Add support for compressed FSFiles to HRIT readers

[sfinkens]

Add support for compressed FSFiles to HRIT readers, in particular for MTSAT. Usage example:

import fsspec
from satpy import Scene
from satpy.readers import FSFile

open_file = fsspec.open("HRIT_MTSAT1_20090101_0630_DK01IR1.gz", compression="gzip")
fs_file = FSFile(open_file)
scn = Scene([fs_file], reader="jami_hrit")
scn.load(["IR1"])

• Tests added
• Fully documented

[codecov]

Codecov Report

Merging #2230 (9eeb735) into main (7a30eb8) will increase coverage by 0.07%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #2230      +/-   ##
==========================================
+ Coverage   94.13%   94.21%   +0.07%     
==========================================
  Files         293      295       +2     
  Lines       45079    45404     +325     
==========================================
+ Hits        42437    42778     +341     
+ Misses       2642     2626      -16     

Flag	Coverage Δ
behaviourtests	4.66% <9.37%> (-0.02%)	⬇️
unittests	94.86% <100.00%> (+0.07%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
satpy/readers/hrit_jma.py	97.94% <ø> (ø)
satpy/readers/__init__.py	98.29% <100.00%> (+0.07%)	⬆️
satpy/readers/hrit_base.py	86.23% <100.00%> (+3.36%)	⬆️
satpy/tests/reader_tests/test_hrit_base.py	96.83% <100.00%> (+0.28%)	⬆️
satpy/readers/seadas_l2.py	96.84% <0.00%> (-1.28%)	⬇️
satpy/composites/ahi.py	100.00% <0.00%> (ø)
satpy/tests/test_composites.py	100.00% <0.00%> (ø)
satpy/tests/reader_tests/test_acspo.py	100.00% <0.00%> (ø)
satpy/tests/reader_tests/test_abi_l2_nc.py	100.00% <0.00%> (ø)
satpy/tests/reader_tests/test_goes_imager_nc.py
... and 14 more

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[coveralls]

Coverage increased (+0.07%) to 94.813% when pulling 9eeb735 on sfinkens:gzipped-hrit into 15be5c1 on pytroll:main.

[pdebuyl]

I don't know fsspec's internal working. Does this create a local cache for compressed files?

[sfinkens]

I'm also new to fsspec, but the following seems to create a permanent cache:

filename = "filecache::/data/HRIT_MTSAT1_20090101_0630_DK01IR1.gz"
open_file = fsspec.open(
    filename_gz,
    compression="gzip",
    filecache={'cache_storage':'/cache/dir'}
)
fs_file = FSFile(open_file)
scn = Scene([fs_file], reader="jami_hrit")
scn.load(["IR1"])

By default caching is disabled.

[pdebuyl]

Ultimately, these objects provide the read methods, etc. Seems fine (even though I start to be a bit afraid of the layers of IO technology!). My question was related to the performance. I guess it makes sense when developing to use local data, and else you don't want to keep cached copies of the data so a default of no cache seems fine.

[djhoese]

If this is really all that is needed to make it work then 👍. Looks good to me. I had one inline comment about maybe moving a method for easier code reading.