Reader raises after EOF

[nvictus]

Calling read with nonzero size on Python file-likes return an empty byte string once EOF is reached.

It seems obstore readers are inconsistent with this behavior and raise an exception instead.

f = open(..., "rb")
f.read()
f.read(1)  # -> b""

f = fsspec.open(..., mode="rb").open()
f.read()
f.read(1)  # -> b""

store = obstore.store.from_url(..., skip_signature=True)
f = obstore.open_reader(store, "")
f.read()
f.read(1)  # OSError: early eof

[kylebarron]

Interesting; I hadn't read that part of the docs closely enough.

The implementation is here:

obstore/obstore/src/buffered.rs

Lines 194 to 196 in 7d91acf

	let mut buf = vec![0; size as _];
	reader.read_exact(&mut buf).await?;
	Ok(Bytes::from(buf).into())

Looks like you should be able to catch the error from reader.read_exact, essentially allowing reading fewer bytes than what's specified in read_exact.

Would you be interested in making a PR?

[nvictus]

Sure thing! 👉 #593

FYI, I replaced the use of read_exact with read to get the number of bytes read in order to truncate the final result.