code: public static void writeXid(ByteBuf buf, Xid xid) {
        if (xid instanceof RemoteXid) {
           ((RemoteXid) xid).writeTo(buf);
        } else {
           ByteBufUtil.writeSignedVInt(buf, xid.getFormatId());
           writeArray(buf, xid.getGlobalTransactionId());
           writeArray(buf, xid.getBranchQualifier());
        }
     }
docs: Writes the {@link Xid} to the {@link ByteBuf}.
  
  @param buf the buffer to write to.
  @param xid the {@link Xid} to encode