Recreate pg_wal if required in barman-cloud-restore

If you run barman-cloud-backup on a data directory where pg_wal is a
symlink, it doesn't include pg_wal in the uploaded tar files, and the
pg_wal directory will not be created if you restore the backup.

We fix this by creating pg_wal (or pg_xlog, depending on the version) in
the destination directory if it does not exist at the end of the backup.

Closes #327

barman/clients/cloud_restore.py

@@ -170,8 +170,8 @@ def download_backup(self, backup_id, destination_dir):
         """
         Download a backup from cloud storage
 
-        :param str wal_name: Name of the WAL file
-        :param str wal_dest: Full path of the destination WAL file
+        :param str backup_id: The backup id to restore
+        :param str destination_dir: Path to the destination directory
         """
 
         backup_info = self.catalog.get_backup_info(backup_id)
@@ -227,6 +227,14 @@ def download_backup(self, backup_id, destination_dir):
             )
             self.cloud_interface.extract_tar(file_info.path, target_dir)
 
+        # If we did not restore the pg_wal directory from one of the uploaded
+        # backup files, we must recreate it here. (If pg_wal was originally a
+        # symlink, it would not have been uploaded.)
+
+        wal_path = os.path.join(destination_dir, backup_info.wal_directory())
+        if not os.path.exists(wal_path):
+            os.mkdir(wal_path)
+
 
 if __name__ == "__main__":
     main()

barman/infofile.py

@@ -584,6 +584,13 @@ def pg_major_version(self):
         else:
             return str(major)
 
+    def wal_directory(self):
+        """
+        Returns "pg_wal" (v10 and above) or "pg_xlog" (v9.6 and below) based on
+        the Postgres version represented by this backup
+        """
+        return "pg_wal" if self.version >= 100000 else "pg_xlog"
+
 
 class LocalBackupInfo(BackupInfo):
     __slots__ = "server", "config", "backup_manager"

tests/test_infofile.py

@@ -594,6 +594,8 @@ def test_pg_version(self, tmpdir):
         b_info = LocalBackupInfo(server, info_file=infofile.strpath)
         # BASE_BACKUP_INFO has version 90400 so expect 9.4
         assert b_info.pg_major_version() == "9.4"
+        assert b_info.wal_directory() == "pg_xlog"
         # Set backup_info.version to 100600 so expect 10
         b_info.version = 100600
         assert b_info.pg_major_version() == "10"
+        assert b_info.wal_directory() == "pg_wal"