WolfSSLEngine.java

/* WolfSSLEngine.java
 *
 * Copyright (C) 2006-2026 wolfSSL Inc.
 *
 * This file is part of wolfSSL.
 *
 * wolfSSL is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * wolfSSL is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1335, USA
 */

package com.wolfssl.provider.jsse;

import com.wolfssl.WolfSSL;
import com.wolfssl.WolfSSLDebug;
import com.wolfssl.WolfSSLException;
import com.wolfssl.WolfSSLByteBufferIORecvCallback;
import com.wolfssl.WolfSSLByteBufferIOSendCallback;
import com.wolfssl.WolfSSLJNIException;
import com.wolfssl.WolfSSLSession;
import com.wolfssl.WolfSSLALPNSelectCallback;
import com.wolfssl.WolfSSLSessionTicketCallback;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.ReadOnlyBufferException;
import java.util.function.BiFunction;
import java.util.List;
import java.util.Arrays;
import java.util.ArrayList;
import java.security.cert.CertificateEncodingException;
import javax.net.ssl.SSLEngine;
import javax.net.ssl.SSLEngineResult;
import javax.net.ssl.SSLEngineResult.HandshakeStatus;
import javax.net.ssl.SSLEngineResult.Status;
import javax.net.ssl.SSLException;
import javax.net.ssl.SSLHandshakeException;
import javax.net.ssl.SSLSession;
import javax.net.ssl.SSLParameters;
import java.net.SocketException;
import java.net.SocketTimeoutException;

/**
 * wolfSSL implementation of SSLEngine.
 *
 * There is more verbose debugging available for this class apart
 * from the normal 'wolfjsse.debug' logging. To enable more verbose
 * logging use both the following system properties:
 *
 * System.setProperty("wolfjsse.debug", "true");
 * System.setProperty("wolfsslengine.debug", "true");
 *
 * This will add extra debug logs around wrap() and unwrap() calls, as well
 * as printing out the data sent/received in the I/O callbacks.
 *
 * @author wolfSSL
 */
public class WolfSSLEngine extends SSLEngine {

    private WolfSSLEngineHelper engineHelper = null;
    private WolfSSLSession ssl = null;
    private com.wolfssl.WolfSSLContext ctx = null;
    private WolfSSLAuthStore authStore = null;
    private WolfSSLParameters params = null;
    private int nativeWantsToWrite = 0;
    private int nativeWantsToRead = 0;
    private HandshakeStatus hs = SSLEngineResult.HandshakeStatus.NOT_HANDSHAKING;

    /* Does TLS handshake need initialization */
    private boolean needInit = true;
    private final Object initLock = new Object();

    /* Have cert/key been loaded? */
    private boolean certKeyLoaded = false;

    private boolean inBoundOpen = true;
    private boolean outBoundOpen = true;

    /* closed completely (post shutdown or before handshake) */
    private boolean closed = true;

    /* handshake started explicitly by user with beginHandshake() */
    private boolean handshakeStartedExplicitly = false;

    /* handshake completed */
    private boolean handshakeFinished = false;

    /* Last return values of ssl.connect() / ssl.accept(). Protected
     * by ioLock. Can be used during state transitions to see if handshake
     * has finished successfully from native wolfSSL perspective. */
    private int lastSSLConnectRet = WolfSSL.SSL_FAILURE;
    private int lastSSLAcceptRet = WolfSSL.SSL_FAILURE;

    /* closeNotify status when shutting down */
    private boolean closeNotifySent = false;
    private boolean closeNotifyReceived = false;

    /* session stored (WOLFSSL_SESSION), relevant on client side */
    private boolean sessionStored = false;

    /* TLS 1.3 session ticket received (on client side) */
    private boolean sessionTicketReceived = false;

    /* Number of session tickets received, incremented in
     * SessionTicketCB callback */
    private int sessionTicketCount = 0;

    /* client/server mode has been set */
    private boolean clientModeSet = false;

    private SendCB sendCb = null;
    private RecvCB recvCb = null;
    private SessionTicketCB sessTicketCb = null;

    private ByteBuffer netData = null;
    private final Object netDataLock = new Object();

    /* Single buffer used to hold application data to be sent, allocated once
     * inside SendAppData, of size SSLSession.getApplicationBufferSize() */
    private ByteBuffer staticAppDataBuf = null;

    /* Default size of internalIOSendBuf, 16k to match TLS record size.
     * TODO - add upper bound on I/O send buf resize allocations. */
    private static final int INTERNAL_IOSEND_BUF_SZ = 16 * 1024;
    /* static buffer used to hold encrypted data to be sent, allocated inside
     * internalSendCb() and expanded only if needed. Synchronize on toSendLock
     * when accessing this buffer. */
    private byte[] internalIOSendBuf = new byte[INTERNAL_IOSEND_BUF_SZ];
    /* Total size of internalIOSendBuf */
    private int internalIOSendBufSz = INTERNAL_IOSEND_BUF_SZ;
    /* Offset into internalIOSendBuf to start writing data */
    private int internalIOSendBufOffset = 0;

    /* Locks for synchronization */
    private final Object ioLock = new Object();
    private final Object toSendLock = new Object();

    /** ALPN selector callback, if set */
    protected BiFunction<SSLEngine, List<String>, String> alpnSelector = null;

    /** Turn on extra/verbose SSLEngine debug logging */
    public boolean extraDebugEnabled = false;

    /** Turn on Send/Recv callback debug to print out bytes sent/received.
     * WARNING: enabling this will slow down sending and receiving data,
     * enough so that app may run into timeouts. Enable with caution. */
    public boolean ioDebugEnabled = false;

    /**
     * Turns on additional debugging based on system properties set.
     */
    private void enableExtraDebug() {
        /* turn on verbose extra debugging if 'wolfsslengine.debug'
         * system property is set */
        String engineDebug  = System.getProperty("wolfsslengine.debug");
        if ((engineDebug != null) && (engineDebug.equalsIgnoreCase("true"))) {
            this.extraDebugEnabled = true;
        }
    }

    /**
     * Turns on additional debugging of I/O data based on system properties set.
     */
    private void enableIODebug() {
        /* turn on verbose extra debugging of bytes sent and received if
         * 'wolfsslengine.io.debug' system property is set */
        String engineIODebug = System.getProperty("wolfsslengine.io.debug");
        if ((engineIODebug != null) &&
            (engineIODebug.equalsIgnoreCase("true"))) {
            this.ioDebugEnabled = true;
        }
    }

    /**
     *  Create a new engine with no hints for session reuse
     *
     * @param ctx JNI level WolfSSLContext
     * @param auth WolfSSLAuthStore to use
     * @param params connection parameters to be used
     * @throws WolfSSLException if there is an issue creating the engine
     */
    protected WolfSSLEngine(com.wolfssl.WolfSSLContext ctx,
            WolfSSLAuthStore auth, WolfSSLParameters params)
            throws WolfSSLException {
        super();
        this.ctx = ctx;
        this.authStore = auth;
        this.params = params.copy();

        try {
            initSSL();
        } catch (WolfSSLJNIException ex) {
            throw new WolfSSLException("Error with WolfSSLEngine init");
        }
        this.engineHelper = new WolfSSLEngineHelper(this.ssl, this.authStore,
            this.params);
    }

    /**
     *  Create a new engine with hints for session reuse
     *
     * @param ctx JNI level WolfSSLContext
     * @param auth WolfSSLAuthStore to use
     * @param params connection parameters to be used
     * @param host to connect to
     * @param port to connect to
     * @throws WolfSSLException if there is an issue creating the engine
     */
    protected WolfSSLEngine(com.wolfssl.WolfSSLContext ctx,
            WolfSSLAuthStore auth, WolfSSLParameters params, String host,
            int port) throws WolfSSLException {
        super(host, port);
        this.ctx = ctx;
        this.authStore = auth;
        this.params = params.copy();

        try {
            initSSL();
        } catch (WolfSSLJNIException ex) {
            throw new WolfSSLException("Error with WolfSSLEngine init");
        }
        this.engineHelper = new WolfSSLEngineHelper(this.ssl, this.authStore,
                this.params, port, host);
    }

    /**
     * Loads the key and certificate for this SSLEngine if not loaded yet.
     *
     * @throws SSLException on error
     */
    private synchronized void LoadCertAndKey() throws SSLException {

        /* Load cert and key */
        if (certKeyLoaded) {
            return;
        }

        try {
            this.engineHelper.LoadKeyAndCertChain(null, this);
            certKeyLoaded = true;
        } catch (CertificateEncodingException | IOException |
                 WolfSSLException e) {
            WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                () -> "failed to load private key and/or cert chain");
            throw new SSLException(e);
        }
    }

    /**
     * Initialize this WolfSSLEngine prior to handshaking.
     *
     * Internal method, should be called before any handshake.
     *
     * This logic is not included directly in WolfSSLEngine constructors
     * to avoid possible 'this' escape before subclass is fully initialized
     * when using 'this' in LoadKeyAndCertChain().
     *
     * @throws SSLException if initialization fails
     */
    private void checkAndInitSSLEngine() throws SSLException {

        final int ret;

        synchronized (initLock) {

            if (!needInit) {
                return;
            }

            LoadCertAndKey();

            this.engineHelper.initHandshake(this);

            if ((this.ssl.dtls() == 1) &&
                (!this.engineHelper.getUseClientMode())) {
                ret = this.ssl.sendHrrCookie(null);
                if (ret == WolfSSL.SSL_SUCCESS) {
                    WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                        () -> "Enabled sending of DTLS cookie in " +
                        "HelloRetryRequest");
                }
                else if (ret < 0) {
                    WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                        () -> "Failed to enable DTLS cookie in " +
                        "HelloRetryRequest, ret: " + ret);
                }
            }

            needInit = false;
            closed = false; /* opened a connection */
        }
    }

    /**
     * Register I/O callbacks and contexts with WolfSSLSession and native
     * wolfSSL. Uses singleton pattern on callbacks.
     *
     * Call unsetSSLCallbacks to unset/unregister these. Since the I/O
     * context is set as the current SSLEngine object, this can prevent
     * garbage collection of this SSLEngine object unless the context
     * is unset from the WolfSSLSession.
     *
     * Protected by ioLock since all I/O operations are dependent on using
     * these underlying I/O callbacks.
     *
     * @throws WolfSSLJNIException on native JNI error
     */
    private void setSSLCallbacks() throws WolfSSLJNIException {

        synchronized (ioLock) {
            if (sendCb == null) {
                sendCb = new SendCB();
            }
            if (recvCb == null) {
                recvCb = new RecvCB();
            }
            ssl.setIORecvByteBuffer(recvCb);
            ssl.setIOSendByteBuffer(sendCb);
            ssl.setIOReadCtx(this);
            ssl.setIOWriteCtx(this);

            /* Session ticket callback */
            if (sessTicketCb == null) {
                sessTicketCb = new SessionTicketCB();
            }
            ssl.setSessionTicketCb(sessTicketCb, this);
        }
    }

    /**
     * Unregister I/O callbacks and contexts with WolfSSLSession and
     * native wolfSSL.
     *
     * Call setSSLCallbacks() to re-register these.
     *
     * Protected with ioLock since all I/O operations are dependent on
     * using these underlying I/O callbacks.
     *
     * @throws WolfSSLJNIException on native JNI error
     */
    private void unsetSSLCallbacks() throws WolfSSLJNIException {

        synchronized (ioLock) {
            ssl.setIORecvByteBuffer(null);
            ssl.setIOSendByteBuffer(null);
            ssl.setIOReadCtx(null);
            ssl.setIOWriteCtx(null);
            ssl.setSessionTicketCb(null, null);
        }
    }

    private void initSSL() throws WolfSSLException, WolfSSLJNIException {

        if (sendCb == null) {
            sendCb = new SendCB();
        }
        if (recvCb == null) {
            recvCb = new RecvCB();
        }
        if (sessTicketCb == null) {
            sessTicketCb = new SessionTicketCB();
        }

        /* will throw WolfSSLException if issue creating WOLFSSL */
        ssl = new WolfSSLSession(ctx, false);

        enableExtraDebug();
        enableIODebug();
    }

    /**
     * Copy buffered data to be sent into provided output ByteBuffer.
     *
     * Data sent will be minimum of either buffered data size or
     * destination buffer remaining space.
     *
     * Returns size of data copied.
     */
    private int CopyOutPacket(ByteBuffer out) {
        int sendSz = 0;

        synchronized (toSendLock) {
            if (this.internalIOSendBuf != null) {
                sendSz = Math.min(this.internalIOSendBufOffset, out.remaining());
                out.put(this.internalIOSendBuf, 0, sendSz);

                if (sendSz != this.internalIOSendBufOffset) {
                    System.arraycopy(this.internalIOSendBuf, sendSz,
                             this.internalIOSendBuf, 0,
                             this.internalIOSendBufOffset - sendSz);
                }
                else {
                    /* reset internalIOSendBufOffset to zero, no data left */
                    this.internalIOSendBufOffset = 0;
                }
            }
        }
        return sendSz;
    }

    /**
     * Helper function, updates internal close_notify alert status
     * and inBound/outBoundOpen.
     */
    private synchronized void UpdateCloseNotifyStatus() {
        int ret;

        synchronized (ioLock) {
            ret = ssl.getShutdown();
        }
        if (ret == (WolfSSL.SSL_RECEIVED_SHUTDOWN |
                    WolfSSL.SSL_SENT_SHUTDOWN)) {
            this.closeNotifySent = true;
            this.closeNotifyReceived = true;
            this.inBoundOpen = false;
            if (this.internalIOSendBufOffset == 0) {
                /* Don't close outbound if we have a close_notify alert
                 * send back to peer. Native wolfSSL may have already generated
                 * it and is reflected in SSL_SENT_SHUTDOWN flag, but we
                 * might have it cached in our Java SSLEngine object still to
                 * be sent. */
                this.outBoundOpen = false;
            }
            closed = true;
        } else if (ret == WolfSSL.SSL_RECEIVED_SHUTDOWN) {
            this.closeNotifyReceived = true;
            this.inBoundOpen = false;
        } else if (ret == WolfSSL.SSL_SENT_SHUTDOWN) {
            this.closeNotifySent = true;
            this.outBoundOpen = false;
        }
    }

    /**
     * Returns if current error in WOLFSSL session should be considered
     * fatal. Used in ClosingConnection() for detection of storing
     * client cache entry.
     *
     * @param ssl WOLFSSL session to check error on
     *
     * @return true if error is not fatal, false if fatal
     */
    private synchronized boolean sslErrorNotFatal(WolfSSLSession ssl) {

        int err;

        if (ssl == null) {
            return false;
        }

        err = ssl.getError(0);
        if (err == 0 ||
            err == WolfSSL.SSL_ERROR_WANT_READ ||
            err == WolfSSL.SSL_ERROR_WANT_WRITE) {
            return true;
        }

        return false;
    }

    /**
     * Handles logic during shutdown
     *
     * @return WolfSSL.SSL_SUCCESS on success, zero or negative on error
     * @throws SocketException if ssl.shutdownSSL() encounters a socket error
     * @throws SocketTimeoutException if ssl.shutdownSSL() times out
     */
    private synchronized int ClosingConnection()
        throws SocketException, SocketTimeoutException {

        int ret;

        /* Save session into WolfSSLAuthStore cache, saves session
         * pointer for resumption if on client side. Protected with ioLock
         * since underlying get1Session can use I/O with peek.
         *
         * Only store session if handshake is finished, SSL_get_error() does
         * not have an active error state, and the session has not been
         * stored previously. */
        synchronized (ioLock) {
            if (this.handshakeFinished && sslErrorNotFatal(ssl) &&
                !this.sessionStored) {
                WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                    () -> "saving WOLFSSL_SESSION into cache");
                this.engineHelper.saveSession();
            }
            else {
                WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                    () -> "not saving WOLFSSL_SESSION into cache, " +
                    "handshake not complete or already stored");
            }
        }

        /* get current close_notify state */
        UpdateCloseNotifyStatus();
        if (this.closeNotifySent && this.closeNotifyReceived) {
            return WolfSSL.SSL_SUCCESS;
        }

        /* send/recv close_notify as needed */
        synchronized (ioLock) {
            ret = ssl.shutdownSSL();
            if (ssl.getError(ret) == WolfSSL.SSL_ERROR_ZERO_RETURN) {
                /* got close_notify alert, reset ret to SSL_SUCCESS to continue
                 * and let corresponding close_notify to be sent */
                WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                    () -> "ClosingConnection(), ssl.getError() is ZERO_RETURN");
                ret = WolfSSL.SSL_SUCCESS;
            }
        }
        UpdateCloseNotifyStatus();

        return ret;
    }

    /**
     * Starts or continues SSL/TLS handshake.
     *
     * @return WolfSSL.SSL_SUCCESS or WolfSSL.SSL_FAILURE
     * @throws SocketException if ssl.connect() or ssl.accept() encounters
     *         a socket exception.
     * @throws SocketTimeoutException if ssl.connect() or ssl.accept()
     *         times out. This should not happen since infinite timeout is
     *         being used for these calls.
     */
    private synchronized int DoHandshake(boolean fromWrap) throws SSLException {
        int ret = WolfSSL.SSL_SUCCESS;
        final int tmpRet;

        try {
            /* If DTLS and calling from wrap() but HandshakeStatus is
             * actually NEED_UNWRAP, this is a signal from the application
             * that we need to retransmit messages */
            if ((this.ssl.dtls() == 1) && fromWrap &&
                (this.hs == SSLEngineResult.HandshakeStatus.NEED_UNWRAP)) {
                synchronized (ioLock) {
                    WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                        () -> "Calling wrap() while status is NEED_UNWRAP, " +
                        "retransmitting DTLS messages");
                    ret = this.ssl.dtlsGotTimeout();
                    if (ret == 0) {
                        ret = WolfSSL.SSL_SUCCESS;
                    }
                }
            }
            if (ret == WolfSSL.SSL_SUCCESS) {
                if (this.getUseClientMode()) {
                    synchronized (ioLock) {
                        ret = this.ssl.connect();
                        lastSSLConnectRet = ret;
                    }
                }
                else {
                    synchronized (ioLock) {
                        ret = this.ssl.accept();
                        lastSSLAcceptRet = ret;
                    }
                }

                tmpRet = ret;
                if (this.getUseClientMode()) {
                    WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                        () -> "ssl.connect() ret:err = " + tmpRet + " : " +
                        ssl.getError(tmpRet));
                }
                else {
                    WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                        () -> "ssl.accept() ret:err = " + tmpRet + " : " +
                        ssl.getError(tmpRet));
                }
            }

        } catch (SocketTimeoutException | SocketException e) {
            SSLHandshakeException hsException = new SSLHandshakeException(
                "Socket error during SSL/TLS handshake: " + e.getMessage());
            hsException.initCause(e);
            throw hsException;
        }

        return ret;
    }

    /**
     * Write application data using ssl.write().
     *
     * Only sends up to maximum app data chunk size
     * (SSLSession.getApplicationBufferSize()).
     *
     * @throws SocketException if ssl.write() encounters a socket error
     * @throws SocketTimeoutException if ssl.write() times out. Shouldn't
     *         happen since this is using an infinite timeout.
     * @return bytes sent on success, negative on error
     */
    private synchronized int SendAppData(ByteBuffer[] in, int ofst, int len)
        throws SocketException, SocketTimeoutException {

        int i = 0;
        int ret = 0;
        int totalIn = 0;
        int sendSz = 0;
        int inputLeft = 0;
        byte[] dataArr;
        int[] pos = new int[len];   /* in[] positions */
        int[] limit = new int[len]; /* in[] limits */

        /* Get total input data size, store input array positions */
        for (i = ofst; i < ofst + len; i++) {
            totalIn += in[i].remaining();
            pos[i] = in[i].position();
            limit[i] = in[i].limit();
        }

        /* Allocate static buffer for application data, clear before use */
        sendSz = this.engineHelper.getSession().getApplicationBufferSize();
        if (this.staticAppDataBuf == null) {
            /* allocate static buffer for application data */
            this.staticAppDataBuf = ByteBuffer.allocateDirect(sendSz);
        }
        this.staticAppDataBuf.clear();

        /* Only send up to maximum app data size chunk */
        sendSz = Math.min(totalIn, sendSz);

        /* gather byte array of sendSz bytes from input buffers */
        inputLeft = sendSz;
        for (i = ofst; i < ofst + len; i++) {
            int bufChunk = Math.min(in[i].remaining(), inputLeft);

            in[i].limit(in[i].position() + bufChunk);       /* set limit */
            this.staticAppDataBuf.put(in[i]);               /* get data */
            inputLeft -= bufChunk;
            in[i].limit(limit[i]);                          /* reset limit */

            if (inputLeft == 0) {
                break; /* reached data size needed, stop reading */
            }
        }

        dataArr = new byte[sendSz];
        this.staticAppDataBuf.rewind();
        this.staticAppDataBuf.get(dataArr);

        final int tmpSendSz = sendSz;
        WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
            () -> "calling ssl.write() with size: " + tmpSendSz);

        synchronized (ioLock) {
            ret = this.ssl.write(dataArr, sendSz);
        }
        if (ret <= 0) {
            /* error, reset in[] positions for next call */
            for (i = ofst; i < ofst + len; i++) {
                in[i].position(pos[i]);
            }
        }

        final int tmpRet = ret;
        WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
            () -> "ssl.write() returning: " + tmpRet);

        return ret;
    }

    @Override
    public synchronized SSLEngineResult wrap(ByteBuffer in, ByteBuffer out)
            throws SSLException {

        if (in == null) {
            throw new SSLException("SSLEngine.wrap() bad arguments");
        }

        return wrap(new ByteBuffer[] { in }, 0, 1, out);
    }

    @Override
    public synchronized SSLEngineResult wrap(ByteBuffer[] in, int ofst, int len,
            ByteBuffer out) throws SSLException {

        int ret = 0, i;
        int produced = 0;
        int consumed = 0;

        /* Set initial status for SSLEngineResult return */
        Status status = SSLEngineResult.Status.OK;

        /* Sanity check buffer arguments. */
        if (in == null || ofst + len > in.length || out == null) {
            throw new SSLException("SSLEngine.wrap() bad arguments");
        }

        if (ofst < 0 || len < 0) {
            throw new IndexOutOfBoundsException();
        }

        for (i = ofst; i < len; ++i) {
            if (in[i] == null) {
                throw new SSLException("SSLEngine.wrap() bad arguments");
            }
        }

        if (out.isReadOnly()) {
            throw new ReadOnlyBufferException();
        }

        if (!this.clientModeSet) {
            throw new IllegalStateException(
                    "setUseClientMode() has not been called on this SSLEngine");
        }

        if (extraDebugEnabled) {
            final Status tmpStatus = status;
            WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                () -> "==== [ entering wrap() ] =============================");
            WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                () -> "setUseClientMode: " +
                this.engineHelper.getUseClientMode());
            for (i = 0; i < len; i++) {
                final int idx = i;
                WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                    () -> "ByteBuffer in["+idx+"].remaining(): " +
                    in[idx].remaining());
                WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                    () -> "ByteBuffer in["+idx+"].position(): " +
                    in[idx].position());
                WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                    () -> "ByteBuffer in["+idx+"].limit(): " +
                    in[idx].limit());
            }
            WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                () -> "ofst: " + ofst + ", len: " + len);
            WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                () -> "out.remaining(): " + out.remaining());
            WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                () -> "out.position(): " + out.position());
            WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                () -> "out.limit(): " + out.limit());
            WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                () -> "internalIOSendBufOffset: " +
                this.internalIOSendBufOffset);
            WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                () -> "closeNotifySent: " + this.closeNotifySent);
            WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                () -> "closeNotifyReceived: " + this.closeNotifyReceived);
            WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                () -> "inBoundOpen: " + this.inBoundOpen);
            WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                () -> "outBoundOpen: " + this.outBoundOpen);
            WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                () -> "status: " + tmpStatus);
            WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                () -> "handshakeStatus: " + hs);
            WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                () -> "handshakeFinished: " + this.handshakeFinished);
            WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                () -> "nativeHandshakeState: " + this.ssl.getStateStringLong());
            WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                () -> "nativeWantsToRead: " + this.nativeWantsToRead);
            WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                () -> "nativeWantsToWrite: " + this.nativeWantsToWrite);
            WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                () -> "=====================================================");
        }

        /* Set wolfSSL I/O callbacks and context for read/write operations */
        try {
            setSSLCallbacks();
        } catch (WolfSSLJNIException e) {
            throw new SSLException(e);
        }

        /* Wrap in try/finally to ensure we unset callbacks on any exit path */
        try {
            if (needInit) {
                checkAndInitSSLEngine();
            }

            synchronized (netDataLock) {
                this.netData = null;
            }

            /* Force out buffer to be large enough to hold max packet size */
            if (out.remaining() <
                this.engineHelper.getSession().getPacketBufferSize()) {
                WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                    () -> "out.remaining() too small (" +
                    out.remaining() + "), need at least: " +
                    this.engineHelper.getSession().getPacketBufferSize());
                return new SSLEngineResult(Status.BUFFER_OVERFLOW, hs, 0, 0);
            }

            /* Copy buffered data to be sent into output buffer */
            produced = CopyOutPacket(out);

            /* Closing down connection if buffered data has been sent and:
             * 1. Outbound has been closed (!outBoundOpen)
             * 2. Inbound is closed and close_notify has been sent
             */
            if (produced >= 0 &&
                (!outBoundOpen || (!inBoundOpen && this.closeNotifySent))) {
                /* Mark SSLEngine status as CLOSED */
                status = SSLEngineResult.Status.CLOSED;
                /* Handshake has finished and SSLEngine is closed, release
                 * global JNI verify callback pointer */
                this.engineHelper.unsetVerifyCallback();

                try {
                    ClosingConnection();
                } catch (SocketException | SocketTimeoutException e) {
                    throw new SSLException(e);
                }
                produced += CopyOutPacket(out);
            }
            else if ((produced > 0) && !inBoundOpen &&
                     (!this.closeNotifySent && !this.closeNotifyReceived)) {
                /* We had buffered data to send, but inbound was already
                 * closed. Most likely this is because we needed to send an
                 * alert to the peer. We should now mark outbound as closed
                 * since we won't be sending anything after the alert went
                 * out. */
                this.outBoundOpen = false;
            }
            else if (produced == 0) {
                /* continue handshake or application data */
                if (!this.handshakeFinished) {
                    ret = DoHandshake(true);
                }
                else {
                    try {
                        ret = SendAppData(in, ofst, len);
                        if (ret > 0) {
                            consumed += ret;
                        }
                    } catch (SocketException | SocketTimeoutException e) {
                        throw new SSLException(e);
                    }
                }

                /* copy any produced data into output buffer */
                produced += CopyOutPacket(out);
            }

            SetHandshakeStatus(ret);

            if (extraDebugEnabled) {
                final HandshakeStatus tmpHs = hs;
                final Status tmpStatus = status;
                final int tmpConsumed = consumed;
                final int tmpProduced = produced;
                WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                    () -> "==== [ exiting wrap() ] ==========================");
                WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                    () -> "setUseClientMode: " +
                    this.engineHelper.getUseClientMode());
                for (i = 0; i < len; i++) {
                    final int idx = i;
                    WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                        () -> "ByteBuffer in["+idx+"].remaining(): " +
                        in[idx].remaining());
                    WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                        () -> "ByteBuffer in["+idx+"].position(): " +
                        in[idx].position());
                    WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                        () -> "ByteBuffer in["+idx+"].limit(): " +
                        in[idx].limit());
                }
                WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                    () -> "ofst: " + ofst + ", len: " + len);
                WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                    () -> "out.remaining(): " + out.remaining());
                WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                    () -> "out.position(): " + out.position());
                WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                    () -> "out.limit(): " + out.limit());
                WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                    () -> "internalIOSendBufOffset: " +
                    this.internalIOSendBufOffset);
                WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                    () -> "closeNotifySent: " + this.closeNotifySent);
                WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                    () -> "closeNotifyReceived: " + this.closeNotifyReceived);
                WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                    () -> "handshakeFinished: " + this.handshakeFinished);
                WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                    () -> "inBoundOpen: " + this.inBoundOpen);
                WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                    () -> "outBoundOpen: " + this.outBoundOpen);
                WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                    () -> "handshakeStatus: " + tmpHs);
                WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                    () -> "status: " + tmpStatus);
                WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                    () -> "consumed: " + tmpConsumed);
                WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                    () -> "produced: " + tmpProduced);
                WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                    () -> "nativeHandshakeState: " +
                    this.ssl.getStateStringLong());
                WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                    () -> "nativeWantsToRead: " + this.nativeWantsToRead);
                WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                    () -> "nativeWantsToWrite: " + this.nativeWantsToWrite);
                WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                    () -> "==================================================");
            }

            return new SSLEngineResult(status, hs, consumed, produced);

        } finally {
            try {
                /* Don't hold references to this SSLEngine object in
                 * WolfSSLSession, can prevent proper garbage collection */
                unsetSSLCallbacks();
            } catch (WolfSSLJNIException e) {
                /* Don't throw from finally block, just log for info */
                WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                    () -> "unsetSSLCallbacks() exception during wrap(), " +
                    "just logging: " + e.getMessage());
            }
        }
    }

    /**
     * Return total remaining space in array of ByteBuffers.
     *
     * @param out array of ByteBuffers to be polled for available space
     * @param ofst offset into out array to begin
     * @param length length of ByteBuffer array
     *
     * @return number of available/remaining bytes in array of ByteBuffers
     * @throws IllegalArgumentException if readonly buffer found
     */
    private static synchronized int getTotalOutputSize(ByteBuffer[] out,
                                          int ofst, int length) {
        int i = 0;
        int maxOutSz = 0;

        for (i = 0; i < length; i++) {
            if (out[i + ofst] == null || out[i + ofst].isReadOnly()) {
                throw new IllegalArgumentException(
                    "null or readonly out buffer found");
            }
            maxOutSz += out[i + ofst].remaining();
        }

        return maxOutSz;
    }

    /**
     * Receive application data using ssl.read() from in buffer, placing
     * processed/decrypted data into out[].
     *
     * @param out output ByteBuffer arrays, to hold processed/decoded plaintext
     * @param ofst offset into out[] array to begin writing data
     * @param length length of out[] array
     *
     * @throws SSLException if ssl.read() encounters socket error
     * @return number of plaintext bytes received, or negative on error.
     */
    private synchronized int RecvAppData(ByteBuffer[] out, int ofst, int length)
        throws SSLException {

        int i, sz, bufSpace;
        int totalRead = 0;
        int maxOutSz = 0;
        int ret = 0;
        int idx = 0; /* index into out[] array */
        final int err;
        byte[] tmp = null;

        /* Calculate maximum output size across ByteBuffer arrays */
        maxOutSz = getTotalOutputSize(out, ofst, length);

        synchronized (ioLock) {
            try {
                /* If we only have one ByteBuffer, skip allocating
                 * separate intermediate byte[] and write directly to underlying
                 * ByteBuffer array */
                if (out.length == 1) {
                    ret = this.ssl.read(out[0], maxOutSz, 0);
                    if ((ret < 0) &&
                        (ssl.getError(ret) == WolfSSL.APP_DATA_READY)) {
                        /* If DTLS, we may need to call SSL_read() again
                         * right away again if app data was received */
                        ret = this.ssl.read(out[0], maxOutSz, 0);
                    }
                }
                else {
                    tmp = new byte[maxOutSz];
                    ret = this.ssl.read(tmp, maxOutSz);
                    if ((ret < 0) &&
                        (ssl.getError(ret) == WolfSSL.APP_DATA_READY)) {
                        /* If DTLS, we may need to call SSL_read() again
                         * right away again if app data was received */
                        ret = this.ssl.read(tmp, maxOutSz);
                    }
                }
            } catch (SocketTimeoutException | SocketException e) {
                throw new SSLException(e);
            }
            final int tmpRet = ret;
            WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                () -> "RecvAppData(), ssl.read() ret = " + tmpRet);

            err = ssl.getError(ret);
        }

        if (ret <= 0) {
            WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                () -> "RecvAppData(), ssl.getError() = " + err);

            switch (err) {
                case WolfSSL.SSL_ERROR_WANT_READ:
                case WolfSSL.SSL_ERROR_WANT_WRITE:
                    WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                        () -> "RecvAppData(), got WANT_READ/WANT_WRITE");
                    break;

                case WolfSSL.APP_DATA_READY:
                    WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                        () -> "RecvAppData(), got APP_DATA_READY");
                    break;

                /* In 0 and ZERO_RETURN cases we may have gotten a
                 * close_notify alert, check on shutdown status */
                case WolfSSL.SSL_ERROR_ZERO_RETURN:
                case 0:
                    if (err == WolfSSL.SSL_ERROR_ZERO_RETURN) {
                        WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                            () -> "RecvAppData(), got ZERO_RETURN");
                    }

                    /* check if is shutdown message */
                    synchronized (ioLock) {
                        if (ssl.getShutdown() ==
                                WolfSSL.SSL_RECEIVED_SHUTDOWN) {
                            WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                                () -> "RecvAppData(), received " +
                                "shutdown message");
                            try {
                                ret = ClosingConnection();
                                if (ret > 0) {
                                    /* Returns number of bytes read,
                                     * 0, or err */
                                    ret = 0;
                                }
                            } catch (SocketException |
                                     SocketTimeoutException e) {
                                throw new SSLException(e);
                            }
                            return ret;
                        }
                    }
                    break;
                default:
                    /* Throw SSLHandshakeException if handshake not finished */
                    if (!this.handshakeFinished) {
                        throw new SSLHandshakeException(
                            "SSL/TLS handshake error in read: " + ret +
                            " , err = " + err);
                    }
                    throw new SSLException(
                        "wolfSSL_read() error: " + ret + " , err = " + err);
            }
        }
        else {
            if (out.length == 1) {
                totalRead = ret;
            }
            else {
                /* write processed data into output buffers */
                for (i = 0; i < ret;) {
                    if (idx + ofst >= length) {
                        /* no more output buffers left */
                        break;
                    }

                    bufSpace = out[idx + ofst].remaining();
                    if (bufSpace == 0) {
                        /* no more space in current out buffer, advance */
                        idx++;
                        continue;
                    }

                    sz = (bufSpace >= (ret - i)) ? (ret - i) : bufSpace;
                    out[idx + ofst].put(tmp, i, sz);
                    i += sz;
                    totalRead += sz;

                    if ((ret - i) > 0) {
                        idx++; /* go to next output buffer */
                    }
                }
            }
        }

        return totalRead;
    }

    @Override
    public synchronized SSLEngineResult unwrap(ByteBuffer in, ByteBuffer out)
            throws SSLException {

        if (out == null) {
            throw new IllegalArgumentException(
                "SSLEngine.unwrap() bad arguments");
        }

        return unwrap(in, new ByteBuffer[] { out }, 0, 1);
    }

    @Override
    public synchronized SSLEngineResult unwrap(ByteBuffer in, ByteBuffer[] out,
            int ofst, int length) throws SSLException {

        int i, ret = 0, err = 0;
        int inPosition = 0;
        int inRemaining = 0;
        int consumed = 0;
        int produced = 0;
        long dtlsPrevDropCount = 0;
        long dtlsCurrDropCount = 0;
        int prevSessionTicketCount = 0;
        final int tmpRet;

        /* Set initial status for SSLEngineResult return */
        Status status = SSLEngineResult.Status.OK;

        /* Sanity check buffer arguments. */
        if (in == null || out == null || ofst + length > out.length) {
            throw new IllegalArgumentException(
                "SSLEngine.unwrap() bad arguments");
        }

        if (ofst < 0 || length < 0) {
            throw new IndexOutOfBoundsException();
        }

        for (i = ofst; i < length; ++i) {
            if (out[i] == null) {
                throw new IllegalArgumentException(
                    "SSLEngine.unwrap() bad arguments");
            }

            if (out[i].isReadOnly()) {
                throw new ReadOnlyBufferException();
            }
        }

        if (!this.clientModeSet) {
            throw new IllegalStateException(
                "setUseClientMode() has not been called on this SSLEngine");
        }

        synchronized (netDataLock) {
            this.netData = in;
            inPosition = in.position();
            inRemaining = in.remaining();
        }

        if (extraDebugEnabled) {
            final SSLEngineResult.Status tmpStatus = status;
            WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                () -> "==== [ entering unwrap() ] ===========================");
            WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                () -> "setUseClientMode: " +
                this.engineHelper.getUseClientMode());
            WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                () -> "in.remaining(): " + in.remaining());
            WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                () -> "in.position(): " + in.position());
            WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                () -> "in.limit(): " + in.limit());
            for (i = 0; i < length; i++) {
                final int idx = i;
                WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                    () -> "out["+idx+"].remaining(): " +
                    out[idx].remaining());
                WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                    () -> "out["+idx+"].position(): " +
                    out[idx].position());
                WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                    () -> "out["+idx+"].limit(): " +
                    out[idx].limit());
            }
            WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                () -> "ofst: " + ofst + ", length: " + length);
            WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                () -> "internalIOSendBufOffset: " +
                this.internalIOSendBufOffset);
            WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                () -> "closeNotifySent: " + this.closeNotifySent);
            WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                () -> "closeNotifyReceived: " + this.closeNotifyReceived);
            WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                () -> "inBoundOpen: " + this.inBoundOpen);
            WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                () -> "outBoundOpen: " + this.outBoundOpen);
            WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                () -> "handshakeFinished: " + this.handshakeFinished);
            WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                () -> "handshakeStatus: " + hs);
            WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                () -> "status: " + tmpStatus);
            WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                () -> "nativeHandshakeState: " + this.ssl.getStateStringLong());
            WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                () -> "nativeWantsToRead: " + this.nativeWantsToRead);
            WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                () -> "nativeWantsToWrite: " + this.nativeWantsToWrite);
            WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                () -> "=====================================================");
        }

        /* Set wolfSSL I/O callbacks and context for read/write operations */
        try {
            setSSLCallbacks();
        } catch (WolfSSLJNIException e) {
            throw new SSLException(e);
        }

        /* Wrap in try/finally to ensure we unset callbacks on any exit path */
        try {
            if (getUseClientMode() && needInit) {
                /* If unwrap() is called before handshake has started, return
                 * WANT_WRAP since we'll need to send a ClientHello first */
                hs = SSLEngineResult.HandshakeStatus.NEED_WRAP;
            }
            else if (hs == SSLEngineResult.HandshakeStatus.NEED_WRAP &&
                     this.internalIOSendBufOffset > 0) {
                /* Already have data buffered to send and in NEED_WRAP state,
                 * just return so wrap() can be called */
                hs = SSLEngineResult.HandshakeStatus.NEED_WRAP;
            }
            else {

                if (needInit) {
                    checkAndInitSSLEngine();
                }

                if (outBoundOpen == false) {
                    try {
                        if (ClosingConnection() == WolfSSL.SSL_SUCCESS) {
                            /* Mark SSLEngine status as CLOSED */
                            status = SSLEngineResult.Status.CLOSED;
                            /* Handshake has finished and SSLEngine is closed,
                             * release, global JNI verify callback pointer */
                            this.engineHelper.unsetVerifyCallback();
                        }
                    } catch (SocketException | SocketTimeoutException e) {
                        throw new SSLException(e);
                    }
                }
                else {
                    /* Get previous DTLS drop count and session ticket count,
                     * before we process any incomming data. Allows us to set
                     * BUFFER_UNDERFLOW status (or not if packet decrypt failed
                     * and was dropped) */
                    synchronized (ioLock) {
                        dtlsPrevDropCount = ssl.getDtlsMacDropCount();
                        prevSessionTicketCount = this.sessionTicketCount;
                    }

                    if (this.handshakeFinished == false) {
                        WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                            () -> "starting or continuing handshake");
                        ret = DoHandshake(false);
                    }
                    else {
                        /* If we have input data, make sure output buffer
                         * length is greater than zero, otherwise ask app to
                         * expand out buffer. There may be edge cases where
                         * this could be tightened up, but this will err on
                         * the side of giving us more output space than we
                         * need. */
                        if (inRemaining > 0 &&
                            getTotalOutputSize(out, ofst, length) == 0) {
                            status = SSLEngineResult.Status.BUFFER_OVERFLOW;
                        }
                        else {

                            WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                                () -> "receiving application data");
                            ret = RecvAppData(out, ofst, length);
                            tmpRet = ret;
                            WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                                () -> "received application data: " + tmpRet +
                                " bytes (from RecvAppData)");
                            if (ret > 0) {
                                produced += ret;
                            }

                            /* Check for BUFFER_OVERFLOW status. This can
                             * happen if we have data cached internally
                             * (in.remaining()) and there is no more output
                             * space. */
                            synchronized (netDataLock) {
                                if (ret == 0 && in.remaining() > 0 &&
                                    getTotalOutputSize(out, ofst,
                                        length) == 0) {
                                    /* We have more data to read, but no more
                                     * out space left in ByteBuffer[], ask for
                                     * more */
                                    status =
                                        SSLEngineResult.Status.BUFFER_OVERFLOW;
                                }
                            }

                            /* Check for BUFFER_OVERFLOW using ssl.pending().
                             * For DTLS only. */
                            if (status == SSLEngineResult.Status.OK) {
                                synchronized (ioLock) {
                                    try {
                                        if (this.ssl.dtls() == 1) {
                                            int pending = this.ssl.pending();
                                            if (pending > 0) {
                                                status = SSLEngineResult.Status.
                                                    BUFFER_OVERFLOW;
                                            }
                                        }
                                    } catch (Exception e) {
                                        WolfSSLDebug.log(getClass(),
                                            WolfSSLDebug.INFO,
                                            () -> "Exception calling "
                                                + "ssl.pending(): " + e);
                                    }
                                }
                            }
                        }

                        /* If we haven't stored session yet, try again. For
                         * TLS 1.3 we may need to wait for session ticket. We
                         * do try right after wolfSSL_connect/accept() finishes,
                         * but we might not have had session ticket at that
                         * time. */
                        synchronized (ioLock) {
                            if (this.handshakeFinished &&
                                (ssl.getError(0) == 0) && !this.sessionStored) {
                                WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                                    () -> "calling engineHelper.saveSession()");
                                int ret2 = this.engineHelper.saveSession();
                                WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                                    () -> "return from saveSession(), ret = " +
                                    ret2);
                                if (ret2 == WolfSSL.SSL_SUCCESS) {
                                    this.sessionStored = true;
                                }
                            }
                        }
                    } /* end DoHandshake() / RecvAppData() */

                    if (outBoundOpen == false || this.closeNotifySent) {
                        /* Mark SSLEngine status as CLOSED */
                        status = SSLEngineResult.Status.CLOSED;
                        /* Handshake has finished and SSLEngine is closed,
                         * release, global JNI verify callback pointer */
                        this.engineHelper.unsetVerifyCallback();
                    }

                    synchronized (ioLock) {
                        err = ssl.getError(ret);
                    }
                    if (ret < 0 && (this.ssl.dtls() == 1) &&
                        (err == WolfSSL.OUT_OF_ORDER_E)) {
                        /* Received out of order DTLS message. Ignore and set
                         * our status to NEED_UNWRAP again to wait for correct
                         * data */
                        WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                            () -> "out of order message, dropping and " +
                            "putting state back to NEED_UNWRAP");
                    }
                    else if (ret < 0 &&
                        (err != WolfSSL.SSL_ERROR_WANT_READ) &&
                        (err != WolfSSL.SSL_ERROR_WANT_WRITE)) {

                        if (err == WolfSSL.UNKNOWN_ALPN_PROTOCOL_NAME_E) {
                            /* Native wolfSSL could not negotiate a common ALPN
                             * protocol */
                            this.inBoundOpen = false;
                            throw new SSLHandshakeException(
                                "Unrecognized protocol name error, ret:err = " +
                                ret + " : " + err);
                        }
                        else {
                            /* Native wolfSSL threw an exception when unwrapping
                             * data, close inbound since we can't receive more
                             * data */
                            this.inBoundOpen = false;
                            if (err == WolfSSL.FATAL_ERROR) {
                                /* If client side and we received fatal alert,
                                 * close outbound since we won't be receiving
                                 * any more data */
                                this.outBoundOpen = false;
                            }
                            /* Throw SSLHandshakeException if handshake not
                             * finished, otherwise throw SSLException for
                             * post-handshake errors */
                            if (!this.handshakeFinished) {
                                throw new SSLHandshakeException(
                                    "SSL/TLS handshake error, ret:err = " +
                                    ret + " : " + err);
                            }
                            throw new SSLException(
                                "wolfSSL error, ret:err = " + ret + " : " +
                                err);
                        }
                    }

                    /* Get DTLS drop count after data has been processed. To be
                     * used below when setting BUFFER_UNDERFLOW status. */
                    synchronized (ioLock) {
                        dtlsCurrDropCount = ssl.getDtlsMacDropCount();
                    }

                    /* Detect if we need to set BUFFER_UNDERFLOW.
                     * If we consume data in unwrap() but it's just a session
                     * ticket, we don't set BUFFER_UNDERFLOW and just continue
                     * on to set status as OK. */
                    synchronized (toSendLock) {
                        synchronized (netDataLock) {
                            if (ret <= 0 &&
                                err == WolfSSL.SSL_ERROR_WANT_READ &&
                                in.remaining() == 0 &&
                                (this.internalIOSendBufOffset == 0) &&
                                (prevSessionTicketCount ==
                                    this.sessionTicketCount)) {

                                if ((this.ssl.dtls() == 0) ||
                                    (this.handshakeFinished &&
                                     (dtlsPrevDropCount ==
                                         dtlsCurrDropCount))) {
                                    /* Need more data. For DTLS only set
                                     * after handshake has completed, since
                                     * apps expect to switch on NEED_UNWRAP
                                     * HandshakeStatus at that point */
                                    status =
                                        SSLEngineResult.Status.BUFFER_UNDERFLOW;
                                }
                            }
                        }
                    }
                }

                synchronized (netDataLock) {
                    consumed += in.position() - inPosition;
                }
                SetHandshakeStatus(ret);
            }

            /* If client side, handshake is done, and we have just received a
             * TLS 1.3 session ticket, we should return FINISHED HandshakeStatus
             * from unwrap() directly but not from getHandshakeStatus(). Keep
             * track of if we have received ticket, so we only set/return this
             * once */
            synchronized (ioLock) {
                if (this.getUseClientMode() && this.handshakeFinished &&
                    this.ssl.hasSessionTicket() &&
                    this.sessionTicketReceived == false) {
                    if (this.ssl.dtls() == 1 &&
                        this.internalIOSendBufOffset > 0) {
                        /* DTLS 1.3 ACK has been produced in response to
                         * session ticket message, let's set HS status to
                         * NEED_WRAP so application knows it needs to be sent */
                        hs = SSLEngineResult.HandshakeStatus.NEED_WRAP;
                    }
                    else {
                        WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                            () -> "received session ticket, returning " +
                            "HandshakeStatus FINISHED");
                        hs = SSLEngineResult.HandshakeStatus.FINISHED;
                    }
                    this.sessionTicketReceived = true;
                }
            }

            if (extraDebugEnabled == true) {
                final Status tmpStatus = status;
                final int tmpConsumed = consumed;
                final int tmpProduced = produced;
                WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                    () -> "==== [ exiting unwrap() ] " +
                    "============================");
                WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                    () -> "setUseClientMode: " +
                    this.engineHelper.getUseClientMode());
                WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                    () -> "in.remaining(): " + in.remaining());
                WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                    () -> "in.position(): " + in.position());
                WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                    () -> "in.limit(): " + in.limit());
                for (i = 0; i < length; i++) {
                    final int idx = i;
                    WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                        () -> "out["+idx+"].remaining(): " +
                        out[idx].remaining());
                    WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                        () -> "out["+idx+"].position(): " +
                        out[idx].position());
                    WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                        () -> "out["+idx+"].limit(): " +
                        out[idx].limit());
                }
                WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                    () -> "ofst: " + ofst + ", length: " + length);
                WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                    () -> "internalIOSendBufOffset: " +
                    this.internalIOSendBufOffset);
                WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                    () -> "handshakeFinished: " + this.handshakeFinished);
                WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                    () -> "closeNotifySent: " + this.closeNotifySent);
                WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                    () -> "closeNotifyReceived: " + this.closeNotifyReceived);
                WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                    () -> "inBoundOpen: " + this.inBoundOpen);
                WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                    () -> "outBoundOpen: " + this.outBoundOpen);
                WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                    () -> "handshakeStatus: " + hs);
                WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                    () -> "status: " + tmpStatus);
                WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                    () -> "consumed: " + tmpConsumed);
                WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                    () -> "produced: " + tmpProduced);
                WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                    () -> "nativeHandshakeState: " +
                    this.ssl.getStateStringLong());
                WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                    () -> "nativeWantsToRead: " + this.nativeWantsToRead);
                WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                    () -> "nativeWantsToWrite: " + this.nativeWantsToWrite);
                WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                    () -> "==================================================");
            }

            return new SSLEngineResult(status, hs, consumed, produced);

        } finally {
            try {
                /* Don't hold references to this SSLEngine object in
                 * WolfSSLSession, can prevent proper garbage collection */
                unsetSSLCallbacks();
            } catch (WolfSSLJNIException e) {
                /* Don't throw from finally block, just log for info */
                WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                    () -> "unsetSSLCallbacks() exception during unwrap(), " +
                    "just logging: " + e.getMessage());
            }
        }
    }

    /**
     * Return if native ssl.connect() or ssl.accept() have finished
     * successfully or not. Used to correctly set this.handshakeFinished
     * from SetHandshakeStatus().
     *
     * Caller of this method should protect it with lock on ioLock.
     *
     * @return true if native handshake finished, otherwise false.
     */
    private boolean sslConnectAcceptSuccess() {
        boolean client = this.engineHelper.getUseClientMode();

        if (client) {
            if (this.lastSSLConnectRet == WolfSSL.SSL_SUCCESS) {
                return true;
            }
        }
        else {
            if (this.lastSSLAcceptRet == WolfSSL.SSL_SUCCESS) {
                return true;
            }
        }

        return false;
    }

    /**
     * Sets handshake status after I/O operation of unwrap(), helper function.
     */
    private synchronized void SetHandshakeStatus(int ret) {

        int err = 0;

        /* Get current wolfSSL error, synchronize on ioLock in case I/O is
         * happening and error state may change */
        synchronized (ioLock) {
            err = ssl.getError(ret);
        }

        /* Lock access to this.internalIOSendBuf and this.toRead */
        synchronized (toSendLock) {
            if (this.handshakeFinished == true) {
                /* close_notify sent by wolfSSL but not across transport yet */
                if (this.closeNotifySent == true &&
                    this.internalIOSendBufOffset > 0) {
                    hs = SSLEngineResult.HandshakeStatus.NEED_WRAP;
                }
                /* close_notify received, need to send one back */
                else if (this.closeNotifyReceived == true &&
                         this.closeNotifySent == false) {
                    hs = SSLEngineResult.HandshakeStatus.NEED_WRAP;
                }
                /* close_notify sent, need to read peer's */
                else if (this.closeNotifySent == true &&
                         this.closeNotifyReceived == false) {
                    /* Receiving close_notify is optional after we have sent
                     * one. Denote that with NOT_HANDSHAKING here */
                    hs = SSLEngineResult.HandshakeStatus.NOT_HANDSHAKING;
                }
                else if (!this.outBoundOpen && !this.closeNotifySent) {
                    /* We just closed outBound, NEED_WRAP to generate and
                     * send close_notify */
                    hs = SSLEngineResult.HandshakeStatus.NEED_WRAP;
                }
                else {
                    hs = SSLEngineResult.HandshakeStatus.NOT_HANDSHAKING;
                }
            }
            else {
                synchronized (netDataLock) {
                    synchronized (ioLock) {
                        if (sslConnectAcceptSuccess() && ssl.handshakeDone() &&
                            (this.internalIOSendBufOffset == 0) &&
                            (this.nativeWantsToWrite == 0) &&
                            (this.nativeWantsToRead == 0)) {

                            this.handshakeFinished = true;
                            hs = SSLEngineResult.HandshakeStatus.FINISHED;
                            this.engineHelper.getSession().updateStoredSessionValues();

                            WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                                () -> "SSL/TLS handshake finished");
                            WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                                () -> "SSL/TLS protocol: " +
                                this.engineHelper.getSession().getProtocol());
                            WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                                () -> "SSL/TLS cipher suite: " +
                                this.engineHelper.getSession().getCipherSuite());
                        }
                        /* give priority of WRAP/UNWRAP to state of our internal
                         * I/O data buffers first, then wolfSSL err status */
                        else if (this.internalIOSendBufOffset > 0) {
                            hs = SSLEngineResult.HandshakeStatus.NEED_WRAP;
                        }
                        else if (this.netData != null &&
                                 this.netData.remaining() > 0 &&
                                 this.inBoundOpen == true) {
                            hs = SSLEngineResult.HandshakeStatus.NEED_UNWRAP;
                        }
                        else if (err == WolfSSL.SSL_ERROR_WANT_READ) {
                            hs = SSLEngineResult.HandshakeStatus.NEED_UNWRAP;
                        }
                        else if (err == WolfSSL.SSL_ERROR_WANT_WRITE) {
                            hs = SSLEngineResult.HandshakeStatus.NEED_WRAP;
                        }
                        else if (err == WolfSSL.OUT_OF_ORDER_E) {
                            hs = SSLEngineResult.HandshakeStatus.NEED_UNWRAP;
                        }
                        else {
                            hs = SSLEngineResult.HandshakeStatus.NOT_HANDSHAKING;
                        }
                    } /* synchronized ioLock */
                } /* synchronized netDataLock */
            }
        } /* synchronized toSendLock */

        return;
    }

    @Override
    public Runnable getDelegatedTask() {
        WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
            () -> "entered getDelegatedTask()");
        /* no tasks left to run */
        return null;
    }

    @Override
    public synchronized void closeInbound() throws SSLException {
        WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
            () -> "entered closeInbound");

        if (!inBoundOpen)
            return;

        if (inBoundOpen && !closed) {
            /* this checks that peer sent back shutdown message */
            throw new SSLException("Closing in bound before shutdown is done");
        }
        else
        {
            inBoundOpen = false;
        }
    }

    @Override
    public synchronized boolean isInboundDone() {
        WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
            () -> "entered isInboundDone()");
        return !inBoundOpen;
    }

    @Override
    public synchronized void closeOutbound() {
        WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
            () -> "entered closeOutbound, outBoundOpen = false");
        outBoundOpen = false;

        /* If handshake has not started yet, close inBound as well */
        if (needInit) {
            inBoundOpen = true;
        }

        /* Update status based on internal state. Some calling applications
         * loop around getHandshakeStatus(), it needs to be up to date. */
        SetHandshakeStatus(0);
    }

    @Override
    public synchronized boolean isOutboundDone() {
        WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
            () -> "entered isOutboundDone()");
        return !outBoundOpen;
    }

    @Override
    public String[] getSupportedCipherSuites() {
        WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
            () -> "entered getSupportedCipherSuites()");
        return WolfSSLEngineHelper.getAllCiphers();
    }

    @Override
    public String[] getEnabledCipherSuites() {
        WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
            () -> "entered getEnabledCipherSuites()");
        return this.engineHelper.getCiphers();
    }

    @Override
    public synchronized void setEnabledCipherSuites(String[] suites) {
        WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
            () -> "entered setEnabledCipherSuites()");
        this.engineHelper.setCiphers(suites);
    }

    @Override
    public String[] getSupportedProtocols() {
        WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
            () -> "entered getSupportedProtocols()");
        return WolfSSLEngineHelper.getAllProtocols();
    }

    @Override
    public synchronized String[] getEnabledProtocols() {
        WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
            () -> "entered getEnabledProtocols()");
        return this.engineHelper.getProtocols();
    }

    @Override
    public synchronized void setEnabledProtocols(String[] protocols) {
        WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
            () -> "entered setEnabledProtocols()");
        this.engineHelper.setProtocols(protocols);
    }

    @Override
    public synchronized SSLSession getSession() {
        WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
            () -> "entered getSession()");

        try {
            /* Need cert loaded for getSession().getLocalCertificates() */
            LoadCertAndKey();
        } catch (SSLException e) {
            return null;
        }

        return this.engineHelper.getSession();
    }

    /**
     * Has the underlying WOLFSSL / WolfSSLSession been resumed / reused.
     * This calls down to native wolfSSL_session_reused()
     *
     * NON-STANDARD API, not part of JSSE. Must cast SSLEngine back
     * to WolfSSLEngine to use.
     *
     * @return true if session has been resumed, otherwise false
     * @throws SSLException if native JNI call fails or underlying
     *         WolfSSLSession has been freed
     */
    public synchronized boolean sessionResumed() throws SSLException {
        if (this.ssl != null) {
            try {
                int resume = this.ssl.sessionReused();
                if (resume == 1) {
                    return true;
                }
            } catch (IllegalStateException | WolfSSLJNIException e) {
                throw new SSLException(e);
            }
        }

        return false;
    }

    public synchronized SSLSession getHandshakeSession() {
        WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
            () -> "entered getHandshakeSession()");

        if (!this.handshakeFinished) {
            /* Only return handshake session during the handshake */
            return this.engineHelper.getSession();
        }

        return null;
    }

    /**
     * Explicitly start the SSL/TLS handshake.
     *
     * This method does not block until handshake is completed, unlike
     * the SSLSocket.startHandshake() method.
     *
     * The handshake may be started implicitly by a call to wrap() or unwrap(),
     * if those methods are called and the handshake is not done yet. In that
     * case, the user has not explicitly started the handshake themselves
     * and may inadvertently call beginHandshake() unknowing that the handshake
     * has already started. For that case, we should just return without
     * error/exception, since the user is just trying to start the first
     * initial handshake.
     *
     * beginHandshake() may also be called again to initiate renegotiation.
     * wolfJSSE does not support renegotiation inside SSLEngine yet. In that
     * case, we throw an SSLException to notify callers renegotiation is not
     * supported.
     *
     * @throws SSLException if a problem was encountered while initiating
     *         a SSL/TLS handshake on this SSLEngine.
     * @throws IllegalStateException if the client/server mode has not yet
     *         been set.
     */
    @Override
    public synchronized void beginHandshake() throws SSLException {
        WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
            () -> "entered beginHandshake()");

        if (!this.clientModeSet) {
            throw new IllegalStateException(
                "setUseClientMode() has not been called on this SSLEngine");
        }

        synchronized (initLock) {
            if (this.handshakeStartedExplicitly) {
                /* Renegotiation (thus calling beginHandshake() multiple times)
                 * is not supported in wolfJSSE SSLEngine implementation yet. If
                 * already called once by user, throw SSLException. */
                throw new SSLException("Renegotiation not supported");
            }
            else if (!this.needInit && !this.handshakeFinished) {
                /* Handshake has started implicitly by wrap() or unwrap(). Simply
                 * return since this is the first time that the user has called
                 * beginHandshake() themselves. */
                this.handshakeStartedExplicitly = true;
                return;
            }
        }

        /* No network data source yet */
        synchronized (netDataLock) {
            this.netData = null;
        }

        if (outBoundOpen == false) {
            throw new SSLException(
                "beginHandshake() called but outbound closed");
        }

        try {
            setSSLCallbacks();
        } catch (WolfSSLJNIException e) {
            throw new SSLException(e);
        }

        try {
            /* will throw SSLHandshakeException if session creation is
               not allowed */
            checkAndInitSSLEngine();

            WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                () -> "calling engineHelper.doHandshake()");

            int ret;
            try {
                ret = this.engineHelper.doHandshake(1, 0);
            } catch (WolfSSLException e) {
                throw new SSLException(
                    "Handshake failed: " + e.getMessage(), e);
            }
            SetHandshakeStatus(ret);

            /* Mark that the user has explicitly started the handshake
             * on this SSLEngine by calling beginHandshake() */
            this.handshakeStartedExplicitly = true;

        } catch (SocketTimeoutException e) {
            e.printStackTrace();
            throw new SSLException(e);

        } finally {
            try {
                /* Don't hold references to this SSLEngine object in
                 * WolfSSLSession, can prevent proper garbage collection */
                unsetSSLCallbacks();
            } catch (Exception e) {
                /* Don't throw from finally block, just log for info */
                WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                    () -> "unsetSSLCallbacks() exception during " +
                    "beginHandshake(), just logging: " + e.getMessage());
            }
        }
    }

    @Override
    public synchronized SSLEngineResult.HandshakeStatus getHandshakeStatus() {
        WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
            () -> "entered getHandshakeStatus(): " + hs);

        /* Update status based on internal state. Some calling applications
         * loop around getHandshakeStatus(), it needs to be up to date. */
        SetHandshakeStatus(0);

        return hs;
    }

    @Override
    public synchronized void setUseClientMode(boolean mode) {
        WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
            () -> "entered setUseClientMode(" + mode + ")");
        this.engineHelper.setUseClientMode(mode);
        this.clientModeSet = true;
    }

    @Override
    public synchronized boolean getUseClientMode() {
        WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
            () -> "entered getUseClientMode()");
        return this.engineHelper.getUseClientMode();
    }

    @Override
    public synchronized void setNeedClientAuth(boolean need) {
        WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
            () -> "entered setNeedClientAuth(" + need + ")");
        this.engineHelper.setNeedClientAuth(need);
    }

    @Override
    public synchronized boolean getNeedClientAuth() {
        WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
            () -> "entered getNeedClientAuth()");
        return this.engineHelper.getNeedClientAuth();
    }

    @Override
    public synchronized void setWantClientAuth(boolean want) {
        WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
            () -> "entered setWantClientAuth(" + want + ")");
        this.engineHelper.setWantClientAuth(want);
    }

    @Override
    public synchronized boolean getWantClientAuth() {
        WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
            () -> "entered getWantClientAuth()");
        return this.engineHelper.getWantClientAuth();
    }

    @Override
    public synchronized void setEnableSessionCreation(boolean flag) {
        WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
            () -> "entered setEnableSessionCreation(" + flag + ")");
        this.engineHelper.setEnableSessionCreation(flag);
    }

    @Override
    public synchronized boolean getEnableSessionCreation() {
        WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
            () -> "entered getEnableSessionCreation()");
        return this.engineHelper.getEnableSessionCreation();
    }

    public synchronized String getApplicationProtocol() {
        WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
            () -> "entered getApplicationProtocol()");
        return this.engineHelper.getAlpnSelectedProtocolString();
    }

    /**
     * Returns the application protocol value negotiated on a handshake
     * currently in progress.
     *
     * After the handshake has finished, this will return null. To get the
     * ALPN protocol negotiated during the handshake, after it has completed,
     * call getApplicationProtocol().
     *
     * Not marked at @Override since this API was added as of
     * Java SE 8 Maintenance Release 3, and Java 7 SSLSocket will not
     * have this.
     *
     * @return String representating the application protocol negotiated
     */
    public synchronized String getHandshakeApplicationProtocol() {

        WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
            () -> "entered getHandshakeApplicationProtocol()");

        if (!this.needInit && !this.handshakeFinished) {
            return this.engineHelper.getAlpnSelectedProtocolString();
        }

        return null;
    }

    /**
     * Returns the callback that selects an application protocol during the
     * SSL/TLS handshake.
     *
     * @return the callback function, or null if no callback has been set
     */
    public synchronized BiFunction<SSLEngine,List<String>,String>
        getHandshakeApplicationProtocolSelector() {

        WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
            () -> "entered getHandshakeApplicationProtocolSelector()");

        return this.alpnSelector;
    }

    /**
     * Registers a callback function that selects an application protocol
     * value for the SSL/TLS handshake.
     *
     * Usage of this callback will override any values set by
     * SSLParameters.setApplicationProtocols().
     *
     * Callback argument descriptions:
     *
     *    SSLEngine - the current SSLEngine, allows for inspection by the
     *                callback if needed
     *    List&lt;String&gt; - List of Strings representing application protocol
     *                   names sent by the peer
     *    String - Result of the callback is an application protocol
     *             name String, or null if none of the peer's protocols
     *             are acceptable. If return value is an empty String,
     *             ALPN will not be used.
     *
     * @param selector callback used to select ALPN protocol for handshake
     */
    public synchronized void setHandshakeApplicationProtocolSelector(
        BiFunction<SSLEngine,List<String>,String> selector) {

        final int ret;

        WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
            () -> "entered setHandshakeApplicationProtocolSelector()");

        if (selector != null) {
            ALPNSelectCallback alpnCb = new ALPNSelectCallback();

            try {
                /* Pass in SSLSocket Object for use inside callback */
                ret = this.ssl.setAlpnSelectCb(alpnCb, this);
                if (ret != WolfSSL.SSL_SUCCESS) {
                    WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                        () -> "Native setAlpnSelectCb() failed, ret = " + ret +
                        ", not setting selector");
                    return;
                }

                /* called from within ALPNSelectCallback during the handshake */
                this.alpnSelector = selector;

            } catch (WolfSSLJNIException e) {
                WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                    () -> "Exception while calling ssl.setAlpnSelectCb, " +
                    "not setting");
            }
        }
    }

    /**
     * Inner class that implement the ALPN select callback which is registered
     * with our com.wolfssl.WolfSSLSession when
     * setHandshakeApplicationProtocolSelector() has been called.
     */
    class ALPNSelectCallback implements WolfSSLALPNSelectCallback
    {
        public int alpnSelectCallback(WolfSSLSession ssl, String[] out,
            String[] in, Object arg) {

            SSLEngine engine = (SSLEngine)arg;
            List<String> peerProtos = new ArrayList<String>();
            final String selected;

            if (alpnSelector == null) {
                WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                    () -> "alpnSelector null inside ALPNSelectCallback");
                return WolfSSL.SSL_TLSEXT_ERR_ALERT_FATAL;
            }

            if (!(arg instanceof SSLEngine)) {
                WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                    () -> "alpnSelectCallback arg not type of SSLEngine");
                return WolfSSL.SSL_TLSEXT_ERR_ALERT_FATAL;
            }

            if (in.length == 0) {
                WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                    () -> "peer protocol list is 0 inside alpnSelectCallback");
                return WolfSSL.SSL_TLSEXT_ERR_ALERT_FATAL;
            }

            WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                () -> "ALPN protos sent by peer: " + Arrays.toString(in));

            for (String s: in) {
                peerProtos.add(s);
            }
            selected = alpnSelector.apply(engine, peerProtos);

            if (selected == null) {
                WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                    () -> "ALPN protocol string is null, no peer match");
                return WolfSSL.SSL_TLSEXT_ERR_ALERT_FATAL;
            }
            else {
                if (selected.isEmpty()) {
                    WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                        () -> "ALPN not being used, selected proto empty");
                    return WolfSSL.SSL_TLSEXT_ERR_NOACK;
                }

                WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                    () -> "ALPN protocol selected by callback: " + selected);
                out[0] = selected;
                return WolfSSL.SSL_TLSEXT_ERR_OK;

            }
        }
    }


    /**
     * Set the SSLParameters for this SSLEngine.
     *
     * @param params SSLParameters to set for this SSLEngine object
     */
    public synchronized void setSSLParameters(SSLParameters params) {
        WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
            () -> "entered setSSLParameters()");
        if (params != null) {
            WolfSSLParametersHelper.importParams(params, this.params);

            /* Store SNI server names in the session for potential resumption */
            if (params.getServerNames() != null &&
                    !params.getServerNames().isEmpty()) {

                WolfSSLImplementSSLSession session =
                    (WolfSSLImplementSSLSession)this.getSession();
                if (session != null) {
                    session.setSNIServerNames(params.getServerNames());
                    WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                        () -> "Captured SNI server names for session caching");
                }
            }
        }
    }

    /**
     * Gets the SSLParameters for this SSLEngine.
     *
     * @return SSLParameters for this SSLEngine object.
     */
    @Override
    public synchronized SSLParameters getSSLParameters() {

        WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
            () -> "entered getSSLParameters()");

        return WolfSSLParametersHelper.decoupleParams(this.params);
    }

    /**
     * Copies buffer to end of to send queue. Encrypted packet is ready to be
     * sent out.
     *
     * @param in byte array with encrypted data to be sent
     * @param sz size of data in input array to be sent
     *
     * @return number of bytes placed into send queue
     */
    protected synchronized int internalSendCb(ByteBuffer in, int sz) {

        synchronized (toSendLock) {
            /* As per JSSE Reference Guide, Section 8 DTLS implementation
             * of wrap() contains at most one record so every DTLS record
             * can be marshaled and delivered to datagram individually. As
             * such, if we have data wait to send before caching more */
            /* TODO - do we need to fragment data here if larger than
             * SSLParameters.getMaximumPacketSize() with DTLS? */
            if (this.ssl.dtls() == 1) {
                if ((this.internalIOSendBuf != null) &&
                    (this.internalIOSendBufOffset > 0)) {
                    /* Cause SSLEngine to only send one packet at a time.
                     * Keep track if wolfSSL had wanted to send data. We will
                     * use that information when setting the handshake
                     * status */
                    if (sz > 0) {
                        this.nativeWantsToWrite = sz;
                    }
                    return -2;
                }

                /* Reset native wants to send data flag. We have cleared
                 * cached data in the object, so this call of the send CB
                 * should be with the desired native data now. */
                this.nativeWantsToWrite = 0;
            }

            if (sz <= 0) {
                /* No data to send */
                return 0;
            }

            /* If we have more data than internal static buffer,
             * grow buffer 2x (or up to sz needed) and copy data over */
            if ((this.internalIOSendBufSz -
                    this.internalIOSendBufOffset) < sz) {
                /* Allocate new buffer to hold data to be sent */
                int newSz = this.internalIOSendBufSz * 2;
                if (newSz < sz) {
                    newSz = sz;
                }
                byte[] newBuf = new byte[newSz];
                System.arraycopy(this.internalIOSendBuf, 0,
                                 newBuf, 0, this.internalIOSendBufOffset);
                this.internalIOSendBuf = newBuf;
                this.internalIOSendBufSz = newSz;
            }

            /* Add data to end of internal static buffer */
            in.get(this.internalIOSendBuf, this.internalIOSendBufOffset, sz);

            if (ioDebugEnabled == true) {
                WolfSSLDebug.logHex(getClass(), WolfSSLDebug.INFO,
                    () -> "CB Write", Arrays.copyOfRange(this.internalIOSendBuf,
                    this.internalIOSendBufOffset,
                    this.internalIOSendBufOffset + sz), sz);
            }

            this.internalIOSendBufOffset += sz;
        }

        return sz;
    }

    /**
     * Internal receive callback. Reads from netData and gives bytes back
     * to native wolfSSL for processing.
     *
     * @param toRead ByteBuffer into which to place data read from transport
     * @param sz number of bytes that should be read/copied from transport
     *
     * @return number of bytes read into toRead array or negative
     *         value on error
     */
    protected synchronized int internalRecvCb(ByteBuffer toRead, int sz) {

        int max = 0;
        int originalLimit = 0;

        synchronized (netDataLock) {
            if (ioDebugEnabled == true) {
                WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                    () -> "CB Read: requesting " + sz + " bytes");
                if (this.netData != null) {
                    WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                        () -> "CB Read: netData.remaining() = " +
                        this.netData.remaining());
                    WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                        () -> "CB Read: netData.position() = " +
                        this.netData.position());
                    WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                        () -> "CB Read: netData.limit() = " +
                        this.netData.limit());
                }
            }

            if (this.netData == null || this.netData.remaining() == 0) {
                if (ioDebugEnabled == true) {
                    WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                        () -> "CB Read: returning WOLFSSL_CBIO_ERR_WANT_READ");
                }
                if (this.ssl.dtls() == 1 && this.handshakeFinished) {
                    this.nativeWantsToRead = 1;
                }
                return WolfSSL.WOLFSSL_CBIO_ERR_WANT_READ;
            }

            /* Reset native wants to read flag */
            this.nativeWantsToRead = 0;

            max = (sz < this.netData.remaining()) ? sz : this.netData.remaining();

            originalLimit = this.netData.limit();
            this.netData.limit(this.netData.position() + max);
            toRead.put(this.netData);
            this.netData.limit(originalLimit);

            /* Print out bytes read from toRead buffer */
            if (ioDebugEnabled == true) {
                int toReadPos = toRead.position();
                /* Move position back to start of data we just wrote */
                toRead.position(toReadPos - max);
                byte[] tmpArr = new byte[max];
                toRead.get(tmpArr, 0, max);
                WolfSSLDebug.logHex(getClass(), WolfSSLDebug.INFO,
                    () -> "CB Read", tmpArr, max);
                /* Restore position */
                toRead.position(toReadPos);
            }

            return max;
        }
    }

    /**
     * Internal session ticket callback. Called when native wolfSSL
     * receives a session ticket from peer.
     *
     * @param ticket byte array containing session ticket data
     *
     * @return 0 on success, negative value on error
     */
    protected synchronized int internalSessionTicketCb(byte[] ticket) {
        WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
            () -> "entered internalSessionTicketCb()");

        if (ticket != null) {
            WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                () -> "Session ticket received, length = " + ticket.length);
            if (ticket.length > 0) {
                this.sessionTicketCount++;
            }
            WolfSSLDebug.log(getClass(), WolfSSLDebug.INFO,
                () -> "Total session tickets received by this SSLEngine: " +
                this.sessionTicketCount);
        }

        return 0;
    }

    private class SendCB implements WolfSSLByteBufferIOSendCallback {

        protected SendCB() {

        }

        public int sendCallback(WolfSSLSession ssl, ByteBuffer toSend, int sz,
                                Object engine) {
            return ((WolfSSLEngine)engine).internalSendCb(toSend, sz);
        }

    }

    private class RecvCB implements WolfSSLByteBufferIORecvCallback {

        protected RecvCB() {

        }

        public int receiveCallback(WolfSSLSession ssl, ByteBuffer buf, int sz,
                                   Object engine) {
            return ((WolfSSLEngine)engine).internalRecvCb(buf, sz);
        }

    }

    private class SessionTicketCB implements WolfSSLSessionTicketCallback {

        protected SessionTicketCB() {
        }

        public int sessionTicketCallback(WolfSSLSession ssl, byte[] ticket,
                                         Object engine) {
            return ((WolfSSLEngine)engine).internalSessionTicketCb(ticket);
        }
    }

    @SuppressWarnings("deprecation")
    @Override
    protected synchronized void finalize() throws Throwable {
        if (this.ssl != null) {
            this.ssl.freeSSL();
            this.ssl = null;
        }
        /* Clear our reference to static application direct ByteBuffer */
        if (this.staticAppDataBuf != null) {
            this.staticAppDataBuf.clear();
            this.staticAppDataBuf = null;
        }
        super.finalize();
    }
}