Support zstd-compressed repositories

A repository may now be compressed using zstd. Extend support
to allow for this, in addition to continuing to support
gzip-encoded repositories.

pyproject.toml

@@ -31,6 +31,7 @@ dependencies = [
     "python-dateutil>=2.8.1,<3",
     "botocore>=1.23.50,<2",
     "lxml>=4.6.5,<5",
+    "zstd>=1.5.5.1",
 ]
 
 [project.optional-dependencies]

rpm_s3_mirror.spec

@@ -13,6 +13,7 @@ Requires:       python3-requests
 Requires:       python3-dateutil
 Requires:       python3-botocore
 Requires:       python3-lxml
+Requires:       python3-zstd
 Requires:       systemd
 Requires:       zchunk
 

rpm_s3_mirror/repository.py

@@ -1,6 +1,7 @@
 # Copyright (c) 2020 Aiven, Helsinki, Finland. https://aiven.io/
 import dataclasses
 import lzma
+import zstd
 import re
 import subprocess
 from abc import abstractmethod
@@ -404,8 +405,15 @@ def _extract_package_list(self, primary: RepodataSection) -> PackageList:
         with self._req(self.session.get, path=primary.location, stream=True) as request:
             with TemporaryDirectory(prefix="/var/tmp/") as temp_dir:
                 local_path = download_repodata_section(primary, request, temp_dir)
-                with gzip.open(local_path) as f:
-                    return PackageList(base_url=self.base_url, packages_xml=f.read())
+
+                try:
+                    with open(local_path, "rb") as f:
+                        packages_xml = zstd.decompress(f.read())
+                except zstd.Error:
+                    with gzip.open(local_path) as f:
+                        packages_xml = f.read()
+
+                return PackageList(base_url=self.base_url, packages_xml=packages_xml)
 
     def parse_repomd(self, xml: Element) -> Dict[str, RepodataSection]:
         sections = {}