added toString for tracing

src/main/java/io/reactivesocket/DefaultReactiveSocket.java

@@ -29,6 +29,7 @@
 import org.reactivestreams.Subscription;
 
 import java.io.IOException;
+import java.util.concurrent.CopyOnWriteArrayList;
 import java.util.concurrent.atomic.AtomicInteger;
 import java.util.function.Consumer;
 
@@ -55,6 +56,7 @@ public class DefaultReactiveSocket implements ReactiveSocket {
     private final RequestHandler clientRequestHandler;
     private final ConnectionSetupHandler responderConnectionHandler;
     private final LeaseGovernor leaseGovernor;
+    private final CopyOnWriteArrayList<Completable> shutdownListeners;
 
     private DefaultReactiveSocket(
         DuplexConnection connection,
@@ -72,6 +74,7 @@ private DefaultReactiveSocket(
         this.responderConnectionHandler = responderConnectionHandler;
         this.leaseGovernor = leaseGovernor;
         this.errorStream = errorStream;
+        this.shutdownListeners = new CopyOnWriteArrayList<>();
     }
 
     /**
@@ -439,15 +442,28 @@ public void addOutput(Frame f, Completable callback) {
 
     };
 
+    @Override
+    public void onShutdown(Completable c) {
+        shutdownListeners.add(c);
+    }
+
     @Override
     public void close() throws Exception {
-        connection.close();
-        leaseGovernor.unregister(responder);
-        if (requester != null) {
-            requester.shutdown();
-        }
-        if (responder != null) {
-            responder.shutdown();
+        try {
+            connection.close();
+            leaseGovernor.unregister(responder);
+            if (requester != null) {
+                requester.shutdown();
+            }
+            if (responder != null) {
+                responder.shutdown();
+            }
+
+            shutdownListeners.forEach(Completable::success);
+
+        } catch (Throwable t) {
+            shutdownListeners.forEach(c -> c.error(t));
+            throw t;
         }
     }
 
@@ -476,4 +492,8 @@ public void cancel() {
             });
         };
     }
+
+    public String toString() {
+        return "duplexConnection=[" + this.connection + "]";
+    }
 }

src/main/java/io/reactivesocket/DuplexConnection.java

@@ -15,6 +15,7 @@
  */
 package io.reactivesocket;
 
+import io.reactivesocket.internal.rx.EmptySubscription;
 import io.reactivesocket.rx.Completable;
 import io.reactivesocket.rx.Observable;
 import org.reactivestreams.Publisher;
@@ -32,6 +33,7 @@ public interface DuplexConnection extends Closeable {
 
 	default void addOutput(Frame frame, Completable callback) {
         addOutput(s -> {
+            s.onSubscribe(EmptySubscription.INSTANCE);
             s.onNext(frame);
             s.onComplete();
         }, callback);

src/main/java/io/reactivesocket/ReactiveSocket.java

@@ -94,6 +94,11 @@ public void error(Throwable e) {
      */
     void onRequestReady(Completable c);
 
+    /**
+     * Registers a completable to be run when an ReactiveSocket is closed
+     */
+    void onShutdown(Completable c);
+
     /**
      * Server granting new lease information to client
      *

src/test/java/io/reactivesocket/ReactiveSocketTest.java

@@ -16,6 +16,7 @@
 package io.reactivesocket;
 
 import io.reactivesocket.lease.FairLeaseGovernor;
+import io.reactivesocket.rx.Completable;
 import io.reactivex.disposables.Disposable;
 import io.reactivex.observables.ConnectableObservable;
 import io.reactivex.subscribers.TestSubscriber;
@@ -256,6 +257,74 @@ private void awaitSocketAvailability(ReactiveSocket socket, long timeout, TimeUn
 		assertTrue("client socket has positive avaibility", socket.availability() > 0.0);
 	}
 
+	@Test(timeout = 2000)
+	public void testShutdownListener() throws Exception {
+		socketClient = DefaultReactiveSocket.fromClientConnection(
+			clientConnection,
+			ConnectionSetupPayload.create("UTF-8", "UTF-8", NO_FLAGS),
+			err -> err.printStackTrace()
+		);
+
+		CountDownLatch latch = new CountDownLatch(1);
+
+		socketClient.onShutdown(new Completable() {
+			@Override
+			public void success() {
+				latch.countDown();
+			}
+
+			@Override
+			public void error(Throwable e) {
+
+			}
+		});
+
+		socketClient.close();
+
+		latch.await();
+	}
+
+	@Test(timeout = 2000)
+	public void testMultipleShutdownListeners() throws Exception {
+		socketClient = DefaultReactiveSocket.fromClientConnection(
+			clientConnection,
+			ConnectionSetupPayload.create("UTF-8", "UTF-8", NO_FLAGS),
+			err -> err.printStackTrace()
+		);
+
+		CountDownLatch latch = new CountDownLatch(2);
+
+		socketClient
+			.onShutdown(new Completable() {
+				@Override
+				public void success() {
+					latch.countDown();
+				}
+
+				@Override
+				public void error(Throwable e) {
+
+				}
+			});
+
+		socketClient
+			.onShutdown(new Completable() {
+				@Override
+				public void success() {
+					latch.countDown();
+				}
+
+				@Override
+				public void error(Throwable e) {
+
+				}
+			});
+
+		socketClient.close();
+
+		latch.await();
+	}
+
 	@Test(timeout=2000)
 	@Theory
 	public void testRequestResponse(int setupFlag) throws InterruptedException {
@@ -269,7 +338,7 @@ public void testRequestResponse(int setupFlag) throws InterruptedException {
 		ts.assertNoErrors();
 		ts.assertValue(TestUtil.utf8EncodedPayload("hello world", null));
 	}
-	
+
 	@Test(timeout=2000, expected=IllegalStateException.class)
 	public void testRequestResponsePremature() throws InterruptedException {
 		socketClient = DefaultReactiveSocket.fromClientConnection(