Add non-blocking send

smack-bosh/src/main/java/org/jivesoftware/smack/bosh/XMPPBOSHConnection.java

@@ -29,17 +29,19 @@ import org.jivesoftware.smack.AbstractXMPPConnection;
 import org.jivesoftware.smack.SmackException;
 import org.jivesoftware.smack.SmackException.GenericConnectionException;
 import org.jivesoftware.smack.SmackException.NotConnectedException;
+import org.jivesoftware.smack.SmackException.OutgoingQueueFullException;
 import org.jivesoftware.smack.SmackException.SmackWrappedException;
 import org.jivesoftware.smack.XMPPConnection;
 import org.jivesoftware.smack.XMPPException;
 import org.jivesoftware.smack.XMPPException.StreamErrorException;
-import org.jivesoftware.smack.packet.Element;
 import org.jivesoftware.smack.packet.IQ;
 import org.jivesoftware.smack.packet.Message;
-import org.jivesoftware.smack.packet.Nonza;
 import org.jivesoftware.smack.packet.Presence;
 import org.jivesoftware.smack.packet.Stanza;
 import org.jivesoftware.smack.packet.StanzaError;
+import org.jivesoftware.smack.packet.TopLevelStreamElement;
+import org.jivesoftware.smack.util.ArrayBlockingQueueWithShutdown;
+import org.jivesoftware.smack.util.Async;
 import org.jivesoftware.smack.util.CloseableUtil;
 import org.jivesoftware.smack.util.PacketParserUtils;
 import org.jivesoftware.smack.xml.XmlPullParser;
@@ -90,6 +92,10 @@ public class XMPPBOSHConnection extends AbstractXMPPConnection {
     @SuppressWarnings("HidingField")
     private final BOSHConfiguration config;
 
+    private final ArrayBlockingQueueWithShutdown<TopLevelStreamElement> outgoingQueue = new ArrayBlockingQueueWithShutdown<>(100, true);
+
+    private Thread writerThread;
+
     // Some flags which provides some info about the current state.
     private boolean isFirstInitialization = true;
     private boolean done = false;
@@ -194,11 +200,16 @@ public class XMPPBOSHConnection extends AbstractXMPPConnection {
             }
         }
 
+        assert writerThread == null || !writerThread.isAlive();
+        outgoingQueue.start();
+        writerThread = Async.go(this::writeElements, this + " Writer");
+
         // If there is no feedback, throw an remote server timeout error
         if (!connected && !done) {
             done = true;
             String errorMessage = "Timeout reached for the connection to "
                     + getHost() + ":" + getPort() + ".";
+            instantShutdown();
             throw new SmackException.SmackMessageException(errorMessage);
         }
 
@@ -207,6 +218,7 @@ public class XMPPBOSHConnection extends AbstractXMPPConnection {
                             "<stream:stream xmlns='jabber:client' xmlns:stream='http://etherx.jabber.org/streams'/>");
             onStreamOpen(parser);
         } catch (XmlPullParserException | IOException e) {
+            instantShutdown();
             throw new AssertionError("Failed to setup stream environment", e);
         }
     }
@@ -234,40 +246,92 @@ public class XMPPBOSHConnection extends AbstractXMPPConnection {
         afterSuccessfulLogin(false);
     }
 
-    @Override
+    private volatile boolean writerThreadRunning;
-    public void sendNonza(Nonza element) throws NotConnectedException {
-        if (done) {
-            throw new NotConnectedException();
-        }
-        sendElement(element);
-    }
 
-    @Override
+    private void writeElements() {
-    protected void sendStanzaInternal(Stanza packet) throws NotConnectedException {
+        writerThreadRunning = true;
-        sendElement(packet);
-    }
-
-    private void sendElement(Element element) {
         try {
-            send(ComposableBody.builder().setPayloadXML(element.toXML(BOSH_URI).toString()).build());
+            while (true) {
-            if (element instanceof Stanza) {
+                TopLevelStreamElement element;
-                firePacketSendingListeners((Stanza) element);
+                try {
+                    element = outgoingQueue.take();
+                } catch (InterruptedException e) {
+                    LOGGER.log(Level.FINE,
+                                    "Writer thread exiting: Outgoing queue was shutdown as signalled by interrupted exception",
+                                    e);
+                    return;
+                }
+
+                String xmlPayload = element.toXML(BOSH_URI).toString();
+                ComposableBody.Builder composableBodyBuilder = ComposableBody.builder().setPayloadXML(xmlPayload);
+                if (sessionID != null) {
+                    BodyQName qName = BodyQName.create(BOSH_URI, "sid");
+                    composableBodyBuilder.setAttribute(qName, sessionID);
+                }
+
+                ComposableBody composableBody = composableBodyBuilder.build();
+
+                try {
+                    client.send(composableBody);
+                } catch (BOSHException e) {
+                    LOGGER.log(Level.WARNING, this + " received BOSHException in writer thread, connection broke!", e);
+                    // TODO: Signal the user that there was an unexpected exception.
+                    return;
+                }
+
+                if (element instanceof Stanza) {
+                    Stanza stanza = (Stanza) element;
+                    firePacketSendingListeners(stanza);
+                }
             }
-        }
+        } catch (Exception exception) {
-        catch (BOSHException e) {
+            LOGGER.log(Level.WARNING, "BOSH writer thread threw", exception);
-            LOGGER.log(Level.SEVERE, "BOSHException in sendStanzaInternal", e);
+        } finally {
+            writerThreadRunning = false;
+            notifyWaitingThreads();
+        }
+    }
+
+    @Override
+    protected void sendInternal(TopLevelStreamElement element) throws NotConnectedException, InterruptedException {
+        throwNotConnectedExceptionIfAppropriate();
+        try {
+            outgoingQueue.put(element);
+        } catch (InterruptedException e) {
+            throwNotConnectedExceptionIfAppropriate();
+            // If the method above did not throw, then the sending thread was interrupted
+            throw e;
+        }
+    }
+
+    @Override
+    protected void sendNonBlockingInternal(TopLevelStreamElement element)
+                    throws NotConnectedException, OutgoingQueueFullException {
+        throwNotConnectedExceptionIfAppropriate();
+        boolean enqueued = outgoingQueue.offer(element);
+        if (!enqueued) {
+            throwNotConnectedExceptionIfAppropriate();
+            throw new OutgoingQueueFullException();
         }
     }
 
-    /**
-     * Closes the connection by setting presence to unavailable and closing the
-     * HTTP client. The shutdown logic will be used during a planned disconnection or when
-     * dealing with an unexpected disconnection. Unlike {@link #disconnect()} the connection's
-     * BOSH stanza reader will not be removed; thus connection's state is kept.
-     *
-     */
     @Override
     protected void shutdown() {
+        instantShutdown();
+    }
+
+    @Override
+    public void instantShutdown() {
+        outgoingQueue.shutdown();
+
+        try {
+            boolean writerThreadTerminated = waitFor(() -> !writerThreadRunning);
+            if (!writerThreadTerminated) {
+                LOGGER.severe("Writer thread of " + this + " did not terminate timely");
+            }
+        } catch (InterruptedException e) {
+            LOGGER.log(Level.FINE, "Interrupted while waiting for writer thread to terminate", e);
+        }
 
         if (client != null) {
             try {
@@ -275,20 +339,15 @@ public class XMPPBOSHConnection extends AbstractXMPPConnection {
             } catch (Exception e) {
                 LOGGER.log(Level.WARNING, "shutdown", e);
             }
-            client = null;
         }
 
-        instantShutdown();
-    }
-
-    @Override
-    public void instantShutdown() {
         setWasAuthenticated();
         sessionID = null;
         done = true;
         authenticated = false;
         connected = false;
         isFirstInitialization = false;
+        client = null;
 
         // Close down the readers and writers.
         CloseableUtil.maybeClose(readerPipe, LOGGER);
@@ -410,14 +469,15 @@ public class XMPPBOSHConnection extends AbstractXMPPConnection {
         // XMPP over BOSH is unusual when it comes to SASL authentication: Instead of sending a new stream open, it
         // requires a special XML element ot be send after successful SASL authentication.
         // See XEP-0206 § 5., especially the following is example 5 of XEP-0206.
-        ComposableBody composeableBody = ComposableBody.builder().setNamespaceDefinition("xmpp",
+        ComposableBody composeableBody = ComposableBody.builder()
-                        XMPPBOSHConnection.XMPP_BOSH_NS).setAttribute(
+                .setNamespaceDefinition("xmpp", XMPPBOSHConnection.XMPP_BOSH_NS)
-                        BodyQName.createWithPrefix(XMPPBOSHConnection.XMPP_BOSH_NS, "restart",
+                .setAttribute(BodyQName.createWithPrefix(XMPPBOSHConnection.XMPP_BOSH_NS, "restart", "xmpp"), "true")
-                                        "xmpp"), "true").setAttribute(
+                .setAttribute(BodyQName.create(XMPPBOSHConnection.BOSH_URI, "to"), getXMPPServiceDomain().toString())
-                        BodyQName.create(XMPPBOSHConnection.BOSH_URI, "to"), getXMPPServiceDomain().toString()).build();
+                .setAttribute(BodyQName.create(BOSH_URI, "sid"), sessionID)
+                .build();
 
         try {
-            send(composeableBody);
+            client.send(composeableBody);
         } catch (BOSHException e) {
             // jbosh's exception API does not really match the one of Smack.
             throw new SmackException.SmackWrappedException(e);

smack-core/src/main/java/org/jivesoftware/smack/AbstractXMPPConnection.java

@@ -51,6 +51,7 @@ import org.jivesoftware.smack.SmackException.AlreadyLoggedInException;
 import org.jivesoftware.smack.SmackException.NoResponseException;
 import org.jivesoftware.smack.SmackException.NotConnectedException;
 import org.jivesoftware.smack.SmackException.NotLoggedInException;
+import org.jivesoftware.smack.SmackException.OutgoingQueueFullException;
 import org.jivesoftware.smack.SmackException.ResourceBindingNotOfferedException;
 import org.jivesoftware.smack.SmackException.SecurityRequiredByClientException;
 import org.jivesoftware.smack.SmackException.SecurityRequiredException;
@@ -460,8 +461,17 @@ public abstract class AbstractXMPPConnection implements XMPPConnection {
     @Override
     public abstract boolean isSecureConnection();
 
-    protected abstract void sendStanzaInternal(Stanza packet) throws NotConnectedException, InterruptedException;
+    // Usually batching is a good idea. So the two
+    // send(Internal|NonBlockingInternal) methods below could be using
+    // Collection<? extends TopLevelStreamElement> as parameter type instead.
+    // TODO: Add "batched send" support. Note that for the non-blocking variant, this probably requires a change in
+    // return type, so that it is possible to signal which messages could be "send" and which not.
 
+    protected abstract void sendInternal(TopLevelStreamElement element) throws NotConnectedException, InterruptedException;
+
+    protected abstract void sendNonBlockingInternal(TopLevelStreamElement element) throws NotConnectedException, OutgoingQueueFullException;
+
+    @SuppressWarnings("deprecation")
     @Override
     public boolean trySendStanza(Stanza stanza) throws NotConnectedException {
         // Default implementation which falls back to sendStanza() as mentioned in the methods javadoc. May be
@@ -476,6 +486,7 @@ public abstract class AbstractXMPPConnection implements XMPPConnection {
         return true;
     }
 
+    @SuppressWarnings("deprecation")
     @Override
     public boolean trySendStanza(Stanza stanza, long timeout, TimeUnit unit)
                     throws NotConnectedException, InterruptedException {
@@ -486,7 +497,14 @@ public abstract class AbstractXMPPConnection implements XMPPConnection {
     }
 
     @Override
-    public abstract void sendNonza(Nonza element) throws NotConnectedException, InterruptedException;
+    public final void sendNonza(Nonza nonza) throws NotConnectedException, InterruptedException {
+        sendInternal(nonza);
+    }
+
+    @Override
+    public final void sendNonzaNonBlocking(Nonza nonza) throws NotConnectedException, OutgoingQueueFullException {
+        sendNonBlockingInternal(nonza);
+    }
 
     @Override
     public abstract boolean isUsingCompression();
@@ -853,8 +871,7 @@ public abstract class AbstractXMPPConnection implements XMPPConnection {
         return stanzaFactory;
     }
 
-    @Override
+    private Stanza preSendStanza(Stanza stanza) throws NotConnectedException {
-    public final void sendStanza(Stanza stanza) throws NotConnectedException, InterruptedException {
         Objects.requireNonNull(stanza, "Stanza must not be null");
         assert stanza instanceof Message || stanza instanceof Presence || stanza instanceof IQ;
 
@@ -873,7 +890,19 @@ public abstract class AbstractXMPPConnection implements XMPPConnection {
         // Invoke interceptors for the new stanza that is about to be sent. Interceptors may modify
         // the content of the stanza.
         Stanza stanzaAfterInterceptors = firePacketInterceptors(stanza);
-        sendStanzaInternal(stanzaAfterInterceptors);
+        return stanzaAfterInterceptors;
+    }
+
+    @Override
+    public final void sendStanza(Stanza stanza) throws NotConnectedException, InterruptedException {
+        stanza = preSendStanza(stanza);
+        sendInternal(stanza);
+    }
+
+    @Override
+    public final void sendStanzaNonBlocking(Stanza stanza) throws NotConnectedException, OutgoingQueueFullException {
+        stanza = preSendStanza(stanza);
+        sendNonBlockingInternal(stanza);
     }
 
     /**
@@ -2006,18 +2035,11 @@ public abstract class AbstractXMPPConnection implements XMPPConnection {
         }, timeout, TimeUnit.MILLISECONDS);
 
         addAsyncStanzaListener(stanzaListener, replyFilter);
-        Runnable sendOperation = () -> {
+        try {
-            try {
+            sendStanzaNonBlocking(stanza);
-                sendStanza(stanza);
+        }
-            }
+        catch (NotConnectedException | OutgoingQueueFullException exception) {
-            catch (NotConnectedException | InterruptedException exception) {
+            future.setException(exception);
-                future.setException(exception);
-            }
-        };
-        if (SmackConfiguration.TRUELY_ASYNC_SENDS) {
-            Async.go(sendOperation);
-        } else {
-            sendOperation.run();
         }
 
         return future;

smack-core/src/main/java/org/jivesoftware/smack/SmackConfiguration.java

@@ -387,13 +387,4 @@ public final class SmackConfiguration {
         }
     }
 
-    /**
-     * If enabled, causes {@link AbstractXMPPConnection} to create a thread for every asynchronous send operation. This
-     * is meant to work-around a shortcoming of Smack 4.4, where certain send operations are not asynchronous even if
-     * they should be. This is an expert setting, do not toggle if you do not understand the consequences or have been
-     * told to do so. Note that it is expected that this will not be needed in future Smack versions.
-     *
-     * @since 4.4.6
-     */
-    public static boolean TRUELY_ASYNC_SENDS = false;
 }

smack-core/src/main/java/org/jivesoftware/smack/SmackException.java

@@ -206,6 +206,12 @@ public abstract class SmackException extends Exception {
         }
     }
 
+    public static class OutgoingQueueFullException extends SmackException {
+
+        private static final long serialVersionUID = 1L;
+
+    }
+
     public static class IllegalStateChangeException extends SmackException {
 
         /**

smack-core/src/main/java/org/jivesoftware/smack/XMPPConnection.java

@@ -22,6 +22,7 @@ import javax.xml.namespace.QName;
 
 import org.jivesoftware.smack.SmackException.NoResponseException;
 import org.jivesoftware.smack.SmackException.NotConnectedException;
+import org.jivesoftware.smack.SmackException.OutgoingQueueFullException;
 import org.jivesoftware.smack.XMPPException.XMPPErrorException;
 import org.jivesoftware.smack.filter.IQReplyFilter;
 import org.jivesoftware.smack.filter.StanzaFilter;
@@ -199,6 +200,8 @@ public interface XMPPConnection {
      * */
     void sendStanza(Stanza stanza) throws NotConnectedException, InterruptedException;
 
+    void sendStanzaNonBlocking(Stanza stanza) throws NotConnectedException, OutgoingQueueFullException;
+
     /**
      * Try to send the given stanza. Returns {@code true} if the stanza was successfully put into the outgoing stanza
      * queue, otherwise, if {@code false} is returned, the stanza could not be scheduled for sending (for example
@@ -213,7 +216,10 @@ public interface XMPPConnection {
      * @return {@code true} if the stanza was successfully scheduled to be send, {@code false} otherwise.
      * @throws NotConnectedException if the connection is not connected.
      * @since 4.4.0
+     * @deprecated use {@link #sendStanzaNonBlocking(Stanza)} instead.
      */
+    // TODO: Remove in Smack 4.7.
+    @Deprecated
     boolean trySendStanza(Stanza stanza) throws NotConnectedException;
 
     /**
@@ -234,7 +240,10 @@ public interface XMPPConnection {
      * @throws NotConnectedException if the connection is not connected.
      * @throws InterruptedException if the calling thread was interrupted.
      * @since 4.4.0
+     * @deprecated use {@link #sendStanzaNonBlocking(Stanza)} instead.
      */
+    // TODO: Remove in Smack 4.7.
+    @Deprecated
     boolean trySendStanza(Stanza stanza, long timeout, TimeUnit unit)  throws NotConnectedException, InterruptedException;
 
     /**
@@ -251,6 +260,8 @@ public interface XMPPConnection {
      */
     void sendNonza(Nonza nonza) throws NotConnectedException, InterruptedException;
 
+    void sendNonzaNonBlocking(Nonza stanza) throws NotConnectedException, OutgoingQueueFullException;
+
     /**
      * Adds a connection listener to this connection that will be notified when
      * the connection closes or fails.

smack-core/src/main/java/org/jivesoftware/smack/c2s/ModularXmppClientToServerConnection.java

@@ -1,6 +1,6 @@
 /**
  *
- * Copyright 2018-2021 Florian Schmaus
+ * Copyright 2018-2022 Florian Schmaus
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -37,6 +37,7 @@ import org.jivesoftware.smack.AbstractXMPPConnection;
 import org.jivesoftware.smack.SmackException;
 import org.jivesoftware.smack.SmackException.NoResponseException;
 import org.jivesoftware.smack.SmackException.NotConnectedException;
+import org.jivesoftware.smack.SmackException.OutgoingQueueFullException;
 import org.jivesoftware.smack.SmackFuture;
 import org.jivesoftware.smack.XMPPException;
 import org.jivesoftware.smack.XMPPException.FailedNonzaException;
@@ -67,7 +68,6 @@ import org.jivesoftware.smack.packet.IQ;
 import org.jivesoftware.smack.packet.Message;
 import org.jivesoftware.smack.packet.Nonza;
 import org.jivesoftware.smack.packet.Presence;
-import org.jivesoftware.smack.packet.Stanza;
 import org.jivesoftware.smack.packet.StreamError;
 import org.jivesoftware.smack.packet.TopLevelStreamElement;
 import org.jivesoftware.smack.packet.XmlEnvironment;
@@ -438,16 +438,7 @@ public final class ModularXmppClientToServerConnection extends AbstractXMPPConne
     }
 
     @Override
-    protected void sendStanzaInternal(Stanza stanza) throws NotConnectedException, InterruptedException {
+    protected void sendInternal(TopLevelStreamElement element) throws NotConnectedException, InterruptedException {
-        sendTopLevelStreamElement(stanza);
-    }
-
-    @Override
-    public void sendNonza(Nonza nonza) throws NotConnectedException, InterruptedException {
-        sendTopLevelStreamElement(nonza);
-    }
-
-    private void sendTopLevelStreamElement(TopLevelStreamElement element) throws NotConnectedException, InterruptedException {
         final XmppClientToServerTransport transport = activeTransport;
         if (transport == null) {
             throw new NotConnectedException();
@@ -457,6 +448,21 @@ public final class ModularXmppClientToServerConnection extends AbstractXMPPConne
         transport.notifyAboutNewOutgoingElements();
     }
 
+    @Override
+    protected void sendNonBlockingInternal(TopLevelStreamElement element) throws NotConnectedException, OutgoingQueueFullException {
+        final XmppClientToServerTransport transport = activeTransport;
+        if (transport == null) {
+            throw new NotConnectedException();
+        }
+
+        boolean enqueued = outgoingElementsQueue.offer(element);
+        if (!enqueued) {
+            throw new OutgoingQueueFullException();
+        }
+
+        transport.notifyAboutNewOutgoingElements();
+    }
+
     @Override
     protected void shutdown() {
         shutdown(false);

smack-core/src/testFixtures/java/org/jivesoftware/smack/DummyConnection.java

@@ -1,6 +1,6 @@
 /**
  *
- * Copyright 2010 Jive Software.
+ * Copyright 2010 Jive Software, 2022 Florian Schmaus.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -23,8 +23,8 @@ import java.util.concurrent.BlockingQueue;
 import java.util.concurrent.LinkedBlockingQueue;
 import java.util.concurrent.TimeUnit;
 
+import org.jivesoftware.smack.SmackException.OutgoingQueueFullException;
 import org.jivesoftware.smack.packet.ExtensionElement;
-import org.jivesoftware.smack.packet.Nonza;
 import org.jivesoftware.smack.packet.Stanza;
 import org.jivesoftware.smack.packet.TopLevelStreamElement;
 
@@ -127,13 +127,16 @@ public class DummyConnection extends AbstractXMPPConnection {
     }
 
     @Override
-    public void sendNonza(Nonza element) {
+    protected void sendInternal(TopLevelStreamElement element) {
         queue.add(element);
     }
 
     @Override
-    protected void sendStanzaInternal(Stanza packet) {
+    protected void sendNonBlockingInternal(TopLevelStreamElement element) throws OutgoingQueueFullException {
-        queue.add(packet);
+        boolean enqueued = queue.add(element);
+        if (!enqueued) {
+            throw new OutgoingQueueFullException();
+        }
     }
 
     /**

smack-core/src/testFixtures/java/org/jivesoftware/smack/ThreadedDummyConnection.java

@@ -26,6 +26,7 @@ import java.util.logging.Logger;
 import org.jivesoftware.smack.packet.IQ;
 import org.jivesoftware.smack.packet.Message;
 import org.jivesoftware.smack.packet.Stanza;
+import org.jivesoftware.smack.packet.TopLevelStreamElement;
 
 /**
  * A threaded dummy connection.
@@ -40,10 +41,11 @@ public class ThreadedDummyConnection extends DummyConnection {
     private volatile boolean timeout = false;
 
     @Override
-    protected void sendStanzaInternal(Stanza packet) {
+    protected void sendInternal(TopLevelStreamElement element) {
-        super.sendStanzaInternal(packet);
+        super.sendInternal(element);
 
-        if (packet instanceof IQ && !timeout) {
+        if (element instanceof IQ && !timeout) {
+            IQ iq = (IQ) element;
             timeout = false;
             // Set reply packet to match one being sent. We haven't started the
             // other thread yet so this is still safe.
@@ -51,11 +53,11 @@ public class ThreadedDummyConnection extends DummyConnection {
 
             // If no reply has been set via addIQReply, then we create a simple reply
             if (replyPacket == null) {
-                replyPacket = IQ.createResultIQ((IQ) packet);
+                replyPacket = IQ.createResultIQ(iq);
                 replyQ.add(replyPacket);
             }
-            replyPacket.setStanzaId(packet.getStanzaId());
+            replyPacket.setStanzaId(iq.getStanzaId());
-            replyPacket.setTo(packet.getFrom());
+            replyPacket.setTo(iq.getFrom());
             if (replyPacket.getType() == null) {
                 replyPacket.setType(IQ.Type.result);
             }

smack-tcp/src/main/java/org/jivesoftware/smack/tcp/XMPPTCPConnection.java

@@ -62,6 +62,7 @@ import org.jivesoftware.smack.SmackException.ConnectionException;
 import org.jivesoftware.smack.SmackException.EndpointConnectionException;
 import org.jivesoftware.smack.SmackException.NotConnectedException;
 import org.jivesoftware.smack.SmackException.NotLoggedInException;
+import org.jivesoftware.smack.SmackException.OutgoingQueueFullException;
 import org.jivesoftware.smack.SmackException.SecurityNotPossibleException;
 import org.jivesoftware.smack.SmackException.SecurityRequiredByServerException;
 import org.jivesoftware.smack.SmackFuture;
@@ -79,12 +80,12 @@ import org.jivesoftware.smack.internal.SmackTlsContext;
 import org.jivesoftware.smack.packet.Element;
 import org.jivesoftware.smack.packet.IQ;
 import org.jivesoftware.smack.packet.Message;
-import org.jivesoftware.smack.packet.Nonza;
 import org.jivesoftware.smack.packet.Presence;
 import org.jivesoftware.smack.packet.Stanza;
 import org.jivesoftware.smack.packet.StartTls;
 import org.jivesoftware.smack.packet.StreamError;
 import org.jivesoftware.smack.packet.StreamOpen;
+import org.jivesoftware.smack.packet.TopLevelStreamElement;
 import org.jivesoftware.smack.proxy.ProxyInfo;
 import org.jivesoftware.smack.sasl.packet.SaslNonza;
 import org.jivesoftware.smack.sm.SMUtils;
@@ -464,7 +465,7 @@ public class XMPPTCPConnection extends AbstractXMPPConnection {
             }
         } else {
             for (Stanza stanza : previouslyUnackedStanzas) {
-                sendStanzaInternal(stanza);
+                sendInternal(stanza);
             }
         }
 
@@ -570,24 +571,38 @@ public class XMPPTCPConnection extends AbstractXMPPConnection {
         initState();
     }
 
-    @Override
+    private interface SmAckAction<E extends Exception> {
-    public void sendNonza(Nonza element) throws NotConnectedException, InterruptedException {
+        void run() throws NotConnectedException, E;
-        packetWriter.sendStreamElement(element);
     }
 
-    @Override
+    private <E extends Exception> void requestSmAckIfNecessary(TopLevelStreamElement element,
-    protected void sendStanzaInternal(Stanza packet) throws NotConnectedException, InterruptedException {
+                    SmAckAction<E> smAckAction) throws NotConnectedException, E {
-        packetWriter.sendStreamElement(packet);
+        if (!isSmEnabled())
-        if (isSmEnabled()) {
+            return;
+
+        if (element instanceof Stanza) {
+            Stanza stanza = (Stanza) element;
             for (StanzaFilter requestAckPredicate : requestAckPredicates) {
-                if (requestAckPredicate.accept(packet)) {
+                if (requestAckPredicate.accept(stanza)) {
-                    requestSmAcknowledgementInternal();
+                    smAckAction.run();
                     break;
                 }
             }
         }
     }
 
+    @Override
+    protected void sendInternal(TopLevelStreamElement element) throws NotConnectedException, InterruptedException {
+        packetWriter.sendStreamElement(element);
+        requestSmAckIfNecessary(element, () -> requestSmAcknowledgementInternal());
+    }
+
+    @Override
+    protected void sendNonBlockingInternal(TopLevelStreamElement element) throws NotConnectedException, OutgoingQueueFullException {
+        packetWriter.sendNonBlocking(element);
+        requestSmAckIfNecessary(element, () -> requestSmAcknowledgementNonBlockingInternal());
+    }
+
     private void connectUsingConfiguration() throws ConnectionException, IOException, InterruptedException {
         RemoteXmppTcpConnectionEndpoints.Result<Rfc6120TcpRemoteConnectionEndpoint> result = RemoteXmppTcpConnectionEndpoints.lookup(config);
 
@@ -1067,7 +1082,7 @@ public class XMPPTCPConnection extends AbstractXMPPConnection {
                             List<Stanza> stanzasToResend = new ArrayList<>(unacknowledgedStanzas.size());
                             unacknowledgedStanzas.drainTo(stanzasToResend);
                             for (Stanza stanza : stanzasToResend) {
-                                sendStanzaInternal(stanza);
+                                XMPPTCPConnection.this.sendInternal(stanza);
                             }
                             // If there where stanzas resent, then request a SM ack for them.
                             // Writer's sendStreamElement() won't do it automatically based on
@@ -1270,6 +1285,22 @@ public class XMPPTCPConnection extends AbstractXMPPConnection {
             }
         }
 
+        /**
+         * Sends the specified element to the server.
+         *
+         * @param element the element to send.
+         * @throws NotConnectedException if the XMPP connection is not connected.
+         * @throws OutgoingQueueFullException if there is no space in the outgoing queue.
+         */
+        protected void sendNonBlocking(Element element) throws NotConnectedException, OutgoingQueueFullException {
+            throwNotConnectedExceptionIfDoneAndResumptionNotPossible();
+            boolean enqueued = queue.offer(element);
+            if (!enqueued) {
+                throwNotConnectedExceptionIfDoneAndResumptionNotPossible();
+                throw new OutgoingQueueFullException();
+            }
+        }
+
         /**
          * Shuts down the stanza writer. Once this method has been called, no further
          * packets will be written to the server.
@@ -1588,6 +1619,10 @@ public class XMPPTCPConnection extends AbstractXMPPConnection {
         packetWriter.sendStreamElement(AckRequest.INSTANCE);
     }
 
+    private void requestSmAcknowledgementNonBlockingInternal() throws NotConnectedException, OutgoingQueueFullException {
+        packetWriter.sendNonBlocking(AckRequest.INSTANCE);
+    }
+
     /**
      * Send a unconditional Stream Management acknowledgment to the server.
      * <p>