KerchunkC - Draft Extension of Kerchunk into C/C++ functionality

Summary

C++ extensions of driver to read virtual Zarr datasets described in JSON metadata format. Optimize s3 reading performance and mult-dimensional reconstruction of array datasets.

See issue here: Unidata/netcdf-c#2777

Latest List of TODOs

• Enable absolute indexing (abstract chunks such that the index for h5 is automatically mapped)
• Enable local file reading (vs. just AWS remote bucket reading for stream of bytes)
• H5Coro Integration (see SlideRule repository)

C++ Files (../code/c++)

• Call chain overview:
  • main.cpp -> json_parse.h -> kerchunk_read.h -> prin_helpers.h -> mult_dim_form.h -> Finish

src

• main.cpp: main entry point for program; key calls include: json_parse() and kerchunk_read()

Include

• config.h: inputs and settings for program
  • e.g. HARDCODED_CHUNK_INDEX, HARDCODED_JSON_PATH
• custom_structs.h: hold custom structs shared across program (excluding layer_t)
• json_parse.h: given json path, parse out metdata relevant for all chunks and for index specific chunks
• json.hpp: nholmann json processing library
• iter_chunk.h: coordinate metadata extraction and runs for multiple chunk indexes
• kerchunk_read.h: given JSON metadata, read s3 stream and perform decompression, shuffling, etc until original array obtained. Calls on mult_dim_form.h to regain full dimensions
• mult_dim_form.h: given flat array, reconstruct the full dimensions as originally stored (bytes read as single flat dimensions from s3 stream)
• print_helpers.h: debug printer functions, controlled by the constant DEBUG_PRINT_ON in config.h

Jupyter Files (../code/jupyter)

• make_kerchunk_refs.ipynb: ipynb to generate JSON metadata from select s3 object
• range_req_dynamic.ipynb: python edition of kerchunk process; use as verification and testing of c++ addition. Includes s3 byte stream, zlib decompression, unshuffle, dtype processing, and xarray comparison