use returncode of iterable_subproccess generator

This commit modifies SshUrlOperations to make use
of the `returncode`-attribute of the generator that
is returned by `with iterable_subprocess`.

This allows to fetch the return code of the subprocess
even if no `IterableSubprocessError` was raised.
This situation can occur, if an exception is raised
in an `iterable_subprocess`-context.

datalad_next/url_operations/ssh.py

@@ -94,17 +94,9 @@ def stat(self,
         cmd = ssh_cat.get_cmd(SshUrlOperations._stat_cmd)
         try:
             with iter_subproc(cmd) as stream:
-                # any exception that is raised in this context and not caught
-                # will prevent the creation of `IterableSubprocessError`. But
-                # we rely on the return code of the ssh-process to signal
-                # specific errors. Therefore, we catch the expected
-                # `StopIteration` here.
-                try:
-                    props = self._get_props(url, stream)
-                except StopIteration:
-                    pass
-        except IterableSubprocessError as e:
-            self._check_return_code(e.returncode, url)
+                props = self._get_props(url, stream)
+        except (IterableSubprocessError, StopIteration):
+            self._check_return_code(stream.returncode, url)
         return {k: v for k, v in props.items() if not k.startswith('_')}
 
     def _get_props(self, url, stream: Generator) -> dict:
@@ -177,44 +169,36 @@ def download(self,
         cmd = ssh_cat.get_cmd(f'{SshUrlOperations._stat_cmd}; {SshUrlOperations._cat_cmd}')
         try:
             with iter_subproc(cmd) as stream:
-                # any exception that is raised in this context and not caught
-                # will prevent the creation of `IterableSubprocessError`. But
-                # we rely on the return code of the ssh-process to signal
-                # specific errors. Therefore, we catch the expected
-                # `StopIteration` here.
-                try:
-                    props = self._get_props(from_url, stream)
-                    expected_size = props['content-length']
-                    # The stream might have changed due to not yet processed, but
-                    # fetched data, that is now chained in front of it. Therefore we
-                    # get the updated stream from the props
-                    download_stream = props.pop('_stream')
-
-                    dst_fp = sys.stdout.buffer \
-                        if to_path is None \
-                        else open(to_path, 'wb')
-
-                    # Localize variable access to minimize overhead
-                    dst_fp_write = dst_fp.write
-
-                    # download can start
-                    for chunk in self._with_progress(
-                            download_stream,
-                            progress_id=progress_id,
-                            label='downloading',
-                            expected_size=expected_size,
-                            start_log_msg=('Download %s to %s', from_url, to_path),
-                            end_log_msg=('Finished download',),
-                            update_log_msg=('Downloaded chunk',)
-                    ):
-                        # write data
-                        dst_fp_write(chunk)
-                        # compute hash simultaneously
-                        hasher.update(chunk)
-                except StopIteration:
-                    pass
-        except IterableSubprocessError as e:
-            self._check_return_code(e.returncode, from_url)
+                props = self._get_props(from_url, stream)
+                expected_size = props['content-length']
+                # The stream might have changed due to not yet processed, but
+                # fetched data, that is now chained in front of it. Therefore we
+                # get the updated stream from the props
+                download_stream = props.pop('_stream')
+
+                dst_fp = sys.stdout.buffer \
+                    if to_path is None \
+                    else open(to_path, 'wb')
+
+                # Localize variable access to minimize overhead
+                dst_fp_write = dst_fp.write
+
+                # download can start
+                for chunk in self._with_progress(
+                        download_stream,
+                        progress_id=progress_id,
+                        label='downloading',
+                        expected_size=expected_size,
+                        start_log_msg=('Download %s to %s', from_url, to_path),
+                        end_log_msg=('Finished download',),
+                        update_log_msg=('Downloaded chunk',)
+                ):
+                    # write data
+                    dst_fp_write(chunk)
+                    # compute hash simultaneously
+                    hasher.update(chunk)
+        except (IterableSubprocessError, StopIteration):
+            self._check_return_code(stream.returncode, from_url)
         finally:
             if dst_fp and to_path is not None:
                 dst_fp.close()