feat: 修改 400问题

server/api/export.py

@@ -82,6 +82,23 @@ def _is_image(url: str, ctype: str) -> bool:
     return bool(re.search(r"\.(jpe?g|png|webp|gif|bmp)(\?|$)", url, re.IGNORECASE))
 
 
+def _image_content_type(data: bytes, url: str, ctype: str) -> str | None:
+    """存储对象无扩展名且 MIME 为 octet-stream 时，按图片文件头识别格式。"""
+    if ctype.split(";")[0].strip().lower().startswith("image/"):
+        return ctype
+    if data.startswith(b"\xff\xd8\xff"):
+        return "image/jpeg"
+    if data.startswith(b"\x89PNG\r\n\x1a\n"):
+        return "image/png"
+    if data.startswith((b"GIF87a", b"GIF89a")):
+        return "image/gif"
+    if data.startswith(b"RIFF") and data[8:12] == b"WEBP":
+        return "image/webp"
+    if data.startswith(b"BM"):
+        return "image/bmp"
+    return ctype if _is_image(url, ctype) else None
+
+
 def _download_disposition(filename: str) -> str:
     """生成兼容中文文件名的下载响应头。
 
@@ -138,7 +155,8 @@ async def export_images(req: ExportImagesRequest):
                     raise HTTPException(status_code=504, detail=str(exc)) from exc
                 except Exception:  # noqa: BLE001
                     continue  # 单张下载失败不中断整包
-                if not _is_image(img.url, ctype):
+                ctype = _image_content_type(data, img.url, ctype)
+                if ctype is None:
                     continue
                 total_source_bytes += len(data)
                 if total_source_bytes > settings.export_zip_max_bytes:
@@ -192,7 +210,8 @@ async def export_image(img: ExportImageItem):
         raise HTTPException(status_code=504, detail=str(exc)) from exc
     except Exception as exc:  # noqa: BLE001
         raise HTTPException(status_code=422, detail="图片下载失败") from exc
-    if not _is_image(img.url, ctype):
+    ctype = _image_content_type(data, img.url, ctype)
+    if ctype is None:
         raise HTTPException(status_code=400, detail="该地址不是图片")
 
     ext = _ext(img.url, ctype)