Fix -0 and --fast in the igzip command line interface

CHANGELOG.rst

@@ -131,6 +131,8 @@ version 1.8.1-dev
 + Fix a crash on macOS and PyPy when there is not enough memory to create the
   internal lock of an ``isal_zlib.Compress``, ``isal_zlib.Decompress``, or
   ``igzip_lib.IgzipDecompressor`` object. It raises ``MemoryError`` now.
++ Fix the ``-0`` and ``--fast`` options of ``python -m isal.igzip``, which
+  compressed at level 2 instead of level 0.
 
 version 1.8.0
 -----------------

src/isal/igzip.py

@@ -305,7 +305,8 @@ def _argument_parser():
         "-3", "--best", action="store_const", dest="compresslevel",
         const=_COMPRESS_LEVEL_BEST,
         help="use compression level 3 (best)")
-    compress_group.set_defaults(compress=True)
+    compress_group.set_defaults(compress=True,
+                                compresslevel=_COMPRESS_LEVEL_TRADEOFF)
     compress_group.add_argument(
         "-d", "--decompress", action="store_const",
         dest="compress",
@@ -333,7 +334,7 @@ def main():
     import shutil  # Only the command line interface needs it
     args = _argument_parser().parse_args()
 
-    compresslevel = args.compresslevel or _COMPRESS_LEVEL_TRADEOFF
+    compresslevel = args.compresslevel
 
     if args.output:
         out_filepath = args.output

tests/test_igzip.py

@@ -220,6 +220,8 @@ def test_compress_stdin_stdout(monkeypatch, capsysbinary, level):
     out, err = capsysbinary.readouterr()
     assert err == b''
     assert gzip.decompress(out) == DATA
+    # The XFL byte of the gzip header is 4 only at the fastest level.
+    assert out[8] == (4 if level == "0" else 0)
 
 
 def test_decompress_infile_outfile(monkeypatch, tmp_path, capsysbinary):