apertis-pkg-pull-updates: add mirror to snapshot.debian.org as a fallback

Sometime the main server of snapshot.debian.org is not sync
which block us from downloading new packages from Debian.
Thus to avoid depending on a single server add a mirror
as fallback.

Signed-off-by: Dylan Aïssi <dylan.aissi@collabora.com>

tools/apertis-pkg-pull-updates

@@ -200,8 +200,11 @@ def should_update(upstream_suite, package_name, local_version, missing_is_fatal=
     return remote_version
   return None
 
-def get_remote_dsc_path(package_name, version):
-  url = 'https://snapshot.debian.org/mr/package/{}/{}/srcfiles?fileinfo=1'.format(package_name, version)
+def get_remote_dsc_path(package_name, version, mirror=False):
+  if not mirror:
+    url = 'https://snapshot.debian.org/mr/package/{}/{}/srcfiles?fileinfo=1'.format(package_name, version)
+  else:
+    url = 'https://snapshot-mlm-01.debian.org/mr/package/{}/{}/srcfiles?fileinfo=1'.format(package_name, version)
   print('fetch', url)
   with urllib.request.urlopen(url) as response:
     data = json.loads(response.read().decode('utf-8'))
@@ -279,7 +282,14 @@ def main():
       remote_version = should_update(suite, package_name, local_version, upstream_suite==suite)
       if remote_version:
           print('update to', remote_version)
-          dsc = re.sub(r'/debian/*', '/', mirror) + '/' + get_remote_dsc_path(package_name, remote_version)
+
+          try:
+            remote_dsc_path = get_remote_dsc_path(package_name, remote_version)
+          except urllib.error.HTTPError:
+            print('⚠️ Fail to get dsc from main snapshot.debian.org, trying from a mirror')
+            remote_dsc_path = get_remote_dsc_path(package_name, remote_version, mirror=True)
+
+          dsc = re.sub(r'/debian/*', '/', mirror) + '/' + remote_dsc_path
           print('download', dsc)
           with tempfile.TemporaryDirectory(prefix='pull-updates') as tmpdir:
             local_dsc = get_remote_sources(dsc, tmpdir)