content: package alkarn.github.io.sslengine.example;
  
  import java.io.FileInputStream;
  import java.io.IOException;
  import java.io.InputStream;
  import java.nio.BufferOverflowException;
  import java.nio.ByteBuffer;
  import java.nio.channels.SocketChannel;
  import java.security.KeyStore;
  import java.util.concurrent.ExecutorService;
  import java.util.concurrent.Executors;
  
  import javax.net.ssl.KeyManager;
  import javax.net.ssl.KeyManagerFactory;
  import javax.net.ssl.SSLContext;
  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.SSLSession;
  import javax.net.ssl.TrustManager;
  import javax.net.ssl.TrustManagerFactory;
  
  import org.apache.log4j.Logger;
  
  /**
   * A class that represents an SSL/TLS peer, and can be extended to create a client or a server.
   * <p/>
   * It makes use of the JSSE framework, and specifically the {@link SSLEngine} logic, which
   * is described by Oracle as "an advanced API, not appropriate for casual use", since
   * it requires the user to implement much of the communication establishment procedure himself.
   * More information about it can be found here: http://docs.oracle.com/javase/8/docs/technotes/guides/security/jsse/JSSERefGuide.html#SSLEngine
   * <p/>
   * {@link NioSslPeer} implements the handshake protocol, required to establish a connection between two peers,
   * which is common for both client and server and provides the abstract {@link NioSslPeer#read(SocketChannel, SSLEngine)} and
   * {@link NioSslPeer#write(SocketChannel, SSLEngine, String)} methods, that need to be implemented by the specific SSL/TLS peer
   * that is going to extend this class.
   *
   * @author <a href="mailto:alex.a.karnezis@gmail.com">Alex Karnezis</a>
   */
  public abstract class NioSslPeer {
  
  	/**
  	 * Class' logger.
  	 */
  	protected final Logger log = Logger.getLogger(getClass());
  
      /**
       * Will contain this peer's application data in plaintext, that will be later encrypted
       * using {@link SSLEngine#wrap(ByteBuffer, ByteBuffer)} and sent to the other peer. This buffer can typically
       * be of any size, as long as it is large enough to contain this peer's outgoing messages.
       * If this peer tries to send a message bigger than buffer's capacity a {@link BufferOverflowException}
       * will be thrown.
       */
      protected ByteBuffer myAppData;
  
      /**
       * Will contain this peer's encrypted data, that will be generated after {@link SSLEngine#wrap(ByteBuffer, ByteBuffer)}
       * is applied on {@link NioSslPeer#myAppData}. It should be initialized using {@link SSLSession#getPacketBufferSize()},
       * which returns the size up to which, SSL/TLS packets will be generated from the engine under a session.
       * All SSLEngine network buffers should be sized at least this large to avoid insufficient space problems when performing wrap and unwrap calls.
       */
      protected ByteBuffer myNetData;
  
      /**
       * Will contain the other peer's (decrypted) application data. It must be large enough to hold the application data
       * from any peer. Can be initialized with {@link SSLSession#getApplicationBufferSize()} for an estimation
       * of the other peer's application data and should be enlarged if this size is not enough.
       */
      protected ByteBuffer peerAppData;
  
      /**
       * Will contain the other peer's encrypted data. The SSL/TLS protocols specify that implementations should produce packets containing at most 16 KB of plaintext,
       * so a buffer sized to this value should normally cause no capacity problems. However, some implementations violate the specification and generate large records up to 32 KB.
       * If the {@link SSLEngine#unwrap(ByteBuffer, ByteBuffer)} detects large inbound packets, the buffer sizes returned by SSLSession will be updated dynamically, so the this peer
       * should check for overflow conditions and enlarge the buffer using the session's (updated) buffer size.
       */
      protected ByteBuffer peerNetData;
  
      /**
       * Will be used to execute tasks that may emerge during handshake in parallel with the server's main thread.
       */
      protected ExecutorService executor = Executors.newSingleThreadExecutor();
  
      protected abstract void read(SocketChannel socketChannel, SSLEngine engine) throws Exception;
  
      protected abstract void write(SocketChannel socketChannel, SSLEngine engine, String message) throws Exception;
  
      /**
       * Implements the handshake protocol between two peers, required for the establishment of the SSL/TLS connection.
       * During the handshake, encryption configuration information - such as the list of available cipher suites - will be exchanged
       * and if the handshake is successful will lead to an established SSL/TLS session.
       *
       * <p/>
       * A typical handshake will usually contain the following steps:
       *
       * <ul>
       *   <li>1. wrap:     ClientHello</li>
       *   <li>2. unwrap:   ServerHello/Cert/ServerHelloDone</li>
       *   <li>3. wrap:     ClientKeyExchange</li>
       *   <li>4. wrap:     ChangeCipherSpec</li>
       *   <li>5. wrap:     Finished</li>
       *   <li>6. unwrap:   ChangeCipherSpec</li>
       *   <li>7. unwrap:   Finished</li>
       * </ul>
       * <p/>
       * Handshake is also used during the end of the session, in order to properly close the connection between the two peers.
       * A proper connection close will typically include the one peer sending a CLOSE message to another, and then wait for
       * the other's CLOSE message to close the transport link. The other peer from his perspective would read a CLOSE message
       * from his peer and then enter the handshake procedure to send his own CLOSE message as well.
       *
       * @param socketChannel - the socket channel that connects the two peers.
       * @param engine - the engine that will be used for encryption/decryption of the data exchanged with the other peer.
       * @return True if the connection handshake was successful or false if an error occurred.
       * @throws IOException - if an error occurs during read/write to the socket channel.
       */
      protected boolean doHandshake(SocketChannel socketChannel, SSLEngine engine) throws IOException {
  
          log.debug("About to do handshake...");
  
          SSLEngineResult result;
          HandshakeStatus handshakeStatus;
  
          // NioSslPeer's fields myAppData and peerAppData are supposed to be large enough to hold all message data the peer
          // will send and expects to receive from the other peer respectively. Since the messages to be exchanged will usually be less
          // than 16KB long the capacity of these fields should also be smaller. Here we initialize these two local buffers
          // to be used for the handshake, while keeping client's buffers at the same size.
          int appBufferSize = engine.getSession().getApplicationBufferSize();
          ByteBuffer myAppData = ByteBuffer.allocate(appBufferSize);
          ByteBuffer peerAppData = ByteBuffer.allocate(appBufferSize);
          myNetData.clear();
          peerNetData.clear();
  
          handshakeStatus = engine.getHandshakeStatus();
          while (handshakeStatus != SSLEngineResult.HandshakeStatus.FINISHED && handshakeStatus != SSLEngineResult.HandshakeStatus.NOT_HANDSHAKING) {
              switch (handshakeStatus) {
              case NEED_UNWRAP:
                  if (socketChannel.read(peerNetData) < 0) {
                      if (engine.isInboundDone() && engine.isOutboundDone()) {
                          return false;
                      }
                      try {
                          engine.closeInbound();
                      } catch (SSLException e) {
                          log.error("This engine was forced to close inbound, without having received the proper SSL/TLS close notification message from the peer, due to end of stream.");
                      }
                      engine.closeOutbound();
                      // After closeOutbound the engine will be set to WRAP state, in order to try to send a close message to the client.
                      handshakeStatus = engine.getHandshakeStatus();
                      break;
                  }
                  peerNetData.flip();
                  try {
                      result = engine.unwrap(peerNetData, peerAppData);
                      peerNetData.compact();
                      handshakeStatus = result.getHandshakeStatus();
                  } catch (SSLException sslException) {
                      log.error("A problem was encountered while processing the data that caused the SSLEngine to abort. Will try to properly close connection...");
                      engine.closeOutbound();
                      handshakeStatus = engine.getHandshakeStatus();
                      break;
                  }
                  switch (result.getStatus()) {
                  case OK:
                      break;
                  case BUFFER_OVERFLOW:
                      // Will occur when peerAppData's capacity is smaller than the data derived from peerNetData's unwrap.
                      peerAppData = enlargeApplicationBuffer(engine, peerAppData);
                      break;
                  case BUFFER_UNDERFLOW:
                      // Will occur either when no data was read from the peer or when the peerNetData buffer was too small to hold all peer's data.
                      peerNetData = handleBufferUnderflow(engine, peerNetData);
                      break;
                  case CLOSED:
                      if (engine.isOutboundDone()) {
                          return false;
                      } else {
                          engine.closeOutbound();
                          handshakeStatus = engine.getHandshakeStatus();
                          break;
                      }
                  default:
                      throw new IllegalStateException("Invalid SSL status: " + result.getStatus());
                  }
                  break;
              case NEED_WRAP:
                  myNetData.clear();
                  try {
                      result = engine.wrap(myAppData, myNetData);
                      handshakeStatus = result.getHandshakeStatus();
                  } catch (SSLException sslException) {
                      log.error("A problem was encountered while processing the data that caused the SSLEngine to abort. Will try to properly close connection...");
                      engine.closeOutbound();
                      handshakeStatus = engine.getHandshakeStatus();
                      break;
                  }
                  switch (result.getStatus()) {
                  case OK :
                      myNetData.flip();
                      while (myNetData.hasRemaining()) {
                          socketChannel.write(myNetData);
                      }
                      break;
                  case BUFFER_OVERFLOW:
                      // Will occur if there is not enough space in myNetData buffer to write all the data that would be generated by the method wrap.
                      // Since myNetData is set to session's packet size we should not get to this point because SSLEngine is supposed
                      // to produce messages smaller or equal to that, but a general handling would be the following:
                      myNetData = enlargePacketBuffer(engine, myNetData);
                      break;
                  case BUFFER_UNDERFLOW:
                      throw new SSLException("Buffer underflow occured after a wrap. I don't think we should ever get here.");
                  case CLOSED:
                      try {
                          myNetData.flip();
                          while (myNetData.hasRemaining()) {
                              socketChannel.write(myNetData);
                          }
                          // At this point the handshake status will probably be NEED_UNWRAP so we make sure that peerNetData is clear to read.
                          peerNetData.clear();
                      } catch (Exception e) {
                          log.error("Failed to send server's CLOSE message due to socket channel's failure.");
                          handshakeStatus = engine.getHandshakeStatus();
                      }
                      break;
                  default:
                      throw new IllegalStateException("Invalid SSL status: " + result.getStatus());
                  }
                  break;
              case NEED_TASK:
                  Runnable task;
                  while ((task = engine.getDelegatedTask()) != null) {
                      executor.execute(task);
                  }
                  handshakeStatus = engine.getHandshakeStatus();
                  break;
              case FINISHED:
                  break;
              case NOT_HANDSHAKING:
                  break;
              default:
                  throw new IllegalStateException("Invalid SSL status: " + handshakeStatus);
              }
          }
  
          return true;
  
      }
  
      protected ByteBuffer enlargePacketBuffer(SSLEngine engine, ByteBuffer buffer) {
          return enlargeBuffer(buffer, engine.getSession().getPacketBufferSize());
      }
  
      protected ByteBuffer enlargeApplicationBuffer(SSLEngine engine, ByteBuffer buffer) {
          return enlargeBuffer(buffer, engine.getSession().getApplicationBufferSize());
      }
  
      /**
       * Compares <code>sessionProposedCapacity<code> with buffer's capacity. If buffer's capacity is smaller,
       * returns a buffer with the proposed capacity. If it's equal or larger, returns a buffer
       * with capacity twice the size of the initial one.
       *
       * @param buffer - the buffer to be enlarged.
       * @param sessionProposedCapacity - the minimum size of the new buffer, proposed by {@link SSLSession}.
       * @return A new buffer with a larger capacity.
       */
      protected ByteBuffer enlargeBuffer(ByteBuffer buffer, int sessionProposedCapacity) {
          if (sessionProposedCapacity > buffer.capacity()) {
              buffer = ByteBuffer.allocate(sessionProposedCapacity);
          } else {
              buffer = ByteBuffer.allocate(buffer.capacity() * 2);
          }
          return buffer;
      }
  
      /**
       * Handles {@link SSLEngineResult.Status#BUFFER_UNDERFLOW}. Will check if the buffer is already filled, and if there is no space problem
       * will return the same buffer, so the client tries to read again. If the buffer is already filled will try to enlarge the buffer either to
       * session's proposed size or to a larger capacity. A buffer underflow can happen only after an unwrap, so the buffer will always be a
       * peerNetData buffer.
       *
       * @param buffer - will always be peerNetData buffer.
       * @param engine - the engine used for encryption/decryption of the data exchanged between the two peers.
       * @return The same buffer if there is no space problem or a new buffer with the same data but more space.
       * @throws Exception
       */
      protected ByteBuffer handleBufferUnderflow(SSLEngine engine, ByteBuffer buffer) {
          if (engine.getSession().getPacketBufferSize() < buffer.limit()) {
              return buffer;
          } else {
              ByteBuffer replaceBuffer = enlargePacketBuffer(engine, buffer);
              buffer.flip();
              replaceBuffer.put(buffer);
              return replaceBuffer;
          }
      }
  
      /**
       * This method should be called when this peer wants to explicitly close the connection
       * or when a close message has arrived from the other peer, in order to provide an orderly shutdown.
       * <p/>
       * It first calls {@link SSLEngine#closeOutbound()} which prepares this peer to send its own close message and
       * sets {@link SSLEngine} to the <code>NEED_WRAP</code> state. Then, it delegates the exchange of close messages
       * to the handshake method and finally, it closes socket channel.
       *
       * @param socketChannel - the transport link used between the two peers.
       * @param engine - the engine used for encryption/decryption of the data exchanged between the two peers.
       * @throws IOException if an I/O error occurs to the socket channel.
       */
      protected void closeConnection(SocketChannel socketChannel, SSLEngine engine) throws IOException  {
          engine.closeOutbound();
          doHandshake(socketChannel, engine);
          socketChannel.close();
      }
  
      /**
       * In addition to orderly shutdowns, an unorderly shutdown may occur, when the transport link (socket channel)
       * is severed before close messages are exchanged. This may happen by getting an -1 or {@link IOException}
       * when trying to read from the socket channel, or an {@link IOException} when trying to write to it.
       * In both cases {@link SSLEngine#closeInbound()} should be called and then try to follow the standard procedure.
       *
       * @param socketChannel - the transport link used between the two peers.
       * @param engine - the engine used for encryption/decryption of the data exchanged between the two peers.
       * @throws IOException if an I/O error occurs to the socket channel.
       */
      protected void handleEndOfStream(SocketChannel socketChannel, SSLEngine engine) throws IOException  {
          try {
              engine.closeInbound();
          } catch (Exception e) {
              log.error("This engine was forced to close inbound, without having received the proper SSL/TLS close notification message from the peer, due to end of stream.");
          }
          closeConnection(socketChannel, engine);
      }
  
      /**
       * Creates the key managers required to initiate the {@link SSLContext}, using a JKS keystore as an input.
       *
       * @param filepath - the path to the JKS keystore.
       * @param keystorePassword - the keystore's password.
       * @param keyPassword - the key's passsword.
       * @return {@link KeyManager} array that will be used to initiate the {@link SSLContext}.
       * @throws Exception
       */
      protected KeyManager[] createKeyManagers(String filepath, String keystorePassword, String keyPassword) throws Exception {
          KeyStore keyStore = KeyStore.getInstance("JKS");
          InputStream keyStoreIS = new FileInputStream(filepath);
          try {
              keyStore.load(keyStoreIS, keystorePassword.toCharArray());
          } finally {
              if (keyStoreIS != null) {
                  keyStoreIS.close();
              }
          }
          KeyManagerFactory kmf = KeyManagerFactory.getInstance(KeyManagerFactory.getDefaultAlgorithm());
          kmf.init(keyStore, keyPassword.toCharArray());
          return kmf.getKeyManagers();
      }
  
      /**
       * Creates the trust managers required to initiate the {@link SSLContext}, using a JKS keystore as an input.
       *
       * @param filepath - the path to the JKS keystore.
       * @param keystorePassword - the keystore's password.
       * @return {@link TrustManager} array, that will be used to initiate the {@link SSLContext}.
       * @throws Exception
       */
      protected TrustManager[] createTrustManagers(String filepath, String keystorePassword) throws Exception {
          KeyStore trustStore = KeyStore.getInstance("JKS");
          InputStream trustStoreIS = new FileInputStream(filepath);
          try {
              trustStore.load(trustStoreIS, keystorePassword.toCharArray());
          } finally {
              if (trustStoreIS != null) {
                  trustStoreIS.close();
              }
          }
          TrustManagerFactory trustFactory = TrustManagerFactory.getInstance(TrustManagerFactory.getDefaultAlgorithm());
          trustFactory.init(trustStore);
          return trustFactory.getTrustManagers();
      }
  
  }
  