74 lines
2.4 KiB
Java
74 lines
2.4 KiB
Java
import transport.Receiver;
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import transport.TimeoutAction;
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public class GBNTReceiver extends Receiver implements TimeoutAction {
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private char sequence;
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boolean firstPacket = true;
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private static final int RECEIVER_TIMEOUT_MS = 1000;
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private State state = State.SETUP;
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enum State {
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SETUP,
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RECEIVING
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}
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private static byte[] generateACK(char sequence) {
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byte[] dest = new byte[2];
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dest[0] = (byte) ((sequence >> 8) & 0xFF);
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dest[1] = (byte) (sequence & 0xFF);
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return dest;
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}
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private static char readBigEndianChar(byte[] src, int offset) {
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return (char) (src[offset] << 8 + src[offset + 1]);
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}
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private static char incrementAndRollover(char c) {
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return (char) ((c + 1) % 65536);
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}
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@Override
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public void timeoutAction() {
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try {
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disconnect();
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} catch (java.lang.InterruptedException ex) {
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System.out.println("Thread interrupted. Exiting directly.");
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System.exit(0);
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}
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}
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@Override
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protected void unreliableReceive(byte[] bytes, int offset, int length) {
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switch(this.state) {
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case SETUP:
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if (length != 2) {
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if (firstPacket) return;
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else {
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state = State.RECEIVING;
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this.unreliableReceive(bytes, offset, length);
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}
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}
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sequence = readBigEndianChar(bytes, 0);
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unreliableSend(bytes, offset, 2);
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firstPacket = false;
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break;
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case RECEIVING:
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if (length == 2) { // if packet is a close packet
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if (incrementAndRollover(this.sequence) != readBigEndianChar(bytes, offset)) return; // ignore if not synchronized
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this.unreliableSend(bytes, offset, 2);
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timeoutAction();
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}
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if (length < 3) return;
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char seq = readBigEndianChar(bytes, 0);
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if (seq != incrementAndRollover(sequence)) return; //drop the packet
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else {
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this.unreliableReceive(bytes, offset + 2, length);
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sequence = incrementAndRollover(sequence);
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this.unreliableSend(generateACK(sequence), 0, 2);
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}
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break;
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}
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}
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}
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