Stop backup.info errors from breaking barman-cloud-backup-list (#363)

Catches exceptions encountered when reading backup.info files
during backup list operations. A warning is logged and we continue
iterating through backup files.

This fixes a problem where a single unreadable backup.info file
would break barman-cloud-backup-list entirely, preventing users
from finding any backups in cloud storage. The specific example
reported was when a backup.info file has the AWS S3 Glacier
storage class however there are other reasons why a backup.info
file might not be readable. In these scenarios we would still
want to list the backup.info files that were readable, so we
therefore catch `Exception`s rather than anything more specific.

Closes #332

barman/cloud.py

@@ -1496,7 +1496,13 @@ def get_backup_list(self):
                 if backup_dir[-1] != "/":
                     continue
                 backup_id = os.path.basename(backup_dir.rstrip("/"))
-                backup_info = self.get_backup_info(backup_id)
+                try:
+                    backup_info = self.get_backup_info(backup_id)
+                except Exception as exc:
+                    logging.warning(
+                        "Unable to open backup.info file for %s: %s" % (backup_id, exc)
+                    )
+                    continue
 
                 if backup_info:
                     backup_list[backup_id] = backup_info

tests/test_cloud.py

@@ -22,11 +22,12 @@
 from azure.core.exceptions import ServiceRequestError
 
 import mock
+from mock.mock import MagicMock
 import pytest
 from boto3.exceptions import Boto3Error
 from botocore.exceptions import ClientError, EndpointConnectionError
 
-from barman.cloud import CloudUploadingError, FileUploadStatistics
+from barman.cloud import CloudBackupCatalog, CloudUploadingError, FileUploadStatistics
 from barman.cloud_providers.aws_s3 import S3CloudInterface
 from barman.cloud_providers.azure_blob_storage import AzureCloudInterface
 
@@ -1057,3 +1058,63 @@ def test_abort_multipart_upload_with_encryption_scope(self, blob_service_mock):
             [], encryption_scope=encryption_scope
         )
         blob_client_mock.delete_blob.assert_called_once_with()
+
+
+class TestCloudBackupCatalog(object):
+    """
+    Tests which verify we can list backups stored in a cloud provider
+    """
+
+    def get_backup_info_file_object(self):
+        """Minimal backup info"""
+        return BytesIO(
+            b"""
+backup_label=None
+end_time=2014-12-22 09:25:27.410470+01:00
+"""
+        )
+
+    def raise_exception(self):
+        raise Exception("something went wrong reading backup.info")
+
+    def mock_remote_open(self, _):
+        """
+        Helper function which alternates between successful and unsuccessful
+        remote_open responses.
+        """
+        try:
+            if self.remote_open_should_succeed:
+                return self.get_backup_info_file_object()
+            else:
+                raise Exception("something went wrong reading backup.info")
+        finally:
+            self.remote_open_should_succeed = not self.remote_open_should_succeed
+
+    def test_can_list_single_backup(self):
+        mock_cloud_interface = MagicMock()
+        mock_cloud_interface.list_bucket.return_value = [
+            "mt-backups/test-server/base/20210723T133818/",
+        ]
+        mock_cloud_interface.remote_open.return_value = (
+            self.get_backup_info_file_object()
+        )
+        catalog = CloudBackupCatalog(mock_cloud_interface, "test-server")
+        backups = catalog.get_backup_list()
+        assert len(backups) == 1
+        assert "20210723T133818" in backups
+
+    def test_backups_can_be_listed_if_one_is_unreadable(self):
+        self.remote_open_should_succeed = True
+        mock_cloud_interface = MagicMock()
+        mock_cloud_interface.list_bucket.return_value = [
+            "mt-backups/test-server/base/20210723T133818/",
+            "mt-backups/test-server/base/20210723T154445/",
+            "mt-backups/test-server/base/20210723T154554/",
+        ]
+        mock_cloud_interface.remote_open.side_effect = self.mock_remote_open
+        catalog = CloudBackupCatalog(mock_cloud_interface, "test-server")
+        backups = catalog.get_backup_list()
+        assert len(backups) == 2
+        assert "20210723T133818" in backups
+        assert "20210723T154445" not in backups
+        assert "20210723T154554" in backups