $this->passhash = $this->query_option('passhash', '');
         $this->options['hasCustomPasshash'] = strcasecmp($this->passhash, Context::$DEFAULT_PASSHASH) !== 0;
         unset($this->options['passhash']);
@@ -250,7 +253,7 @@ public function get_thumbs($requests) {
 
         foreach ($requests as $req) {
             $thumb = new Thumb($this);
-            $hrefs[] = $thumb->thumb($req['type'], $req['href'], $req['width'], $req['height']);
+            $hrefs[] = $thumb->thumb($req['type'], $req['href']);
         }
 
         return $hrefs;

src/_h5ai/private/php/ext/class-thumb.php

@@ -25,7 +25,7 @@ public function __construct($context) {
         }
     }
 
-    public function thumb($type, $source_href, $width, $height) {
+    public function thumb($type, $source_href) {
         $source_path = $this->context->to_path($source_href);
         if (!file_exists($source_path) || Util::starts_with($source_path, $this->setup->get('CACHE_PUB_PATH'))) {
             return null;
@@ -49,7 +49,7 @@ public function thumb($type, $source_href, $width, $height) {
             $capture_path = $source_path;
         }
 
-        return $this->thumb_href($capture_path, $width, $height);
+        return $this->thumb_href($capture_path, $this->context->thumbnail_width, $this->context->thumbnail_height);
     }
 
     private function thumb_href($source_path, $width, $height) {

src/_h5ai/public/css/lib/view/view.less

@@ -48,6 +48,8 @@
         .thumb {
             max-width: none;
             max-height: none;
+            object-fit: cover;
+            object-position: 50% 50%;
         }
     }
 

src/_h5ai/public/js/lib/ext/thumbnails.js

@@ -13,7 +13,6 @@ const settings = Object.assign({
     exif: false,
     chunksize: 20
 }, allsettings.thumbnails);
-const landscapeRatio = 4 / 3;
 
 
 const queueItem = (queue, item) => {
@@ -35,7 +34,6 @@ const queueItem = (queue, item) => {
         queue.push({
             type,
             href: item.absHref,
-            ratio: 1,
             callback: src => {
                 if (src && item.$view) {
                     item.thumbSquare = src;
@@ -51,7 +49,6 @@ const queueItem = (queue, item) => {
         queue.push({
             type,
             href: item.absHref,
-            ratio: landscapeRatio,
             callback: src => {
                 if (src && item.$view) {
                     item.thumbRational = src;
@@ -67,8 +64,6 @@ const requestQueue = queue => {
         return {
             type: req.type,
             href: req.href,
-            width: Math.round(settings.size * req.ratio),
-            height: settings.size
         };
     });