public byte []
toWire(int maxLength) {
	DNSOutput out = new DNSOutput();
	toWire(out, maxLength);
	size = out.current();
	return out.toByteArray();
}
Returns an array containing the wire format representation of the Message
with the specified maximum length.  This will generate a truncated
message (with the TC bit) if the message doesn't fit, and will also
sign the message with the TSIG key set by a call to setTSIG().  This
method may return null if the message could not be rendered at all; this
could happen if maxLength is smaller than a DNS header, for example.
@param maxLength The maximum length of the message.
@return The wire format of the message, or null if the message could not be
rendered into the specified length.
@see Flags
@see TSIG
src/main/java/core/org/xbill/DNS/Message.java