Misleading Exceptions

[andersbogsnes]

I just updated to 0.3.0 and am adapting my own libraries to these changes - great to have support for azure blob storage 12!

I noticed that some of the exceptions are overly broad and gives the end-user a misleading error message.

For example, passing invalid credentials will raise a FileNotFoundError, suppressing Azure Blob Storages AuthorizationFailure.

Example:
While running Azurite:

>>> connection_string = "DefaultEndpointsProtocol=http;AccountName=devstoreaccount1;AccountKey=test;BlobEndpoint=http://127.0.0.1:10000/devstoreaccount1;" # Notice invalid AccountKey here

>>> abfs = AzureBlobFileSystem(account_name="test", connection_string=connection_string)
>>> abfs.ls(".")
azure.core.exceptions.HttpResponseError: Server failed to authenticate the request. Make sure the value of the Authorization header is formed correctly including the signature.
RequestId:63c0f3c2-d764-48dd-b7fa-522322a61e79
Time:2020-05-25T14:01:15.322Z
ErrorCode:AuthorizationFailure
Error:
  
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
  File "<input>", line 1, in <module>
  File "/home/anders/.pyenv/versions/feature_env/lib/python3.8/site-packages/adlfs/core.py", line 534, in ls
    raise FileNotFoundError(f"File {path} does not exist!!")
FileNotFoundError: File  does not exist!!

I would expect to either have a custom exception I can catch, or to let through the Azure exception so that the user can handle it.

As-is, I can't handle an Authentication issue separately from other issues when using adlfs in my libraries.

[andersbogsnes]

I'd be happy to work on a PR if there is an agreement that this is an issue 😄

[hayesgb]

Thanks @andersbogsnes . Agree this is an issue, and if you have some time to work on it that would be great.

However, I added one unit test (test_ls_0), which calls fs.ls("."), and if I
update the ls() method to simply allow the Exception to pass through, but this then causes some of the glob tests to fail. For the moment, I will leave the FileNotFoundError in place, but I've propagated this up to master with the test marked as xfail.

[andersbogsnes]

Ran into some more issues with exceptions here: https://github.com/dask/adlfs/blob/07aabb7beea34b640c75991f07142154f8f39b3c/adlfs/core.py#L754

(It's trying to raise a string, which errors)

I'm working on a PR in my downtime, but was wondering if there's a need to introduce an exception hierarchy of some sort. Does fsspec have an opinion on that? What type of exception should be raised here?

[hayesgb]

The only error I have seen in this block is a ResourceNotFound error. If we get back something else, we should probably raise a RuntimeError in this block, and propagate the error message {e} back to the user.

[hayesgb]

Closed on PR#72