Add info about the codec used for compression

[FrancescAlted]

Currently, the info subcommand does not offer info on the codec used for compressing a file:

$ blpk i p.dat.blp
blpk: bloscpack header: 
blpk:     format_version=3,
blpk:     offsets=True,
blpk:     metadata=False,
blpk:     checksum='adler32',
blpk:     typesize=8,
blpk:     chunk_size=1.0M (1048576B),
blpk:     last_chunk=962.0K (985088B),
blpk:     nchunks=763,
blpk:     max_app_chunks=7630
blpk: 'offsets':
blpk: [67176,257788,400131,536937,653836,...]

I think the recently added get_clib(cbuffer) function in python-blosc 1.2.1 should help here.

[esc]

Yes and no. One could print the clib version of, for example the first chunk. However, since when using append it is perfectly fine to use a different codec for different chunks, that might not be entirely reliable. One could also print the codec used in all chunks, but that would defeat the purpose of the info subcommand, which by design is meant to return quickly and read only the header of the file. Best solution would be to add a new field to the Bloscpack header, which can contain the clib int or -1 if it is non-uniform. The problem with that being, that of course the header definition must change and the code to handle this must be written. ;)

[FrancescAlted]

Ah yes, makes perfect sense. In fact, in the future it would be nice to add a special compression mode in Blosc (either c-blosc or python-blosc) so that a codec could be chosen automatically in order to optimize compression ratio, speed, or a balance between them.

So I agree that it makes non sense this to be supported at all, except for the case where the clib is enforced to be uniform.