feat(download): add experimental aria2 backend

tests/services/test_download_manager_basic.py

@@ -179,6 +179,7 @@ async def test_successful_download_uses_defaults(
         progress_callback,
         model_type,
         download_id,
+        transfer_backend=None,
     ):
         captured.update(
             {
@@ -268,6 +269,7 @@ async def test_download_uses_active_mirrors(
         progress_callback,
         model_type,
         download_id,
+        transfer_backend=None,
     ):
         captured["download_urls"] = download_urls
         return {"success": True}
@@ -288,6 +290,214 @@ async def test_download_uses_active_mirrors(
     assert captured["download_urls"] == ["https://mirror.example/file.safetensors"]
 
 
+@pytest.mark.asyncio
+async def test_pause_resume_cancel_delegate_to_aria2_backend(monkeypatch):
+    manager = DownloadManager()
+
+    task = asyncio.create_task(asyncio.sleep(60))
+    manager._download_tasks["download-1"] = task
+    manager._pause_events["download-1"] = download_manager.DownloadStreamControl()
+    manager._active_downloads["download-1"] = {
+        "transfer_backend": "aria2",
+        "status": "downloading",
+    }
+
+    class DummyAria2Downloader:
+        def __init__(self):
+            self.calls = []
+
+        async def pause_download(self, download_id):
+            self.calls.append(("pause", download_id))
+            return {"success": True, "message": "paused"}
+
+        async def resume_download(self, download_id):
+            self.calls.append(("resume", download_id))
+            return {"success": True, "message": "resumed"}
+
+        async def cancel_download(self, download_id):
+            self.calls.append(("cancel", download_id))
+            return {"success": True, "message": "cancelled"}
+
+        async def has_transfer(self, download_id):
+            self.calls.append(("has_transfer", download_id))
+            return True
+
+    dummy_aria2 = DummyAria2Downloader()
+    monkeypatch.setattr(
+        download_manager,
+        "get_aria2_downloader",
+        AsyncMock(return_value=dummy_aria2),
+    )
+
+    pause_result = await manager.pause_download("download-1")
+    assert pause_result["success"] is True
+    assert manager._active_downloads["download-1"]["status"] == "paused"
+
+    resume_result = await manager.resume_download("download-1")
+    assert resume_result["success"] is True
+    assert manager._active_downloads["download-1"]["status"] == "downloading"
+
+    cancel_result = await manager.cancel_download("download-1")
+    assert cancel_result["success"] is True
+    assert task.cancelled() or task.done()
+    assert dummy_aria2.calls == [
+        ("has_transfer", "download-1"),
+        ("pause", "download-1"),
+        ("has_transfer", "download-1"),
+        ("resume", "download-1"),
+        ("cancel", "download-1"),
+    ]
+
+
+@pytest.mark.asyncio
+async def test_cancel_allows_queued_aria2_task_without_transfer(monkeypatch):
+    manager = DownloadManager()
+
+    started = asyncio.Event()
+
+    async def blocked_task():
+        started.set()
+        await asyncio.sleep(60)
+
+    task = asyncio.create_task(blocked_task())
+    await started.wait()
+
+    manager._download_tasks["download-queued"] = task
+    manager._active_downloads["download-queued"] = {
+        "transfer_backend": "aria2",
+        "status": "queued",
+    }
+
+    class DummyAria2Downloader:
+        async def cancel_download(self, download_id):
+            return {"success": False, "error": "Download task not found"}
+
+    monkeypatch.setattr(
+        download_manager,
+        "get_aria2_downloader",
+        AsyncMock(return_value=DummyAria2Downloader()),
+    )
+
+    result = await manager.cancel_download("download-queued")
+
+    assert result["success"] is True
+    assert task.cancelled() or task.done()
+
+
+@pytest.mark.asyncio
+async def test_pause_resume_queued_aria2_task_without_transfer(monkeypatch):
+    manager = DownloadManager()
+
+    task = asyncio.create_task(asyncio.sleep(60))
+    manager._download_tasks["download-queued"] = task
+    manager._pause_events["download-queued"] = download_manager.DownloadStreamControl()
+    manager._active_downloads["download-queued"] = {
+        "transfer_backend": "aria2",
+        "status": "waiting",
+        "bytes_per_second": 12.0,
+    }
+
+    class DummyAria2Downloader:
+        def __init__(self):
+            self.calls = []
+
+        async def has_transfer(self, download_id):
+            self.calls.append(("has_transfer", download_id))
+            return False
+
+        async def pause_download(self, download_id):
+            self.calls.append(("pause", download_id))
+            return {"success": True, "message": "paused"}
+
+        async def resume_download(self, download_id):
+            self.calls.append(("resume", download_id))
+            return {"success": True, "message": "resumed"}
+
+    dummy_aria2 = DummyAria2Downloader()
+    monkeypatch.setattr(
+        download_manager,
+        "get_aria2_downloader",
+        AsyncMock(return_value=dummy_aria2),
+    )
+
+    pause_result = await manager.pause_download("download-queued")
+    assert pause_result == {"success": True, "message": "Download paused successfully"}
+    assert manager._active_downloads["download-queued"]["status"] == "paused"
+    assert manager._pause_events["download-queued"].is_paused() is True
+
+    resume_result = await manager.resume_download("download-queued")
+    assert resume_result == {"success": True, "message": "Download resumed successfully"}
+    assert manager._active_downloads["download-queued"]["status"] == "downloading"
+    assert manager._pause_events["download-queued"].is_set() is True
+    assert dummy_aria2.calls == [
+        ("has_transfer", "download-queued"),
+        ("has_transfer", "download-queued"),
+    ]
+
+    task.cancel()
+    with pytest.raises(asyncio.CancelledError):
+        await task
+
+
+@pytest.mark.asyncio
+async def test_download_uses_captured_backend_when_settings_change(
+    monkeypatch, scanners, metadata_provider, tmp_path
+):
+    manager = DownloadManager()
+    settings = get_settings_manager()
+    settings.settings["download_backend"] = "aria2"
+
+    semaphore = asyncio.Semaphore(0)
+    manager._download_semaphore = semaphore
+
+    captured = {}
+
+    async def fake_execute_original_download(
+        self,
+        model_id,
+        model_version_id,
+        save_dir,
+        relative_path,
+        progress_callback,
+        use_default_paths,
+        download_id=None,
+        transfer_backend="python",
+        source=None,
+        file_params=None,
+    ):
+        captured["transfer_backend"] = transfer_backend
+        return {"success": True}
+
+    monkeypatch.setattr(
+        DownloadManager,
+        "_execute_original_download",
+        fake_execute_original_download,
+    )
+
+    download_task = asyncio.create_task(
+        manager.download_from_civitai(
+            model_version_id=99,
+            save_dir=str(tmp_path),
+            use_default_paths=True,
+            progress_callback=None,
+            source=None,
+        )
+    )
+
+    await asyncio.sleep(0)
+    assert len(manager._active_downloads) == 1
+    download_id = next(iter(manager._active_downloads))
+    assert manager._active_downloads[download_id]["transfer_backend"] == "aria2"
+
+    settings.settings["download_backend"] = "python"
+    semaphore.release()
+
+    result = await download_task
+
+    assert result["success"] is True
+    assert captured["transfer_backend"] == "aria2"
+
+
 @pytest.mark.asyncio
 async def test_download_aborts_when_version_exists(
     monkeypatch, scanners, metadata_provider