From c993c6cbabc8cc62cde5a0f302097b30e218d1da Mon Sep 17 00:00:00 2001
From: Stephan Finkensieper <stephan.finkensieper@dwd.de>
Date: Mon, 10 Oct 2022 10:19:43 +0000
Subject: [PATCH] Add support for gzipped HRIT files

---
 satpy/readers/hrit_base.py                 | 15 +++++++-----
 satpy/readers/utils.py                     |  3 +++
 satpy/tests/reader_tests/test_hrit_base.py | 27 ++++++++++++++++++++++
 3 files changed, 39 insertions(+), 6 deletions(-)

diff --git a/satpy/readers/hrit_base.py b/satpy/readers/hrit_base.py
index 9bd0990f00..9c7e9b0e57 100644
--- a/satpy/readers/hrit_base.py
+++ b/satpy/readers/hrit_base.py
@@ -356,7 +356,8 @@ def __init__(self, filename, mda):
         self.bpp = mda['number_of_bits_per_pixel']
         self.compressed = mda['compression_flag_for_data'] == 1
         self.offset = mda['total_header_length']
-        self.zipped = os.fspath(filename).endswith('.bz2')
+        self.bzipped = os.fspath(filename).endswith('.bz2')
+        self.gzipped = os.fspath(filename).endswith('.gz')
 
     def read_data(self):
         """Read the data."""
@@ -367,12 +368,14 @@ def read_data(self):
         return data
 
     def _read_data_from_file(self):
-        # check, if 'filename' is a file on disk,
-        #  or a file like obj, possibly residing already in memory
-        try:
+        if self._should_read_from_disk():
             return self._read_data_from_disk()
-        except (FileNotFoundError, AttributeError):
-            return self._read_file_like()
+        return self._read_file_like()
+
+    def _should_read_from_disk(self):
+        is_bz2_or_wavelet = self.bzipped or self.compressed
+        is_uncompressed = not (is_bz2_or_wavelet or self.gzipped)
+        return is_bz2_or_wavelet or is_uncompressed
 
     def _read_data_from_disk(self):
         # For reading the image data, unzip_context is faster than generic_open
diff --git a/satpy/readers/utils.py b/satpy/readers/utils.py
index 289d73b382..cf95bafaff 100644
--- a/satpy/readers/utils.py
+++ b/satpy/readers/utils.py
@@ -18,6 +18,7 @@
 """Helper functions for satpy readers."""
 
 import bz2
+import gzip
 import logging
 import os
 import shutil
@@ -288,6 +289,8 @@ def generic_open(filename, *args, **kwargs):
     """
     if os.fspath(filename).endswith('.bz2'):
         fp = bz2.open(filename, *args, **kwargs)
+    elif os.fspath(filename).endswith(".gz"):
+        fp = gzip.open(filename)
     else:
         try:
             fp = filename.open(*args, **kwargs)
diff --git a/satpy/tests/reader_tests/test_hrit_base.py b/satpy/tests/reader_tests/test_hrit_base.py
index aa461d4237..76a26e5f96 100644
--- a/satpy/tests/reader_tests/test_hrit_base.py
+++ b/satpy/tests/reader_tests/test_hrit_base.py
@@ -18,6 +18,7 @@
 """The HRIT base reader tests package."""
 
 import bz2
+import gzip
 import os
 import unittest
 from datetime import datetime
@@ -156,6 +157,14 @@ def stub_bzipped_hrit_file(tmp_path):
     return filename
 
 
+@pytest.fixture
+def stub_gzipped_hrit_file(tmp_path):
+    """Create a stub gzipped hrit file."""
+    filename = tmp_path / "some_hrit_file.gz"
+    create_stub_hrit(filename, open_fun=gzip.open)
+    return filename
+
+
 @pytest.fixture
 def stub_compressed_hrit_file(tmp_path):
     """Create a stub compressed hrit file."""
@@ -244,6 +253,24 @@ def test_read_band_bzipped2_filepath(self, stub_bzipped_hrit_file):
         res = self.reader.read_band('VIS006', None)
         assert res.compute().shape == (464, 3712)
 
+    def test_read_band_gzipped_filepath(self, stub_gzipped_hrit_file):
+        """Test reading a single band from a gzipped file."""
+        self.reader.filename = stub_gzipped_hrit_file
+
+        res = self.reader.read_band('VIS006', None)
+        assert res.compute().shape == (464, 3712)
+
+    def test_read_band_gzip_stream(self, stub_gzipped_hrit_file):
+        """Test reading a single band from a gzip stream."""
+        import fsspec
+        filename = stub_gzipped_hrit_file
+
+        fs_file = fsspec.open(filename)
+        self.reader.filename = FSFile(fs_file)
+
+        res = self.reader.read_band('VIS006', None)
+        assert res.compute().shape == (464, 3712)
+
 
 def fake_decompress(infile, outdir='.'):
     """Fake decompression."""