backend: fix tests for zst compression on F39+

Fix fedora-copr#2832

Since F39 we are using zst compression for repodata instead of gz.
https://fedoraproject.org/wiki/Changes/createrepo_c_1.0.0

backend/copr-backend.spec

@@ -56,6 +56,7 @@ BuildRequires: python3-retask
 BuildRequires: python3-setproctitle
 BuildRequires: python3-sphinx
 BuildRequires: python3-tabulate
+BuildRequires: python3-zstandard
 BuildRequires: modulemd-tools >= 0.6
 BuildRequires: prunerepo >= %prunerepo_version
 BuildRequires: dnf

backend/tests/test_modifyrepo.py

@@ -547,9 +547,10 @@ def test_comps_present(self, f_third_build):
             pass
 
         assert call_copr_repo(chrootdir)
-        name = glob.glob(os.path.join(chrootdir, "repodata", "*-comps.xml.gz"))
-        assert os.path.exists(name[0])
 
+        name = glob.glob(os.path.join(chrootdir, "repodata", "*-comps.xml.*"))
+        assert os.path.exists(name[0])
+        assert name[0].endswith((".zst", ".gz"))
 
     @skip("Works locally and in Copr but fails in Koji")
     @mock.patch("copr_prune_results.LOG", logging.getLogger())

backend/tests/testlib/repodata.py

@@ -7,6 +7,14 @@
 import gzip
 from xml.dom import minidom
 
+try:
+    # This import tracebacks on F37 but we need it only on F39+
+    # pylint: disable=import-outside-toplevel
+    from zstandard import ZstdDecompressor
+except ImportError:
+    pass
+
+
 def load_primary_xml(dirname):
     '''
     Parse priary.xml from the given repodata directory path, and return
@@ -16,8 +24,7 @@ def load_primary_xml(dirname):
     hrefs = set()
     names = set()
     primary = glob.glob(os.path.join(dirname, '*primary*xml*'))[0]
-    with gzip.open(primary) as fprimary:
-        xml_content = fprimary.read()
+    xml_content = extract(primary)
 
     dom = minidom.parseString(xml_content)
 
@@ -36,3 +43,14 @@ def load_primary_xml(dirname):
         'hrefs': hrefs,
         'names': names,
     }
+
+def extract(path):
+    if path.endswith(".zst"):
+        with open(path, "rb") as fp:
+            decompressor = ZstdDecompressor()
+            return decompressor.stream_reader(fp).read()
+
+    if path.endswith(".gz"):
+        with gzip.open(path) as fp:
+            return fp.read()
+    raise ValueError("Unexpected extension: {0}".format(path))