Improve error with missing dataset DOI

[mih]

Current state:

% DATAVERSE_API_TOKEN=5367f732-36bd-46ed-975a-9eeaeb98fe74  git annex initremote dv1 encryption=none type=external externaltype=dataverse url=http://localhost:8080
initremote dv1 
git-annex: external special remote error: ERROR: GET HTTP 404 - http://localhost:8080/api/v1/datasets/:persistentId/?persistentId=. MSG: {"status":"ERROR","message":"Dataset with Persistent ID  not found."}
failed
initremote: 1 failed

[bpoldrack]

Generally there are two ways of doing that in a special remote, assuming the problem is based on some exception (in that case a ConnectionError from the requests package.

1. Have low level log for the actual exception and kinda decouple the user facing message:

try:
    do_the_request()
except requests.exceptions.ConnectionError as exc:
    # This will make sure the exception itself including its traceback, `__cause__`, `__context` is logged:
    ce =CapturedException(exc)
    # Form a proper user message.
    # Note: `CapturedException` provides a couple of properties to reuse (parts of) the original exception.
    self.message("Connection for purpose X failed due to {reason}".format(ce.message))
    sys.exit(1)  # Not sure if needed from the top of my head

2. Include more generic information, which may be needed for debugging or really understanding the issue

try:
    do_the_request()
except RequestException as exc:
    # Note, that `RequestException` is more general
    raise ValueError("New message to provide context to the user") from exc

This will result in the an error message like New message to provide context to the user -- caused by -- ERROR: GET HTTP 404 - http://localhost:8080/api/v1/datasets/:persistentId/?persistentId=. ....

[jernsting]

Related to #48? I would opt for the second option

[jernsting]

Already done in #74