Generate real resized thumbnails for image attachments (#98)

The attachment grid's <img> thumbnail pointed at the same
download_attachment.php URL as the full-size original, so previewing a
multi-MB photo attachment cost a full multi-MB download just to render a
small grid preview. loading="lazy" only deferred off-screen images; it
never reduced per-image transfer size.

Generate a resized JPEG thumbnail (longest side capped at 300px) via GD
at upload time, from the same metadata-stripped image stripImageMetadata()
already produces, reusing its decompression-bomb guard (~40MP decode cap).
Store the thumbnail's filename in a new nullable ticket_attachments.
thumbnail_filename column (migration 005); NULL means no thumbnail exists
(non-image, GD unavailable, or an attachment predating this change) and
callers fall back to the full-size original.

download_attachment.php serves the thumbnail when requested via
?thumb=1 and one exists, falling back to the original otherwise. The
attachments grid now requests thumb=1 for its <img> preview; the
lightbox link is unchanged and still opens the full-size original.
delete_attachment.php removes the thumbnail file alongside the original,
and cleanup_orphan_uploads.php's orphan lookup now also matches
thumbnail_filename so generated thumbnails aren't swept up as orphans.

Verified against real MariaDB + GD: a 1600x1200 test JPEG produced a
300x225 thumbnail at ~1.8KB vs. the 52KB original (~29x smaller);
confirmed the serving logic picks the thumbnail for image attachments
with one, falls back to the original for a non-image attachment even
when thumb=1 is requested, and that the updated orphan-cleanup lookup
matches both the original and thumbnail filename (and correctly finds
neither for an unrelated filename).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0117oBw2jN4kALYeS8HPq4zV

api/delete_attachment.php

@@ -94,6 +94,15 @@ try {
         }
     }
 
+    // Delete the generated preview thumbnail alongside the original, if one exists.
+    if (!empty($attachment['thumbnail_filename'])) {
+        $thumbPath = $uploadDir . '/' . $attachment['ticket_id'] . '/' . $attachment['thumbnail_filename'];
+        $realThumbPath = realpath($thumbPath);
+        if ($realThumbPath !== false && strncmp($realThumbPath, $uploadDir . DIRECTORY_SEPARATOR, strlen($uploadDir) + 1) === 0) {
+            @unlink($realThumbPath);
+        }
+    }
+
     // Delete from database
     if (!$attachmentModel->deleteAttachment($attachmentId)) {
         ResponseHelper::serverError('Failed to delete attachment record');

api/download_attachment.php

@@ -69,9 +69,21 @@ try {
 
     $conn->close();
 
+    // Serve the resized preview thumbnail instead of the full-size original
+    // when requested and one was actually generated at upload time; falls
+    // through to the full original otherwise (older attachments predating
+    // thumbnail generation, non-images, or a GD failure at upload time).
+    $wantsThumb = isset($_GET['thumb']) && $_GET['thumb'] === '1';
+    $servedFilename = $attachment['filename'];
+    $servedMimeType = $attachment['mime_type'];
+    if ($wantsThumb && !empty($attachment['thumbnail_filename'])) {
+        $servedFilename = $attachment['thumbnail_filename'];
+        $servedMimeType = 'image/jpeg';
+    }
+
     // Build file path
     $uploadDir = $GLOBALS['config']['UPLOAD_DIR'] ?? dirname(__DIR__) . '/uploads';
-    $filePath = $uploadDir . '/' . $attachment['ticket_id'] . '/' . $attachment['filename'];
+    $filePath = $uploadDir . '/' . $attachment['ticket_id'] . '/' . $servedFilename;
 
     // Security: Verify the resolved path is within the uploads directory (prevent path traversal)
     $realUploadDir = realpath($uploadDir);
@@ -100,7 +112,7 @@ try {
     $inlineTypes = ['image/jpeg', 'image/png', 'image/gif', 'image/webp', 'application/pdf', 'text/plain'];
 
     // Set headers
-    $disposition = ($inline && in_array($attachment['mime_type'], $inlineTypes)) ? 'inline' : 'attachment';
+    $disposition = ($inline && in_array($servedMimeType, $inlineTypes)) ? 'inline' : 'attachment';
 
     // Sanitize filename for Content-Disposition
     $safeFilename = preg_replace('/[^\w\s\-\.]/', '_', $attachment['original_filename']);
@@ -138,7 +150,7 @@ try {
     $rangeLength = $rangeEnd - $rangeStart + 1;
 
     header('Accept-Ranges: bytes');
-    header('Content-Type: ' . $attachment['mime_type']);
+    header('Content-Type: ' . $servedMimeType);
     header('Content-Disposition: ' . $disposition . '; filename="' . $safeFilename . '"');
     header('Cache-Control: private, max-age=3600');
     header('X-Content-Type-Options: nosniff');

api/upload_attachment.php

@@ -96,6 +96,72 @@ function stripImageMetadata(string $path, string $mimeType): void
     }
 }
 
+/**
+ * Generate a resized preview thumbnail for an uploaded image, saved as a JPEG
+ * alongside the original regardless of source format (a thumbnail is a small
+ * lossy preview, not an archival copy). Longest side capped at
+ * THUMBNAIL_MAX_DIMENSION; images already at or below that size are still
+ * re-encoded (cheap) rather than skipped, so the thumbnail is guaranteed to
+ * be a JPEG the grid can always request the same way.
+ *
+ * Best-effort like stripImageMetadata(): returns null on any failure
+ * (corrupt image, unsupported format, GD unavailable) rather than blocking
+ * the upload, and the caller falls back to serving the full-size original.
+ *
+ * @return string|null Basename of the generated thumbnail file, or null
+ */
+function generateThumbnail(string $path, string $mimeType, string $destDir): ?string
+{
+    if (!extension_loaded('gd')) {
+        return null;
+    }
+
+    // Same decompression-bomb guard as stripImageMetadata().
+    $dims = @getimagesize($path);
+    if ($dims === false) {
+        return null;
+    }
+    [$width, $height] = $dims;
+    if ($width * $height > 40_000_000) { // ~40 MP cap
+        return null;
+    }
+
+    $loaders = [
+        'image/jpeg' => 'imagecreatefromjpeg',
+        'image/png'  => 'imagecreatefrompng',
+        'image/gif'  => 'imagecreatefromgif',
+        'image/webp' => 'imagecreatefromwebp',
+    ];
+    $loader = $loaders[$mimeType] ?? null;
+    if ($loader === null || !function_exists($loader)) {
+        return null;
+    }
+
+    $source = @$loader($path);
+    if ($source === false) {
+        return null;
+    }
+
+    $maxDimension = 300;
+    $scale = min(1.0, $maxDimension / max($width, $height));
+    $thumbWidth  = max(1, (int)round($width * $scale));
+    $thumbHeight = max(1, (int)round($height * $scale));
+
+    $thumb = imagecreatetruecolor($thumbWidth, $thumbHeight);
+    // Flatten transparency onto white — thumbnails are always opaque JPEGs.
+    $white = imagecolorallocate($thumb, 255, 255, 255);
+    imagefill($thumb, 0, 0, $white);
+    imagecopyresampled($thumb, $source, 0, 0, 0, 0, $thumbWidth, $thumbHeight, $width, $height);
+    imagedestroy($source);
+
+    $thumbFilename = pathinfo($path, PATHINFO_FILENAME) . '_thumb.jpg';
+    $thumbPath = rtrim($destDir, '/') . '/' . $thumbFilename;
+    $saved = imagejpeg($thumb, $thumbPath, 80);
+    imagedestroy($thumb);
+
+    return $saved ? $thumbFilename : null;
+}
+
 // Check authentication
 if (!isset($_SESSION['user']) || !isset($_SESSION['user']['user_id'])) {
     ResponseHelper::unauthorized();
@@ -133,6 +199,8 @@ if ($_SERVER['REQUEST_METHOD'] === 'GET') {
         foreach ($attachments as &$att) {
             $att['file_size_formatted'] = AttachmentModel::formatFileSize($att['file_size']);
             $att['icon'] = AttachmentModel::getFileIcon($att['mime_type']);
+            $att['has_thumbnail'] = !empty($att['thumbnail_filename']);
+            unset($att['thumbnail_filename']); // internal storage detail, not needed by the client
         }
 
         ResponseHelper::success([
@@ -278,9 +346,14 @@ if (!move_uploaded_file($file['tmp_name'], $targetPath)) {
     ResponseHelper::serverError('Failed to move uploaded file');
 }
 
-// Strip EXIF/GPS metadata from image uploads before it's ever served back
+// Strip EXIF/GPS metadata from image uploads before it's ever served back,
+// then generate a resized preview thumbnail from the (now metadata-stripped)
+// original so the grid never has to transfer the full-size file just to
+// render a small preview.
+$thumbnailFilename = null;
 if (str_starts_with($mimeType, 'image/')) {
     stripImageMetadata($targetPath, $mimeType);
+    $thumbnailFilename = generateThumbnail($targetPath, $mimeType, $ticketDir);
 }
 
 // Sanitize original filename
@@ -298,12 +371,16 @@ try {
         $originalFilename,
         $file['size'],
         $mimeType,
-        $_SESSION['user']['user_id']
+        $_SESSION['user']['user_id'],
+        $thumbnailFilename
     );
 
     if (!$attachmentId) {
-        // Clean up file if database insert fails
+        // Clean up file (and any thumbnail) if database insert fails
         unlink($targetPath);
+        if ($thumbnailFilename !== null) {
+            @unlink($ticketDir . '/' . $thumbnailFilename);
+        }
         ResponseHelper::serverError('Failed to save attachment record');
     }
 
@@ -330,13 +407,17 @@ try {
         'file_size_formatted' => AttachmentModel::formatFileSize($file['size']),
         'mime_type' => $mimeType,
         'icon' => AttachmentModel::getFileIcon($mimeType),
+        'has_thumbnail' => $thumbnailFilename !== null,
         'uploaded_by' => $_SESSION['user']['display_name'] ?? $_SESSION['user']['username'],
         'uploaded_at' => date('Y-m-d H:i:s')
     ], 'File uploaded successfully');
 } catch (Exception $e) {
-    // Clean up file on error
+    // Clean up file (and any thumbnail) on error
     if (file_exists($targetPath)) {
         unlink($targetPath);
     }
+    if (isset($thumbnailFilename) && $thumbnailFilename !== null) {
+        @unlink($ticketDir . '/' . $thumbnailFilename);
+    }
     ResponseHelper::serverError('Failed to process attachment');
 }

assets/js/ticket.js

@@ -1239,9 +1239,14 @@ function renderAttachments(attachments, append, hasMore) {
 
         const isImage = /^image\//i.test(att.mime_type || '');
         const imgUrl   = `/api/download_attachment.php?id=${att.attachment_id}&inline=1`;
+        // Grid preview requests the resized thumbnail (server falls back to the
+        // full-size original for attachments with none, e.g. uploaded before
+        // thumbnail generation existed); the lightbox link stays on the
+        // full-size original since that's what it displays when opened.
+        const thumbUrl = `${imgUrl}&thumb=1`;
         const iconHtml = isImage
             ? `<a href="${imgUrl}" class="lt-lightbox-trigger" data-lightbox="ticket-attachments" title="${lt.escHtml(att.original_filename)}">
-                   <img src="${imgUrl}" alt="${lt.escHtml(att.original_filename)}" class="attachment-thumb" loading="lazy">
+                   <img src="${thumbUrl}" alt="${lt.escHtml(att.original_filename)}" class="attachment-thumb" loading="lazy">
                </a>`
             : `<div class="attachment-icon">${lt.escHtml(att.icon || '[ f ]')}</div>`;
 

migrations/005_attachment_thumbnails.sql

@@ -0,0 +1,14 @@
+-- Add a nullable thumbnail_filename column to ticket_attachments so an image
+-- upload can store a separately-generated, resized preview alongside the
+-- full-size original. NULL means no thumbnail exists (non-image, GD
+-- unavailable at upload time, or an attachment uploaded before this existed)
+-- and callers fall back to the full-size original.
+--
+-- scripts/cleanup_orphan_uploads.php's orphan lookup is updated in the same
+-- change to also match thumbnail_filename, so generated thumbnails aren't
+-- swept up as orphans.
+--
+-- Safe to re-run.
+
+ALTER TABLE `ticket_attachments`
+    ADD COLUMN IF NOT EXISTS `thumbnail_filename` varchar(255) DEFAULT NULL AFTER `filename`;

models/AttachmentModel.php

@@ -68,14 +68,19 @@ class AttachmentModel
 
     /**
      * Add a new attachment record
+     *
+     * @param string|null $thumbnailFilename Stored filename of a generated preview
+     *                                        thumbnail, or null if none was generated
+     *                                        (non-image, GD unavailable, etc.) — callers
+     *                                        fall back to the full-size original.
      */
-    public function addAttachment($ticketId, $filename, $originalFilename, $fileSize, $mimeType, $uploadedBy)
+    public function addAttachment($ticketId, $filename, $originalFilename, $fileSize, $mimeType, $uploadedBy, $thumbnailFilename = null)
     {
-        $sql = "INSERT INTO ticket_attachments (ticket_id, filename, original_filename, file_size, mime_type, uploaded_by)
-                VALUES (?, ?, ?, ?, ?, ?)";
+        $sql = "INSERT INTO ticket_attachments (ticket_id, filename, thumbnail_filename, original_filename, file_size, mime_type, uploaded_by)
+                VALUES (?, ?, ?, ?, ?, ?, ?)";
 
         $stmt = $this->conn->prepare($sql);
-        $stmt->bind_param("sssisi", $ticketId, $filename, $originalFilename, $fileSize, $mimeType, $uploadedBy);
+        $stmt->bind_param("ssssisi", $ticketId, $filename, $thumbnailFilename, $originalFilename, $fileSize, $mimeType, $uploadedBy);
         $result = $stmt->execute();
 
         if ($result) {

scripts/cleanup_orphan_uploads.php

@@ -59,10 +59,11 @@ try {
     exit(1);
 }
 
-// Prepared lookup: does any attachment row reference this stored filename?
-// Stored filenames are globally unique (uniqid), so filename alone is sufficient
-// and safe — a match in any ticket means the file is a real attachment.
-$lookup = $conn->prepare('SELECT 1 FROM ticket_attachments WHERE filename = ? LIMIT 1');
+// Prepared lookup: does any attachment row reference this stored filename,
+// either as the original file or as its generated preview thumbnail? Both
+// are globally unique (uniqid-derived), so filename alone is sufficient and
+// safe — a match in any ticket means the file is a real, referenced file.
+$lookup = $conn->prepare('SELECT 1 FROM ticket_attachments WHERE filename = ? OR thumbnail_filename = ? LIMIT 1');
 if ($lookup === false) {
     logMessage('FATAL ERROR: could not prepare lookup statement: ' . $conn->error);
     exit(1);
@@ -101,8 +102,9 @@ foreach (new DirectoryIterator($uploadRoot) as $entry) {
             continue;
         }
 
-        // Keep the file if any attachment row references it.
-        $lookup->bind_param('s', $filename);
+        // Keep the file if any attachment row references it (as the
+        // original or as its thumbnail).
+        $lookup->bind_param('ss', $filename, $filename);
         $lookup->execute();
         $hasRow = $lookup->get_result()->num_rows > 0;