Path normalization will make some valid s3 keys inaccessible

[bogovicj]

... and that's okay by me.

Object keys names in s3 can be weird.

For example, it is possible to have an object at key a/../obj inside some bucket. where .. is part of the object key and does not indicate the parent folder as it would on a usual local file system. In other words, on s3 a/../obj != obj where on a local filesystem a/../obj == obj. As well, keys may contain . or "" (empty string) delimited by slashes, akin to having a folder called "." or "". See the examples below.

Normalization of paths in n5 currently treats the following as equivalent:

• a/obj
• /a/obj
• a/./obj
• ./a/obj
• a/b/../obj
• ././/a/.///obj

but these are all potentially unique keys in an s3 bucket. I don't see a compelling reason to try to make this work right now. Rather, we'll strongly recommend not to use ., .., or `` (empty string) in keys as in the above examples.

ping @cmhulbert

touch obj # Make an empty file

# Put obj in the bucket root
$ aws s3 cp obj s3://n5-zarr-tests/
upload: ./obj to s3://n5-zarr-tests/obj

# Put obj at the key '/obj'
# think: obj is in a folder named "" (empty string) inside the bucket root
$ aws s3 cp obj s3://n5-zarr-tests//
upload: ./obj to s3://n5-zarr-tests//obj

# Put obj at the key './obj'
# think: obj is in a folder named "." (dot) inside the bucket root
$ aws s3 cp obj s3://n5-zarr-tests/./ 
upload: ./obj to s3://n5-zarr-tests/./obj

# S3 not happy
$ aws s3 cp obj s3://n5-zarr-tests/../
upload failed: ./obj to s3://n5-zarr-tests/../obj An error occurred (400) when calling the PutObject operation: Bad Request

# Put obj at the key 'a/../obj'
$ aws s3 cp obj s3://n5-zarr-tests/a/../
upload: ./obj to s3://n5-zarr-tests/a/../obj

# Make keys with two different empty strings
aws s3 cp obj 's3://n5-zarr-tests/a/ /'
aws s3 cp obj 's3://n5-zarr-tests/a/  /'

# The results of the above
$ aws s3 ls --recursive s3://n5-zarr-tests
2023-07-03 11:01:13          0 ./obj
2023-07-03 11:01:02          0 /obj
2023-07-03 11:02:36          0 a/  /obj
2023-07-03 11:02:01          0 a/ /obj
2023-07-03 11:01:32          0 a/../obj
2023-07-03 11:00:35          0 obj