download returns useful message when HTTP status code is 412

[nanjiangshu]

Related issue(s) and PR(s)
This PR closes #623

Description
sda-cli returns the original message when the HTTP status code is 412. When the status code is others, still return just the status code to avoid exposing unnecessary information to the user

How to test
That unit test and integration tests pass.

[jbygdell]

Suggested change

	switch res.StatusCode {
	case http.StatusOK:
	return resBody, nil
	case http.StatusPreconditionFailed: // Return the original message from the server in case of 412
	return nil, errors.New(strings.TrimSpace(string(resBody)))
	default:
	return nil, fmt.Errorf("server returned status %d", res.StatusCode)
	}
	if res.StatusCode != http.StatusOK {
	return nil, errors.New(strings.TrimSpace(string(resBody)))
	}
	return resBody, nil

We shouldn't treat this as a special case. It's better to always return any error string to the user.

[nanjiangshu]

I'm not quite sure if it's better to always return any error string to the user. We had a previous issue to filter error messages returned from the API and just show the HTTP code. For this special case (412), I'm pretty sure error messages returned from the API are quite clean, but not sure for all the other cases.

[KarlG-nbis]

Not directly related to this PR, but to me if would be cleaner if we remove the appVersion variable, and instead update the functions that uses it to take the version as a argument, eg:

func datasetCase(token, version string) error {
...
}

And we would pass the version from the Download invocation

[nanjiangshu]

I agree. We should note this in the future refactoring issue.