code: function writeSrv(buff, val, label_index) {
    assertUndefined(val.priority, 'SRV record requires "priority"');
    assertUndefined(val.weight, 'SRV record requires "weight"');
    assertUndefined(val.port, 'SRV record requires "port"');
    assertUndefined(val.target, 'SRV record requires "target"');
    buff.writeUInt16BE(val.priority & 0xFFFF);
    buff.writeUInt16BE(val.weight & 0xFFFF);
    buff.writeUInt16BE(val.port & 0xFFFF);
    namePack(val.target, buff, label_index);
    return WRITE_RESOURCE_DONE;
  }
docs: SRV: https://tools.ietf.org/html/rfc2782 TODO: SRV fixture failing for '_xmpp-server._tcp.gmail.com.srv.js'