/*
 * Copyright 2014 The Netty Project
 *
 * The Netty Project licenses this file to you under the Apache License,
 * version 2.0 (the "License"); you may not use this file except in compliance
 * with the License. You may obtain a copy of the License at:
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations
 * under the License.
 */
package io.netty.handler.ssl;

import io.netty.buffer.ByteBuf;
import io.netty.buffer.ByteBufAllocator;
import io.netty.buffer.Unpooled;
import io.netty.util.internal.EmptyArrays;
import io.netty.util.internal.PlatformDependent;
import io.netty.util.internal.StringUtil;
import io.netty.util.internal.logging.InternalLogger;
import io.netty.util.internal.logging.InternalLoggerFactory;
import org.apache.tomcat.jni.Buffer;
import org.apache.tomcat.jni.SSL;

import javax.net.ssl.SSLEngine;
import javax.net.ssl.SSLEngineResult;
import javax.net.ssl.SSLEngineResult.HandshakeStatus;
import javax.net.ssl.SSLException;
import javax.net.ssl.SSLHandshakeException;
import javax.net.ssl.SSLParameters;
import javax.net.ssl.SSLPeerUnverifiedException;
import javax.net.ssl.SSLSession;
import javax.net.ssl.SSLSessionBindingEvent;
import javax.net.ssl.SSLSessionBindingListener;
import javax.net.ssl.SSLSessionContext;
import javax.security.cert.X509Certificate;
import java.nio.ByteBuffer;
import java.nio.ReadOnlyBufferException;
import java.security.Principal;
import java.security.cert.Certificate;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.concurrent.atomic.AtomicIntegerFieldUpdater;

import static io.netty.handler.ssl.ApplicationProtocolConfig.SelectedListenerFailureBehavior;
import static io.netty.util.internal.ObjectUtil.checkNotNull;
import static javax.net.ssl.SSLEngineResult.HandshakeStatus.*;
import static javax.net.ssl.SSLEngineResult.Status.*;

/**
 * Implements a {@link SSLEngine} using
 * <a href="https://www.openssl.org/docs/crypto/BIO_s_bio.html#EXAMPLE">OpenSSL BIO abstractions</a>.
 */
public final class OpenSslEngine extends SSLEngine {

    private static final InternalLogger logger = InternalLoggerFactory.getInstance(OpenSslEngine.class);

    private static final Certificate[] EMPTY_CERTIFICATES = EmptyArrays.EMPTY_CERTIFICATES;
    private static final X509Certificate[] EMPTY_X509_CERTIFICATES = EmptyArrays.EMPTY_JAVAX_X509_CERTIFICATES;

    private static final SSLException ENGINE_CLOSED = new SSLException("engine closed");
    private static final SSLException RENEGOTIATION_UNSUPPORTED = new SSLException("renegotiation unsupported");
    private static final SSLException ENCRYPTED_PACKET_OVERSIZED = new SSLException("encrypted packet oversized");
    static {
        ENGINE_CLOSED.setStackTrace(EmptyArrays.EMPTY_STACK_TRACE);
        RENEGOTIATION_UNSUPPORTED.setStackTrace(EmptyArrays.EMPTY_STACK_TRACE);
        ENCRYPTED_PACKET_OVERSIZED.setStackTrace(EmptyArrays.EMPTY_STACK_TRACE);

        AtomicIntegerFieldUpdater<OpenSslEngine> destroyedUpdater =
                PlatformDependent.newAtomicIntegerFieldUpdater(OpenSslEngine.class, "destroyed");
        if (destroyedUpdater == null) {
            destroyedUpdater = AtomicIntegerFieldUpdater.newUpdater(OpenSslEngine.class, "destroyed");
        }
        DESTROYED_UPDATER = destroyedUpdater;
    }

    private static final int MAX_PLAINTEXT_LENGTH = 16 * 1024; // 2^14
    private static final int MAX_COMPRESSED_LENGTH = MAX_PLAINTEXT_LENGTH + 1024;
    private static final int MAX_CIPHERTEXT_LENGTH = MAX_COMPRESSED_LENGTH + 1024;

    // Protocols
    private static final String PROTOCOL_SSL_V2_HELLO = "SSLv2Hello";
    private static final String PROTOCOL_SSL_V2 = "SSLv2";
    private static final String PROTOCOL_SSL_V3 = "SSLv3";
    private static final String PROTOCOL_TLS_V1 = "TLSv1";
    private static final String PROTOCOL_TLS_V1_1 = "TLSv1.1";
    private static final String PROTOCOL_TLS_V1_2 = "TLSv1.2";

    private static final String[] SUPPORTED_PROTOCOLS = {
            PROTOCOL_SSL_V2_HELLO,
            PROTOCOL_SSL_V2,
            PROTOCOL_SSL_V3,
            PROTOCOL_TLS_V1,
            PROTOCOL_TLS_V1_1,
            PROTOCOL_TLS_V1_2
    };
    private static final Set<String> SUPPORTED_PROTOCOLS_SET = new HashSet<String>(Arrays.asList(SUPPORTED_PROTOCOLS));

    // Header (5) + Data (2^14) + Compression (1024) + Encryption (1024) + MAC (20) + Padding (256)
    static final int MAX_ENCRYPTED_PACKET_LENGTH = MAX_CIPHERTEXT_LENGTH + 5 + 20 + 256;

    static final int MAX_ENCRYPTION_OVERHEAD_LENGTH = MAX_ENCRYPTED_PACKET_LENGTH - MAX_PLAINTEXT_LENGTH;

    private static final AtomicIntegerFieldUpdater<OpenSslEngine> DESTROYED_UPDATER;

    private static final String INVALID_CIPHER = "SSL_NULL_WITH_NULL_NULL";

    private static final long EMPTY_ADDR = Buffer.address(Unpooled.EMPTY_BUFFER.nioBuffer());

    private static final SSLEngineResult NEED_UNWRAP_OK = new SSLEngineResult(OK, NEED_UNWRAP, 0, 0);
    private static final SSLEngineResult NEED_UNWRAP_CLOSED = new SSLEngineResult(CLOSED, NEED_UNWRAP, 0, 0);
    private static final SSLEngineResult NEED_WRAP_OK = new SSLEngineResult(OK, NEED_WRAP, 0, 0);
    private static final SSLEngineResult NEED_WRAP_CLOSED = new SSLEngineResult(CLOSED, NEED_WRAP, 0, 0);
    private static final SSLEngineResult CLOSED_NOT_HANDSHAKING = new SSLEngineResult(CLOSED, NOT_HANDSHAKING, 0, 0);

    // OpenSSL state
    private long ssl;
    private long networkBIO;

    private enum HandshakeState {
        /**
         * Not started yet.
         */
        NOT_STARTED,
        /**
         * Started via unwrap/wrap.
         */
        STARTED_IMPLICITLY,
        /**
         * Started via {@link #beginHandshake()}.
         */
        STARTED_EXPLICITLY,

        /**
         * Handshake is finished.
         */
        FINISHED
    }

    private HandshakeState handshakeState = HandshakeState.NOT_STARTED;
    private boolean receivedShutdown;
    private volatile int destroyed;

    private volatile ClientAuth clientAuth = ClientAuth.NONE;

    private volatile String endPointIdentificationAlgorithm;
    // Store as object as AlgorithmConstraints only exists since java 7.
    private volatile Object algorithmConstraints;

    // SSL Engine status variables
    private boolean isInboundDone;
    private boolean isOutboundDone;
    private boolean engineClosed;

    private final boolean clientMode;
    private final ByteBufAllocator alloc;
    private final OpenSslEngineMap engineMap;
    private final OpenSslApplicationProtocolNegotiator apn;
    private final boolean rejectRemoteInitiatedRenegation;
    private final OpenSslSession session;
    private final Certificate[] localCerts;
    private final ByteBuffer[] singleSrcBuffer = new ByteBuffer[1];
    private final ByteBuffer[] singleDstBuffer = new ByteBuffer[1];

    // This is package-private as we set it from OpenSslContext if an exception is thrown during
    // the verification step.
    SSLHandshakeException handshakeException;

    /**
     * Creates a new instance
     *
     * @param sslCtx an OpenSSL {@code SSL_CTX} object
     * @param alloc the {@link ByteBufAllocator} that will be used by this engine
     */
    @Deprecated
    public OpenSslEngine(long sslCtx, ByteBufAllocator alloc,
                         @SuppressWarnings("unused") String fallbackApplicationProtocol) {
        this(sslCtx, alloc, false, null, OpenSslContext.NONE_PROTOCOL_NEGOTIATOR, OpenSslEngineMap.EMPTY, false,
                ClientAuth.NONE);
    }

    OpenSslEngine(long sslCtx, ByteBufAllocator alloc,
                  boolean clientMode, OpenSslSessionContext sessionContext,
                  OpenSslApplicationProtocolNegotiator apn, OpenSslEngineMap engineMap,
                  boolean rejectRemoteInitiatedRenegation,
                  ClientAuth clientAuth) {
        this(sslCtx, alloc, clientMode, sessionContext, apn, engineMap, rejectRemoteInitiatedRenegation, null, -1,
                null, clientAuth);
    }

    OpenSslEngine(long sslCtx, ByteBufAllocator alloc,
                  boolean clientMode, OpenSslSessionContext sessionContext,
                  OpenSslApplicationProtocolNegotiator apn, OpenSslEngineMap engineMap,
                  boolean rejectRemoteInitiatedRenegation, String peerHost, int peerPort,
                  Certificate[] localCerts,
                  ClientAuth clientAuth) {
        super(peerHost, peerPort);
        OpenSsl.ensureAvailability();
        if (sslCtx == 0) {
            throw new NullPointerException("sslCtx");
        }

        this.alloc = checkNotNull(alloc, "alloc");
        this.apn = checkNotNull(apn, "apn");
        ssl = SSL.newSSL(sslCtx, !clientMode);
        session = new OpenSslSession(sessionContext);
        networkBIO = SSL.makeNetworkBIO(ssl);
        this.clientMode = clientMode;
        this.engineMap = engineMap;
        this.rejectRemoteInitiatedRenegation = rejectRemoteInitiatedRenegation;
        this.localCerts = localCerts;

        // Set the client auth mode, this needs to be done via setClientAuth(...) method so we actually call the
        // needed JNI methods.
        setClientAuth(clientMode ? ClientAuth.NONE : checkNotNull(clientAuth, "clientAuth"));
    }

    @Override
    public synchronized SSLSession getHandshakeSession() {
        // Javadocs state return value should be:
        // null if this instance is not currently handshaking, or if the current handshake has not
        // progressed far enough to create a basic SSLSession. Otherwise, this method returns the
        // SSLSession currently being negotiated.
        switch(handshakeState) {
        case NOT_STARTED:
        case FINISHED:
            return null;
        default:
            return session;
        }
    }

    /**
     * Returns the pointer to the {@code SSL} object for this {@link OpenSslEngine}.
     * Be aware that it is freed as soon as the {@link #finalize()} or {@link #shutdown} method is called.
     * At this point {@code 0} will be returned.
     */
    public synchronized long sslPointer() {
        return ssl;
    }

    /**
     * Destroys this engine.
     */
    public synchronized void shutdown() {
        if (DESTROYED_UPDATER.compareAndSet(this, 0, 1)) {
            engineMap.remove(ssl);
            SSL.freeSSL(ssl);
            SSL.freeBIO(networkBIO);
            ssl = networkBIO = 0;

            // internal errors can cause shutdown without marking the engine closed
            isInboundDone = isOutboundDone = engineClosed = true;
        }

        // On shutdown clear all errors
        SSL.clearError();
    }

    /**
     * Write plaintext data to the OpenSSL internal BIO
     *
     * Calling this function with src.remaining == 0 is undefined.
     */
    private int writePlaintextData(final ByteBuffer src) {
        final int pos = src.position();
        final int limit = src.limit();
        final int len = Math.min(limit - pos, MAX_PLAINTEXT_LENGTH);
        final int sslWrote;

        if (src.isDirect()) {
            final long addr = Buffer.address(src) + pos;
            sslWrote = SSL.writeToSSL(ssl, addr, len);
            if (sslWrote > 0) {
                src.position(pos + sslWrote);
            }
        } else {
            ByteBuf buf = alloc.directBuffer(len);
            try {
                final long addr = memoryAddress(buf);

                src.limit(pos + len);

                buf.setBytes(0, src);
                src.limit(limit);

                sslWrote = SSL.writeToSSL(ssl, addr, len);
                if (sslWrote > 0) {
                    src.position(pos + sslWrote);
                } else {
                    src.position(pos);
                }
            } finally {
                buf.release();
            }
        }
        return sslWrote;
    }

    /**
     * Write encrypted data to the OpenSSL network BIO.
     */
    private int writeEncryptedData(final ByteBuffer src) {
        final int pos = src.position();
        final int len = src.remaining();
        final int netWrote;
        if (src.isDirect()) {
            final long addr = Buffer.address(src) + pos;
            netWrote = SSL.writeToBIO(networkBIO, addr, len);
            if (netWrote >= 0) {
                src.position(pos + netWrote);
            }
        } else {
            final ByteBuf buf = alloc.directBuffer(len);
            try {
                final long addr = memoryAddress(buf);

                buf.setBytes(0, src);

                netWrote = SSL.writeToBIO(networkBIO, addr, len);
                if (netWrote >= 0) {
                    src.position(pos + netWrote);
                } else {
                    src.position(pos);
                }
            } finally {
                buf.release();
            }
        }

        return netWrote;
    }

    /**
     * Read plaintext data from the OpenSSL internal BIO
     */
    private int readPlaintextData(final ByteBuffer dst) {
        final int sslRead;
        if (dst.isDirect()) {
            final int pos = dst.position();
            final long addr = Buffer.address(dst) + pos;
            final int len = dst.limit() - pos;
            sslRead = SSL.readFromSSL(ssl, addr, len);
            if (sslRead > 0) {
                dst.position(pos + sslRead);
            }
        } else {
            final int pos = dst.position();
            final int limit = dst.limit();
            final int len = Math.min(MAX_ENCRYPTED_PACKET_LENGTH, limit - pos);
            final ByteBuf buf = alloc.directBuffer(len);
            try {
                final long addr = memoryAddress(buf);

                sslRead = SSL.readFromSSL(ssl, addr, len);
                if (sslRead > 0) {
                    dst.limit(pos + sslRead);
                    buf.getBytes(0, dst);
                    dst.limit(limit);
                }
            } finally {
                buf.release();
            }
        }

        return sslRead;
    }

    /**
     * Read encrypted data from the OpenSSL network BIO
     */
    private int readEncryptedData(final ByteBuffer dst, final int pending) {
        final int bioRead;

        if (dst.isDirect() && dst.remaining() >= pending) {
            final int pos = dst.position();
            final long addr = Buffer.address(dst) + pos;
            bioRead = SSL.readFromBIO(networkBIO, addr, pending);
            if (bioRead > 0) {
                dst.position(pos + bioRead);
                return bioRead;
            }
        } else {
            final ByteBuf buf = alloc.directBuffer(pending);
            try {
                final long addr = memoryAddress(buf);

                bioRead = SSL.readFromBIO(networkBIO, addr, pending);
                if (bioRead > 0) {
                    int oldLimit = dst.limit();
                    dst.limit(dst.position() + bioRead);
                    buf.getBytes(0, dst);
                    dst.limit(oldLimit);
                    return bioRead;
                }
            } finally {
                buf.release();
            }
        }

        return bioRead;
    }

    private SSLEngineResult readPendingBytesFromBIO(
            ByteBuffer dst, int bytesConsumed, int bytesProduced, HandshakeStatus status) throws SSLException {
        // Check to see if the engine wrote data into the network BIO
        int pendingNet = SSL.pendingWrittenBytesInBIO(networkBIO);
        if (pendingNet > 0) {

            // Do we have enough room in dst to write encrypted data?
            int capacity = dst.remaining();
            if (capacity < pendingNet) {
                return new SSLEngineResult(BUFFER_OVERFLOW,
                        mayFinishHandshake(status != FINISHED ? getHandshakeStatus(pendingNet) : status),
                                           bytesConsumed, bytesProduced);
            }

            // Write the pending data from the network BIO into the dst buffer
            int produced = readEncryptedData(dst, pendingNet);

            if (produced <= 0) {
                // We ignore BIO_* errors here as we use in memory BIO anyway and will do another SSL_* call later
                // on in which we will produce an exception in case of an error
                SSL.clearError();
            } else {
                bytesProduced += produced;
                pendingNet -= produced;
            }
            // If isOuboundDone is set, then the data from the network BIO
            // was the close_notify message -- we are not required to wait
            // for the receipt the peer's close_notify message -- shutdown.
            if (isOutboundDone) {
                shutdown();
            }

            return new SSLEngineResult(getEngineStatus(),
                                       mayFinishHandshake(status != FINISHED ? getHandshakeStatus(pendingNet) : status),
                                       bytesConsumed, bytesProduced);
        }
        return null;
    }

    @Override
    public synchronized SSLEngineResult wrap(
            final ByteBuffer[] srcs, final int offset, final int length, final ByteBuffer dst) throws SSLException {

        // Check to make sure the engine has not been closed
        if (isDestroyed()) {
            return CLOSED_NOT_HANDSHAKING;
        }

        // Throw required runtime exceptions
        if (srcs == null) {
            throw new IllegalArgumentException("srcs is null");
        }
        if (dst == null) {
            throw new IllegalArgumentException("dst is null");
        }

        if (offset >= srcs.length || offset + length > srcs.length) {
            throw new IndexOutOfBoundsException(
                    "offset: " + offset + ", length: " + length +
                            " (expected: offset <= offset + length <= srcs.length (" + srcs.length + "))");
        }

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

        HandshakeStatus status = NOT_HANDSHAKING;
        // Prepare OpenSSL to work in server mode and receive handshake
        if (handshakeState != HandshakeState.FINISHED) {
            if (handshakeState != HandshakeState.STARTED_EXPLICITLY) {
                // Update accepted so we know we triggered the handshake via wrap
                handshakeState = HandshakeState.STARTED_IMPLICITLY;
            }

            status = handshake();
            if (status == NEED_UNWRAP) {
                return NEED_UNWRAP_OK;
            }

            if (engineClosed) {
                return NEED_UNWRAP_CLOSED;
            }
        }

        int bytesProduced = 0;

        // There was no pending data in the network BIO -- encrypt any application data
        int bytesConsumed = 0;
        int endOffset = offset + length;
        for (int i = offset; i < endOffset; ++ i) {
            final ByteBuffer src = srcs[i];
            if (src == null) {
                throw new IllegalArgumentException("srcs[" + i + "] is null");
            }
            while (src.hasRemaining()) {

                // Write plaintext application data to the SSL engine
                int result = writePlaintextData(src);
                if (result > 0) {
                    bytesConsumed += result;
                } else {
                    int sslError = SSL.getError(ssl, result);
                    switch (sslError) {
                    case SSL.SSL_ERROR_ZERO_RETURN:
                        // This means the connection was shutdown correctly, close inbound and outbound
                        if (!receivedShutdown) {
                            closeAll();
                        }
                        // fall-trough!
                    case SSL.SSL_ERROR_WANT_READ:
                    case SSL.SSL_ERROR_WANT_WRITE:
                        // Break here as this means we need check if there is something pending in the BIO
                        break;
                    default:
                        // Everything else is considered as error
                        throw shutdownWithError("SSL_write");
                    }
                }

                SSLEngineResult pendingNetResult = readPendingBytesFromBIO(dst, bytesConsumed, bytesProduced, status);
                if (pendingNetResult != null) {
                    return pendingNetResult;
                }
            }
        }
        // We need to check if pendingWrittenBytesInBIO was checked yet, as we may not checked if the srcs was empty,
        // or only contained empty buffers.
        if (bytesConsumed == 0) {
            SSLEngineResult pendingNetResult = readPendingBytesFromBIO(dst, 0, bytesProduced, status);
            if (pendingNetResult != null) {
                return pendingNetResult;
            }
        }

        return newResult(bytesConsumed, bytesProduced, status);
    }

    /**
     * Log the error, shutdown the engine and throw an exception.
     */
    private SSLException shutdownWithError(String operations) {
        String err = SSL.getLastError();
        return shutdownWithError(operations, err);
    }

    private SSLException shutdownWithError(String operation, String err) {
        if (logger.isDebugEnabled()) {
            logger.debug("{} failed: OpenSSL error: {}", operation, err);
        }

        // There was an internal error -- shutdown
        shutdown();
        if (handshakeState == HandshakeState.FINISHED) {
            return new SSLException(err);
        }
        return new SSLHandshakeException(err);
    }

    public synchronized SSLEngineResult unwrap(
            final ByteBuffer[] srcs, int srcsOffset, final int srcsLength,
            final ByteBuffer[] dsts, final int dstsOffset, final int dstsLength) throws SSLException {

        // Check to make sure the engine has not been closed
        if (isDestroyed()) {
            return CLOSED_NOT_HANDSHAKING;
        }

        // Throw required runtime exceptions
        if (srcs == null) {
            throw new NullPointerException("srcs");
        }
        if (srcsOffset >= srcs.length
                || srcsOffset + srcsLength > srcs.length) {
            throw new IndexOutOfBoundsException(
                    "offset: " + srcsOffset + ", length: " + srcsLength +
                    " (expected: offset <= offset + length <= srcs.length (" + srcs.length + "))");
        }
        if (dsts == null) {
            throw new IllegalArgumentException("dsts is null");
        }
        if (dstsOffset >= dsts.length || dstsOffset + dstsLength > dsts.length) {
            throw new IndexOutOfBoundsException(
                    "offset: " + dstsOffset + ", length: " + dstsLength +
                    " (expected: offset <= offset + length <= dsts.length (" + dsts.length + "))");
        }
        long capacity = 0;
        final int endOffset = dstsOffset + dstsLength;
        for (int i = dstsOffset; i < endOffset; i ++) {
            ByteBuffer dst = dsts[i];
            if (dst == null) {
                throw new IllegalArgumentException("dsts[" + i + "] is null");
            }
            if (dst.isReadOnly()) {
                throw new ReadOnlyBufferException();
            }
            capacity += dst.remaining();
        }

        HandshakeStatus status = NOT_HANDSHAKING;
        // Prepare OpenSSL to work in server mode and receive handshake
        if (handshakeState != HandshakeState.FINISHED) {
            if (handshakeState != HandshakeState.STARTED_EXPLICITLY) {
                // Update accepted so we know we triggered the handshake via wrap
                handshakeState = HandshakeState.STARTED_IMPLICITLY;
            }

            status = handshake();
            if (status == NEED_WRAP) {
                return NEED_WRAP_OK;
            }
            if (engineClosed) {
                return NEED_WRAP_CLOSED;
            }
        }

        final int srcsEndOffset = srcsOffset + srcsLength;
        long len = 0;
        for (int i = srcsOffset; i < srcsEndOffset; i++) {
            ByteBuffer src = srcs[i];
            if (src == null) {
                throw new IllegalArgumentException("srcs[" + i + "] is null");
            }
            len += src.remaining();
        }

        // protect against protocol overflow attack vector
        if (len > MAX_ENCRYPTED_PACKET_LENGTH) {
            isInboundDone = true;
            isOutboundDone = true;
            engineClosed = true;
            shutdown();
            throw ENCRYPTED_PACKET_OVERSIZED;
        }

        // Write encrypted data to network BIO
        int bytesConsumed = 0;
        if (srcsOffset < srcsEndOffset) {
            do {
                ByteBuffer src = srcs[srcsOffset];
                int remaining = src.remaining();
                if (remaining == 0) {
                    // We must skip empty buffers as BIO_write will return 0 if asked to write something
                    // with length 0.
                    srcsOffset ++;
                    continue;
                }
                int written = writeEncryptedData(src);
                if (written > 0) {
                    bytesConsumed += written;

                    if (written == remaining) {
                        srcsOffset ++;
                    } else {
                        // We were not able to write everything into the BIO so break the write loop as otherwise
                        // we will produce an error on the next write attempt, which will trigger a SSL.clearError()
                        // later.
                        break;
                    }
                } else {
                    // BIO_write returned a negative or zero number, this means we could not complete the write
                    // operation and should retry later.
                    // We ignore BIO_* errors here as we use in memory BIO anyway and will do another SSL_* call later
                    // on in which we will produce an exception in case of an error
                    SSL.clearError();
                    break;
                }
            } while (srcsOffset < srcsEndOffset);
        }

        rejectRemoteInitiatedRenegation();

        // Number of produced bytes
        int bytesProduced = 0;

        if (capacity > 0) {
            // Write decrypted data to dsts buffers
            int idx = dstsOffset;
            while (idx < endOffset) {
                ByteBuffer dst = dsts[idx];
                if (!dst.hasRemaining()) {
                    idx ++;
                    continue;
                }

                int bytesRead = readPlaintextData(dst);

                // TODO: We may want to consider if we move this check and only do it in a less often called place at
                // the price of not being 100% accurate, like for example when calling SSL.getError(...).
                rejectRemoteInitiatedRenegation();

                if (bytesRead > 0) {
                    bytesProduced += bytesRead;

                    if (!dst.hasRemaining()) {
                        idx ++;
                    } else {
                        // We read everything return now.
                        return newResult(bytesConsumed, bytesProduced, status);
                    }
                } else {
                    int sslError = SSL.getError(ssl, bytesRead);
                    switch (sslError) {
                    case SSL.SSL_ERROR_ZERO_RETURN:
                        // This means the connection was shutdown correctly, close inbound and outbound
                        if (!receivedShutdown) {
                            closeAll();
                        }
                        // fall-trough!
                    case SSL.SSL_ERROR_WANT_READ:
                    case SSL.SSL_ERROR_WANT_WRITE:
                        // break to the outer loop
                        return newResult(bytesConsumed, bytesProduced, status);
                    default:
                        return sslReadErrorResult(SSL.getLastErrorNumber(), bytesConsumed, bytesProduced);
                    }
                }
            }
        } else {
            // If the capacity of all destination buffers is 0 we need to trigger a SSL_read anyway to ensure
            // everything is flushed in the BIO pair and so we can detect it in the pendingAppData() call.
            if (SSL.readFromSSL(ssl, EMPTY_ADDR, 0) <= 0) {
                // We do not check SSL_get_error as we are not interested in any error that is not fatal.
                int err = SSL.getLastErrorNumber();
                if (OpenSsl.isError(err)) {
                    return sslReadErrorResult(err, bytesConsumed, bytesProduced);
                }
            }
        }
        if (pendingAppData() > 0) {
            // We filled all buffers but there is still some data pending in the BIO buffer, return BUFFER_OVERFLOW.
            return new SSLEngineResult(
                    BUFFER_OVERFLOW, mayFinishHandshake(status != FINISHED ? getHandshakeStatus(): status),
                    bytesConsumed, bytesProduced);
        }

        // Check to see if we received a close_notify message from the peer.
        if (!receivedShutdown && (SSL.getShutdown(ssl) & SSL.SSL_RECEIVED_SHUTDOWN) == SSL.SSL_RECEIVED_SHUTDOWN) {
            closeAll();
        }

        return newResult(bytesConsumed, bytesProduced, status);
    }

    private SSLEngineResult sslReadErrorResult(int err, int bytesConsumed, int bytesProduced) throws SSLException {
        String errStr = SSL.getErrorString(err);

        // Check if we have a pending handshakeException and if so see if we need to consume all pending data from the
        // BIO first or can just shutdown and throw it now.
        // This is needed so we ensure close_notify etc is correctly send to the remote peer.
        // See https://github.com/netty/netty/issues/3900
        if (SSL.pendingWrittenBytesInBIO(networkBIO) > 0) {
            if (handshakeException == null && handshakeState != HandshakeState.FINISHED) {
                // we seems to have data left that needs to be transfered and so the user needs
                // call wrap(...). Store the error so we can pick it up later.
                handshakeException = new SSLHandshakeException(errStr);
            }
            return new SSLEngineResult(OK, NEED_WRAP, bytesConsumed, bytesProduced);
        }
        throw shutdownWithError("SSL_read", errStr);
    }

    private int pendingAppData() {
        // There won't be any application data until we're done handshaking.
        // We first check handshakeFinished to eliminate the overhead of extra JNI call if possible.
        return handshakeState == HandshakeState.FINISHED ? SSL.pendingReadableBytesInSSL(ssl) : 0;
    }

    private SSLEngineResult newResult(
            int bytesConsumed, int bytesProduced, HandshakeStatus status) throws SSLException {
       return new SSLEngineResult(
               getEngineStatus(), mayFinishHandshake(status != FINISHED ? getHandshakeStatus() : status)
               , bytesConsumed, bytesProduced);
    }

    private void closeAll() throws SSLException {
        receivedShutdown = true;
        closeOutbound();
        closeInbound();
    }

    private void rejectRemoteInitiatedRenegation() throws SSLHandshakeException {
        if (rejectRemoteInitiatedRenegation && SSL.getHandshakeCount(ssl) > 1) {
            // TODO: In future versions me may also want to send a fatal_alert to the client and so notify it
            // that the renegotiation failed.
            shutdown();
            throw new SSLHandshakeException("remote-initiated renegotation not allowed");
        }
    }

    public SSLEngineResult unwrap(final ByteBuffer[] srcs, final ByteBuffer[] dsts) throws SSLException {
        return unwrap(srcs, 0, srcs.length, dsts, 0, dsts.length);
    }

    private ByteBuffer[] singleSrcBuffer(ByteBuffer src) {
        singleSrcBuffer[0] = src;
        return singleSrcBuffer;
    }

    private void resetSingleSrcBuffer() {
        singleSrcBuffer[0] = null;
    }

    private ByteBuffer[] singleDstBuffer(ByteBuffer src) {
        singleDstBuffer[0] = src;
        return singleDstBuffer;
    }

    private void resetSingleDstBuffer() {
        singleDstBuffer[0] = null;
    }

    @Override
    public synchronized SSLEngineResult unwrap(
            final ByteBuffer src, final ByteBuffer[] dsts, final int offset, final int length) throws SSLException {
        try {
            return unwrap(singleSrcBuffer(src), 0, 1, dsts, offset, length);
        } finally {
            resetSingleSrcBuffer();
        }
    }

    @Override
    public synchronized SSLEngineResult wrap(ByteBuffer src, ByteBuffer dst) throws SSLException {
        try {
            return wrap(singleSrcBuffer(src), dst);
        } finally {
            resetSingleSrcBuffer();
        }
    }

    @Override
    public synchronized SSLEngineResult unwrap(ByteBuffer src, ByteBuffer dst) throws SSLException {
        try {
            return unwrap(singleSrcBuffer(src), singleDstBuffer(dst));
        } finally {
            resetSingleSrcBuffer();
            resetSingleDstBuffer();
        }
    }

    @Override
    public synchronized SSLEngineResult unwrap(ByteBuffer src, ByteBuffer[] dsts) throws SSLException {
        try {
            return unwrap(singleSrcBuffer(src), dsts);
        } finally {
            resetSingleSrcBuffer();
        }
    }

    @Override
    public Runnable getDelegatedTask() {
        // Currently, we do not delegate SSL computation tasks
        // TODO: in the future, possibly create tasks to do encrypt / decrypt async

        return null;
    }

    @Override
    public synchronized void closeInbound() throws SSLException {
        if (isInboundDone) {
            return;
        }

        isInboundDone = true;
        engineClosed = true;

        shutdown();

        if (handshakeState != HandshakeState.NOT_STARTED && !receivedShutdown) {
            throw new SSLException(
                    "Inbound closed before receiving peer's close_notify: possible truncation attack?");
        }
    }

    @Override
    public synchronized boolean isInboundDone() {
        return isInboundDone || engineClosed;
    }

    @Override
    public synchronized void closeOutbound() {
        if (isOutboundDone) {
            return;
        }

        isOutboundDone = true;
        engineClosed = true;

        if (handshakeState != HandshakeState.NOT_STARTED && !isDestroyed()) {
            int mode = SSL.getShutdown(ssl);
            if ((mode & SSL.SSL_SENT_SHUTDOWN) != SSL.SSL_SENT_SHUTDOWN) {
                int err = SSL.shutdownSSL(ssl);
                if (err < 0) {
                    int sslErr = SSL.getError(ssl, err);
                    switch (sslErr) {
                    case SSL.SSL_ERROR_NONE:
                    case SSL.SSL_ERROR_WANT_ACCEPT:
                    case SSL.SSL_ERROR_WANT_CONNECT:
                    case SSL.SSL_ERROR_WANT_WRITE:
                    case SSL.SSL_ERROR_WANT_READ:
                    case SSL.SSL_ERROR_WANT_X509_LOOKUP:
                    case SSL.SSL_ERROR_ZERO_RETURN:
                        // Nothing to do here
                        break;
                    case SSL.SSL_ERROR_SYSCALL:
                    case SSL.SSL_ERROR_SSL:
                        if (logger.isDebugEnabled()) {
                            logger.debug("SSL_shutdown failed: OpenSSL error: {}", SSL.getLastError());
                        }
                        // There was an internal error -- shutdown
                        shutdown();
                        break;
                    default:
                        SSL.clearError();
                        break;
                    }
                }
            }
        } else {
            // engine closing before initial handshake
            shutdown();
        }
    }

    @Override
    public synchronized boolean isOutboundDone() {
        return isOutboundDone;
    }

    @Override
    public String[] getSupportedCipherSuites() {
        Set<String> availableCipherSuites = OpenSsl.availableCipherSuites();
        return availableCipherSuites.toArray(new String[availableCipherSuites.size()]);
    }

    @Override
    public String[] getEnabledCipherSuites() {
        final String[] enabled;
        synchronized (this) {
            if (!isDestroyed()) {
                enabled = SSL.getCiphers(ssl);
            } else {
                return EmptyArrays.EMPTY_STRINGS;
            }
        }
        if (enabled == null) {
            return EmptyArrays.EMPTY_STRINGS;
        } else {
            for (int i = 0; i < enabled.length; i++) {
                String mapped = toJavaCipherSuite(enabled[i]);
                if (mapped != null) {
                    enabled[i] = mapped;
                }
            }
            return enabled;
        }
    }

    @Override
    public void setEnabledCipherSuites(String[] cipherSuites) {
        checkNotNull(cipherSuites, "cipherSuites");

        final StringBuilder buf = new StringBuilder();
        for (String c: cipherSuites) {
            if (c == null) {
                break;
            }

            String converted = CipherSuiteConverter.toOpenSsl(c);
            if (converted == null) {
                converted = c;
            }

            if (!OpenSsl.isCipherSuiteAvailable(converted)) {
                throw new IllegalArgumentException("unsupported cipher suite: " + c + '(' + converted + ')');
            }

            buf.append(converted);
            buf.append(':');
        }

        if (buf.length() == 0) {
            throw new IllegalArgumentException("empty cipher suites");
        }
        buf.setLength(buf.length() - 1);

        final String cipherSuiteSpec = buf.toString();

        synchronized (this) {
            if (!isDestroyed()) {
                try {
                    SSL.setCipherSuites(ssl, cipherSuiteSpec);
                } catch (Exception e) {
                    throw new IllegalStateException("failed to enable cipher suites: " + cipherSuiteSpec, e);
                }
            } else {
                throw new IllegalStateException("failed to enable cipher suites: " + cipherSuiteSpec);
            }
        }
    }

    @Override
    public String[] getSupportedProtocols() {
        return SUPPORTED_PROTOCOLS.clone();
    }

    @Override
    public String[] getEnabledProtocols() {
        List<String> enabled = new ArrayList<String>();
        // Seems like there is no way to explict disable SSLv2Hello in openssl so it is always enabled
        enabled.add(PROTOCOL_SSL_V2_HELLO);

        int opts;
        synchronized (this) {
            if (!isDestroyed()) {
                opts = SSL.getOptions(ssl);
            } else {
                return enabled.toArray(new String[1]);
            }
        }
        if ((opts & SSL.SSL_OP_NO_TLSv1) == 0) {
            enabled.add(PROTOCOL_TLS_V1);
        }
        if ((opts & SSL.SSL_OP_NO_TLSv1_1) == 0) {
            enabled.add(PROTOCOL_TLS_V1_1);
        }
        if ((opts & SSL.SSL_OP_NO_TLSv1_2) == 0) {
            enabled.add(PROTOCOL_TLS_V1_2);
        }
        if ((opts & SSL.SSL_OP_NO_SSLv2) == 0) {
            enabled.add(PROTOCOL_SSL_V2);
        }
        if ((opts & SSL.SSL_OP_NO_SSLv3) == 0) {
            enabled.add(PROTOCOL_SSL_V3);
        }
        return enabled.toArray(new String[enabled.size()]);
    }

    @Override
    public void setEnabledProtocols(String[] protocols) {
        if (protocols == null) {
            // This is correct from the API docs
            throw new IllegalArgumentException();
        }
        boolean sslv2 = false;
        boolean sslv3 = false;
        boolean tlsv1 = false;
        boolean tlsv1_1 = false;
        boolean tlsv1_2 = false;
        for (String p: protocols) {
            if (!SUPPORTED_PROTOCOLS_SET.contains(p)) {
                throw new IllegalArgumentException("Protocol " + p + " is not supported.");
            }
            if (p.equals(PROTOCOL_SSL_V2)) {
                sslv2 = true;
            } else if (p.equals(PROTOCOL_SSL_V3)) {
                sslv3 = true;
            } else if (p.equals(PROTOCOL_TLS_V1)) {
                tlsv1 = true;
            } else if (p.equals(PROTOCOL_TLS_V1_1)) {
                tlsv1_1 = true;
            } else if (p.equals(PROTOCOL_TLS_V1_2)) {
                tlsv1_2 = true;
            }
        }
        synchronized (this) {
            if (!isDestroyed()) {
                // Enable all and then disable what we not want
                SSL.setOptions(ssl, SSL.SSL_OP_ALL);

                // Clear out options which disable protocols
                SSL.clearOptions(ssl, SSL.SSL_OP_NO_SSLv2 | SSL.SSL_OP_NO_SSLv3 | SSL.SSL_OP_NO_TLSv1 |
                    SSL.SSL_OP_NO_TLSv1_1 | SSL.SSL_OP_NO_TLSv1_2);

                int opts = 0;
                if (!sslv2) {
                    opts |= SSL.SSL_OP_NO_SSLv2;
                }
                if (!sslv3) {
                    opts |= SSL.SSL_OP_NO_SSLv3;
                }
                if (!tlsv1) {
                    opts |= SSL.SSL_OP_NO_TLSv1;
                }
                if (!tlsv1_1) {
                    opts |= SSL.SSL_OP_NO_TLSv1_1;
                }
                if (!tlsv1_2) {
                    opts |= SSL.SSL_OP_NO_TLSv1_2;
                }

                // Disable protocols we do not want
                SSL.setOptions(ssl, opts);
            } else {
                throw new IllegalStateException("failed to enable protocols: " + Arrays.asList(protocols));
            }
        }
    }

    @Override
    public SSLSession getSession() {
        return session;
    }

    @Override
    public synchronized void beginHandshake() throws SSLException {
        switch (handshakeState) {
            case STARTED_IMPLICITLY:
                checkEngineClosed();

                // A user did not start handshake by calling this method by him/herself,
                // but handshake has been started already by wrap() or unwrap() implicitly.
                // Because it's the user's first time to call this method, it is unfair to
                // raise an exception.  From the user's standpoint, he or she never asked
                // for renegotiation.

                handshakeState = HandshakeState.STARTED_EXPLICITLY; // Next time this method is invoked by the user,
                                                                    // we should raise an exception.
                break;
            case STARTED_EXPLICITLY:
                // Nothing to do as the handshake is not done yet.
                break;
            case FINISHED:
                if (clientMode) {
                    // Only supported for server mode at the moment.
                    throw RENEGOTIATION_UNSUPPORTED;
                }
                // For renegotiate on the server side we need to issue the following command sequence with openssl:
                //
                // SSL_renegotiate(ssl)
                // SSL_do_handshake(ssl)
                // ssl->state = SSL_ST_ACCEPT
                // SSL_do_handshake(ssl)
                //
                // Bcause of this we fall-through to call handshake() after setting the state, as this will also take
                // care of updating the internal OpenSslSession object.
                //
                // See also:
                // https://github.com/apache/httpd/blob/2.4.16/modules/ssl/ssl_engine_kernel.c#L812
                // http://h71000.www7.hp.com/doc/83final/ba554_90007/ch04s03.html
                if (SSL.renegotiate(ssl) != 1 || SSL.doHandshake(ssl) != 1) {
                    throw shutdownWithError("renegotiation failed");
                }

                SSL.setState(ssl, SSL.SSL_ST_ACCEPT);
                // fall-through
            case NOT_STARTED:
                handshakeState = HandshakeState.STARTED_EXPLICITLY;
                handshake();
                break;
            default:
                throw new Error();
        }
    }

    private void checkEngineClosed() throws SSLException {
        if (engineClosed || isDestroyed()) {
            throw ENGINE_CLOSED;
        }
    }

    private static HandshakeStatus pendingStatus(int pendingStatus) {
        // Depending on if there is something left in the BIO we need to WRAP or UNWRAP
        return pendingStatus > 0 ? NEED_WRAP : NEED_UNWRAP;
    }

    private HandshakeStatus handshake() throws SSLException {
        if (handshakeState == HandshakeState.FINISHED) {
            return FINISHED;
        }
        checkEngineClosed();

        // Check if we have a pending handshakeException and if so see if we need to consume all pending data from the
        // BIO first or can just shutdown and throw it now.
        // This is needed so we ensure close_notify etc is correctly send to the remote peer.
        // See https://github.com/netty/netty/issues/3900
        SSLHandshakeException exception = handshakeException;
        if (exception != null) {
            if (SSL.pendingWrittenBytesInBIO(networkBIO) > 0) {
                // There is something pending, we need to consume it first via a WRAP so we not loose anything.
                return NEED_WRAP;
            }
            // No more data left to send to the remote peer, so null out the exception field, shutdown and throw
            // the exception.
            handshakeException = null;
            shutdown();
            throw exception;
        }

        // Adding the OpenSslEngine to the OpenSslEngineMap so it can be used in the AbstractCertificateVerifier.
        engineMap.add(this);

        int code = SSL.doHandshake(ssl);
        if (code <= 0) {
            // Check if we have a pending exception that was created during the handshake and if so throw it after
            // shutdown the connection.
            if (handshakeException != null) {
                exception = handshakeException;
                handshakeException = null;
                shutdown();
                throw exception;
            }

            int sslError = SSL.getError(ssl, code);

            switch (sslError) {
            case SSL.SSL_ERROR_WANT_READ:
            case SSL.SSL_ERROR_WANT_WRITE:
                return pendingStatus(SSL.pendingWrittenBytesInBIO(networkBIO));
            default:
                // Everything else is considered as error
                throw shutdownWithError("SSL_do_handshake");
            }
        }
        // if SSL_do_handshake returns > 0 or sslError == SSL.SSL_ERROR_NAME it means the handshake was finished.
        session.handshakeFinished();
        return FINISHED;
    }

    private static long memoryAddress(ByteBuf buf) {
        if (buf.hasMemoryAddress()) {
            return buf.memoryAddress();
        } else {
            return Buffer.address(buf.nioBuffer());
        }
    }

    private SSLEngineResult.Status getEngineStatus() {
        return engineClosed? CLOSED : OK;
    }

    private SSLEngineResult.HandshakeStatus mayFinishHandshake(SSLEngineResult.HandshakeStatus status)
            throws SSLException {
        if (status == NOT_HANDSHAKING && handshakeState != HandshakeState.FINISHED) {
            // If the status was NOT_HANDSHAKING and we not finished the handshake we need to call
            // SSL_do_handshake() again
            return handshake();
        }
        return status;
    }

    @Override
    public synchronized SSLEngineResult.HandshakeStatus getHandshakeStatus() {
        // Check if we are in the initial handshake phase or shutdown phase
        return needPendingStatus() ? pendingStatus(SSL.pendingWrittenBytesInBIO(networkBIO)) : NOT_HANDSHAKING;
    }

    private SSLEngineResult.HandshakeStatus getHandshakeStatus(int pending) {
        // Check if we are in the initial handshake phase or shutdown phase
        return needPendingStatus() ? pendingStatus(pending) : NOT_HANDSHAKING;
    }

    private boolean needPendingStatus() {
        return handshakeState != HandshakeState.NOT_STARTED && !isDestroyed()
               && (handshakeState != HandshakeState.FINISHED || engineClosed);
    }

    /**
     * Converts the specified OpenSSL cipher suite to the Java cipher suite.
     */
    private String toJavaCipherSuite(String openSslCipherSuite) {
        if (openSslCipherSuite == null) {
            return null;
        }

        String prefix = toJavaCipherSuitePrefix(SSL.getVersion(ssl));
        return CipherSuiteConverter.toJava(openSslCipherSuite, prefix);
    }

    /**
     * Converts the protocol version string returned by {@link SSL#getVersion(long)} to protocol family string.
     */
    private static String toJavaCipherSuitePrefix(String protocolVersion) {
        final char c;
        if (protocolVersion == null || protocolVersion.length() == 0) {
            c = 0;
        } else {
            c = protocolVersion.charAt(0);
        }

        switch (c) {
        case 'T':
            return "TLS";
        case 'S':
            return "SSL";
        default:
            return "UNKNOWN";
        }
    }

    @Override
    public void setUseClientMode(boolean clientMode) {
        if (clientMode != this.clientMode) {
            throw new UnsupportedOperationException();
        }
    }

    @Override
    public boolean getUseClientMode() {
        return clientMode;
    }

    @Override
    public void setNeedClientAuth(boolean b) {
        setClientAuth(b ? ClientAuth.REQUIRE : ClientAuth.NONE);
    }

    @Override
    public boolean getNeedClientAuth() {
        return clientAuth == ClientAuth.REQUIRE;
    }

    @Override
    public void setWantClientAuth(boolean b) {
        setClientAuth(b ? ClientAuth.OPTIONAL : ClientAuth.NONE);
    }

    @Override
    public boolean getWantClientAuth() {
        return clientAuth == ClientAuth.OPTIONAL;
    }

    private void setClientAuth(ClientAuth mode) {
        if (clientMode) {
            return;
        }
        synchronized (this) {
            if (clientAuth == mode) {
                // No need to issue any JNI calls if the mode is the same
                return;
            }
            switch (mode) {
                case NONE:
                    SSL.setVerify(ssl, SSL.SSL_CVERIFY_NONE, OpenSslContext.VERIFY_DEPTH);
                    break;
                case REQUIRE:
                    SSL.setVerify(ssl, SSL.SSL_CVERIFY_REQUIRE, OpenSslContext.VERIFY_DEPTH);
                    break;
                case OPTIONAL:
                    SSL.setVerify(ssl, SSL.SSL_CVERIFY_OPTIONAL, OpenSslContext.VERIFY_DEPTH);
                    break;
            }
            clientAuth = mode;
        }
    }

    @Override
    public void setEnableSessionCreation(boolean b) {
        if (b) {
            throw new UnsupportedOperationException();
        }
    }

    @Override
    public boolean getEnableSessionCreation() {
        return false;
    }

    @Override
    public SSLParameters getSSLParameters() {
        SSLParameters sslParameters = super.getSSLParameters();

        if (PlatformDependent.javaVersion() >= 7) {
            sslParameters.setEndpointIdentificationAlgorithm(endPointIdentificationAlgorithm);
            SslParametersUtils.setAlgorithmConstraints(sslParameters, algorithmConstraints);
        }
        return sslParameters;
    }

    @Override
    public void setSSLParameters(SSLParameters sslParameters) {
        super.setSSLParameters(sslParameters);

        if (PlatformDependent.javaVersion() >= 7) {
            endPointIdentificationAlgorithm = sslParameters.getEndpointIdentificationAlgorithm();
            algorithmConstraints = sslParameters.getAlgorithmConstraints();
        }
    }

    @Override
    @SuppressWarnings("FinalizeDeclaration")
    protected void finalize() throws Throwable {
        super.finalize();
        // Call shutdown as the user may have created the OpenSslEngine and not used it at all.
        shutdown();
    }

    private boolean isDestroyed() {
        return destroyed != 0;
    }

    private final class OpenSslSession implements SSLSession, ApplicationProtocolAccessor {
        private final OpenSslSessionContext sessionContext;

        // These are guarded by synchronized(OpenSslEngine.this) as handshakeFinished() may be triggered by any
        // thread.
        private X509Certificate[] x509PeerCerts;
        private String protocol;
        private String applicationProtocol;
        private Certificate[] peerCerts;
        private String cipher;
        private byte[] id;
        private long creationTime;

        // lazy init for memory reasons
        private Map<String, Object> values;

        OpenSslSession(OpenSslSessionContext sessionContext) {
            this.sessionContext = sessionContext;
        }

        @Override
        public byte[] getId() {
            synchronized (OpenSslEngine.this) {
                if (id == null) {
                    return EmptyArrays.EMPTY_BYTES;
                }
                return id.clone();
            }
        }

        @Override
        public SSLSessionContext getSessionContext() {
            return sessionContext;
        }

        @Override
        public long getCreationTime() {
            synchronized (OpenSslEngine.this) {
                if (creationTime == 0 && !isDestroyed()) {
                    creationTime = SSL.getTime(ssl) * 1000L;
                }
            }
            return creationTime;
        }

        @Override
        public long getLastAccessedTime() {
            // TODO: Add proper implementation
            return getCreationTime();
        }

        @Override
        public void invalidate() {
            synchronized (OpenSslEngine.this) {
                if (!isDestroyed()) {
                    SSL.setTimeout(ssl, 0);
                }
            }
        }

        @Override
        public boolean isValid() {
            synchronized (OpenSslEngine.this) {
                if (!isDestroyed()) {
                    return System.currentTimeMillis() - (SSL.getTimeout(ssl) * 1000L) < (SSL.getTime(ssl) * 1000L);
                }
            }
            return false;
        }

        @Override
        public void putValue(String name, Object value) {
            if (name == null) {
                throw new NullPointerException("name");
            }
            if (value == null) {
                throw new NullPointerException("value");
            }
            Map<String, Object> values = this.values;
            if (values == null) {
                // Use size of 2 to keep the memory overhead small
                values = this.values = new HashMap<String, Object>(2);
            }
            Object old = values.put(name, value);
            if (value instanceof SSLSessionBindingListener) {
                ((SSLSessionBindingListener) value).valueBound(new SSLSessionBindingEvent(this, name));
            }
            notifyUnbound(old, name);
        }

        @Override
        public Object getValue(String name) {
            if (name == null) {
                throw new NullPointerException("name");
            }
            if (values == null) {
                return null;
            }
            return values.get(name);
        }

        @Override
        public void removeValue(String name) {
            if (name == null) {
                throw new NullPointerException("name");
            }
            Map<String, Object> values = this.values;
            if (values == null) {
                return;
            }
            Object old = values.remove(name);
            notifyUnbound(old, name);
        }

        @Override
        public String[] getValueNames() {
            Map<String, Object> values = this.values;
            if (values == null || values.isEmpty()) {
                return EmptyArrays.EMPTY_STRINGS;
            }
            return values.keySet().toArray(new String[values.size()]);
        }

        private void notifyUnbound(Object value, String name) {
            if (value instanceof SSLSessionBindingListener) {
                ((SSLSessionBindingListener) value).valueUnbound(new SSLSessionBindingEvent(this, name));
            }
        }

        /**
         * Finish the handshake and so init everything in the {@link OpenSslSession} that should be accessable by
         * the user.
         */
        void handshakeFinished() throws SSLException {
            synchronized (OpenSslEngine.this) {
                if (!isDestroyed()) {
                    id = SSL.getSessionId(ssl);
                    cipher = toJavaCipherSuite(SSL.getCipherForSSL(ssl));
                    protocol = SSL.getVersion(ssl);

                    initPeerCerts();
                    selectApplicationProtocol();

                    handshakeState = HandshakeState.FINISHED;
                } else {
                    throw new SSLException("Already closed");
                }
            }
        }

        /**
         * Init peer certificates that can be obtained via {@link #getPeerCertificateChain()}
         * and {@link #getPeerCertificates()}.
         */
        private void initPeerCerts() {
            // Return the full chain from the JNI layer.
            byte[][] chain = SSL.getPeerCertChain(ssl);
            final byte[] clientCert;
            if (!clientMode) {
                // if used on the server side SSL_get_peer_cert_chain(...) will not include the remote peer
                // certificate. We use SSL_get_peer_certificate to get it in this case and add it to our
                // array later.
                //
                // See https://www.openssl.org/docs/ssl/SSL_get_peer_cert_chain.html
                clientCert = SSL.getPeerCertificate(ssl);
            } else {
                clientCert = null;
            }

            if (chain == null && clientCert == null) {
                peerCerts = EMPTY_CERTIFICATES;
                x509PeerCerts = EMPTY_X509_CERTIFICATES;
            } else {
                int len = chain != null ? chain.length : 0;

                int i = 0;
                Certificate[] peerCerts;
                if (clientCert != null) {
                    len++;
                    peerCerts = new Certificate[len];
                    peerCerts[i++] = new OpenSslX509Certificate(clientCert);
                } else {
                    peerCerts = new Certificate[len];
                }
                if (chain != null) {
                    X509Certificate[] pCerts = new X509Certificate[chain.length];

                    for (int a = 0; a < pCerts.length; ++i, ++a) {
                        byte[] bytes = chain[a];
                        pCerts[a] = new OpenSslJavaxX509Certificate(bytes);
                        peerCerts[i] = new OpenSslX509Certificate(bytes);
                    }
                    x509PeerCerts = pCerts;
                } else {
                    x509PeerCerts = EMPTY_X509_CERTIFICATES;
                }
                this.peerCerts = peerCerts;
            }
        }

        /**
         * Select the application protocol used.
         */
        private void selectApplicationProtocol() throws SSLException {
            SelectedListenerFailureBehavior behavior = apn.selectedListenerFailureBehavior();
            List<String> protocols = apn.protocols();
            String applicationProtocol;
            switch (apn.protocol()) {
            case NONE:
                break;
            // We always need to check for applicationProtocol == null as the remote peer may not support
            // the TLS extension or may have returned an empty selection.
            case ALPN:
                applicationProtocol = SSL.getAlpnSelected(ssl);
                if (applicationProtocol != null) {
                    this.applicationProtocol = selectApplicationProtocol(
                            protocols, behavior, applicationProtocol);
                }
                break;
            case NPN:
                applicationProtocol = SSL.getNextProtoNegotiated(ssl);
                if (applicationProtocol != null) {
                    this.applicationProtocol = selectApplicationProtocol(
                            protocols, behavior, applicationProtocol);
                }
                break;
            case NPN_AND_ALPN:
                applicationProtocol = SSL.getAlpnSelected(ssl);
                if (applicationProtocol == null) {
                    applicationProtocol = SSL.getNextProtoNegotiated(ssl);
                }
                if (applicationProtocol != null) {
                    this.applicationProtocol = selectApplicationProtocol(
                            protocols, behavior, applicationProtocol);
                }
                break;
            default:
                throw new Error();
            }
        }

        private String selectApplicationProtocol(List<String> protocols,
                                                        SelectedListenerFailureBehavior behavior,
                                                        String applicationProtocol) throws SSLException {
            if (behavior == SelectedListenerFailureBehavior.ACCEPT) {
                return applicationProtocol;
            } else {
                int size = protocols.size();
                assert size > 0;
                if (protocols.contains(applicationProtocol)) {
                    return applicationProtocol;
                } else {
                    if (behavior == SelectedListenerFailureBehavior.CHOOSE_MY_LAST_PROTOCOL) {
                        return protocols.get(size - 1);
                    } else {
                        throw new SSLException("unknown protocol " + applicationProtocol);
                    }
                }
            }
        }

        @Override
        public Certificate[] getPeerCertificates() throws SSLPeerUnverifiedException {
            synchronized (OpenSslEngine.this) {
                if (peerCerts == null || peerCerts.length == 0) {
                    throw new SSLPeerUnverifiedException("peer not verified");
                }
                return peerCerts;
            }
        }

        @Override
        public Certificate[] getLocalCertificates() {
            if (localCerts == null) {
                return null;
            }
            return localCerts.clone();
        }

        @Override
        public X509Certificate[] getPeerCertificateChain() throws SSLPeerUnverifiedException {
            synchronized (OpenSslEngine.this) {
                if (x509PeerCerts == null || x509PeerCerts.length == 0) {
                    throw new SSLPeerUnverifiedException("peer not verified");
                }
                return x509PeerCerts;
            }
        }

        @Override
        public Principal getPeerPrincipal() throws SSLPeerUnverifiedException {
            Certificate[] peer = getPeerCertificates();
            // No need for null or length > 0 is needed as this is done in getPeerCertificates()
            // already.
            return ((java.security.cert.X509Certificate) peer[0]).getSubjectX500Principal();
        }

        @Override
        public Principal getLocalPrincipal() {
            Certificate[] local = localCerts;
            if (local == null || local.length == 0) {
                return null;
            }
            return ((java.security.cert.X509Certificate) local[0]).getIssuerX500Principal();
        }

        @Override
        public String getCipherSuite() {
            synchronized (OpenSslEngine.this) {
                if (cipher == null) {
                    return INVALID_CIPHER;
                }
                return cipher;
            }
        }

        @Override
        public String getProtocol() {
            String protocol = this.protocol;
            if (protocol == null) {
                synchronized (OpenSslEngine.this) {
                    if (!isDestroyed()) {
                        protocol = SSL.getVersion(ssl);
                    } else {
                        protocol = StringUtil.EMPTY_STRING;
                    }
                }
            }
            return protocol;
        }

        @Override
        public String getApplicationProtocol() {
            synchronized (OpenSslEngine.this) {
                return applicationProtocol;
            }
        }

        @Override
        public String getPeerHost() {
            return OpenSslEngine.this.getPeerHost();
        }

        @Override
        public int getPeerPort() {
            return OpenSslEngine.this.getPeerPort();
        }

        @Override
        public int getPacketBufferSize() {
            return MAX_ENCRYPTED_PACKET_LENGTH;
        }

        @Override
        public int getApplicationBufferSize() {
            return MAX_PLAINTEXT_LENGTH;
        }
    }
}
