MulticastSocket's receive() method acting strangely

Question

In the Java 2 API documentation, the DatagramSocket.receive( DatagramPacket dp ) method is said to block until a packet is available to read. But i wrote an app that reads a 1.3 mbps multicast (mpeg-1 video) which sends out 1024 byte packets and the java app, after reading a few 1024 byte packets, starts to read smaller and smaller packets until the packets are just 34 bytes, and don't contain any data. I have one DatagramPacket object that's being read in this manner:
The loop, after reading the packet, sends a datagrampacket that uses the same data buffer out a different port, to a different address. (A multicast to unicast bridge)
while( true ) {
multicastsock.receive( dp );
Any ideas why its not blocking until its actually receiving a packet after a while, or why it sees the packet but not the data?
Thank you

Answer 1

So, you're sending multiple packages, right?
receive() blocks until <b>one</b> package is received.
I doubt you can't get data (if it's really in there).
Did you try to debug it (print it or smth.) with smth. like
DatagramPacket confirmationPacket = new DatagramPacket(buf, buf.length);
socket.receive(confirmationPacket);
String received = new String(confirmationPacket.getData());