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241
src/main/java/li/cil/oc2/common/inet/StreamSessionImpl.java
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241
src/main/java/li/cil/oc2/common/inet/StreamSessionImpl.java
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package li.cil.oc2.common.inet;
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import li.cil.oc2.api.inet.StreamSession;
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import li.cil.oc2.common.Config;
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import javax.annotation.Nullable;
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import java.nio.ByteBuffer;
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import java.time.Instant;
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import java.time.temporal.ChronoUnit;
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import java.util.Random;
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public class StreamSessionImpl extends SessionBase implements StreamSession {
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private static final Random random = new Random();
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private final StreamSessionDiscriminator discriminator;
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// Data from session layer implementation
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private final ByteBuffer receiveBuffer = ByteBuffer.allocate(Config.streamBufferSize);
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private int receiveWindow = 0;
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private int nextSegmentMark = 0; // for retransmission
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// Data from virtual machine
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private final ByteBuffer sendBuffer = ByteBuffer.allocate(Config.streamBufferSize);
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private int mySequence = random.nextInt();
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private int vmSequence;
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private final TcpHeader header = new TcpHeader();
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private boolean needsAcknowledgment = false;
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private Instant retransmitTime = Instant.now();
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/////////////////////////////////////////////////////////////////////////
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public StreamSessionImpl(
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final int ipAddress,
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final short port,
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final StreamSessionDiscriminator discriminator
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) {
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super(ipAddress, port);
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this.discriminator = discriminator;
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sendBuffer.limit(0);
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}
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private int computeWindow() {
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return sendBuffer.remaining();
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}
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public boolean newConnection(final ByteBuffer data) {
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final boolean correct = header.read(data);
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if (!correct) {
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return false;
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}
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final boolean isInitiation = header.isConnectionInitiation();
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if (!isInitiation) {
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return false;
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}
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vmSequence = header.sequenceNumber;
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receiveWindow = header.window;
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return true;
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}
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private void acceptConnection(final ByteBuffer data) {
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header.acceptConnection(mySequence++, ++vmSequence, computeWindow());
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header.write(data);
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data.flip();
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setState(States.ESTABLISHED);
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}
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private void denyConnection(final ByteBuffer data) {
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header.denyConnection(mySequence, vmSequence + 1);
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header.write(data);
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data.flip();
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}
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private boolean onPacket(final ByteBuffer data) {
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final boolean correct = header.read(data);
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if (!correct) {
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return false;
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}
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if (header.syn) {
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return false;
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}
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if (header.sequenceNumber != vmSequence) {
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return false;
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}
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if (header.ack) {
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// Segment received
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if (header.acknowledgmentNumber != mySequence) {
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return false;
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}
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receiveWindow = header.window;
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final int newPosition = receiveBuffer.position() - nextSegmentMark;
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receiveBuffer.position(nextSegmentMark);
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receiveBuffer.compact();
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receiveBuffer.position(newPosition);
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receiveBuffer.limit(receiveBuffer.capacity());
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nextSegmentMark = 0;
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} else {
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receiveWindow = header.window;
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}
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if (header.psh) {
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// Data to be sent
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final int length = data.remaining();
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if (length > computeWindow()) {
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// TODO: State changed, but packet rejected
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return false;
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}
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vmSequence += length;
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sendBuffer.compact();
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sendBuffer.limit(sendBuffer.limit() + length);
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sendBuffer.put(data);
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needsAcknowledgment = true;
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}
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if (header.fin) {
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setState(States.FINISH);
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++vmSequence;
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}
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return true;
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}
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private void pushNextReceivedDataTo(final ByteBuffer data) {
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final int position = data.position();
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data.position(position + TcpHeader.MIN_HEADER_SIZE_NO_PORTS);
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// Copy payload (yes, it is easier to prepare payload first)
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final int recvPos = receiveBuffer.position();
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final int recvLim = receiveBuffer.limit();
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receiveBuffer.limit(nextSegmentMark);
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receiveBuffer.position(0);
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data.put(receiveBuffer);
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receiveBuffer.position(recvPos);
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receiveBuffer.limit(recvLim);
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data.position(position);
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// Update time
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retransmitTime = Instant.now().plus(Config.tcpRetransmissionTimeoutMs, ChronoUnit.MILLIS);
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}
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private boolean preparePacket(final ByteBuffer data) {
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final int length = receiveBuffer.position();
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header.urg = false;
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header.syn = false;
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header.rst = false;
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header.ack = needsAcknowledgment;
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header.sequenceNumber = mySequence - nextSegmentMark;
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header.acknowledgmentNumber = vmSequence;
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header.maxSegmentSize = -1;
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header.urgentPointer = 0;
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header.window = computeWindow();
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header.psh = length != 0;
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if (header.psh) {
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header.fin = false;
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// We have something to receive
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if (nextSegmentMark == 0) {
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// Acknowledged, prepare next segment
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nextSegmentMark = Math.min(Math.min(receiveWindow, length), data.remaining() - TcpHeader.MIN_HEADER_SIZE_NO_PORTS);
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mySequence += nextSegmentMark;
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pushNextReceivedDataTo(data);
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} else {
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// Packet is already sent, is retransmission required?
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if (retransmitTime.compareTo(Instant.now()) > 0) {
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return false; // no
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} else {
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pushNextReceivedDataTo(data);
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}
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}
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} else {
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header.fin = getState() == States.FINISH;
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header.window = 0;
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}
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header.write(data);
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return true;
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}
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public boolean onSend(final ByteBuffer data) {
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switch (getState()) {
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case NEW:
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return newConnection(data);
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case ESTABLISHED:
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case FINISH:
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return onPacket(data);
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case REJECT:
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case EXPIRED:
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throw new IllegalStateException();
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}
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return false;
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}
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public boolean onReceive(final ByteBuffer data) {
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switch (getState()) {
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case NEW:
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acceptConnection(data);
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return true;
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case ESTABLISHED:
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case FINISH:
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return preparePacket(data);
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case REJECT:
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denyConnection(data);
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return true;
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case EXPIRED:
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throw new IllegalStateException();
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}
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return false;
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}
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@Override
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public StreamSessionDiscriminator getDiscriminator() {
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return discriminator;
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}
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@Override
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public ByteBuffer getReceiveBuffer() {
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return receiveBuffer;
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}
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@Override
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public ByteBuffer getSendBuffer() {
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return sendBuffer;
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}
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@Nullable
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public Instant whenCoolOff() {
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if (nextSegmentMark != 0) {
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return retransmitTime;
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} else {
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return null;
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}
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}
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@Override
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public void connect() {
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if (getState() != States.NEW)
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throw new IllegalStateException();
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setState(States.ESTABLISHED);
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}
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public TcpHeader getHeader() {
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return header;
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}
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}
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