Fall back from link upload to next file transfer

src/scitacean/transfer/link.py

@@ -225,8 +225,10 @@ def connect_for_upload(
             "`LinkFileTransfer` cannot be used for uploading files. "
             "If you have direct access to the file server, consider either "
             "copying the files into place or writing them directly to the "
-            "'remote folder'."
+            "'remote folder'. See also scitacean.transfer.copy.CopyFileTransfer.",
         )
+        # This is needed to make this function a context manager:
+        yield LinkUploadConnection(source_folder=self.source_folder)  # type: ignore[unreachable]
 
 
 __all__ = ["LinkDownloadConnection", "LinkFileTransfer", "LinkUploadConnection"]

src/scitacean/transfer/select.py

@@ -151,7 +151,7 @@ def _connect_first_suitable(
                     # a different transfer if the actual download / upload fails
                     # but only if connecting fails.
                     connection = connection_manager.__enter__()
-                except RuntimeError as error:
+                except (RuntimeError, NotImplementedError) as error:
                     errors.append(error)
                     continue
                 success = True

tests/transfer/link_test.py

@@ -88,7 +88,8 @@ def test_link_transfer_cannot_upload() -> None:
     ds = Dataset(type="raw", source_folder=RemotePath("/data/upload"))
     linker = LinkFileTransfer()
     with pytest.raises(NotImplementedError):
-        linker.connect_for_upload(ds, cast(RemotePath, ds.source_folder))
+        with linker.connect_for_upload(ds, cast(RemotePath, ds.source_folder)):
+            ...
 
 
 def test_link_transfer_raises_if_file_does_not_exist(

tests/transfer/select_transfer_test.py

@@ -3,6 +3,7 @@
 from __future__ import annotations
 
 import dataclasses
+import sys
 from collections.abc import Iterator
 from contextlib import contextmanager
 from pathlib import Path
@@ -11,6 +12,8 @@
 import pytest
 
 from scitacean import Dataset, File, RemotePath
+from scitacean.transfer.copy import CopyFileTransfer
+from scitacean.transfer.link import LinkFileTransfer
 from scitacean.transfer.select import SelectFileTransfer
 
 
@@ -300,3 +303,24 @@ def test_select_upload_uses_second_child_transfer_success(dataset: Dataset) -> N
     assert transfer_2.uploaded == [file.local_path]
     assert not transfer_2.downloaded
     assert not transfer_2.reverted
+
+
+@pytest.mark.skipif(
+    sys.platform.startswith("win"),
+    reason="Copy and link transfers do not support Windows",
+)
+@pytest.mark.parametrize("hard_link", [True, False])
+def test_copy_and_link_transfers_fall_back(dataset: Dataset, hard_link: bool) -> None:
+    copier = CopyFileTransfer(hard_link=hard_link)
+    linker = LinkFileTransfer()
+    fallback = SuccessfulTransfer()
+    transfer = SelectFileTransfer([copier, linker, fallback])
+
+    file = File.from_local("/not-a-real-parent/local_file", remote_path="remote_file")
+    with transfer.connect_for_upload(dataset, RemotePath("remote_file")) as con:
+        con.upload_files(file)
+
+    assert not fallback.is_open_for_download
+    assert fallback.uploaded == [file.local_path]
+    assert not fallback.downloaded
+    assert not fallback.reverted