/**
* Send a data packet and wait for ack in one operation. This method employs a timer that resends
* the packet until an ack is received (or the timeout is reached). <br>
* <br>
* This method sets the {@link #lastDataPacketSent} variable. This method can only be used in the
* Established state, see {@link State}.
*
* @param packet the packet to be sent.
* @return The ack-package received for the send packet (NB: ack can be null)
* @throws IOException thrown if unable to send packet.
* @see no.ntnu.fp.net.cl.ClSocket#send(KtnDatagram)
*/
protected synchronized KtnDatagram sendDataPacketWithRetransmit(KtnDatagram packet)
throws IOException {
if (state != State.ESTABLISHED)
throw new IllegalStateException("Should only be used in ESTABLISHED state.");
if (packet.getFlag() != Flag.NONE)
throw new IllegalArgumentException("Packet must be a data packet.");
/*
* Algorithm: 1 Start a timer used to resend the packet with a specified
* interval, and that immediately starts trying (sending the first
* packet as well as the retransmits). 2 Wait for the ACK using
* receiveAck(). 3 Cancel the timer. 4 Return the ACK-packet.
*/
lastDataPacketSent = packet;
// Create a timer that sends the packet and retransmits every
// RETRANSMIT milliseconds until cancelled.
Timer timer = new Timer();
timer.scheduleAtFixedRate(new SendTimer(new ClSocket(), packet), 0, RETRANSMIT);
KtnDatagram ack = receiveAck();
timer.cancel();
return ack;
}
/**
* Send an ack or synack for the given packet. <br>
* If the send fails, there is no retransmission of the ack-packet: Just wait for the other side
* to retransmit the original packet.<br>
* <br>
* This method relies on {@link #constructInternalPacket(Flag)}, i.e. myAddress, myPort,
* remoteAddress, remotePort and sequenceNo must be initialized properly.
*
* @param packetToAck The packet that should be acked
* @param synAck true if a synack should be sent, false if a regular ack, see {@link
* KtnDatagram.Flag}.
* @throws ConnectException Thrown if unable to send packet.
* @see #constructInternalPacket(Flag)
*/
protected synchronized void sendAck(KtnDatagram packetToAck, boolean synAck)
throws IOException, ConnectException {
/*
* Algorithm: Generate a new ack packet based on the packet given as
* input Try to send the ack Catch a ConnectException if the sending
* failed - and write this to the Log.
*/
int tries = 3;
boolean sent = false;
KtnDatagram ackToSend = constructInternalPacket(synAck ? Flag.SYN_ACK : Flag.ACK);
ackToSend.setAck(packetToAck.getSeq_nr());
// Send the ack, trying at most `tries' times.
Log.writeToLog(ackToSend, "Sending Ack: " + ackToSend.getAck(), "AbstractConnection");
do {
try {
new ClSocket().send(ackToSend);
sent = true;
} catch (ClException e) {
Log.writeToLog(
ackToSend,
"CLException: Could not establish a " + "connection to the specified address/port!",
"AbstractConnection");
} catch (ConnectException e) {
// Silently ignore: Maybe recipient was processing and didn't
// manage to call receiveAck() before we were ready to send.
try {
Thread.sleep(100);
} catch (InterruptedException ex) {
}
}
} while (!sent && (tries-- > 0));
if (!sent) {
nextSequenceNo--;
throw new ConnectException("Unable to send ACK.");
}
}
/**
* Construct a datagram with the given flag. <br>
* <br>
* Note: This method *depends* on the values of `remotePort', `remoteAddress', `myPort',
* `myAddress' and `sequenceNo'. Failing to set these before calling this method causes undefined
* behaviour. Also note that if you want to set values to something else than the default, you
* must construct the packet manually or alter the returned object.<br>
* <br>
* This method also increments the sequenceNo.<br>
* <br>
* This method sets the following fields:
*
* <ol>
* <li>Remote address
* <li>Remote port
* <li>Local address
* <li>Local port
* <li>Flag
* <li>Sequence no.
* <li>Payload to null.
* </ol>
*
* @param flag Flag for the packet, see {@link KtnDatagram.Flag}. Setting this to
* KtnDatagram.Flag.NONE constructs a packet with no flag or data, and makes no sense.
* @return Initialised flagged datagram.
*/
protected KtnDatagram constructInternalPacket(Flag flag) {
KtnDatagram packet = new KtnDatagram();
packet.setDest_port(remotePort);
packet.setDest_addr(remoteAddress);
packet.setSrc_addr(myAddress);
packet.setSrc_port(myPort);
packet.setFlag(flag);
packet.setSeq_nr(nextSequenceNo++);
packet.setPayload(null);
return packet;
}
/**
* Construct a datagram with the given payload. <br>
* <br>
* Note: This method *depends* on the values of `remotePort', `remoteAddress', `myPort',
* `myAddress' and `sequenceNo'. Failing to set these before calling this method causes undefined
* behaviour. Also note that if you want to set values to something else than the default, you
* must construct the packet manually or alter the returned object.<br>
* <br>
* This method also increments the sequenceNo.<br>
* <br>
* This method sets the following fields:
*
* <ol>
* <li>Remote address
* <li>Remote port
* <li>Local address
* <li>Local port
* <li>Flag to NONE.
* <li>Sequence no.
* <li>Payload.
* </ol>
*
* @param payload Payload for packet, can not be null.
* @return Initialised datagram.
*/
protected KtnDatagram constructDataPacket(String payload) {
if (payload == null) throw new IllegalArgumentException("Payload can not be null.");
KtnDatagram packet = new KtnDatagram();
packet.setDest_port(remotePort);
packet.setDest_addr(remoteAddress);
packet.setSrc_addr(myAddress);
packet.setSrc_port(myPort);
packet.setFlag(Flag.NONE);
packet.setSeq_nr(nextSequenceNo++);
packet.setPayload(payload);
return packet;
}
/**
* Waits for an ACK or SYN_ACK. Blocks until the ack is recieved. Returns null if no ack recieved
* after the specified time, see {@link AbstractConnection#TIMEOUT}. <br>
* <br>
* If a FIN-packet is received and the state is not ESTABLISHED, this will also be returned.<br>
* <br>
* If a FIN-packet is received and the connection is in ESTABLISHED state, an EOFException is
* thrown. It calls {@link #isValid(KtnDatagram)} on FIN-packets in ESTABLISHED state, before an
* EOFException is thrown.
*
* @return The ACK or SYN_ACK KtnDatagram recieved (can be null), may also be a FIN if not in
* established state.
* @throws IOException If caused by the underlying connectionless layer.
* @throws EOFException If a FIN-packet is received in ESTABLISHED state.
*/
protected KtnDatagram receiveAck() throws IOException, EOFException {
/*
* Acquire monitor for this instance, and see if another thread runs
* receive on our port. If so, see if that thread gets the packet that
* was meant for us.
*/
synchronized (this) {
long before, after;
before = System.currentTimeMillis();
while (isReceiving) {
try {
wait(TIMEOUT); // wait with timeout
} catch (InterruptedException e) {
/* do nothing */
}
after = System.currentTimeMillis();
// If an ack for us has arrived, return it.
// check internalQueue
if (!internalQueue.isEmpty()) {
KtnDatagram packet = internalQueue.get(0);
if (packet.getFlag() == Flag.ACK || packet.getFlag() == Flag.SYN_ACK) {
return internalQueue.remove(0);
}
}
// If no packet arrived, see if timeout has expired.
else if ((after - before) > TIMEOUT) {
return null;
}
}
// When we get here, this thread has not got its packet, and it's
// allowed to enter the listening part of doReceive().
isReceiving = true;
}
Log.writeToLog("Waiting for incoming packet in receiveAck()", "AbstractConnection");
KtnDatagram incomingPacket;
// We are waiting for an ack or syn_ack packet
long start = System.currentTimeMillis();
while (System.currentTimeMillis() - start < TIMEOUT) {
ClSocketReceiver receiver = new ClSocketReceiver(myPort);
receiver.start();
// Wait at most what is left of the TIMEOUT period for thread to
// die, but never less than 1 millisecond
try {
receiver.join(Math.max(TIMEOUT - (System.currentTimeMillis() - start), 1));
} catch (InterruptedException e) {
/* do nothing */
}
receiver.stopReceive();
incomingPacket = receiver.getPacket();
if (incomingPacket == null) {
// No packet was received
synchronized (this) {
isReceiving = false;
notifyAll();
return null;
}
} else {
// We have a packet
if (incomingPacket.getFlag() != Flag.NONE) {
// Packet is internal
Log.writeToLog("Received an internal packet in receiveAck", "AbstractConnection");
if (incomingPacket.getFlag() == Flag.FIN && state == State.ESTABLISHED) {
// A FIN-packet has arrived in established state,
// stop receiving and throw and exception
disconnectRequest = incomingPacket;
synchronized (this) {
isReceiving = false;
notifyAll();
throw new EOFException("FIN packet received.");
}
} else if (incomingPacket.getFlag() == Flag.ACK
|| incomingPacket.getFlag() == Flag.SYN_ACK
|| incomingPacket.getFlag() == Flag.FIN) {
// Not a FIN packet in established state, return if it
// is SYN, SYN_ACK or FIN
synchronized (this) {
isReceiving = false;
notifyAll();
return incomingPacket;
}
} else {
// Not a packet we want to return, continue looping.
synchronized (this) {
internalQueue.add(incomingPacket);
notifyAll();
}
}
} else {
// Packet was meant for the application, continue
// listening until timeout.
Log.writeToLog("Received an external packet in receiveAck", "AbstractConnection");
synchronized (this) {
synchronized (this) {
externalQueue.add(incomingPacket);
notifyAll();
}
}
}
}
}
// We have now waited at least TIMEOUT milliseconds, still no
// packet.
synchronized (this) {
isReceiving = false;
notifyAll();
return null;
}
}
/**
* Receives a packet from the connectionless layer. This function handles concurrency issues
* related to that only one thread may listen to a port at the same time.<br>
* <br>
* It calls {@link #isValid(KtnDatagram)} on FIN-packets in ESTABLISHED state, before an
* EOFException is thrown.
*
* @param internal true if you want to receive non-external packet, i.e. not a packet with data
* intended for the application. False otherwise.
* @return A received datagram
* @throws IOException If the underlying connectionless layer throws an IOException.
* @throws EOFException If a packet with a FIN-flag was received in ESTABLISHED state.
*/
protected KtnDatagram receivePacket(boolean internal) throws IOException, EOFException {
/*
* Acquire monitor for this instance, and see if another thread runs
* receive on our port. If so, see if that thread gets the packet that
* was meant for us.
*/
synchronized (this) {
long before, after;
before = System.currentTimeMillis();
while (isReceiving) {
try {
if (internal) wait(TIMEOUT); // wait with timeout
else wait(); // wait (potentially) forever
} catch (InterruptedException e) {
/* do nothing */
}
after = System.currentTimeMillis();
// If a packet for us has arrived, return it.
if (internal) {
// Case 1: Internal (protocol) caller, check internalQueue
if (!internalQueue.isEmpty()) {
return internalQueue.remove(0);
}
// If no packet arrived, see if timeout has expired.
else if ((after - before) > TIMEOUT) {
return null;
}
} else {
// Case 2: Non-internal (application) caller, check
// externalQueue
if (!externalQueue.isEmpty()) {
return externalQueue.remove(0);
}
// else try loop again unless connection is free
}
}
// When we get here, this thread has not got its packet, and it's
// allowed to enter the listening part of doReceive().
isReceiving = true;
}
Log.writeToLog("Waiting for incoming packet in doReceive()", "AbstractConnection");
KtnDatagram incomingPacket;
/*
* Waiting for internal and external packets should be handled
* differently. Waiting for internal packets should time out.
*/
if (internal) {
// We are waiting for an internal packet, ie. a packet with a flag
long start = System.currentTimeMillis();
while (System.currentTimeMillis() - start < TIMEOUT) {
ClSocketReceiver receiver = new ClSocketReceiver(myPort);
receiver.start();
// Wait at most what is left of the TIMEOUT period for thread to
// die, but never less than 1 millisecond
try {
long timeout = TIMEOUT - (System.currentTimeMillis() - start);
receiver.join(Math.max(timeout, 1));
} catch (InterruptedException e) {
/* do nothing */
}
receiver.stopReceive();
incomingPacket = receiver.getPacket();
if (incomingPacket == null) {
// No packet was received
synchronized (this) {
isReceiving = false;
notifyAll();
return null;
}
} else {
// We have a packet
if (incomingPacket.getFlag() != Flag.NONE) {
// Packet is internal
Log.writeToLog("Received an internal packet in doReceive", "AbstractConnection");
if (incomingPacket.getFlag() == Flag.FIN && state == State.ESTABLISHED) {
// A FIN-packet has arrived in established state,
// stop receiving and throw and exception
disconnectRequest = incomingPacket;
synchronized (this) {
isReceiving = false;
notifyAll();
throw new EOFException("FIN packet received.");
}
} else {
// Not a FIN packet in established state, return it
// normally.
synchronized (this) {
isReceiving = false;
notifyAll();
return incomingPacket;
}
}
} else {
// Packet was meant for the application, continue
// listening until timeout.
Log.writeToLog("Received an external packet in doReceive", "AbstractConnection");
synchronized (this) {
synchronized (this) {
externalQueue.add(incomingPacket);
notifyAll();
}
}
}
}
}
// We have now waited at least TIMEOUT milliseconds, still no
// packet.
synchronized (this) {
isReceiving = false;
notifyAll();
return null;
}
} else {
// We are waiting for a packet to an external application, ie. a
// packet with no flags. Can possibly wait forever.
incomingPacket = new ClSocket().receive(myPort);
if (incomingPacket == null) {
// We should get a packet, try again.
synchronized (this) {
isReceiving = false;
notifyAll();
}
return receivePacket(internal);
} else {
// We have a packet
if (incomingPacket.getFlag() != Flag.NONE) {
// Packet is internal
Log.writeToLog("Received an internal packet in doReceive", "AbstractConnection");
if (incomingPacket.getFlag() == Flag.FIN && state == State.ESTABLISHED) {
// A FIN-packet has arrived in established state,
// stop receiving and throw and exception
disconnectRequest = incomingPacket;
synchronized (this) {
isReceiving = false;
notifyAll();
throw new EOFException("FIN packet received.");
}
} else {
// Not a FIN packet, continue listening
synchronized (this) {
internalQueue.add(incomingPacket);
isReceiving = false;
notifyAll();
}
return receivePacket(internal);
}
} else {
// Packet was meant for the application, yei!
Log.writeToLog("Received an external packet in doReceive", "AbstractConnection");
synchronized (this) {
isReceiving = false;
notifyAll();
return incomingPacket;
}
}
}
}
}
