Check at nc_open if file appears to be in NCZarr/Zarr format. #2658
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re: Issue Unidata#2656 Charlie Zender notes that *nc_open()* does not immediately detect that the given path refers to a file not in zarr format. Rather it fails later when trying to read the (meta-)data. The reason is that the Zarr format is highly decentralized. There is no easily testable magic number or superblock to look for. In effect the only way to see if a directory is Zarr is to successfully read it. It is possible to heuristically detect that a path refers to an NCZarr/Zarr file by doing a breadth-first search of the file tree starting at the given path. If the search encounters a file whose name starts with ".z", then assume it is a legitimate NCZarr/Zarr file. Of course, this test could be costly. One hopes that in practice that it is not. In addition to this fix, a corresponding test case was added. ## Other Changes re: PR Unidata#2529 There was an error under Cygwin for this PR that is fixed in this PR. The fix was to convert all *noinst_* references to *check_*.
WardF
previously approved these changes
Apr 12, 2023
WardF
previously approved these changes
Apr 12, 2023
WardF
approved these changes
Apr 12, 2023
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Charlie Zender notes that nc_open() does not immediately detect that the given path refers to a file not in zarr format. Rather it fails later when trying to read the (meta-)data.
The reason is that the Zarr format is highly decentralized. There is no easily testable magic number or superblock to look for. In effect the only way to see if a directory is Zarr is to successfully read it.
It is possible to heuristically detect that a path refers to an NCZarr/Zarr file by doing a breadth-first search of the file tree starting at the given path. If the search encounters a file whose name starts with ".z", then assume it is a legitimate NCZarr/Zarr file. Of course, this test could be costly. One hopes that in practice that it is not.
In addition to this fix, a corresponding test case was added.
Other Changes