Add a basic WebP decoder to extract EXIF

wcfsetup/install/files/lib/system/image/WebPDecoder.class.php

@@ -0,0 +1,102 @@
+<?php
+
+namespace wcf\system\image;
+
+
+/**
+ * Provides some very basic functions to decode WebP images.
+ *
+ * @author      Alexander Ebert
+ * @copyright   2001-2025 WoltLab GmbH
+ * @license     GNU Lesser General Public License <http://opensource.org/licenses/lgpl-license.php>
+ * @since       6.1
+ */
+final class WebPDecoder
+{
+    /**
+     * Decodes the EXIF data contained in a WebP VP8X container.
+     */
+    public static function extractExifData(string $filename): array
+    {
+        // We're offloading the EXIF decoding task for `exif_read_data()` which
+        // cannot process WebP.
+        if (!\function_exists('exif_read_data')) {
+            return [];
+        }
+
+        $data = \file_get_contents($filename);
+        if (\strlen($data) <= 30) {
+            // The RIFF header for VP8X is at least 30 bytes.
+            return [];
+        }
+
+        // A WebP image must start with "RIFF" in ascii, followed by four bytes
+        // for the chunk length and then read "WEBP" at offset 8.
+        if (!(\substr($data, 0, 4) === "RIFF" && \substr($data, 8, 4) === "WEBP")) {
+            return [];
+        }
+
+        // Only VP8X contains EXIF data.
+        if (!(\substr($data, 12, 4) === "VP8X")) {
+            return [];
+        }
+
+        // Check if the EXIF bit is set.
+        $flags = \ord(\substr($data, 20, 1));
+        $hasExif = ((1 << (8 - 5)) & $flags) > 0;
+        if (!$hasExif) {
+            return [];
+        }
+
+        // Find the EXIF chunk.
+        $exifData = null;
+        $offset = 30;
+        while ($offset < \strlen($data)) {
+            $chunkHeader = \substr($data, $offset, 4);
+            // 'V' = uint32LE
+            $chunkSize = \unpack('V', \substr($data, $offset + 4, 4))[1];
+            $offset += 8;
+
+            if ($chunkHeader !== 'EXIF') {
+                // "If Chunk Size is odd, a single padding byte -- which MUST be
+                // 0 to conform with RIFF -- is added."
+                $paddingByte = $chunkSize % 2;
+                $offset += $chunkSize + $paddingByte;
+
+                continue;
+            }
+
+            $exifData = \substr($data, $offset, $chunkSize);
+        }
+
+        if ($exifData === null) {
+            return [];
+        }
+
+        // A tiny JPEG used as the host for the EXIF data.
+        // See https://github.com/mathiasbynens/small/blob/267b39f682598eebb0dafe7590b1504be79b5cad/jpeg.jpg
+        $jpg1x1px = \hex2bin("ffd8ffdb004300030202020202030202020303030304060404040404080606050609080a0a090809090a0c0f0c0a0b0e0b09090d110d0e0f101011100a0c12131210130f101010ffc9000b080001000101011100ffcc000600101005ffda0008010100003f00d2cf20ffd9");
+
+        $offset = 2;
+        // Check if the second tag is the JFIF tag.
+        if ($jpg1x1px[2] === 0xff && $jpg1x1px[3] === 0xe0) {
+            $offset += 2 + (($jpg1x1px[4] << 8) | $jpg1x1px[5]);
+        }
+
+        // Add the markers for the EXIF sequence in JPEGs.
+        $exifData = "\xFF\xE1\xC3\xEF\x45\x78\x69\x66\x00\x00" . $exifData;
+
+        $exif = \exif_read_data(
+            \sprintf(
+                "data://image/jpeg;base64,%s",
+                \base64_encode(\substr($jpg1x1px, 0, $offset) . $exifData . \substr($jpg1x1px, $offset)),
+            ),
+        );
+
+        if ($exif === false) {
+            return [];
+        }
+
+        return $exif;
+    }
+}

wcfsetup/install/files/lib/util/ExifUtil.class.php

@@ -2,6 +2,8 @@
 
 namespace wcf\util;
 
+use wcf\system\image\WebPDecoder;
+
 /**
  * Provides exif-related functions.
  *
@@ -84,14 +86,20 @@ private function __construct()
      */
     public static function getExifData($filename)
     {
-        if (\function_exists('exif_read_data')) {
-            $exifData = @\exif_read_data($filename, '', true);
-            if ($exifData !== false) {
-                return $exifData;
-            }
+        if (!\function_exists('exif_read_data')) {
+            return [];
+        }
+
+        if (FileUtil::getMimeType($filename) === 'image/webp') {
+            return WebPDecoder::extractExifData($filename);
         }
 
-        return [];
+        $exifData = @\exif_read_data($filename, '', true);
+        if ($exifData === false) {
+            return [];
+        }
+
+        return $exifData;
     }
 
     /**