Provide more informative error messages for obs.put_async with incorrect "mode"

[maxrjones]

We noticed in the Obstore <-> Zarr-Python integration that using obs.put_async(self.store, key, buf, mode="create") raises a NotImplementedError. A different error type would make it more clear to the user that "create" needs to be "Create" (notice capitalization) (e.g., kylebarron/zarr-python#16).

[kylebarron]

Hmm I'm not sure what you're seeing. Any capitalization should work:

obstore/obstore/src/put.rs

Lines 31 to 34 in 28ba07a

	let s = s.to_ascii_lowercase();
	match s.as_str() {
	"create" => Ok(Self(PutMode::Create)),
	"overwrite" => Ok(Self(PutMode::Overwrite)),

[kylebarron]

The underlying object_store::error::NotImplemented error gets returned as a Python builtin NotImplementedError:

obstore/pyo3-object_store/src/error.rs

Lines 136 to 138 in 28ba07a

	object_store::Error::NotImplemented => {
	PyNotImplementedError::new_err(format!("{err:#?}"))
	}

So what you're probably seeing is an error thrown by object_store

[kylebarron]

Your error is coming from here: https://github.com/apache/arrow-rs/blob/b666e424e8f395e9a9bb9950ffab1f968312e103/object_store/src/aws/mod.rs#L172

This is because S3 just added conditional puts recently, and it's not yet the default behavior.
It will be in the next release apache/arrow-rs#7181, which will also remove this NotImplemented case: https://github.com/apache/arrow-rs/pull/7181/files#diff-463799e28d6cd175bcf4dd2b296385646ebed96271da65b05a02ab133d31c82cR172

For now, I think you have to explicitly opt-in when you create the S3Store
https://developmentseed.org/obstore/latest/api/store/aws/#obstore.store.S3ConfigInput.conditional_put

You need to set conditional_put="etag" I believe.

[maxrjones]

https://github.com/maxrjones/zarr-obstore-performance/blob/main/notebooks/zarr-obstore-write.ipynb shows the error. I wasn't able to quickly make a simpler example with just Zarr (rather than xarray + zarr), I guess Zarr's arr[:] = set syntax must use set rather than set_if_not_exists.

I won't have time for more debugging until Friday, but I could rerun the test notebook with any changes to see if it works.