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)

server/tests/test_export.py

@@ -8,6 +8,8 @@ import zipfile
 from pathlib import Path
 from unittest.mock import AsyncMock, patch
 
+from fastapi import HTTPException
+
 SERVER_DIR = Path(__file__).resolve().parents[1]
 if str(SERVER_DIR) not in sys.path:
     sys.path.insert(0, str(SERVER_DIR))
@@ -16,6 +18,23 @@ from api.export import ExportImageItem, ExportImagesRequest, export_image, expor
 
 
 class ExportImageTests(unittest.IsolatedAsyncioTestCase):
+    async def test_extensionless_image_with_generic_mime_can_be_downloaded(self) -> None:
+        image = ExportImageItem(url="https://example.com/assets/opaque-key", key="upload")
+        png = b"\x89PNG\r\n\x1a\n" + b"image bytes"
+        with patch("api.export._download", new=AsyncMock(return_value=(png, "application/octet-stream"))):
+            response = await export_image(image)
+
+        self.assertEqual(response.status_code, 200)
+        self.assertEqual(response.media_type, "image/png")
+        self.assertIn('filename="upload.png"', response.headers["content-disposition"])
+
+    async def test_extensionless_non_image_is_rejected(self) -> None:
+        image = ExportImageItem(url="https://example.com/assets/opaque-key")
+        with patch("api.export._download", new=AsyncMock(return_value=(b"not an image", "application/octet-stream"))):
+            with self.assertRaises(HTTPException) as raised:
+                await export_image(image)
+        self.assertEqual(raised.exception.status_code, 400)
+
     async def test_chinese_filename_uses_rfc5987_header(self) -> None:
         image = ExportImageItem(
             url="https://example.com/image.png",