/*
    *  Licensed to the Apache Software Foundation (ASF) under one
    *  or more contributor license agreements.  See the NOTICE file
    *  distributed with this work for additional information
    *  regarding copyright ownership.  The ASF 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 org.apache.mina.filter.ssl;
  
  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;
  
  /**
   * 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 The Apache MINA Project (dev@mina.apache.org)
   * @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;
     
     /** 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) {
         this(sslContext, START_HANDSHAKE);
     }
 
     /**
      * 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) {
         if (sslContext == null) {
             throw new NullPointerException("sslContext");
         }
 
         this.sslContext = sslContext;
         this.autoStart = autoStart;
     }
 
     /**
      * 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, session);
         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 {
                     // forward read encrypted data to SSL handler
                     handler.messageReceived(nextFilter, buf.buf());
 
                     // 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;
                 }
             }
         }
 
         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 {
             // 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<WriteRequest>(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>() {
                         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 The Apache MINA Project (dev@mina.apache.org)
      */
     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;
         }
     }
 }