6 files changed, 247 insertions, 0 deletions
diff --git a/src/main/java/derms/net/runicast/Ack.java b/src/main/java/derms/net/runicast/Ack.java
new file mode 100644
index 0000000..df2211c
--- /dev/null
+++ b/src/main/java/derms/net/runicast/Ack.java
@@ -0,0 +1,12 @@
+package derms.net.runicast;
+
+import java.io.Serializable;
+
+/** A message acknowledgement. */
+class Ack implements Serializable {
+    final long seq; // The sequence number of the acknowledged message.
+
+    Ack(long seq) {
+        this.seq = seq;
+    }
+}
diff --git a/src/main/java/derms/net/runicast/Message.java b/src/main/java/derms/net/runicast/Message.java
new file mode 100644
index 0000000..802cdb5
--- /dev/null
+++ b/src/main/java/derms/net/runicast/Message.java
@@ -0,0 +1,33 @@
+package derms.net.runicast;
+
+import derms.net.MessagePayload;
+
+import java.io.Serializable;
+
+class Message<T extends MessagePayload> implements Serializable {
+    final long seq; // Sequence number.
+    final T payload;
+
+    Message(long seq, T payload) {
+        this.seq = seq;
+        this.payload = payload;
+    }
+
+    @Override
+    public int hashCode() { return (int) seq * payload.hash(); }
+
+    @Override
+    public boolean equals(Object obj) {
+        if (obj == null)
+            return false;
+        if (obj.getClass() != this.getClass())
+            return false;
+        Message<?> other = (Message<?>) obj;
+        if (other.payload.getClass() != this.payload.getClass())
+            return false;
+        return other.seq == this.seq && other.payload.equals(this.payload);
+    }
+
+    @Override
+    public String toString() { return getClass().getSimpleName() + "{" + seq + ", " + payload + "}"; }
+}
diff --git a/src/main/java/derms/net/runicast/ReceiveAcks.java b/src/main/java/derms/net/runicast/ReceiveAcks.java
new file mode 100644
index 0000000..0f585ff
--- /dev/null
+++ b/src/main/java/derms/net/runicast/ReceiveAcks.java
@@ -0,0 +1,59 @@
+package derms.net.runicast;
+
+import derms.net.ConcurrentDatagramSocket;
+import derms.net.MessagePayload;
+import derms.net.Packet;
+
+import java.io.IOException;
+import java.net.DatagramPacket;
+import java.net.SocketTimeoutException;
+import java.util.Queue;
+import java.util.concurrent.atomic.AtomicLong;
+import java.util.logging.Logger;
+
+/** Receive acknowledgements. Remove messages from the sent queue once they are acknowledged. */
+class ReceiveAcks<T extends MessagePayload> implements Runnable {
+    private static final int bufSize = 8192;
+
+    private final AtomicLong unacked;
+    private final Queue<Message<T>> sent;
+    private final ConcurrentDatagramSocket sock;
+    private final Logger log;
+
+    ReceiveAcks(AtomicLong unacked, Queue<Message<T>> sent, ConcurrentDatagramSocket sock) {
+        this.unacked = unacked;
+        this.sent = sent;
+        this.sock = sock;
+        this.log = Logger.getLogger(getClass().getName());
+    }
+
+    @Override
+    public void run() {
+        DatagramPacket pkt = new DatagramPacket(new byte[bufSize], bufSize);
+        for (;;) {
+            try {
+                sock.receive(pkt);
+                Ack ack = Packet.decode(pkt, Ack.class);
+                recvAck(ack.seq);
+            } catch (SocketTimeoutException e) {
+                if (Thread.interrupted()) {
+                    log.info("Interrupted.");
+                    return;
+                }
+            } catch (IOException | ClassNotFoundException | ClassCastException e) {
+                log.warning(e.getMessage());
+            }
+        }
+    }
+
+    private void recvAck(long ack) {
+        unacked.updateAndGet((unacked) -> {
+            if (ack >= unacked)
+                return ack+1;
+            return unacked;
+        });
+
+        while (!sent.isEmpty() && sent.peek().seq <= ack)
+            sent.remove();
+    }
+}
diff --git a/src/main/java/derms/net/runicast/ReliableUnicastReceiver.java b/src/main/java/derms/net/runicast/ReliableUnicastReceiver.java
new file mode 100644
index 0000000..3d63a6f
--- /dev/null
+++ b/src/main/java/derms/net/runicast/ReliableUnicastReceiver.java
@@ -0,0 +1,4 @@
+package derms.net.runicast;
+
+public class ReliableUnicastReceiver {
+}
diff --git a/src/main/java/derms/net/runicast/ReliableUnicastSender.java b/src/main/java/derms/net/runicast/ReliableUnicastSender.java
new file mode 100644
index 0000000..2a0943a
--- /dev/null
+++ b/src/main/java/derms/net/runicast/ReliableUnicastSender.java
@@ -0,0 +1,82 @@
+package derms.net.runicast;
+
+import derms.net.ConcurrentDatagramSocket;
+import derms.net.MessagePayload;
+import derms.net.Packet;
+
+import java.io.IOException;
+import java.net.DatagramPacket;
+import java.net.InetSocketAddress;
+import java.net.SocketException;
+import java.time.Duration;
+import java.util.Queue;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.LinkedBlockingQueue;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicLong;
+import java.util.logging.Logger;
+
+public class ReliableUnicastSender<T extends MessagePayload> {
+    private static final Duration soTimeout = Duration.ofMillis(500); // Socket timeout.
+    private static final Duration terminationTimeout = Duration.ofSeconds(1);
+
+    private final AtomicLong next; // Next sequence number.
+    private final AtomicLong unacked; // Sequence number of first unacknowledged message.
+    private final Queue<Message<T>> sent;
+    private final ConcurrentDatagramSocket sock;
+    private final Logger log;
+    private final ExecutorService pool;
+
+    /**
+     * @param raddr Remote IP address to connect to.
+     */
+    ReliableUnicastSender(InetSocketAddress raddr) throws IOException {
+        this.next = new AtomicLong(0);
+        this.unacked = new AtomicLong(0);
+        this.sent = new LinkedBlockingQueue<Message<T>>();
+        this.sock = new ConcurrentDatagramSocket();
+        this.sock.connect(raddr);
+        this.sock.setSoTimeout(soTimeout);
+        this.log = Logger.getLogger(getClass().getName());
+        this.pool = Executors.newCachedThreadPool();
+        pool.execute(new ReceiveAcks<T>(unacked, sent, sock));
+        pool.execute(new Retransmit<T>(unacked, sent, sock));
+    }
+
+    public void send(T payload) throws IOException {
+        Message<T> msg = new Message<T>(next.get(), payload);
+        DatagramPacket pkt = Packet.encode(msg, sock.getRemoteSocketAddress());
+        sock.send(pkt);
+        sent.add(msg);
+        next.incrementAndGet();
+    }
+
+    /** Wait for all messages to be acknowledged and close the connection. */
+    public void close() throws InterruptedException {
+        // Wait for receiver to acknowledge all sent messages.
+        while (unacked.get() < next.get()) {
+            Thread.yield();
+            if (Thread.interrupted())
+                throw new InterruptedException();
+        }
+
+        closeNow();
+    }
+
+    /** Close the connection immediately, without waiting for acknowledgements. */
+    public void closeNow() {
+        log.info("Shutting down.");
+        pool.shutdownNow();
+        try {
+            if (!pool.awaitTermination(terminationTimeout.toMillis(), TimeUnit.MILLISECONDS))
+                log.warning("Thread pool did not terminate after " + terminationTimeout);
+        } catch (InterruptedException e) {
+            log.warning("Interrupted while terminating thread pool: " + e.getMessage());
+            // Preserve interrupt status.
+            Thread.currentThread().interrupt();
+        }
+
+        sock.close();
+    }
+}
diff --git a/src/main/java/derms/net/runicast/Retransmit.java b/src/main/java/derms/net/runicast/Retransmit.java
new file mode 100644
index 0000000..affd00c
--- /dev/null
+++ b/src/main/java/derms/net/runicast/Retransmit.java
@@ -0,0 +1,57 @@
+package derms.net.runicast;
+
+import derms.net.ConcurrentDatagramSocket;
+import derms.net.MessagePayload;
+import derms.net.Packet;
+import derms.util.Wait;
+
+import java.io.IOException;
+import java.net.DatagramPacket;
+import java.time.Duration;
+import java.util.Queue;
+import java.util.concurrent.atomic.AtomicLong;
+import java.util.logging.Logger;
+
+/** Retransmit unacknowledged messages. */
+class Retransmit<T extends MessagePayload> implements Runnable {
+    private static final Duration timeout = Duration.ofMillis(500);
+
+    private final AtomicLong unacked;
+    private final Queue<Message<T>> sent;
+    private final ConcurrentDatagramSocket sock;
+    private final Logger log;
+
+    Retransmit(AtomicLong unacked, Queue<Message<T>> sent, ConcurrentDatagramSocket sock) {
+        this.unacked = unacked;
+        this.sent = sent;
+        this.sock = sock;
+        this.log = Logger.getLogger(getClass().getName());
+    }
+
+    @Override
+    public void run() {
+        try {
+            for (;;) {
+                Wait.forDuration(timeout);
+
+                for (Message<T> msg : sent) {
+                    if (msg.seq >= unacked.get()) {
+                        retransmit(msg);
+                    }
+                }
+            }
+        } catch (InterruptedException e) {
+            log.info("Interrupted.");
+        }
+    }
+
+    private void retransmit(Message<T> msg) {
+        try {
+            DatagramPacket pkt = Packet.encode(msg, sock.getRemoteSocketAddress());
+            sock.send(pkt);
+            log.info("Retransmitted " + msg);
+        } catch (IOException e) {
+            log.warning("Failed to retransmit " + msg + ": " + e.getMessage());
+        }
+    }
+}