fix(download): treat blank save path as default directory

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

app/application/directory.py

@@ -839,6 +839,21 @@ def _validate_download_save_path_value(
     raise ValueError("保存路径不在允许的下载目录范围内")
 
 
+def specified_download_save_path(save_path: Optional[str]) -> Optional[str]:
+    """
+    返回调用方真正指定的下载保存目录，空白值视为未指定。
+
+    旧版订阅编辑界面会把清空的保存目录持久化为空字符串，它表示使用默认下载目录，
+    不能当作非法路径交给 validate_download_save_path 拒绝。
+
+    :param save_path: 订阅、事件或接口传入的保存目录
+    :return: 原样保留的非空保存目录；空值或纯空白返回 None
+    """
+    if save_path is None or not str(save_path).strip():
+        return None
+    return save_path
+
+
 def validate_download_save_path(save_path: str) -> str:
     """
     校验用户传入的下载保存目录，/download/paths 暴露的下载目录配置是允许写入的公共合同。

app/chain/download/submission.py

@@ -9,7 +9,10 @@ from typing import Any, Callable, Dict, Optional, Set, Tuple, Union, cast
 from urllib.parse import urlencode, urljoin, urlparse
 
 from app.application.configuration import get_chain_runtime_config_snapshot
-from app.application.directory import validate_download_save_path
+from app.application.directory import (
+    specified_download_save_path,
+    validate_download_save_path,
+)
 from app.application.download.admission import SubscriptionDownloadGovernance
 from app.application.site.sites import SitesHelper  # pylint: disable=import-error,no-name-in-module
 from app.application.torrent.download import TorrentHelper
@@ -293,6 +296,8 @@ class _DownloadResourceOwner(_DownloadOwnerBase):
             username: Optional[str],
     ) -> tuple[Optional[str], Optional[str]]:
         """应用资源下载事件覆盖，并校验事件返回的下载目录。"""
+        # 空白保存目录表示使用默认下载目录，事件订阅方也只会看到 None。
+        save_path = specified_download_save_path(save_path)
         meta = context.meta_info
         media = context.media_info
         event_data = ResourceDownloadEventData(
@@ -319,7 +324,9 @@ class _DownloadResourceOwner(_DownloadOwnerBase):
                 )
                 return save_path, "下载被事件取消"
             if event_data.options and "save_path" in event_data.options:
-                save_path = cast(Optional[str], event_data.options.get("save_path"))
+                save_path = specified_download_save_path(
+                    cast(Optional[str], event_data.options.get("save_path"))
+                )
         if save_path is None:
             return None, None
         try:

app/chain/download/subtitle.py

@@ -12,6 +12,7 @@ from app.application.configuration import get_chain_runtime_config_snapshot
 from app.application.directory import (
     DirectoryHelper,
     build_media_download_path,
+    specified_download_save_path,
     validate_download_save_path,
 )
 from app.application.torrent.download import TorrentHelper
@@ -321,6 +322,7 @@ class DownloadSubtitleOwner(_DownloadOwnerBase):
         根据媒体信息解析下载目录。
         """
         storage = 'local'
+        save_path = specified_download_save_path(save_path)
         if save_path is not None:
             try:
                 validated_save_path = validate_download_save_path(save_path)

tests/test_download_chain.py

@@ -577,6 +577,69 @@ def test_download_single_supplements_category_before_download_event(monkeypatch)
     assert context.media_info.tmdb_id == 12345
 
 
+@pytest.mark.parametrize("save_path", ["", "   "])
+def test_resource_download_event_treats_blank_save_path_as_default(monkeypatch, save_path):
+    """旧订阅持久化的空白保存目录表示使用默认目录，不能被路径校验拒绝。"""
+    captured = {}
+
+    def keep_event(_event_type, event_data):
+        """记录事件订阅方看到的保存目录。"""
+        captured["save_path"] = event_data.options["save_path"]
+        return SimpleNamespace(event_data=event_data)
+
+    monkeypatch.setattr(eventmanager, "send_event", keep_event)
+    context = Context(
+        meta_info=MetaInfo("测试剧集 S01E01"),
+        media_info=MediaInfo(type=MediaType.TV, title="测试剧集"),
+        torrent_info=TorrentInfo(title="测试剧集 S01E01"),
+    )
+
+    result = DownloadChain._apply_resource_download_event(
+        context, None, None, "Subscribe|{}", None, save_path, None, None,
+    )
+
+    assert result == (None, None)
+    assert captured["save_path"] is None
+
+
+def test_resource_download_event_treats_blank_override_as_default(monkeypatch):
+    """事件把保存目录改成空白时同样回到默认目录。"""
+
+    def blank_override(_event_type, event_data):
+        """模拟插件清空保存目录。"""
+        event_data.options["save_path"] = " "
+        return SimpleNamespace(event_data=event_data)
+
+    monkeypatch.setattr(eventmanager, "send_event", blank_override)
+    context = Context(
+        meta_info=MetaInfo("测试剧集 S01E01"),
+        media_info=MediaInfo(type=MediaType.TV, title="测试剧集"),
+        torrent_info=TorrentInfo(title="测试剧集 S01E01"),
+    )
+
+    result = DownloadChain._apply_resource_download_event(
+        context, None, None, None, None, "/downloads/tv", None, None,
+    )
+
+    assert result == (None, None)
+
+
+def test_resource_download_event_still_rejects_invalid_save_path(monkeypatch):
+    """非空白的非法保存目录仍按白名单拒绝。"""
+    monkeypatch.setattr(eventmanager, "send_event", lambda *_args: None)
+    context = Context(
+        meta_info=MetaInfo("测试剧集 S01E01"),
+        media_info=MediaInfo(type=MediaType.TV, title="测试剧集"),
+        torrent_info=TorrentInfo(title="测试剧集 S01E01"),
+    )
+
+    result = DownloadChain._apply_resource_download_event(
+        context, None, None, None, None, "relative/path", None, None,
+    )
+
+    assert result == ("relative/path", "保存路径必须是绝对路径")
+
+
 def test_download_single_persists_custom_words_snapshot(monkeypatch):
     """下载成功登记历史时，应把传入的订阅识别词原样存入快照，供整理时原样复现识别。"""
     captured = {}

tests/test_download_save_path_alias.py

@@ -4,7 +4,11 @@ from unittest.mock import patch
 
 import pytest
 
-from app.application.directory import DirectoryHelper, validate_download_save_path
+from app.application.directory import (
+    DirectoryHelper,
+    specified_download_save_path,
+    validate_download_save_path,
+)
 from app.chain.download.subtitle import DownloadSubtitleOwner
 from app.domain.context import MediaInfo
 from app.schemas.system import TransferDirectoryConf
@@ -139,3 +143,18 @@ def test_resolve_media_download_dir_surfaces_unknown_alias_error():
     with patch.object(DirectoryHelper, "get_download_dirs", return_value=dirs):
         result = DownloadSubtitleOwner._resolve_media_download_dir(media, save_path="不存在的库")
     assert result == (None, None, "未找到名为「不存在的库」的下载目录")
+
+
+@pytest.mark.parametrize(("value", "expected"), [(None, None), ("", None), ("  ", None), ("剧集库", "剧集库")])
+def test_specified_download_save_path_treats_blank_as_unspecified(value, expected):
+    """空白保存目录视为未指定，非空值原样交给后续校验。"""
+    assert specified_download_save_path(value) == expected
+
+
+def test_resolve_media_download_dir_uses_default_dir_for_blank_save_path():
+    """空字符串保存目录走媒体默认下载目录，而不是报“保存路径不能为空”。"""
+    default_dir = TransferDirectoryConf(name="剧集库", priority=1, storage="local", download_path="/downloads/tv")
+    media = MediaInfo(type=MediaType.TV, title="测试剧集")
+    with patch.object(DirectoryHelper, "get_dir", return_value=default_dir):
+        result = DownloadSubtitleOwner._resolve_media_download_dir(media, save_path="")
+    assert result == ("local", Path("/downloads/tv"), "")