fix: modify resource download (#258)

* fix: modify resource download

Author: lu-yg

base/src/main/java/com/tinyengine/it/common/utils/ImageThumbnailGenerator.java

@@ -215,6 +215,26 @@ public static String extractCleanBase64(String input) {
         return trimmed;
     }
 
+    /**
+     * 从 Base64 数据中提取 MIME 类型
+     * @param base64Data 完整的 Base64 数据（包含 data:image/png;base64, 前缀）
+     * @return 提取到的 MIME 类型，如 "image/png", "image/svg+xml"
+     */
+    public static String extractContentType(String base64Data) {
+        if (base64Data == null || !base64Data.startsWith("data:")) {
+            throw new IllegalArgumentException("Invalid Base64 data format");
+        }
+
+        Pattern pattern = Pattern.compile("^data:([^;]+);");
+        Matcher matcher = pattern.matcher(base64Data);
+
+        if (matcher.find()) {
+            return matcher.group(1);
+        }
+
+        throw new IllegalArgumentException("Cannot extract content type from Base64 data");
+    }
+
     /**
      * MIME类型转格式
      */

base/src/main/java/com/tinyengine/it/controller/ResourceController.java

@@ -270,14 +270,13 @@ public void getResource(@RequestParam("data") String data, HttpServletResponse r
         String cleanBase64 = ImageThumbnailGenerator.extractCleanBase64(base64Data);
         byte[] imageBytes = Base64.getDecoder().decode(cleanBase64);
 
-        String detectedType = ImageThumbnailGenerator.detectFormatFromBase64(base64Data);
-        String fileExtension = detectedType.equals("jpeg") ? "jpg" : detectedType;
+        String detectedType = ImageThumbnailGenerator.extractContentType(base64Data);
 
         String fileName = useOriginal ? resource.getName() : "thumbnail_" + resource.getName();
         // URL编码文件名
         String encodedFileName = URLEncoder.encode(fileName, StandardCharsets.UTF_8)
                 .replace("+", "%20");
-        response.setContentType("image/" + detectedType);
+        response.setContentType(detectedType);
 
         // 只使用 filename* 格式，避免中文字符直接出现在header中
         response.setHeader("Content-Disposition",