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  1. #1
    Join Date
    Jul 2004

    Question DatagramPacket to read non-constant sized UDP message


    I need to receive UDP packages through DatagramPacket.

    Since the message's length is not constant, I need to read the length first.

    I know the protocol definition for this customized package, say,

    -- id 2 bytes
    -- length 2 bytes
    -- body n bytes, (n = length)

    I want to read the length first, then read the whole message (or the rest of the message, ie. the body).

    The question is, after reading the header( first 4 bytes), when I call the readMsg again, should I read the length of the whole message or just the body ? ( Is the header still in the buffer ?)

    I tried, it seems the former one works, but I don't understand why. If the header is still there after being read out, when the buffer will be cleared for the next UDP message ?

    And, what if the sender sends very fast, even faster than the receiver can read. Where will the data that are not read be ?


    	public byte[] readMsg(int num)throws IOException {
    		// create a packet buffer to store data from packets received.
    		byte inBuf[] = new byte[num];
    		DatagramPacket inPkt = new DatagramPacket(inBuf, num);
    		// receive the reply from server.
    		return inPkt.getData();
    Last edited by wu7up; March 23rd, 2012 at 01:58 PM.

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