def wal_files(server, backup_id)
      lines = run_barman_command("list-files --target wal #{server} #{backup_id}")
      wal_files = parse_wal_files_list(lines)
      xlog_db = read_xlog_db(server)
      wal_files.each do |w|
        wal = "#{w.timeline}#{w.xlog}#{w.segment}"
        entry = xlog_db[wal]
        w.size = entry[:size]
        w.compression = entry[:compression]
        w.created = entry[:created].to_i
      end
      return wal_files
    end
def wal_files(server, backup_id)
      lines = run_barman_command("list-files --target wal #{server} #{backup_id}")
      wal_files = parse_wal_files_list(lines)
      xlog_db = read_xlog_db(server)
      wal_files.each do |w|
        wal = "#{w.timeline}#{w.xlog}#{w.segment}"
        entry = xlog_db[wal]
        w.size = entry[:size]
        w.compression = entry[:compression]
        w.created = entry[:created].to_i
      end
      return wal_files
    end
Instructs barman to list all wal files for a specific backup id
 @param [String] server server name
 @param [String] backup_id id of the backup
 @return [WalFiles] an array of {WalFile}
 @raise [RuntimeError] if wal file duplicates are found in xlog.db
 @raise [RuntimeError] if barman lists a wal file but no information could be found in xlog.db