[21.01] Improve feedback for remote file listing exceptions.

[jmchilton]

What did you do?

• Added more verbose exception handling and more correct status code exception handling to the remote files API endpoint.

Why did you make this change?

Proposing an alternative to part of #11580.

How to test the changes?

• Instructions for manual testing are as follows:
  1. See notes from @abretaud below about how he tested this.

[abretaud]

Ok, tested ✔️ (I played with /etc/hosts while galaxy was listing remote content)

It looks good I think:

And got this in the server logs:

Traceback (most recent call last):
  File "/opt/galaxy_dev/galaxy-dist/.venv/lib/python3.6/site-packages/urllib3/connection.py", line 160, in _new_conn
    (self._dns_host, self.port), self.timeout, **extra_kw
  File "/opt/galaxy_dev/galaxy-dist/.venv/lib/python3.6/site-packages/urllib3/util/connection.py", line 84, in create_connection
    raise err
  File "/opt/galaxy_dev/galaxy-dist/.venv/lib/python3.6/site-packages/urllib3/util/connection.py", line 74, in create_connection
    sock.connect(sa)
TimeoutError: [Errno 110] Connection timed out

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/opt/galaxy_dev/galaxy-dist/.venv/lib/python3.6/site-packages/urllib3/connectionpool.py", line 677, in urlopen
    chunked=chunked,
  File "/opt/galaxy_dev/galaxy-dist/.venv/lib/python3.6/site-packages/urllib3/connectionpool.py", line 381, in _make_request
    self._validate_conn(conn)
  File "/opt/galaxy_dev/galaxy-dist/.venv/lib/python3.6/site-packages/urllib3/connectionpool.py", line 978, in _validate_conn
    conn.connect()
  File "/opt/galaxy_dev/galaxy-dist/.venv/lib/python3.6/site-packages/urllib3/connection.py", line 309, in connect
    conn = self._new_conn()
  File "/opt/galaxy_dev/galaxy-dist/.venv/lib/python3.6/site-packages/urllib3/connection.py", line 172, in _new_conn
    self, "Failed to establish a new connection: %s" % e
urllib3.exceptions.NewConnectionError: <urllib3.connection.HTTPSConnection object at 0x7f84cb22ad30>: Failed to establish a new connection: [Errno 110] Connection timed out

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/opt/galaxy_dev/galaxy-dist/.venv/lib/python3.6/site-packages/requests/adapters.py", line 449, in send
    timeout=timeout
  File "/opt/galaxy_dev/galaxy-dist/.venv/lib/python3.6/site-packages/urllib3/connectionpool.py", line 727, in urlopen
    method, url, error=e, _pool=self, _stacktrace=sys.exc_info()[2]
  File "/opt/galaxy_dev/galaxy-dist/.venv/lib/python3.6/site-packages/urllib3/util/retry.py", line 446, in increment
    raise MaxRetryError(_pool, url, error or ResponseError(cause))
urllib3.exceptions.MaxRetryError: HTTPSConnectionPool(host='data-access.cesgo.org', port=443): Max retries exceeded with url: //remote.php/webdav/foobar.pdf (Caused by NewConnectionError('<urllib3.connection.HTTPSConnection object at 0x7f84cb22ad30>: Failed to establish a new connection: [Errno 110] Connection timed out',))

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/opt/galaxy_dev/galaxy-dist/.venv/lib/python3.6/site-packages/webdav2/client.py", line 58, in _wrapper
    res = fn(self, *args, **kw)
  File "/opt/galaxy_dev/galaxy-dist/.venv/lib/python3.6/site-packages/webdav2/client.py", line 626, in info
    headers=self.get_header('info')
  File "/opt/galaxy_dev/galaxy-dist/.venv/lib/python3.6/site-packages/requests/api.py", line 61, in request
    return session.request(method=method, url=url, **kwargs)
  File "/opt/galaxy_dev/galaxy-dist/.venv/lib/python3.6/site-packages/requests/sessions.py", line 530, in request
    resp = self.send(prep, **send_kwargs)
  File "/opt/galaxy_dev/galaxy-dist/.venv/lib/python3.6/site-packages/requests/sessions.py", line 643, in send
    r = adapter.send(request, **kwargs)
  File "/opt/galaxy_dev/galaxy-dist/.venv/lib/python3.6/site-packages/requests/adapters.py", line 516, in send
    raise ConnectionError(e, request=request)
requests.exceptions.ConnectionError: HTTPSConnectionPool(host='data-access.cesgo.org', port=443): Max retries exceeded with url: //remote.php/webdav/foobar.pdf (Caused by NewConnectionError('<urllib3.connection.HTTPSConnection object at 0x7f84cb22ad30>: Failed to establish a new connection: [Errno 110] Connection timed out',))

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "lib/galaxy/webapps/galaxy/api/remote_files.py", line 72, in index
    index = file_source.list(file_source_path.path, recursive=recursive, user_context=user_context)
  File "lib/galaxy/files/sources/_pyfilesystem2.py", line 39, in list
    return list(map(to_dict, res))
  File "/opt/galaxy_dev/galaxy-dist/.venv/lib/python3.6/site-packages/fs/base.py", line 1266, in <genexpr>
    for name in self.listdir(path)
  File "/opt/galaxy_dev/galaxy-dist/.venv/lib/python3.6/site-packages/webdavfs/webdavfs.py", line 248, in getinfo
    info = self.client.info(_path.encode('utf-8'))
  File "/opt/galaxy_dev/galaxy-dist/.venv/lib/python3.6/site-packages/webdav2/client.py", line 60, in _wrapper
    raise NotConnection(self.webdav.hostname)
webdav2.exceptions.NotConnection: Not connection with https://data-access.cesgo.org/