code: function(c) {
      if (c) {
        if (c.error) {
          ee.emit('error', new error.BackupError('InvalidChange', `Received invalid change: ${c}`));
        } else if (c.changes) {
          var obj = { id: c.id };
          buffer.push(obj);
          processBuffer(false);
        } else if (c.last_seq) {
          lastSeq = c.last_seq;
        }
      }
    }
docs: called once per received change