/**
 * Copyright 2007-2016, Kaazing Corporation. All rights reserved.
 *
 * Licensed 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 org.kaazing.gateway.transport.ssl.bridge.filter;

import java.net.InetSocketAddress;
import java.util.ArrayList;
import java.util.List;

import javax.net.ssl.SSLContext;
import javax.net.ssl.SSLEngine;
import javax.net.ssl.SSLException;
import javax.net.ssl.SSLHandshakeException;
import javax.net.ssl.SSLSession;

import org.apache.mina.core.buffer.IoBuffer;
import org.apache.mina.core.filterchain.IoFilterAdapter;
import org.apache.mina.core.filterchain.IoFilterChain;
import org.apache.mina.core.future.DefaultWriteFuture;
import org.apache.mina.core.future.IoFuture;
import org.apache.mina.core.future.IoFutureListener;
import org.apache.mina.core.future.WriteFuture;
import org.apache.mina.core.service.IoHandler;
import org.apache.mina.core.session.AttributeKey;
import org.apache.mina.core.session.IoSession;
import org.apache.mina.core.write.WriteRequest;
import org.apache.mina.core.write.WriteRequestWrapper;
import org.apache.mina.core.write.WriteToClosedSessionException;
import org.slf4j.Logger;

import org.kaazing.mina.core.session.AbstractIoSessionEx;
import org.kaazing.mina.core.session.IoSessionEx;

/**
 * An SSL filter that encrypts and decrypts the data exchanged in the session.
 * Adding this filter triggers SSL handshake procedure immediately by sending
 * a SSL 'hello' message, so you don't need to call
 * {@link #startSsl(IoSession)} manually unless you are implementing StartTLS
 * (see below).  If you don't want the handshake procedure to start
 * immediately, please specify {@code false} as {@code autoStart} parameter in
 * the constructor.
 * <p>
 * This filter uses an {@link SSLEngine} which was introduced in Java 5, so
 * Java version 5 or above is mandatory to use this filter. And please note that
 * this filter only works for TCP/IP connections.
 * <p>
 *
 * <h2>Implementing StartTLS</h2>
 * <p>
 * You can use {@link #DISABLE_ENCRYPTION_ONCE} attribute to implement StartTLS:
 * <pre>
 * public void messageReceived(IoSession session, Object message) {
 *    if (message instanceof MyStartTLSRequest) {
 *        // Insert SSLFilter to get ready for handshaking
 *        session.getFilterChain().addFirst(sslFilter);
 *
 *        // Disable encryption temporarilly.
 *        // This attribute will be removed by SSLFilter
 *        // inside the Session.write() call below.
 *        session.setAttribute(SSLFilter.DISABLE_ENCRYPTION_ONCE, Boolean.TRUE);
 *
 *        // Write StartTLSResponse which won't be encrypted.
 *        session.write(new MyStartTLSResponse(OK));
 *
 *        // Now DISABLE_ENCRYPTION_ONCE attribute is cleared.
 *        assert session.getAttribute(SSLFilter.DISABLE_ENCRYPTION_ONCE) == null;
 *    }
 * }
 * </pre>
 *
 * @author <a href="http://mina.apache.org">Apache MINA Project</a>
 * @org.apache.xbean.XBean
 */
public class SslFilter extends IoFilterAdapter {
    /**
     * A session attribute key that stores underlying {@link SSLSession}
     * for each session.
     */
    public static final AttributeKey SSL_SESSION = new AttributeKey(SslFilter.class, "session");

    /**
     * A session attribute key that makes next one write request bypass
     * this filter (not encrypting the data).  This is a marker attribute,
     * which means that you can put whatever as its value. ({@link Boolean#TRUE}
     * is preferred.)  The attribute is automatically removed from the session
     * attribute map as soon as {@link IoSession#write(Object)} is invoked,
     * and therefore should be put again if you want to make more messages
     * bypass this filter.  This is especially useful when you implement
     * StartTLS.
     */
    public static final AttributeKey DISABLE_ENCRYPTION_ONCE = new AttributeKey(SslFilter.class, "disableOnce");

    /**
     * A session attribute key that makes this filter to emit a
     * {@link IoHandler#messageReceived(IoSession, Object)} event with a
     * special message ({@link #SESSION_SECURED} or {@link #SESSION_UNSECURED}).
     * This is a marker attribute, which means that you can put whatever as its
     * value. ({@link Boolean#TRUE} is preferred.)  By default, this filter
     * doesn't emit any events related with SSL session flow control.
     */
    public static final AttributeKey USE_NOTIFICATION = new AttributeKey(SslFilter.class, "useNotification");

    /**
     * A session attribute key that should be set to an {@link InetSocketAddress}.
     * Setting this attribute causes
     * {@link SSLContext#createSSLEngine(String, int)} to be called passing the
     * hostname and port of the {@link InetSocketAddress} to get an
     * {@link SSLEngine} instance. If not set {@link SSLContext#createSSLEngine()}
     * will be called.<br/>
     * Using this feature {@link SSLSession} objects may be cached and reused
     * when in client mode.
     *
     * @see SSLContext#createSSLEngine(String, int)
     */
    public static final AttributeKey PEER_ADDRESS = new AttributeKey(SslFilter.class, "peerAddress");

    /**
     * A special message object which is emitted with a {@link IoHandler#messageReceived(IoSession, Object)}
     * event when the session is secured and its {@link #USE_NOTIFICATION}
     * attribute is set.
     */
    public static final SslFilterMessage SESSION_SECURED = new SslFilterMessage(
            "SESSION_SECURED");

    /**
     * A special message object which is emitted with a {@link IoHandler#messageReceived(IoSession, Object)}
     * event when the session is not secure anymore and its {@link #USE_NOTIFICATION}
     * attribute is set.
     */
    public static final SslFilterMessage SESSION_UNSECURED = new SslFilterMessage(
            "SESSION_UNSECURED");

    private static final AttributeKey NEXT_FILTER = new AttributeKey(SslFilter.class, "nextFilter");
    private static final AttributeKey SSL_HANDLER = new AttributeKey(SslFilter.class, "handler");

    /** The SslContext used */
    private final SSLContext sslContext;

    /** A flag used to tell the filter to start the handshake immediately */
    private final boolean autoStart;
   
    private final Logger logger;
 
    /** A flag used to determinate if the handshake should start immediately */
    private static final boolean START_HANDSHAKE = true;

    private boolean client;

    private boolean needClientAuth;

    private boolean wantClientAuth;

    private String[] enabledCipherSuites;

    private String[] enabledProtocols;

    /**
     * Creates a new SSL filter using the specified {@link SSLContext}.
     * The handshake will start immediately.
     */
    public SslFilter(SSLContext sslContext, Logger logger) {
        this(sslContext, START_HANDSHAKE, logger);
    }

    /**
     * Creates a new SSL filter using the specified {@link SSLContext}.
     * If the <code>autostart</code> flag is set to <code>true</code>, the
     * handshake will start immediately.
     */
    public SslFilter(SSLContext sslContext, boolean autoStart, Logger logger) {
        if (sslContext == null) {
            throw new NullPointerException("sslContext");
        }

        this.sslContext = sslContext;
        this.autoStart = autoStart;
        this.logger = logger;
    }

    /**
     * Returns the underlying {@link SSLSession} for the specified session.
     *
     * @return <tt>null</tt> if no {@link SSLSession} is initialized yet.
     */
    public SSLSession getSslSession(IoSession session) {
        return (SSLSession) session.getAttribute(SSL_SESSION);
    }

    /**
     * (Re)starts SSL session for the specified <tt>session</tt> if not started yet.
     * Please note that SSL session is automatically started by default, and therefore
     * you don't need to call this method unless you've used TLS closure.
     *
     * @return <tt>true</tt> if the SSL session has been started, <tt>false</tt> if already started.
     * @throws SSLException if failed to start the SSL session
     */
    public boolean startSsl(IoSession session) throws SSLException {
        SslHandler handler = getSslSessionHandler(session);
        boolean started;
        synchronized (handler) {
            if (handler.isOutboundDone()) {
                NextFilter nextFilter = (NextFilter) session
                        .getAttribute(NEXT_FILTER);
                handler.destroy();
                handler.init();
                handler.handshake(nextFilter);
                started = true;
            } else {
                started = false;
            }
        }

        handler.flushScheduledEvents();
        return started;
    }

    /**
     * Returns <tt>true</tt> if and only if the specified <tt>session</tt> is
     * encrypted/decrypted over SSL/TLS currently.  This method will start
     * to retun <tt>false</tt> after TLS <tt>close_notify</tt> message
     * is sent and any messages written after then is not goinf to get encrypted.
     */
    public boolean isSslStarted(IoSession session) {
        SslHandler handler = (SslHandler) session.getAttribute(SSL_HANDLER);
        
        if (handler == null) {
            return false;
        }

        synchronized (handler) {
            return !handler.isOutboundDone();
        }
    }

    /**
     * Stops the SSL session by sending TLS <tt>close_notify</tt> message to
     * initiate TLS closure.
     *
     * @param session the {@link IoSession} to initiate TLS closure
     * @throws SSLException if failed to initiate TLS closure
     * @throws IllegalArgumentException if this filter is not managing the specified session
     */
    public WriteFuture stopSsl(IoSession session) throws SSLException {
        SslHandler handler = getSslSessionHandler(session);
        NextFilter nextFilter = (NextFilter) session.getAttribute(NEXT_FILTER);
        WriteFuture future;
        synchronized (handler) {
            future = initiateClosure(nextFilter, session);
        }

        handler.flushScheduledEvents();

        return future;
    }

    /**
     * Returns <tt>true</tt> if the engine is set to use client mode
     * when handshaking.
     */
    public boolean isUseClientMode() {
        return client;
    }

    /**
     * Configures the engine to use client (or server) mode when handshaking.
     */
    public void setUseClientMode(boolean clientMode) {
        this.client = clientMode;
    }

    /**
     * Returns <tt>true</tt> if the engine will <em>require</em> client authentication.
     * This option is only useful to engines in the server mode.
     */
    public boolean isNeedClientAuth() {
        return needClientAuth;
    }

    /**
     * Configures the engine to <em>require</em> client authentication.
     * This option is only useful for engines in the server mode.
     */
    public void setNeedClientAuth(boolean needClientAuth) {
        this.needClientAuth = needClientAuth;
    }

    /**
     * Returns <tt>true</tt> if the engine will <em>request</em> client authentication.
     * This option is only useful to engines in the server mode.
     */
    public boolean isWantClientAuth() {
        return wantClientAuth;
    }

    /**
     * Configures the engine to <em>request</em> client authentication.
     * This option is only useful for engines in the server mode.
     */
    public void setWantClientAuth(boolean wantClientAuth) {
        this.wantClientAuth = wantClientAuth;
    }

    /**
     * Returns the list of cipher suites to be enabled when {@link SSLEngine}
     * is initialized.
     *
     * @return <tt>null</tt> means 'use {@link SSLEngine}'s default.'
     */
    public String[] getEnabledCipherSuites() {
        return enabledCipherSuites;
    }

    /**
     * Sets the list of cipher suites to be enabled when {@link SSLEngine}
     * is initialized.
     *
     * @param cipherSuites <tt>null</tt> means 'use {@link SSLEngine}'s default.'
     */
    public void setEnabledCipherSuites(String[] cipherSuites) {
        this.enabledCipherSuites = cipherSuites;
    }

    /**
     * Returns the list of protocols to be enabled when {@link SSLEngine}
     * is initialized.
     *
     * @return <tt>null</tt> means 'use {@link SSLEngine}'s default.'
     */
    public String[] getEnabledProtocols() {
        return enabledProtocols;
    }

    /**
     * Sets the list of protocols to be enabled when {@link SSLEngine}
     * is initialized.
     *
     * @param protocols <tt>null</tt> means 'use {@link SSLEngine}'s default.'
     */
    public void setEnabledProtocols(String[] protocols) {
        this.enabledProtocols = protocols;
    }

    @Override
    public void onPreAdd(IoFilterChain parent, String name,
            NextFilter nextFilter) throws SSLException {
        if (parent.contains(SslFilter.class)) {
            throw new IllegalStateException(
                    "Only one " + SslFilter.class.getName() + " is permitted.");
        }

        IoSession session = parent.getSession();
        session.setAttribute(NEXT_FILTER, nextFilter);

        // Create an SSL handler and start handshake.
        SslHandler handler = new SslHandler(this, sslContext, (IoSessionEx) session, logger);
        session.setAttribute(SSL_HANDLER, handler);
    }

    @Override
    public void onPostAdd(IoFilterChain parent, String name,
            NextFilter nextFilter) throws SSLException {
        if (autoStart) {
            initiateHandshake(nextFilter, parent.getSession());
        }
    }

    @Override
    public void onPreRemove(IoFilterChain parent, String name,
            NextFilter nextFilter) throws SSLException {
        IoSession session = parent.getSession();
        stopSsl(session);
        session.removeAttribute(NEXT_FILTER);
        session.removeAttribute(SSL_HANDLER);
    }

    // IoFilter impl.
    @Override
    public void sessionClosed(NextFilter nextFilter, IoSession session)
            throws SSLException {
        SslHandler handler = getSslSessionHandler(session);
        try {
            synchronized (handler) {
                // release resources
                handler.destroy();
            }

            handler.flushScheduledEvents();
        } finally {
            // notify closed session
            nextFilter.sessionClosed(session);
        }
    }

    @Override
    public void messageReceived(NextFilter nextFilter, IoSession session,
            Object message) throws SSLException {
        SslHandler handler = getSslSessionHandler(session);
        synchronized (handler) {
            if (!isSslStarted(session) && handler.isInboundDone()) {
                handler.scheduleMessageReceived(nextFilter, message);
            } else {
                IoBuffer buf = (IoBuffer) message;
                try {
                    // We set this lookup key on a per-message basis, in
                    // order to be prepared for handling a renegotiation,
                    // which could be triggered by this message.  As soon as
                    // we are done, we set the cached "current session" back
                    // to null for this thread, in preparation of handling
                    // other messages/requests.
                    SslCertificateSelectionFilter.setCurrentSession(session, isUseClientMode());

                    // forward read encrypted data to SSL handler
                    handler.messageReceived(nextFilter, buf.buf());
                    SslCertificateSelectionFilter.setCurrentSession(null, isUseClientMode());

                    // Handle data to be forwarded to application or written to net
                    handleSslData(nextFilter, handler);

                    if (handler.isInboundDone()) {
                        if (handler.isOutboundDone()) {
                            handler.destroy();
                        } else {
                            initiateClosure(nextFilter, session);
                        }

                        if (buf.hasRemaining()) {
                            // Forward the data received after closure.
                            handler.scheduleMessageReceived(nextFilter, buf);
                        }
                    }
                } catch (SSLException ssle) {
                    if (!handler.isHandshakeComplete()) {
                        SSLException newSsle = new SSLHandshakeException(
                            "SSL handshake failed.");
                        newSsle.initCause(ssle);
                        ssle = newSsle;
                    }

                    throw ssle;
                } finally {
                    // This is a paranoid failsafe check to ensure that
                    // the cached "current session" is ALWAYS nulled out;
                    // we are not sure when an exception might be thrown.
                    SslCertificateSelectionFilter.setCurrentSession(null, isUseClientMode());
                }
            }
        }

        handler.flushScheduledEvents();
    }

    @Override
    public void messageSent(NextFilter nextFilter, IoSession session,
            WriteRequest writeRequest) {
        if (writeRequest instanceof EncryptedWriteRequest) {
            EncryptedWriteRequest wrappedRequest = (EncryptedWriteRequest) writeRequest;
            nextFilter.messageSent(session, wrappedRequest.getParentRequest());
        } else if (writeRequest == AbstractIoSessionEx.REGISTERED_EVENT) {
            // Session has been realigned, need to reset NEXT_FILTER so it has the new filter chain for the new IO thread
            session.setAttribute(NEXT_FILTER, nextFilter);
        } else {
            // ignore extra buffers used for handshaking
        }
    }

    @Override
    public void exceptionCaught(NextFilter nextFilter, IoSession session,
            Throwable cause) throws Exception {

        if (cause instanceof WriteToClosedSessionException) {
            // Filter out SSL close notify, which is likely to fail to flush
            // due to disconnection.
            WriteToClosedSessionException e = (WriteToClosedSessionException) cause;
            List<WriteRequest> failedRequests = e.getRequests();
            boolean containsCloseNotify = false;
            for (WriteRequest r: failedRequests) {
                if (isCloseNotify(r.getMessage())) {
                    containsCloseNotify = true;
                    break;
                }
            }
            
            if (containsCloseNotify) {
                if (failedRequests.size() == 1) {
                    // close notify is the only failed request; bail out.
                    return;
                }
                
                List<WriteRequest> newFailedRequests =
                    new ArrayList<>(failedRequests.size() - 1);
                for (WriteRequest r: failedRequests) {
                    if (!isCloseNotify(r.getMessage())) {
                        newFailedRequests.add(r);
                    }
                }
                
                if (newFailedRequests.isEmpty()) {
                    // the failedRequests were full with close notify; bail out.
                    return;
                }
                
                cause = new WriteToClosedSessionException(
                        newFailedRequests, cause.getMessage(), cause.getCause());
            }
        }
        
        nextFilter.exceptionCaught(session, cause);
    }
        
    private boolean isCloseNotify(Object message) {
        if (!(message instanceof IoBuffer)) {
            return false;
        }
        
        IoBuffer buf = (IoBuffer) message;
        int offset = buf.position();
        return buf.remaining() == 23 &&
               buf.get(offset + 0) == 0x15 && buf.get(offset + 1) == 0x03 &&
               buf.get(offset + 2) == 0x01 && buf.get(offset + 3) == 0x00 &&
               buf.get(offset + 4) == 0x12;
    }

    @Override
    public void filterWrite(NextFilter nextFilter, IoSession session,
            WriteRequest writeRequest) throws SSLException {
        boolean needsFlush = true;
        SslHandler handler = getSslSessionHandler(session);
        synchronized (handler) {
            if (!isSslStarted(session)) {
                handler.scheduleFilterWrite(nextFilter,
                        writeRequest);
            }
            // Don't encrypt the data if encryption is disabled.
            else if (session.containsAttribute(DISABLE_ENCRYPTION_ONCE)) {
                // Remove the marker attribute because it is temporary.
                session.removeAttribute(DISABLE_ENCRYPTION_ONCE);
                handler.scheduleFilterWrite(nextFilter,
                        writeRequest);
            } else {
                // Otherwise, encrypt the buffer.
                IoBuffer buf = (IoBuffer) writeRequest.getMessage();

                if (handler.isWritingEncryptedData()) {
                    // data already encrypted; simply return buffer
                    handler.scheduleFilterWrite(nextFilter, writeRequest);
                } else if (handler.isHandshakeComplete()) {
                    // SSL encrypt
                    int pos = buf.position();
                    handler.encrypt(buf.buf());
                    buf.position(pos);
                    IoBuffer encryptedBuffer = handler.fetchOutNetBuffer();
                    handler.scheduleFilterWrite(
                            nextFilter,
                            new EncryptedWriteRequest(
                                    writeRequest, encryptedBuffer));
                } else {
                    if (session.isConnected()) {
                        // Handshake not complete yet.
                        handler.schedulePreHandshakeWriteRequest(nextFilter,
                                writeRequest);
                    }
                    needsFlush = false;
                }
            }
        }

        if (needsFlush) {
            handler.flushScheduledEvents();
        }
    }

    @Override
    public void filterClose(final NextFilter nextFilter, final IoSession session)
            throws SSLException {
        SslHandler handler = (SslHandler) session.getAttribute(SSL_HANDLER);
        if (handler == null) {
            // The connection might already have closed, or
            // SSL might have not started yet.
            nextFilter.filterClose(session);
            return;
        }

        WriteFuture future = null;
        try {
            synchronized (handler) {
                if (isSslStarted(session)) {
                    future = initiateClosure(nextFilter, session);
                    future.addListener(new IoFutureListener<IoFuture>() {
                        @Override
                        public void operationComplete(IoFuture future) {
                            nextFilter.filterClose(session);
                        }
                    });
                }
            }

            handler.flushScheduledEvents();
        } finally {
            if (future == null) {
                nextFilter.filterClose(session);
            }
        }
    }

    private void initiateHandshake(NextFilter nextFilter, IoSession session)
            throws SSLException {
        SslHandler handler = getSslSessionHandler(session);
        
        synchronized (handler) {
            handler.handshake(nextFilter);
        }
        
        handler.flushScheduledEvents();
    }

    private WriteFuture initiateClosure(NextFilter nextFilter, IoSession session)
            throws SSLException {
        SslHandler handler = getSslSessionHandler(session);
        // if already shut down
        if (!handler.closeOutbound()) {
            return DefaultWriteFuture.newNotWrittenFuture(
                    session, new IllegalStateException("SSL session is shut down already."));
        }

        // there might be data to write out here?
        WriteFuture future = handler.writeNetBuffer(nextFilter);
        if (future == null) {
            future = DefaultWriteFuture.newWrittenFuture(session);
        }

        if (handler.isInboundDone()) {
            handler.destroy();
        }

        if (session.containsAttribute(USE_NOTIFICATION)) {
            handler.scheduleMessageReceived(nextFilter, SESSION_UNSECURED);
        }

        return future;
    }

    // Utiliities

    private void handleSslData(NextFilter nextFilter, SslHandler handler)
            throws SSLException {
        // Flush any buffered write requests occurred before handshaking.
        if (handler.isHandshakeComplete()) {
            handler.flushPreHandshakeEvents();
        }

        // Write encrypted data to be written (if any)
        handler.writeNetBuffer(nextFilter);

        // handle app. data read (if any)
        handleAppDataRead(nextFilter, handler);
    }

    private void handleAppDataRead(NextFilter nextFilter, SslHandler handler) {
        // forward read app data
        IoBuffer readBuffer = handler.fetchAppBuffer();
        if (readBuffer.hasRemaining()) {
            handler.scheduleMessageReceived(nextFilter, readBuffer);
        }
    }

    private SslHandler getSslSessionHandler(IoSession session) {
        SslHandler handler = (SslHandler) session.getAttribute(SSL_HANDLER);
        
        if (handler == null) {
            throw new IllegalStateException();
        }
        
        if (handler.getParent() != this) {
            throw new IllegalArgumentException("Not managed by this filter.");
        }
        
        return handler;
    }

    /**
     * A message that is sent from {@link SslFilter} when the connection became
     * secure or is not secure anymore.
     *
     * @author <a href="http://mina.apache.org">Apache MINA Project</a>
     */
    public static class SslFilterMessage {
        private final String name;

        private SslFilterMessage(String name) {
            this.name = name;
        }

        @Override
        public String toString() {
            return name;
        }
    }

    private static class EncryptedWriteRequest extends WriteRequestWrapper {
        private final IoBuffer encryptedMessage;

        private EncryptedWriteRequest(WriteRequest writeRequest,
                IoBuffer encryptedMessage) {
            super(writeRequest);
            this.encryptedMessage = encryptedMessage;
        }

        @Override
        public Object getMessage() {
            return encryptedMessage;
        }
    }
}

