Avoid connecting to PostgreSQL while reading a backup.info file

Prevent Barman from opening a PostgreSQL transaction that lasts until
termination, even in operations that should not require to speak with
Postgres (i.e. list-backup or recover).

This fixes a regression introduced with systemid check code.

Signed-off-by: Marco Nenciarini <marco.nenciarini@2ndquadrant.it>
Signed-off-by: Leonardo Cecchi <leonardo.cecchi@2ndquadrant.it>

barman/backup.py

@@ -390,6 +390,7 @@ def backup(self, wait=False, wait_timeout=None):
             backup_info = LocalBackupInfo(
                 self.server,
                 backup_id=datetime.datetime.now().strftime('%Y%m%dT%H%M%S'))
+            backup_info.set_attribute('systemid', self.server.systemid)
             backup_info.save()
             self.backup_cache_add(backup_info)
             output.info(

barman/infofile.py

@@ -596,7 +596,6 @@ def __init__(self, server, info_file=None, backup_id=None, **kwargs):
                     'both info_file and backup_id parameters are set')
             self.backup_id = backup_id
             self.filename = self.get_filename()
-            self.systemid = server.systemid
             # Check if a backup info file for a given server and a given ID
             # already exists. If so load the values from the file.
             if os.path.exists(self.filename):

tests/test_infofile.py

@@ -26,7 +26,9 @@
 
 from barman.infofile import (BackupInfo, Field, FieldListFile, LocalBackupInfo,
                              WalFileInfo, load_datetime_tz)
-from testing_helpers import build_backup_manager, build_mocked_server
+from testing_helpers import (build_backup_manager, build_mocked_server,
+                             build_real_server)
+
 
 BASE_BACKUP_INFO = """backup_label=None
 begin_offset=40
@@ -579,3 +581,25 @@ def test_xlog_segment_size(self, tmpdir):
         # load the data from the backup.info file
         b_info = LocalBackupInfo(server, info_file=infofile.strpath)
         assert b_info.xlog_segment_size == 1 << 24
+
+    @mock.patch('barman.postgres.PostgreSQLConnection.connect')
+    def test_backupinfo_load(self, connect_mock, tmpdir):
+        server = build_real_server(
+            main_conf={
+                'basebackups_directory': tmpdir.strpath
+            },
+        )
+
+        # Build a fake backup info and try to load id, to ensure that we won't
+        # need a PostgreSQL connection to do that
+        backup_dir = tmpdir.mkdir('fake_backup_id')
+        info_file = backup_dir.join('backup.info')
+        info_file.write(BASE_BACKUP_INFO)
+
+        # Monkey patch the PostgreSQL connection function to raise a
+        # RuntimeError
+        connect_mock.side_effect = RuntimeError
+
+        # The following constructor will raise a RuntimeError if we are
+        # needing a PostgreSQL connection
+        LocalBackupInfo(server, backup_id="fake_backup_id")