Passing callbacks to get_file calls used by CacheFileSystems

Hi Fsspec experts,

I'm presently using Fsspec with one of the built in caching file systems, WholeFileCacheFileSystem, and enjoy using the callback feature that is present in functions like .get() to communicate to users the download progress of getting files from remote file stores. I am dealing is some files that are several Gb.

Since I largely want to pipe these remote files into downstream load functions (like numpy.load() for example) I use .open() which gets a IOReader instead of .get() since I just want a copy of it in the cache not elsewhere on the system. The trouble is that despite these caching file systems using .get_file to pull from remote when the file is not present in the cache, a callback passed with .open doesn't make it all the way to the get call.

Since the default callback in fsspec is to do nothing, my users are left without knowledge of if the program is doing anything while its pulling files.

I propose modifying lines such as:

• https://github.com/fsspec/filesystem_spec/blob/master/fsspec/implementations/cached.py#L706
• https://github.com/fsspec/filesystem_spec/blob/master/fsspec/implementations/cached.py#L870

To include kwargs that are relevant to get_file. Unfortunately present kwargs in the WholeFileCacheFileSystem._open() can have some parameters not accepted by get_file, thus some filtering solution is needed.

For the package I'm working on, I have a pretty primitive fix just to verify it works:

if "callback" in kwargs:  # Patch here
    self.fs.get_file(path, fn, callback=kwargs["callback"])
else:
    self.fs.get_file(path, fn)

but a potential full fix would be a more complete solution that covers all parameters in get_file. I'm curious what the maintainers think. I'd be happy to open a PR if something simple like this is fine for the built in caching file systems.

Here's a minimal working example I am testing using the Tqdm plug in, fsspec version 2024.2.0 and above. I haven't tested this with many other file systems other than Http and also a third party file system for Huggingface.

url = "https://upload.wikimedia.org/wikipedia/en/4/42/Master_chief_halo_infinite.png"
fs_http = HTTPFileSystem(block_size=2**10)
fs_http = WholeFileCacheFileSystem(
    fs=fs_http, cache_storage=".cache", same_names=True
)

filename = os.path.basename(url)
with TqdmCallback(
    tqdm_kwargs={
        "desc": "desc",
        "bar_format": f"Downloading {filename}: " +"{percentage:.0f}%|{bar}{r_bar}",
        "unit": "B",
        "unit_scale": True,
        "unit_divisor": 1024,
    },
) as callback:
    f = fs_http.open(url, callback=callback)

(Note, with the fix and on second run, no progress bar is shown because file is loaded from cache as expected.)

Thanks!

Start in fsspec/implementations/cached.py at the WholeFileCacheFileSystem._open() call sites around lines 706 and 870, then inspect the underlying get_file parameters. Ensure supported callback information reaches downloads without forwarding incompatible kwargs, while cache hits avoid a download callback. No specific test file is named in the issue.